path: root/src/ninep/ctl.zig

//! The command files and the status they answer. Writing a line to `look` is
//! a right click on it and writing one to `exec` a middle click, at the
//! active pane from the root and at that pane from /pane/<n>/; reading either
//! answers the serials the last command made or touched. /status reports the
//! editor. The root ctl reads the settings and takes the session's builtins;
//! a pane's ctl reads its acme status line and takes acme's verbs `get`,
//! `lock` and `unlock` and the builtins that act on a pane.
const std = @import("std");
const pardes = @import("../pardes.zig");
const look = @import("../look.zig");
const panes = @import("../panes.zig");
const config = @import("../config.zig");
const fs = @import("../fs.zig");
const tagline = @import("../tagline.zig");
const layout = @import("../layout.zig");
const builtins = @import("../builtins.zig");
const exec_line = @import("../exec.zig");
const tree = @import("tree.zig");
const pane_files = @import("pane.zig");

const Pardes = pardes.Pardes;
const Pane = pardes.Pane;
const MAX_PANES = pardes.MAX_PANES;
const Req = tree.Req;
const Reply = tree.Reply;
const E = tree.E;

// ---- which panes a command made or touched ----

const Serials = struct {
    list: [MAX_PANES]u32 = undefined,
    len: usize = 0,

    fn snapshot(p: *Pardes) Serials {
        var s: Serials = .{};
        for (p.panes) |slot| if (slot) |pane| {
            s.list[s.len] = pane.serial;
            s.len += 1;
        };
        return s;
    }
};

fn noteResult(p: *Pardes, serial: u32) void {
    for (p.fs.results[0..p.fs.results_len]) |known| if (known == serial) return;
    if (p.fs.results_len == p.fs.results.len) return;
    p.fs.results[p.fs.results_len] = serial;
    p.fs.results_len += 1;
}

/// Runs one look or exec from the pane `id`, then records the panes it
/// created; failing that, a look records the pane it focused and an exec
/// the pane it acted on (even one it closed).
pub fn run(p: *Pardes, id: usize, exec: bool, text: []const u8, in_tag: bool) void {
    const context = p.panes[id].?.serial;
    // A pane an event reader holds hears its clicks instead of acting on
    // them (editors/acme/look.c:53 and exec.c:173 send them to winevent),
    // and a line written to a look or exec is a click: on that pane, or for
    // the root's, on the pane with the keyboard. The reader writes the
    // record back to have it done.
    // A click in a column's or the workspace's tag is not the pane's.
    if (!in_tag and p.panes[id].?.fs.readers > 0) {
        const named = std.meta.stringToEnum(Builtin, exec_line.commandText(text)) != null;
        var flag: u32 = pardes.ctlfs.events.flag_expansion;
        if (named) flag |= pardes.ctlfs.events.flag_builtin;
        if (!exec and !named and std.mem.indexOfAny(u8, text, "/.:") != null) flag |= pardes.ctlfs.events.flag_filename;
        _ = pardes.ctlfs.events.noteAction(p, id, if (exec) .body_exec else .body_look, 0, 0, flag, text);
        return noteResult(p, context);
    }
    const before = Serials.snapshot(p);
    // An exec answers the pane it went to: a command pane it reused, or
    // the terminal it typed into.
    p.look_missed = false;
    const went: ?usize = if (exec) pardes.exec.execute(p, id, text) else blk: {
        look.lookAt(p, id, text);
        break :blk null;
    };
    // A look that found nothing answers nothing, not the pane before it.
    if (!exec and p.look_missed) return;
    const after = Serials.snapshot(p);
    var created = false;
    for (after.list[0..after.len]) |serial| if (std.mem.indexOfScalar(u32, before.list[0..before.len], serial) == null) {
        // A look's hits buffer is how it found the text, not where: it
        // answers the pane the hit is selected in.
        if (!exec) if (p.paneBySerial(serial)) |made| if (p.panes[made].?.file) |f| if (f.output) |o| if (o.from == .search) continue;
        noteResult(p, serial);
        created = true;
    };
    if (created) return;
    if (went) |dst| if (p.panes[dst]) |pane| return noteResult(p, pane.serial);
    noteResult(p, if (exec) context else (p.panes[p.active] orelse return).serial);
}

/// A write's messages, a line each, except that an `Edit` line takes the
/// lines after it while its `{` group or `a`/`c`/`i` text block is open
/// (sam_edit.needsMore): a block written whole reaches Edit whole, never
/// as lines of their own.
const Messages = struct {
    p: *Pardes,
    data: []const u8,
    at: usize = 0,

    fn init(p: *Pardes, data: []const u8) Messages {
        return .{ .p = p, .data = data };
    }

    fn next(m: *Messages) ?[]const u8 {
        if (m.at >= m.data.len) return null;
        const start = m.at;
        var end = std.mem.indexOfScalarPos(u8, m.data, start, '\n') orelse m.data.len;
        m.at = end + 1;
        const first = std.mem.trim(u8, m.data[start..end], " \t\r");
        const edit = "Edit";
        if (!std.mem.startsWith(u8, first, edit) or (first.len > edit.len and first[edit.len] != ' ' and first[edit.len] != '\t'))
            return first;
        end = editEnd(m.p, m.data, start, end, true).?;
        m.at = end + 1;
        return std.mem.trim(u8, m.data[start..end], " \t\r");
    }
};

/// Where the Edit block whose first line is `data[start..first_end]` ends:
/// the end of its last line, taking the lines after it while its `{`
/// group or a/c/i text block is open. Out of lines, the end of `data` when
/// `to_end` (a write run whole), else null (wait for more). Only a line
/// that could end what is open is parsed again with all before it: within
/// a text block, just a `.` line. The arena copy of each parse is freed.
fn editEnd(p: *Pardes, data: []const u8, start: usize, first_end: usize, to_end: bool) ?usize {
    const sam = @import("../sam_edit.zig");
    const edit = "Edit";
    const arena = p.scratch.allocator();
    var end = first_end;
    var wait = sam.waitsFor(arena, std.mem.trim(u8, data[start..end], " \t\r")[edit.len..]);
    while (wait != .none) {
        if (end >= data.len) return if (to_end) data.len else null;
        const next = std.mem.indexOfScalarPos(u8, data, end + 1, '\n') orelse
            (if (to_end) data.len else return null);
        const line = std.mem.trim(u8, data[end + 1 .. next], " \t\r");
        end = next;
        if (wait == .text and !std.mem.eql(u8, line, ".")) continue;
        wait = sam.waitsFor(arena, std.mem.trim(u8, data[start..end], " \t\r")[edit.len..]);
    }
    return end;
}

/// How much of `data` is whole messages, as `Messages` reads them: lines
/// ended by a newline, an Edit block only once it closes. The rest waits
/// for more (tree.Open.pending).
pub fn completeEnd(p: *Pardes, data: []const u8) usize {
    const edit = "Edit";
    var whole: usize = 0;
    var at: usize = 0;
    while (std.mem.indexOfScalarPos(u8, data, at, '\n')) |nl| {
        const start = at;
        var end = nl;
        const first = std.mem.trim(u8, data[start..end], " \t\r");
        if (std.mem.startsWith(u8, first, edit) and (first.len == edit.len or first[edit.len] == ' ' or first[edit.len] == '\t'))
            end = editEnd(p, data, start, end, false) orelse return whole;
        at = end + 1;
        whole = at;
    }
    return whole;
}

// ---- look and exec ----

/// One command per line, checked whole before any line runs: a line is the
/// clicked text itself, so it may not be empty or carry control characters.
/// A null `serial` clicks at whichever pane is active as each line runs,
/// which is what the root's own look and exec mean; a serial stays put.
pub fn command(p: *Pardes, req: Req, serial: ?u32, exec: bool, in_tag: bool) Reply {
    for ([2]bool{ false, true }) |apply| {
        if (apply) p.fs.results_len = 0;
        var it = Messages.init(p, req.data);
        while (it.next()) |text| {
            if (text.len == 0) continue;
            // Only an Edit block holds newlines (Messages).
            for (text) |c| if (c < ' ' and c != '\t' and c != '\n') return Reply.fail(req.tag, E.INVAL);
            if (exec) if (tooLong(req, text)) |refusal| return refusal;
            if (!apply) continue;
            const id = if (serial) |s| p.paneBySerial(s) orelse break else p.active;
            if (p.panes[id] == null) return Reply.fail(req.tag, E.NOENT);
            p.fs.no_pane_slot = false;
            run(p, id, exec, text, in_tag);
            // A pane it would have opened had no slot: the write fails, and
            // a look reads back nothing.
            if (p.fs.no_pane_slot) {
                p.fs.results_len = 0;
                return tree.failText(req.tag, E.IO, p.fs.ename[0..p.fs.no_pane_slot_len]);
            }
        }
    }
    return .{ .tag = req.tag, .written = @intCast(req.data.len) };
}

pub const e_too_long = std.fmt.comptimePrint("a command line is at most {d} bytes", .{pardes.exec.command_max});

/// A line an exec would run as a command, over the most a command line may
/// be: refused whole, before anything runs, rather than said on the message
/// row after the write succeeded. A builtin's line (Msg, an Edit block) may
/// be longer.
pub fn tooLong(req: Req, line: []const u8) ?Reply {
    if (line.len <= pardes.exec.command_max) return null;
    const cmd = exec_line.commandText(line);
    const word = cmd[0 .. std.mem.indexOfAny(u8, cmd, " \t+") orelse cmd.len];
    if (std.meta.stringToEnum(Builtin, word) != null) return null;
    return tree.failText(req.tag, E.INVAL, e_too_long);
}

pub fn resultsLen(p: *Pardes) u64 {
    var n: u64 = 0;
    for (p.fs.results[0..p.fs.results_len]) |serial| {
        var digits: [16]u8 = undefined;
        n += (std.fmt.bufPrint(&digits, "{d}\n", .{serial}) catch unreachable).len;
    }
    return n;
}

/// The panes the open's last write touched (tree.Open.results); with no
/// open, the session's last.
pub fn readResults(p: *Pardes, req: Req) Reply {
    const out = p.fs.stage(p.gpa);
    const o = tree.openOf(p, req);
    const kept = if (o) |open| open.results.list[0..open.results.len] else p.fs.results[0..p.fs.results_len];
    for (kept) |serial|
        out.print(p.gpa, "{d}\n", .{serial}) catch return Reply.fail(req.tag, E.NOMEM);
    const open = o orelse return tree.stagedReply(p, req);
    if (!open.results.wrote) return tree.stagedReply(p, req);
    var at = req;
    at.off = open.results.read;
    const reply = tree.stagedReply(p, at);
    open.results.read += reply.payload.staged;
    return reply;
}

// ---- /status ----

fn statusText(p: *Pardes, buf: []u8) []const u8 {
    var w = std.Io.Writer.fixed(buf);
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    const pid: u32 = if (comptime pardes.hosted) @intCast(std.c.getpid()) else 0;
    w.print("pid {d}\nversion {s}\npanes {d}\n", .{ pid, pardes.version, count }) catch {};
    return w.buffered();
}

pub const status_text_cap = 64 + pardes.version.len;

pub fn statusLen(p: *Pardes) u64 {
    var buf: [status_text_cap]u8 = undefined;
    return statusText(p, &buf).len;
}

pub fn readStatus(p: *Pardes, req: Req) Reply {
    var buf: [status_text_cap]u8 = undefined;
    const out = p.fs.stage(p.gpa);
    out.appendSlice(p.gpa, statusText(p, &buf)) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

// ---- /pane/<n>/ctl ----

fn writeQuoted(w: *std.Io.Writer, s: []const u8) !void {
    const plain = s.len > 0 and for (s) |c| {
        if (c <= ' ' or c == '\'') break false;
    } else true;
    if (plain) return w.writeAll(s);
    try w.writeByte('\'');
    for (s) |c| {
        if (c == '\'') try w.writeByte('\'');
        try w.writeByte(c);
    }
    try w.writeByte('\'');
}

pub const pane_text_cap = 7 * 12 + 2 * 256 + 4 + "notcurrent ".len + 48;

/// acme's winctlprint: serial, tag length, body length, a reserved zero, the
/// dirty flag, then the width in cells, the font and the tab width. Then
/// rio's word for whether the window has the keyboard, `current` or
/// `notcurrent` (rio(4), wctl), which acme's line has no room for because
/// acme has one window for input at a time only by the mouse.
pub fn paneText(p: *Pardes, pane: *Pane, buf: []u8) []const u8 {
    var w = std.Io.Writer.fixed(buf);
    w.print("{d:>11} {d:>11} {d:>11} {d:>11} {d:>11} {d:>11} ", .{
        pane.serial,
        pane_files.tagOf(p, pane).len,
        // A terminal's body is its history, read whole on an open's first read.
        if (pane.isTerminal()) panes.Terminal.screenTextLen(pane) else pane_files.bodyOf(pane).len,
        @as(u32, 0),
        @intFromBool(pane_files.dirtyOf(pane)),
        pane.cols,
    }) catch return w.buffered();
    const font = p.settings.font.effective_name.get();
    writeQuoted(&w, if (font.len == 0) "default" else font) catch return w.buffered();
    // While a column's or the workspace's tag has the keyboard, no pane does.
    const current = p.panes[p.active] == pane and !p.header_focus;
    w.print(" {d:>11} {s} ", .{ config.tab_width, if (current) "current" else "notcurrent" }) catch {};
    // A terminal bound as a REPL ends with its id, `python-a`.
    var idbuf: [48]u8 = undefined;
    const id = exec_line.replId(&idbuf, pane);
    if (id.len > 0) w.print("{s} ", .{id}) catch {};
    return w.buffered();
}

// ---- control messages: the builtins, by scope ----

const Builtin = builtins.registry.Builtin();

/// Refuses a control message, quoting it the way Plan 9's cmderror does
/// (kernel/misc/parse.c:82): `unknown control message "Bogus 3"`.
fn refuse(p: *Pardes, req: Req, why: []const u8, line: []const u8) Reply {
    const room = p.fs.ename.len -| (why.len + 3);
    const text = std.fmt.bufPrint(&p.fs.ename, "{s} \"{s}\"", .{ why, line[0..@min(line.len, room)] }) catch why;
    return tree.failText(req.tag, E.INVAL, text);
}

/// `refuse`, saying which ctl takes the message instead.
fn refuseTo(p: *Pardes, req: Req, why: []const u8, line: []const u8, ctl: []const u8) Reply {
    const room = p.fs.ename.len -| (why.len + ctl.len + 18);
    const text = std.fmt.bufPrint(&p.fs.ename, "{s} \"{s}\": write it to {s}", .{ why, line[0..@min(line.len, room)], ctl }) catch why;
    return tree.failText(req.tag, E.INVAL, text);
}

/// Checks one line written to a ctl as a builtin of `scope` before any line
/// of the write runs: a word the registry knows, of this ctl's scope, given
/// an argument if and only if it takes or requires one, and for a setting a
/// value it takes.
/// Answers the refusal, or null. Words are the builtins' own, capitalised
/// as on a tag; acme's lowercase verbs are the pane ctl's and alias none.
fn checkBuiltin(p: *Pardes, req: Req, line: []const u8, scope: builtins.Scope) ?Reply {
    const sp = std.mem.indexOfAny(u8, line, " \t");
    const word = line[0 .. sp orelse line.len];
    const arg = if (sp) |s| std.mem.trim(u8, line[s + 1 ..], " \t") else "";
    const b = std.meta.stringToEnum(Builtin, word) orelse {
        // A setting this build's frontend cannot show (Lift, GripWidth on a
        // terminal) is known, and says so rather than sound misspelt.
        if (config.Runtime.find(word) != null) {
            var why: [64]u8 = undefined;
            return refuse(p, req, std.fmt.bufPrint(&why, "{s} is GUI-only", .{word}) catch "GUI-only", line);
        }
        return refuse(p, req, "unknown control message", line);
    };
    // Edit is the one pane word the root takes too: at the active pane.
    if (builtins.registry.scope(b) != scope and b != .Edit)
        return refuseTo(p, req, if (scope == .pane) "not a window control message" else "not a session control message", line, if (scope == .pane)
            "/ctl"
        else if (b == .Delcol or b == .Joincol)
            "col/<serial>/ctl" // a column's own ctl, the one /layout names
        else
            "pane/<n>/ctl");
    if (arg.len > 0 and !builtins.registry.takesArg(b)) return refuse(p, req, "wrong #args in control message", line);
    if (arg.len == 0 and builtins.registry.requiresArg(b)) return refuse(p, req, "wrong #args in control message", line);
    const setting = config.Runtime.find(word) orelse return null;
    const takes = switch (setting.action) {
        .theme => for (pardes.themes) |t| {
            if (std.mem.eql(u8, t.name, arg)) break true;
        } else {
            // `refuse` quotes the line after it, in what is left of 128.
            var near: [40]u8 = undefined;
            var why: [104]u8 = undefined;
            return refuse(p, req, std.fmt.bufPrint(&why, "bad value in control message; like it: {s}; ThemeSel lists all", .{pardes.colors.themesNear(&near, arg)}) catch "bad value in control message", line);
        },
        .font => config.Runtime.FontSpec.parse(arg) != null,
        else => probe: {
            var probe = p.settings;
            break :probe probe.apply(setting, if (arg.len > 0) arg else null);
        },
    };
    if (takes) return null;
    var why: [104]u8 = undefined;
    return refuse(p, req, if (config.Runtime.choices(setting.action)) |values|
        std.fmt.bufPrint(&why, "bad value in control message; takes {s}", .{values}) catch "bad value in control message"
    else
        "bad value in control message", line);
}

/// Runs a checked control message at pane `id`, as a click on its word
/// would. Answers the refusal when it would have opened a prompt for an
/// argument, which nobody writing to a file is there to type, or when it
/// reported an error: `Mount: AlreadyMounted "Mount peer /tmp/s"`.
pub fn runBuiltin(p: *Pardes, req: Req, id: usize, line: []const u8) ?Reply {
    p.fs.no_prompt = true;
    p.fs.refused = false;
    p.fs.failure_len = 0;
    defer p.fs.no_prompt = false;
    // What a ctl write touched reads back from /look and /exec as a click's
    // does (`run`), so a script that made a pane with `Tty` finds it there.
    const context = p.panes[id].?.serial;
    const before = Serials.snapshot(p);
    _ = exec_line.executeBuiltinLine(p, id, line);
    const after = Serials.snapshot(p);
    var created = false;
    for (after.list[0..after.len]) |serial| if (std.mem.indexOfScalar(u32, before.list[0..before.len], serial) == null) {
        noteResult(p, serial);
        created = true;
    };
    if (!created) noteResult(p, context);
    if (p.fs.refused) return refuse(p, req, e_prompt, line);
    if (p.fs.failure_len == 0) return null;
    // An Edit's failure names what failed (the pattern that missed): its
    // line, a program, is not quoted after it.
    const edit = std.mem.startsWith(u8, line, "Edit ") or std.mem.eql(u8, line, "Edit");
    const refusal = if (edit) tree.failText(req.tag, E.IO, p.fs.failure[0..p.fs.failure_len]) else refuse(p, req, p.fs.failure[0..p.fs.failure_len], line);
    return .{ .tag = req.tag, .status = .err, .errno = E.IO, .ename = refusal.ename };
}

const e_prompt = "control message needs its argument";

// ---- the root ctl ----

/// Every setting, one a line, in the words a write of it takes, so that the
/// file read back is the configuration, as webfs's ctl reads (webfs(4)).
/// What is not a setting -- platform, themes, where the config came from --
/// is /status's or the Config window's.
fn writeSettings(p: *Pardes, w: *std.Io.Writer) !void {
    try writeSettingsOf(p, &p.settings, w);
    try w.writeAll("LocationsConfig ");
    try p.locations_config.write(w);
    try w.writeByte('\n');
    if (comptime builtins.Pet.enabled) try w.print("Pet {s}\n", .{@tagName(p.settings.pet)});
}

/// The setting words of `s`, one a line, as the root ctl reads them; a Dump
/// keeps those that differ from a fresh session's (dump.zig).
pub fn writeSettingsOf(p: *Pardes, s: *const config.Runtime, w: *std.Io.Writer) !void {
    inline for (config.Runtime.settings) |setting| {
        if (comptime !setting.enabled(builtins.capabilities)) continue;
        const word = setting.word;
        switch (setting.action) {
            .toggle => |field| try w.print("{s} {s}\n", .{ word, if (@field(s, @tagName(field))) "on" else "off" }),
            .theme => try w.print("{s} {s}\n", .{ word, if (s == &p.settings) p.theme().name else pardes.themes[s.theme].name }),
            .shell => {
                const chosen = s.shell.requested.get();
                try w.print("{s} {s}\n", .{ word, if (chosen.len > 0) chosen else config.defaultShell() });
            },
            .font => {
                const requested = s.font.requested_name.get();
                const name = if (requested.len > 0) requested else s.font.effective_name.get();
                const size = if (s.font.requested_size_hundredths != 0) s.font.requested_size_hundredths else s.font.effective_size_hundredths;
                if (name.len > 0 and size != 0)
                    try w.print("{s} {s}:{d}.{d:0>2}\n", .{ word, name, size / 100, size % 100 })
                else if (name.len > 0)
                    try w.print("{s} {s}\n", .{ word, name });
            },
            .tagline_size => try w.print("{s} {d}\n", .{ word, s.font.tagline_percent }),
            .window_opacity => try w.print("{s} {d}\n", .{ word, s.window_opacity }),
            .window_blur => try w.print("{s} {d}\n", .{ word, s.window_blur }),
            .choice => |which| switch (which) {
                inline else => |field| try w.print("{s} {s}\n", .{ word, @tagName(@field(s, @tagName(field))) }),
            },
            .message_ms => |which| try w.print("{s} {d}\n", .{ word, @field(s, "message_" ++ @tagName(which) ++ "_ms") }),
            // The directory in effect, as Config reports it; bare only when
            // there is none (no home to put the default in).
            .dump_dir => {
                var buf: [900]u8 = undefined;
                if (pardes.dump.directory(&buf, s.dump_dir.get())) |dir| try w.print("{s} {s}\n", .{ word, dir }) else try w.print("{s}\n", .{word});
            },
            .transition => |effect| try w.print("{s} {s}\n", .{ word, if (s.panel_transition == effect) "on" else "off" }),
            .scene => |effect| if (s.post.level(effect) == 0) try w.print("{s} off\n", .{word}) else try w.print("{s} {d}\n", .{ word, s.post.level(effect) }),
            .shader => for (s.post.list()) |entry| if (entry.scene == null) try w.print("{s} {s}\n", .{ word, entry.path.get() }),
            .shader_animation => try w.print("{s} {s}\n", .{ word, @tagName(s.shader_animation) }),
            .lift => try w.print("{s} {s}\n", .{ word, @tagName(s.lift) }),
            .motion => try w.print("{s} {s}\n", .{ word, @tagName(s.motion) }),
            .inactive_dim => try w.print("{s} {d}\n", .{ word, s.inactive_dim }),
            .grip_width => try w.print("{s} {d}\n", .{ word, s.grip_width }),
        }
    }
}

pub fn rootLen(p: *Pardes) u64 {
    var buf: [256]u8 = undefined;
    var counting: std.Io.Writer.Discarding = .init(&buf);
    writeSettings(p, &counting.writer) catch return 0;
    return counting.fullCount();
}

pub fn readRoot(p: *Pardes, req: Req) Reply {
    var text: std.Io.Writer.Allocating = .init(p.scratch.allocator());
    writeSettings(p, &text.writer) catch return Reply.fail(req.tag, E.NOMEM);
    p.fs.stage(p.gpa).appendSlice(p.gpa, text.written()) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

/// One session builtin a line, at whichever pane has the keyboard as each
/// runs, as the root's look and exec click there; all are checked first.
pub fn writeRoot(p: *Pardes, req: Req) Reply {
    for ([2]bool{ false, true }) |apply| {
        if (apply) p.fs.results_len = 0;
        var it = Messages.init(p, req.data);
        while (it.next()) |line| {
            if (line.len == 0) continue;
            if (std.mem.startsWith(u8, line, "size ") or std.mem.eql(u8, line, "size")) {
                const size = sizeOf(line) orelse return refuse(p, req, e_size, line);
                // A frontend's window is the size; only a session none is
                // attached to (--detach, unattended) takes one written.
                if (!p.unattended) return refuse(p, req, "size: a frontend is attached and owns the size", line);
                if (apply) {
                    const was: [2]u16 = .{ p.screen_w, p.screen_h };
                    p.update(.{ .resize = .{ .cols = size[0], .rows = size[1] } });
                    p.sync();
                    // Every pane keeps its tag and two rows, as placement
                    // leaves them: a size too small for that is refused.
                    if (!pardes.layout.everyPaneRoomy(p)) {
                        p.update(.{ .resize = .{ .cols = was[0], .rows = was[1] } });
                        p.sync();
                        return refuse(p, req, "size: too small for the panes, each its tag and 2 rows", line);
                    }
                }
                continue;
            }
            if (!apply) {
                if (checkBuiltin(p, req, line, .session)) |refusal| return refusal;
                continue;
            }
            if (p.panes[p.active] == null) return Reply.fail(req.tag, E.NOENT);
            p.fs.session_write = true;
            defer p.fs.session_write = false;
            if (runBuiltin(p, req, p.active, line)) |refusal| return refusal;
        }
    }
    return .{ .tag = req.tag, .written = @intCast(req.data.len) };
}

const size_min = [2]u16{ 20, 6 };
const size_max = [2]u16{ 4096, 4096 };
const e_size = std.fmt.comptimePrint("size takes <cols> <rows>, at least {d}x{d}, at most {d}x{d}", .{ size_min[0], size_min[1], size_max[0], size_max[1] });

/// `size <cols> <rows>`, within size_min and size_max.
fn sizeOf(line: []const u8) ?[2]u16 {
    var it = std.mem.tokenizeAny(u8, line["size".len..], " \t");
    const cols = std.fmt.parseInt(u16, it.next() orelse return null, 10) catch return null;
    const rows = std.fmt.parseInt(u16, it.next() orelse return null, 10) catch return null;
    if (it.next() != null or cols < size_min[0] or rows < size_min[1] or cols > size_max[0] or rows > size_max[1]) return null;
    return .{ cols, rows };
}

// ---- /commands ----

/// Every builtin the registry holds, one a line: its word, `arg` when it
/// takes one, and which ctl takes it, `root` or `pane` -- the registry
/// itself, so a new builtin is listed the moment it exists.
/// A builtin's doc comment, its first sentence, from the source itself: a
/// line of /commands says what each word does without a second copy of it.
fn summaryOf(word: []const u8, buf: []u8) []const u8 {
    const source = @embedFile("../builtins.zig");
    var needle_buf: [64]u8 = undefined;
    const needle = std.fmt.bufPrint(&needle_buf, "\npub const {s} = struct", .{word}) catch return "";
    const at = std.mem.indexOf(u8, source, needle) orelse return "";
    // Back over the `///` lines just above it.
    var start = at + 1;
    while (start > 0) {
        const prev_end = start - 1;
        const prev_start = if (std.mem.lastIndexOfScalar(u8, source[0..prev_end], '\n')) |nl| nl + 1 else 0;
        if (!std.mem.startsWith(u8, std.mem.trimStart(u8, source[prev_start..prev_end], " "), "///")) break;
        start = prev_start;
    }
    var w = std.Io.Writer.fixed(buf);
    var lines = std.mem.splitScalar(u8, source[start .. at + 1], '\n');
    while (lines.next()) |line| {
        const text = std.mem.trim(u8, std.mem.trimStart(u8, std.mem.trimStart(u8, line, " "), "/"), " ");
        if (text.len == 0) continue;
        if (w.buffered().len > 0) w.writeByte(' ') catch break;
        w.writeAll(text) catch break;
    }
    const all = stripCitations(w.buffered());
    // The first sentence, whole: to a `.` that ends one.
    var i: usize = 0;
    while (std.mem.indexOfScalarPos(u8, all, i, '.')) |dot| : (i = dot + 1) {
        if (dot + 1 == all.len or all[dot + 1] == ' ') return all[0 .. dot + 1];
    }
    return all;
}

/// Drops a parenthesis that cites source (`(editors/acme/exec.c:892)`,
/// `(exec.c, \`kill\`; acme.c's WKill)`): a reader of /commands wants what
/// the word does, not where acme has it. In place; answers the rest.
fn stripCitations(text: []u8) []u8 {
    var out: usize = 0;
    var i: usize = 0;
    while (i < text.len) {
        if (text[i] == '(') if (std.mem.indexOfScalarPos(u8, text, i, ')')) |close| {
            const inside = text[i + 1 .. close];
            if (std.mem.indexOf(u8, inside, ".c") != null or std.mem.indexOf(u8, inside, ".zig") != null) {
                // With the space before it, and a colon after it kept.
                if (out > 0 and text[out - 1] == ' ') out -= 1;
                i = close + 1;
                continue;
            }
        };
        text[out] = text[i];
        out += 1;
        i += 1;
    }
    return text[0..out];
}

fn writeCommands(w: *std.Io.Writer) !void {
    for (std.enums.values(Builtin)) |b| {
        // Edit is a pane's word the root's ctl takes too, at the active pane.
        const scope: []const u8 = if (b == .Edit) "both" else if (builtins.registry.scope(b) == .session) "root" else "pane";
        try w.print("{s}{s} {s}", .{
            @tagName(b),
            if (builtins.registry.takesArg(b)) " arg" else "",
            scope,
        });
        // A setting that chooses among words: the words, comma-joined. Bare,
        // it steps to the next of them (a two-valued one flips).
        if (config.Runtime.find(@tagName(b))) |setting| if (config.Runtime.choices(setting.action)) |values| {
            try w.writeByte(' ');
            var parts = std.mem.splitSequence(u8, values, ", ");
            var first = true;
            while (parts.next()) |v| : (first = false) try w.print("{s}{s}", .{ if (first) "" else ",", v });
        };
        // Then ` -- ` and what it does, when its source says.
        var summary_buf: [2048]u8 = undefined;
        const summary = summaryOf(@tagName(b), &summary_buf);
        if (summary.len > 0) {
            // The sentence whole unless it is long, then cut between words.
            const kept = @import("../Messages.zig").clip(summary, 240);
            try w.print(" -- {s}{s}", .{ kept, if (kept.len < summary.len) "…" else "" });
        }
        try w.writeByte('\n');
    }
}

pub fn commandsLen() u64 {
    var buf: [256]u8 = undefined;
    var counting: std.Io.Writer.Discarding = .init(&buf);
    writeCommands(&counting.writer) catch return 0;
    return counting.fullCount();
}

pub fn readCommands(p: *Pardes, req: Req) Reply {
    var text: std.Io.Writer.Allocating = .init(p.scratch.allocator());
    writeCommands(&text.writer) catch return Reply.fail(req.tag, E.NOMEM);
    p.fs.stage(p.gpa).appendSlice(p.gpa, text.written()) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

// ---- /focus ----

/// The pane with the keyboard, which a write of a serial moves, the way
/// writing `current` to rio's wctl does (rio(4)). While a column's or the
/// workspace's tag has it, no pane does, and this reads empty. A write
/// gives the keyboard and nothing else: a folded pane stays folded, as
/// rio keeps `current` apart from `unhide`.
pub fn readFocus(p: *Pardes, req: Req) Reply {
    const out = p.fs.stage(p.gpa);
    if (p.header_focus) return tree.stagedReply(p, req);
    const pane = p.panes[p.active] orelse return tree.stagedReply(p, req);
    out.print(p.gpa, "{d}\n", .{pane.serial}) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

pub fn writeFocus(p: *Pardes, req: Req) Reply {
    const text = std.mem.trim(u8, req.data, " \t\r\n");
    const serial = std.fmt.parseInt(u32, text, 10) catch return tree.failText(req.tag, E.INVAL, tree.e_bad_ctl);
    const id = p.paneBySerial(serial) orelse return tree.failText(req.tag, E.NOENT, e_no_pane);
    // The keyboard goes to the pane itself, off any header that had it, and
    // its column becomes the active one, as the user's click there would
    // make it: pane/new and a look place there next, whatever Placement.
    tagline.exitHeader(p);
    p.active = id;
    if (pardes.layout.findPane(p, id)) |at| p.setActiveColumn(at.col);
    return .{ .tag = req.tag, .written = @intCast(req.data.len) };
}

const e_no_pane = "no such pane";

pub fn readPane(p: *Pardes, req: Req, pane: *Pane) Reply {
    var buf: [pane_text_cap]u8 = undefined;
    const out = p.fs.stage(p.gpa);
    out.appendSlice(p.gpa, paneText(p, pane, &buf)) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

/// `get` reloads the buffer from the name it carries, wherever that name
/// resolves. Any other line is a builtin that acts on a pane (`Del`,
/// `Save f`), run at this one; a session's builtin is the root ctl's.
///
/// `lock` and `unlock` are acme's (editors/acme/xfid.c:603-611), so that a
/// client can make an edit of several writes to addr and data without
/// another's landing in between. As in acme the lock binds only the clients
/// that ask for it; a write to any other file is never refused for it, nor
/// is the person at the keyboard. It belongs to the open that wrote it,
/// which alone may `unlock`, and closing that open or the pane gives it up.
/// Where acme's qlock blocks a second locker, this refuses it at once with
/// `file in use`, and the client tries again: through a kernel or FUSE
/// mount a blocked write holds the file's writes, the holder's own `unlock`
/// and close among them, so a waiting lock would never be let in.
pub fn writePane(p: *Pardes, req: Req, pane: *Pane) Reply {
    // This open's handle is what holds the lock; a write that came on no
    // writable open (the editor's own) has none.
    const mine: ?u32 = if (tree.openOf(p, req)) |o| (if (o.what == .ctl) req.handle else null) else null;
    // The pane keeps the holder's handle, which names that open only on
    // this pane's ctl node; one that no longer does holds nothing.
    if (pane.fs.lock) |h| {
        const o = tree.openOf(p, .{ .tag = 0, .op = .write, .node = tree.Node.of(pane.serial, .ctl), .handle = h });
        if (o == null or o.?.what != .ctl) pane.fs.lock = null;
    }
    const other = pane.fs.lock != null and pane.fs.lock != mine;
    const serial = pane.serial;
    // Checked whole before anything applies, so a write that must wait for
    // the lock has done nothing yet when it goes again.
    for ([2]bool{ false, true }) |apply| {
        if (apply) p.fs.results_len = 0;
        var held = !other and pane.fs.lock != null;
        var it = Messages.init(p, req.data);
        while (it.next()) |line| {
            if (line.len == 0) continue;
            // A line before this one may have closed the pane (`Del`).
            if (apply and p.paneBySerial(serial) == null) return Reply.fail(req.tag, E.NOENT);
            if (std.mem.eql(u8, line, "get")) {
                if (!apply) continue;
                // Quoting the line, as a builtin's refusal (Save's) does.
                if (getRefused(p, pane)) |said_in_ename| {
                    // refuse writes ename, where the words are: copy them out.
                    var said_buf: [320]u8 = undefined;
                    const said = said_buf[0..said_in_ename.len];
                    @memcpy(said, said_in_ename);
                    const r = refuse(p, req, said, line);
                    return .{ .tag = req.tag, .status = .err, .errno = E.IO, .ename = r.ename };
                }
                const errno = get(p, pane);
                if (errno != 0) return Reply.fail(req.tag, errno);
            } else if (std.mem.eql(u8, line, "lock")) {
                if (mine == null) return tree.failText(req.tag, E.INVAL, tree.e_bad_ctl);
                if (other) return tree.failText(req.tag, E.BUSY, e_locked);
                held = true;
                if (apply) pane.fs.lock = mine;
            } else if (std.mem.eql(u8, line, "unlock")) {
                if (!held) return tree.failText(req.tag, E.INVAL, e_not_locked);
                held = false;
                if (apply) pane.fs.lock = null;
            } else if (std.mem.eql(u8, line, "answer")) {
                // With a question up, what it offers.
                var offered: [64]u8 = undefined;
                if (p.questionChoices(p.paneBySerial(serial).?, &offered)) |choices| {
                    var why: [96]u8 = undefined;
                    return tree.failText(req.tag, E.INVAL, std.fmt.bufPrint(&p.fs.ename, "answer takes {s} or -", .{choices}) catch std.fmt.bufPrint(&why, "answer takes a choice or -", .{}) catch "answer takes a choice or -");
                }
                return tree.failText(req.tag, E.INVAL, "answer takes a choice or -");
            } else if (std.mem.startsWith(u8, line, "answer ") and p.panes[p.paneBySerial(serial).?].?.prompt == .save) {
                // Save's path, asked over 9P (`ask <serial> save path`).
                if (!apply) continue;
                const id = p.paneBySerial(serial).?;
                const asked = p.panes[id].?;
                const path = std.mem.trim(u8, line["answer ".len..], " ");
                var rec: [300]u8 = undefined;
                pardes.ctlfs.events.notePath(p, "answer", std.fmt.bufPrint(&rec, "{d} {s}", .{ serial, path[0..@min(path.len, 256)] }) catch "");
                if (!std.mem.eql(u8, path, "-")) exec_line.saveTo(p, id, path);
                asked.closePrompt();
            } else if (std.mem.startsWith(u8, line, "answer ")) {
                // The pane's question (its `ask` in the log), answered.
                const choice = std.mem.trim(u8, line["answer ".len..], " ");
                const id = p.paneBySerial(serial).?;
                var offered: [64]u8 = undefined;
                const choices = p.questionChoices(id, &offered) orelse return refuse(p, req, "no question asked", line);
                // Only a choice the question offers answers it; anything
                // else leaves it standing, and says what it takes.
                if (!std.mem.eql(u8, choice, "-") and (choice.len != 1 or std.mem.indexOfScalar(u8, choices, choice[0]) == null)) {
                    var why: [96]u8 = undefined;
                    return refuse(p, req, std.fmt.bufPrint(&why, "answer takes {s} or -", .{choices}) catch "answer takes a choice or -", line);
                }
                if (apply) _ = p.answerQuestion(id, if (choice[0] == '-') null else choice[0]);
            } else if (!apply) {
                if (checkBuiltin(p, req, line, .pane)) |refusal| return refusal;
            } else if (runBuiltin(p, req, p.paneBySerial(serial).?, line)) |refusal| {
                return refusal;
            }
        }
    }
    return .{ .tag = req.tag, .written = @intCast(req.data.len) };
}

const e_not_locked = "pane not locked by this open";
/// Who holds it is another open of this ctl, whose client pardes cannot name.
const e_locked = tree.e_in_use ++ ": another open of this ctl holds the lock";

/// acme's get asks winclean first (exec.c:513): unsaved text is warned
/// about once, and the same get again, nothing edited since, discards it.
fn getRefused(p: *Pardes, pane: *Pane) ?[]const u8 {
    const f = pane_files.fileOf(pane) orelse return null;
    if (!panes.Output.fileTraits(f.output).saves or f.revision == f.saved_revision) return null;
    // Dirty by a rename alone is no text to lose: only edits are asked about.
    const saved = f.saved_hash orelse return null;
    if (std.hash.Wyhash.hash(0, f.content) == saved) return null;
    if (pane.discard_warned) |w| if (w.revision == f.revision and w.by == .get) return null;
    pane.discard_warned = .{ .revision = f.revision, .by = .get };
    const said = std.fmt.bufPrint(&p.fs.ename, "{s}: Modified (get again to discard)", .{f.path}) catch "Modified (get again to discard)";
    p.setMessage(p.paneBySerial(pane.serial).?, said);
    return said;
}

fn get(p: *Pardes, pane: *Pane) u16 {
    const f = pane_files.fileOf(pane) orelse return 0;
    if (!panes.Output.fileTraits(f.output).saves) return 0;
    const bytes = fs.read(p, f.path) catch |err| return switch (err) {
        error.FileNotFound => E.NOENT,
        else => E.IO,
    };
    panes.File.pushUndo(p, pane);
    panes.File.setContent(p, f, bytes);
    f.saved_revision = f.revision;
    f.saved_hash = std.hash.Wyhash.hash(0, f.content);
    f.disk_newer = null;
    return 0;
}

// ---- tests ----

const testing = std.testing;
const th = @import("testing.zig");
const call = th.call;
const rd = th.rd;
const wr = th.wr;
const withFile = th.withFile;
const serialOf = th.serialOf;
const Node = tree.Node;
const Status = tree.Status;
const root_status = @intFromEnum(tree.TopFile.status);
const root_look = @intFromEnum(tree.TopFile.look);
const root_exec = @intFromEnum(tree.TopFile.exec);

test "pane ctl read is index's five fields plus width in cells, font, tab width and whether it is current" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const pane = p.panes[0].?;

    const a = rd(p, Node.of(pane.serial, .ctl), 0, 4096);
    try testing.expectEqual(Status.ok, a.reply.status);
    var want: std.ArrayList(u8) = .empty;
    defer want.deinit(gpa);
    try want.print(gpa, "{d:>11} {d:>11} {d:>11} {d:>11} {d:>11} {d:>11} {s} {d:>11} current ", .{
        pane.serial, pane_files.tagOf(p, pane).len, @as(usize, 2), 0, 0, pane.cols, "default", config.tab_width,
    });
    try testing.expectEqualStrings(want.items, a.bytes);
    try testing.expectEqual(@as(u64, a.bytes.len), call(p, .{ .tag = 1, .op = .getattr, .node = Node.of(pane.serial, .ctl) }).reply.attr.size);

    var quoted: [64]u8 = undefined;
    var w = std.Io.Writer.fixed(&quoted);
    try writeQuoted(&w, "DejaVu Sans Mono");
    try testing.expectEqualStrings("'DejaVu Sans Mono'", w.buffered());
    w = std.Io.Writer.fixed(&quoted);
    try writeQuoted(&w, "it's");
    try testing.expectEqualStrings("'it''s'", w.buffered());
}

test "commands lists every builtin with its argument and the ctl that takes it" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const node = @intFromEnum(tree.TopFile.commands);
    const listed = rd(p, node, 0, 1 << 16);
    try testing.expectEqual(@as(u64, listed.bytes.len), call(p, .{ .tag = 1, .op = .getattr, .node = node }).reply.attr.size);
    try testing.expectEqual(E.PERM, wr(p, node, "Del\n").errno());
    var lines: usize = 0;
    var it = std.mem.tokenizeScalar(u8, listed.bytes, '\n');
    while (it.next()) |line| : (lines += 1) {
        var words = std.mem.tokenizeScalar(u8, line, ' ');
        const b = std.meta.stringToEnum(Builtin, words.next().?).?;
        if (builtins.registry.takesArg(b)) try testing.expectEqualStrings("arg", words.next().?);
        try testing.expectEqualStrings(if (b == .Edit) "both" else if (builtins.registry.scope(b) == .session) "root" else "pane", words.next().?);
        if (config.Runtime.find(@tagName(b))) |s| if (config.Runtime.choices(s.action) != null) try testing.expect(words.next() != null);
        // Then, where the source has one, ` -- ` and what it does.
        if (words.next()) |dashes| try testing.expectEqualStrings("--", dashes);
    }
    try testing.expectEqual(std.enums.values(Builtin).len, lines);
    for ([_][]const u8{ "\nDel arg pane -- ", "\nNewcol root -- ", "\nSave arg pane", "\nVerbose arg root on,off", "\nPlacement arg root acme,pardes", "\nUndo pane -- ", "\nEdit arg both -- acme's Edit" }) |row|
        try testing.expect(std.mem.indexOf(u8, listed.bytes, row) != null);
}

test "Undo and Redo on a pane's ctl step its body through its edits" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const serial = serialOf(p);
    const body = Node.of(serial, .body);
    try testing.expectEqual(Status.ok, wr(p, body, "two\n").reply.status);
    try testing.expectEqualStrings("one\ntwo\n", rd(p, body, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Undo").reply.status);
    try testing.expectEqualStrings("one\n", rd(p, body, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Redo").reply.status);
    try testing.expectEqualStrings("one\ntwo\n", rd(p, body, 0, 64).bytes);
    // Nothing left: said, and the write still succeeds, as acme's is silent.
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Redo").reply.status);
    try testing.expect(th.logHas(p, "Redo: nothing to redo"));
    _ = wr(p, Node.of(serial, .ctl), "Undo");
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Undo").reply.status);
    try testing.expect(th.logHas(p, "Undo: nothing to undo"));
    // Said again word for word, it is that line counted, as err's are.
    for (0..3) |_| _ = wr(p, Node.of(serial, .ctl), "Undo");
    try testing.expect(th.logHas(p, "Undo: nothing to undo (x4)\n"));
}

test "focus reads the pane with the keyboard, and a serial written to it moves the keyboard there" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const first = serialOf(p);
    const second = try th.newPane(p);
    const focus = @intFromEnum(tree.TopFile.focus);
    var line: [16]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&line, "{d}\n", .{second}), rd(p, focus, 0, 64).bytes);
    try testing.expectEqual(@as(u64, rd(p, focus, 0, 64).bytes.len), call(p, .{ .tag = 1, .op = .getattr, .node = focus }).reply.attr.size);
    try testing.expect(std.mem.endsWith(u8, rd(p, Node.of(first, .ctl), 0, 4096).bytes, " notcurrent "));

    // A header has the keyboard: no pane does, and a write takes it back.
    tagline.enterHeader(p, null);
    try testing.expectEqualStrings("", rd(p, focus, 0, 64).bytes);
    try testing.expectEqual(@as(u64, 0), call(p, .{ .tag = 1, .op = .getattr, .node = focus }).reply.attr.size);
    try testing.expect(std.mem.endsWith(u8, rd(p, Node.of(second, .ctl), 0, 4096).bytes, " notcurrent "));
    try testing.expectEqual(Status.ok, wr(p, focus, try std.fmt.bufPrint(&line, "{d}\n", .{first})).reply.status);
    try testing.expect(!p.header_focus);
    try testing.expectEqual(p.paneBySerial(first).?, p.active);
    try testing.expect(std.mem.endsWith(u8, rd(p, Node.of(first, .ctl), 0, 4096).bytes, " current "));
    try testing.expect(std.mem.endsWith(u8, rd(p, Node.of(second, .ctl), 0, 4096).bytes, " notcurrent "));

    try testing.expectEqualStrings(e_no_pane, wr(p, focus, "99999\n").reply.ename);
    try testing.expectEqual(E.NOENT, wr(p, focus, "99999").errno());
    for ([_][]const u8{ "", "two", "-1", "1 2" }) |bad| try testing.expectEqual(E.INVAL, wr(p, focus, bad).errno());
    try testing.expectEqual(p.paneBySerial(first).?, p.active);

    // Focus gives the keyboard only: a folded pane stays folded.
    const folded = p.paneBySerial(second).?;
    layout.toggleCollapse(p, folded);
    try testing.expect(p.panes[folded].?.collapsed);
    try testing.expectEqual(Status.ok, wr(p, focus, try std.fmt.bufPrint(&line, "{d}", .{second})).reply.status);
    try testing.expectEqual(folded, p.active);
    try testing.expect(p.panes[folded].?.collapsed);
}

test "the pane ctl takes acme's verbs and the pane's builtins, and refuses the rest in Plan 9's words" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "one\ntwo\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    // acme's other ctl words have files of their own here, and a builtin is
    // its own capitalised word: `Get`, `DEL` and `del` are none of them.
    for ([_][]const u8{
        "menu", "nomenu",     "dump echo hi", "font Go Mono", "lock x", "bogus", "DEL",
        "put",  "del",        "delete",       "clean",        "dirty",  "show",  "mark",
        "Get",  "limit=addr", "get x",        "look /tmp",    "exec Del",
    }) |bad| {
        const refused = wr(p, ctl_node, bad);
        try testing.expectEqual(E.INVAL, refused.errno());
        var want: [64]u8 = undefined;
        try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "unknown control message \"{s}\"", .{bad}), refused.reply.ename);
    }
    try testing.expectEqualStrings("not a window control message \"Newcol\": write it to /ctl", wr(p, ctl_node, "Newcol").reply.ename);
    try testing.expectEqualStrings("not a window control message \"Verbose off\": write it to /ctl", wr(p, ctl_node, "Verbose off").reply.ename);
    try testing.expectEqualStrings("wrong #args in control message \"Collapse now\"", wr(p, ctl_node, "Collapse now").reply.ename);
    // Checked whole first: a bad line anywhere and nothing ran.
    try testing.expectEqual(E.INVAL, wr(p, ctl_node, "Msg first\nbogus").errno());
    try testing.expect(p.panes[0].?.msg_len == 0 or !std.mem.eql(u8, p.panes[0].?.msg[0..p.panes[0].?.msg_len], "first"));

    // A pane's builtin runs at that pane.
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "Msg from ctl\n").reply.status);
    const pane = p.panes[p.paneBySerial(serial).?].?;
    try testing.expectEqualStrings("from ctl", pane.msg[0..pane.msg_len]);
    // One that means nothing bare is refused before anything runs.
    try testing.expectEqualStrings("wrong #args in control message \"Find\"", wr(p, ctl_node, "Find").reply.ename);
    try testing.expectEqual(E.INVAL, wr(p, ctl_node, "Msg first\nMsg").errno());
    try testing.expect(!std.mem.eql(u8, pane.msg[0..pane.msg_len], "first"));
    try testing.expect(pane.prompt == .none);
    try testing.expect(!p.fs.no_prompt);
    // Save with no name on a scratch would ask for one: refused, not asked.
    const other = try th.newPane(p);
    try testing.expectEqualStrings(e_prompt ++ " \"Save\"", wr(p, Node.of(other, .ctl), "Save").reply.ename);
    try testing.expect(p.panes[p.paneBySerial(other).?].?.prompt == .none);
    // A line after the one that closed the pane has nowhere to run.
    try testing.expectEqual(E.NOENT, wr(p, Node.of(other, .ctl), "Del\nMsg after").errno());
    try testing.expect(p.paneBySerial(other) == null);
}

test "the root ctl reads the settings as a write takes them, and takes the session's builtins" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const first = rd(p, root_ctl, 0, 1 << 16);
    try testing.expectEqual(Status.ok, first.reply.status);
    const settings = try gpa.dupe(u8, first.bytes);
    defer gpa.free(settings);
    try testing.expectEqual(@as(u64, settings.len), call(p, .{ .tag = 1, .op = .getattr, .node = root_ctl }).reply.attr.size);
    try testing.expect(std.mem.indexOf(u8, settings, "Verbose on\n") != null);
    try testing.expect(std.mem.indexOf(u8, settings, "LocationsConfig ") != null);
    // Settings only: nothing /status or the Config window says.
    try testing.expect(std.mem.indexOf(u8, settings, "Platform") == null);
    try testing.expect(std.mem.indexOf(u8, settings, "requested") == null);

    // Every line written back is taken, and changes nothing.
    try testing.expectEqual(Status.ok, wr(p, root_ctl, settings).reply.status);
    try testing.expectEqualStrings(settings, rd(p, root_ctl, 0, 1 << 16).bytes);

    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Verbose off\n").reply.status);
    try testing.expect(!p.settings.verbose);
    try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 1 << 16).bytes, "Verbose off\n") != null);
    const columns = p.ncol;
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Newcol\n").reply.status);
    try testing.expectEqual(columns + 1, p.ncol);

    try testing.expectEqualStrings("not a session control message \"Del\": write it to pane/<n>/ctl", wr(p, root_ctl, "Del").reply.ename);
    try testing.expectEqualStrings("unknown control message \"Nonsense 1\"", wr(p, root_ctl, "Nonsense 1").reply.ename);
    try testing.expectEqualStrings("bad value in control message; takes on, off \"Verbose maybe\"", wr(p, root_ctl, "Verbose maybe").reply.ename);
    try testing.expectEqualStrings("bad value in control message; takes acme, pardes \"Placement east\"", wr(p, root_ctl, "Placement east").reply.ename);
    const no_theme = wr(p, root_ctl, "Theme no-such-theme").reply.ename;
    try testing.expectStringStartsWith(no_theme, "bad value in control message; like it: n");
    try testing.expect(std.mem.endsWith(u8, no_theme, "; ThemeSel lists all \"Theme no-such-theme\""));
    try testing.expectEqualStrings("wrong #args in control message \"Newcol 2\"", wr(p, root_ctl, "Newcol 2").reply.ename);
    try testing.expectEqualStrings("wrong #args in control message \"Theme\"", wr(p, root_ctl, "Theme").reply.ename);
    // A bare required word fails the check, so the line before never runs.
    try testing.expectEqual(E.INVAL, wr(p, root_ctl, "Verbose on\nMount").errno());
    try testing.expect(!p.settings.verbose);
    // A builtin that fails as it runs fails the write, quoting its error and
    // its line; the lines before it have taken effect, as in acme.
    const failed = wr(p, root_ctl, "Verbose on\nMount x\nVerbose off");
    try testing.expectEqual(E.IO, failed.errno());
    try testing.expectEqualStrings("Mount name dial: missing argument \"Mount x\"", failed.reply.ename);
    try testing.expect(p.settings.verbose);
    try testing.expect(!p.fs.no_prompt);
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Verbose off").reply.status);
}


test "a second lock is refused until the holder unlocks or closes, and binds nobody else" {
    const p = try withFile(testing.allocator, "one\ntwo\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    const w = struct {
        fn ctl(pp: *Pardes, node: u64, h: u32, data: []const u8) th.Answer {
            return call(pp, .{ .tag = 4, .op = .write, .node = node, .handle = h, .data = data });
        }
    };
    const a = call(p, .{ .tag = 1, .op = .open, .node = ctl_node, .omode = 2 }).reply.handle;
    const b = call(p, .{ .tag = 2, .op = .open, .node = ctl_node, .omode = 1 }).reply.handle;
    try testing.expect(a != 0 and b != 0 and a != b);
    // Reading the status line holds nothing, so it cannot lock either.
    try testing.expectEqual(@as(u32, 0), call(p, .{ .tag = 3, .op = .open, .node = ctl_node }).reply.handle);
    try testing.expectEqual(E.INVAL, wr(p, ctl_node, "lock\n").errno());

    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, a, "lock\n").reply.status);
    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, a, "lock\n").reply.status);
    // Another open's lock is refused at once, and so is its unlock; writes
    // to the pane's other files are not.
    try testing.expectEqualStrings(e_locked, w.ctl(p, ctl_node, b, "lock\n").reply.ename);
    try testing.expectEqual(E.BUSY, w.ctl(p, ctl_node, b, "lock\n").errno());
    try testing.expectEqualStrings(e_not_locked, w.ctl(p, ctl_node, b, "unlock\n").reply.ename);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .addr), "1").reply.status);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .data), "ONE\n").reply.status);
    try testing.expectEqualStrings("ONE\ntwo\n", p.panes[0].?.file.?.content);

    // Once the holder unlocks, the other's try takes it.
    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, a, "unlock\n").reply.status);
    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, b, "lock\n").reply.status);
    try testing.expectEqual(E.BUSY, w.ctl(p, ctl_node, a, "lock\nunlock\n").errno());
    // Closing the holder gives it up.
    _ = call(p, .{ .tag = 5, .op = .release, .node = ctl_node, .handle = b });
    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, a, "lock\nunlock\nlock\n").reply.status);
    try testing.expectEqual(E.INVAL, w.ctl(p, ctl_node, a, "unlock\nunlock\n").errno());
    try testing.expectEqual(@as(?u32, a), p.panes[0].?.fs.lock);

    // The lock lives and dies with the pane.
    const other = try th.newPane(p);
    const other_ctl = Node.of(other, .ctl);
    const c = call(p, .{ .tag = 6, .op = .open, .node = other_ctl, .omode = 1 }).reply.handle;
    try testing.expectEqual(Status.ok, w.ctl(p, other_ctl, c, "lock\n").reply.status);
    try testing.expectEqual(Status.ok, th.rmdir(p, Node.of(other, .dir)).reply.status);
    try testing.expectEqual(E.NOENT, w.ctl(p, other_ctl, c, "lock\n").errno());
    for ([_]u64{ ctl_node, other_ctl }, [_]u32{ a, c }) |node, h|
        _ = call(p, .{ .tag = 7, .op = .release, .node = node, .handle = h });
    try testing.expect(p.panes[0].?.fs.lock == null);
    for (p.fs.opens) |o| try testing.expect(o.node == 0);
}

test "Edit through a pane's ctl renames every foo in one undo step, and a failed one changes nothing" {
    const p = try withFile(testing.allocator, "foo x foo y foo\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    const body = Node.of(serial, .body);
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "Edit ,x/foo/c/foobar/\n").reply.status);
    try testing.expectEqualStrings("foobar x foobar y foobar\n", rd(p, body, 0, 64).bytes);
    const failed = wr(p, ctl_node, "Edit ,s/nothing/x/\n");
    try testing.expectEqual(E.IO, failed.errno());
    try testing.expectStringStartsWith(failed.reply.ename, "Edit: no substitution");
    try testing.expectEqualStrings("foobar x foobar y foobar\n", rd(p, body, 0, 64).bytes);
    // The whole rename is one undo step.
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "Undo").reply.status);
    try testing.expectEqualStrings("foo x foo y foo\n", rd(p, body, 0, 64).bytes);
}

test "a write of an Edit block carries it whole, to a pane's ctl, the root's ctl and exec" {
    const p = try withFile(testing.allocator, "foo x\nfoo y\n");
    defer p.deinit();
    const serial = serialOf(p);
    const body = Node.of(serial, .body);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Edit ,x/foo/{\ni/[/\na/]/\n}\n").reply.status);
    try testing.expectEqualStrings("[foo] x\n[foo] y\n", rd(p, body, 0, 64).bytes);
    p.active = p.paneBySerial(serial).?;
    try testing.expectEqual(Status.ok, wr(p, @intFromEnum(tree.TopFile.ctl), "Edit ,x/\\[/{\nc/</\n}\n").reply.status);
    try testing.expectEqualStrings("<foo] x\n<foo] y\n", rd(p, body, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "Edit $a\nend\n.\n").reply.status);
    try testing.expectEqualStrings("<foo] x\n<foo] y\nend\n", rd(p, body, 0, 64).bytes);
    // An unclosed group is refused, and nothing after it runs as a line.
    try testing.expectEqual(E.IO, wr(p, Node.of(serial, .ctl), "Edit ,x/foo/{\nd\n").errno());
    try testing.expectEqualStrings("<foo] x\n<foo] y\nend\n", rd(p, body, 0, 64).bytes);
}

test "dirty goes back to 0 when the text is the saved text again" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const serial = serialOf(p);
    const dirty = Node.of(serial, .dirty);
    try testing.expectEqualStrings("0\n", rd(p, dirty, 0, 8).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .body), "two\n").reply.status);
    try testing.expectEqualStrings("1\n", rd(p, dirty, 0, 8).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Undo").reply.status);
    try testing.expectEqualStrings("0\n", rd(p, dirty, 0, 8).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Redo").reply.status);
    try testing.expectEqualStrings("1\n", rd(p, dirty, 0, 8).bytes);
}

test "a message from a root ctl write is the session's in the log" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.update(.tick); // the pane's `new` is logged before the log is opened
    while (p.nextEffect()) |_| {}
    const log = @intFromEnum(tree.TopFile.log);
    const f = call(p, .{ .tag = 1, .op = .open, .node = log }).reply.handle;
    const frozen = call(p, .{ .tag = 2, .op = .read, .node = log, .handle = f, .size = 8192 }).bytes.len;
    _ = call(p, .{ .tag = 3, .op = .write, .node = log, .handle = f, .data = "follow" });
    try testing.expectEqual(Status.ok, wr(p, @intFromEnum(tree.TopFile.ctl), "Kill\n").reply.status);
    // What it said, the session's; its own words name it, so its Verbose
    // announcement gives way to them.
    try testing.expectEqualStrings("msg - Kill: nothing running\n", call(p, .{ .tag = 5, .op = .read, .node = log, .handle = f, .off = frozen, .size = 4096 }).bytes);
}

test "a look takes acme's :addr and file:addr, and a miss changes nothing" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "foo x foo y\nbar\n");
    defer p.deinit();
    const serial = serialOf(p);
    const look_node = Node.of(serial, .look);
    const dot = Node.of(serial, .dot);
    // :addr is an address in this pane, evaluated from its dot.
    try testing.expectEqual(Status.ok, wr(p, look_node, ":/y/\n").reply.status);
    try testing.expectEqualStrings("         10          11 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, look_node, ":#4\n").reply.status);
    try testing.expectEqualStrings("          4           4 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, look_node, ":/foo/\n").reply.status); // from #4: the second foo
    try testing.expectEqualStrings("          6           9 ", rd(p, dot, 0, 64).bytes);
    // file:addr names the pane's own file here.
    var line: [256]u8 = undefined;
    const path = p.panes[0].?.file.?.path;
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&line, "{s}:/bar/\n", .{path})).reply.status);
    try testing.expectEqualStrings("         12          15 ", rd(p, dot, 0, 64).bytes);
    // A miss: no buffer, the selection kept, and it says so.
    const panes_before = p.panes.len - std.mem.count(?*pardes.Pane, &p.panes, &.{null});
    try testing.expectEqual(Status.ok, wr(p, look_node, "zzqq\n").reply.status);
    try testing.expectEqual(panes_before, p.panes.len - std.mem.count(?*pardes.Pane, &p.panes, &.{null}));
    try testing.expectEqualStrings("         12          15 ", rd(p, dot, 0, 64).bytes);
    try testing.expectStringStartsWith(p.panes[0].?.msg[0..p.panes[0].?.msg_len], "Look: no match");
    // A hit answers the pane the text is selected in, not its hits buffer.
    try testing.expectEqual(Status.ok, wr(p, look_node, "foo\n").reply.status);
    var own: [16]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&own, "{d}\n", .{serial}), rd(p, look_node, 0, 64).bytes);
    // A pattern with a blank in it; 0/re/ searches from the top, whatever dot is.
    try testing.expectEqual(Status.ok, wr(p, look_node, ":/foo y/\n").reply.status);
    try testing.expectEqualStrings("          6          11 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&line, "{s}:0/foo/\n", .{path})).reply.status);
    try testing.expectEqualStrings("          0           3 ", rd(p, dot, 0, 64).bytes);
    // file:N selects the line; a line past the end moves nothing and reads back empty.
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&line, "{s}:2\n", .{path})).reply.status);
    try testing.expectEqualStrings("         12          16 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&line, "{s}:99\n", .{path})).reply.status);
    try testing.expectEqualStrings("         12          16 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqualStrings("", rd(p, look_node, 0, 64).bytes);
    try testing.expectStringStartsWith(p.panes[0].?.msg[0..p.panes[0].?.msg_len], "Look: ");
}

test "the root look's file:/re/ goes on from the dot, and a miss leaves the dot as it was" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "foo x foo y\nfoo\n");
    defer p.deinit();
    const dot = Node.of(serialOf(p), .dot);
    const root = @intFromEnum(tree.TopFile.look);
    var line: [256]u8 = undefined;
    const path = p.panes[0].?.file.?.path;
    const again = try std.fmt.bufPrint(&line, "{s}:/foo/\n", .{path});
    for ([_][]const u8{ "          0           3 ", "          6           9 ", "         12          15 ", "          0           3 " }) |want| {
        try testing.expectEqual(Status.ok, wr(p, root, again).reply.status);
        try testing.expectEqualStrings(want, rd(p, dot, 0, 64).bytes);
    }
    try testing.expectEqual(Status.ok, wr(p, root, try std.fmt.bufPrint(&line, "{s}:/zzqq/\n", .{path})).reply.status);
    try testing.expectEqualStrings("          0           3 ", rd(p, dot, 0, 64).bytes);
}

test "a look's miss repeats the path whole up to 256 bytes, then cuts it with an ellipsis" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const root = @intFromEnum(tree.TopFile.look);
    const long = "some/deeply/nested/directory/that/goes/on/and/on/with/a_rather_long_file_name.txt";
    var line: [512]u8 = undefined;
    _ = wr(p, root, try std.fmt.bufPrint(&line, "{s}\n", .{long}));
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&line, "look: no match for \"{s}\"\n", .{long})));
    const huge = "é" ** 150; // 300 bytes: cut at 256, between characters
    _ = wr(p, root, huge ++ "\n");
    try testing.expect(th.logHas(p, "look: no match for \"" ++ "é" ** 128 ++ "…\"\n"));
}

test "exec runs a builtin at the pane and records the pane it acted on" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "Msg fs-ran\n");
    defer p.deinit();
    const serial = serialOf(p);
    const pane = p.panes[0].?;
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "Msg from exec\n").reply.status);
    try testing.expectEqualStrings("from exec", pane.msg[0..pane.msg_len]);
    var expected: [16]u8 = undefined;
    const own = try std.fmt.bufPrint(&expected, "{d}\n", .{serial});
    try testing.expectEqualStrings(own, rd(p, root_exec, 0, 4096).bytes);
    // Either command file reads back what the last one did.
    try testing.expectEqualStrings(own, rd(p, Node.of(serial, .look), 0, 4096).bytes);
    try testing.expectEqual(@as(u64, own.len), call(p, .{ .tag = 1, .op = .getattr, .node = root_exec }).reply.attr.size);

    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "New\n").reply.status);
    const made = p.panes[p.active].?;
    try testing.expect(made.serial != serial);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{made.serial}), rd(p, root_exec, 0, 4096).bytes);

    try testing.expectEqual(Status.ok, wr(p, Node.of(made.serial, .exec), "Del\n").reply.status);
    try testing.expect(p.paneBySerial(made.serial) == null);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{made.serial}), rd(p, root_exec, 0, 4096).bytes);
}

test "status reads the editor, and look and exec validate whole batches" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "Msg root\n");
    defer p.deinit();
    const status = rd(p, root_status, 0, 4096);
    try testing.expectEqual(Status.ok, status.reply.status);
    var lines = std.mem.tokenizeScalar(u8, status.bytes, '\n');
    try testing.expect(std.mem.startsWith(u8, lines.next().?, "pid "));
    var expected: [64]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "version {s}", .{pardes.version}), lines.next().?);
    var live: usize = 0;
    for (p.panes) |slot| live += @intFromBool(slot != null);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "panes {d}", .{live}), lines.next().?);
    try testing.expect(lines.next() == null);
    const stat = call(p, .{ .tag = 1, .op = .getattr, .node = root_status });
    try testing.expectEqual(@as(u64, status.bytes.len), stat.reply.attr.size);
    try testing.expectEqual(@as(u16, 0o444), stat.reply.attr.mode);
    try testing.expectEqual(E.PERM, wr(p, root_status, "anything\n").errno());
    try testing.expectEqualStrings("", rd(p, root_exec, 0, 4096).bytes);

    const serial = p.next_serial;
    for ([_][]const u8{ "Msg a\x00b", "Msg x\nMsg \x01y\n" }) |invalid| {
        try testing.expectEqual(E.INVAL, wr(p, root_exec, invalid).errno());
        try testing.expectEqual(serial, p.next_serial);
    }
    // An empty write is a no-op, not a command.
    try testing.expectEqual(Status.ok, wr(p, root_exec, "\n \n").reply.status);
    try testing.expectEqualStrings("", rd(p, root_exec, 0, 4096).bytes);
    try testing.expectEqualStrings(status.bytes, rd(p, root_status, 0, 4096).bytes);

    const pane = p.panes[0].?;
    try testing.expectEqual(Status.ok, wr(p, root_exec, "Msg hello there\n").reply.status);
    try testing.expectEqualStrings("hello there", pane.msg[0..pane.msg_len]);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{pane.serial}), rd(p, root_exec, 0, 4096).bytes);

    try testing.expectEqual(Status.ok, wr(p, root_look, "/virtual/index\n").reply.status);
    const opened = p.panes[p.active].?;
    try testing.expectEqualStrings("/virtual/index", opened.file.?.path);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{opened.serial}), rd(p, root_look, 0, 4096).bytes);

    try testing.expectEqual(Status.ok, wr(p, root_exec, "New\n").reply.status);
    const made = p.panes[p.active].?;
    try testing.expect(made.serial != opened.serial);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{made.serial}), rd(p, root_exec, 0, 4096).bytes);
}

test "look opens spaced paths and locations without editing the source pane" {
    if (!fs.platform_has_fs) return error.SkipZigTest;
    const gpa = testing.allocator;
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "two words.zig", .data = "first\nsecond\nthird\n" });
    var path_buf: [4096]u8 = undefined;
    const path = path_buf[0..try tmp.dir.realPathFile(testing.io, "two words.zig", &path_buf)];
    const p = try withFile(gpa, "source stays intact\n");
    defer p.deinit();
    const source = p.panes[0].?;
    const look_node = Node.of(source.serial, .look);
    const revision = source.file.?.revision;
    const undo_len = source.file.?.history.undo_len;
    source.body.cur_col = 3;
    var clicked: [4200]u8 = undefined;
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&clicked, "{s}:2:3\n", .{path})).reply.status);
    const opened = p.panes[p.active].?;
    try testing.expect(opened != source);
    try testing.expectEqualStrings(path, opened.file.?.path);
    try testing.expectEqualStrings("first\nsecond\nthird\n", opened.file.?.content);
    try testing.expectEqual(@as(i32, 1), opened.body.cur_row);
    try testing.expectEqual(@as(i32, 2), opened.body.cur_col);
    try testing.expectEqualStrings("source stays intact\n", source.file.?.content);
    try testing.expectEqual(revision, source.file.?.revision);
    try testing.expectEqual(undo_len, source.file.?.history.undo_len);
    try testing.expectEqual(@as(i32, 3), source.body.cur_col);
    var expected: [16]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{opened.serial}), rd(p, root_look, 0, 4096).bytes);

    p.active = 0;
    try testing.expectEqual(Status.ok, wr(p, root_look, try std.fmt.bufPrint(&clicked, "{s}:3:2\n", .{path})).reply.status);
    try testing.expect(p.panes[p.active].? == opened);
    try testing.expectEqual(@as(i32, 2), opened.body.cur_row);
    try testing.expectEqual(@as(i32, 1), opened.body.cur_col);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{opened.serial}), rd(p, root_look, 0, 4096).bytes);
}

test "look validates the whole batch before opening virtual files" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "source\n");
    defer p.deinit();
    const source = p.panes[0].?;
    const look_node = Node.of(source.serial, .look);
    const serial = p.next_serial;
    for ([_][]const u8{
        "/virtual/index\x00ignored", "/virtual/index\n/virtual/\x01index\n",
    }) |invalid| {
        try testing.expectEqual(E.INVAL, wr(p, look_node, invalid).errno());
        try testing.expectEqual(serial, p.next_serial);
        try testing.expectEqual(@as(usize, 0), p.active);
        try testing.expectEqualStrings("source\n", source.file.?.content);
    }
    try testing.expectEqual(Status.ok, wr(p, look_node, "/n/self/index\n").reply.status);
    const opened = p.panes[p.active].?;
    try testing.expectEqualStrings("/virtual/index", opened.file.?.path);
    try testing.expect(std.mem.indexOf(u8, opened.file.?.content, "/test.txt") != null);
    try testing.expectEqualStrings("source\n", source.file.?.content);
}

test "get reloads the pane from disk and reports a missing file without losing dirty contents" {
    const gpa = testing.allocator;
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "note.txt", .data = "from disk\n" });
    var directory_buf: [4096]u8 = undefined;
    const directory = directory_buf[0..try tmp.dir.realPath(testing.io, &directory_buf)];
    var path_buf: [4096]u8 = undefined;
    const path = try std.fmt.bufPrint(&path_buf, "{s}/note.txt", .{directory});

    const p = try withFile(gpa, "in memory\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    const pane = p.panes[0].?;

    var name: [std.fs.max_path_bytes + 8]u8 = undefined;
    _ = wr(p, Node.of(serial, .name), try std.fmt.bufPrint(&name, "{s}\n", .{path}));
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "get\n").reply.status);
    try testing.expectEqualStrings("from disk\n", pane.file.?.content);
    try testing.expect(!pane_files.dirtyOf(pane));
    try testing.expect(pane.file.?.history.undo_len > 0);

    _ = wr(p, Node.of(serial, .name), try std.fmt.bufPrint(&name, "{s}/missing.txt\n", .{directory}));
    _ = wr(p, Node.of(serial, .body), "unsaved\n");
    // Unsaved text is asked about once, as acme's get asks winclean.
    const asked = wr(p, ctl_node, "get\n");
    try testing.expectEqual(E.IO, asked.errno());
    try testing.expect(std.mem.endsWith(u8, asked.reply.ename, ": Modified (get again to discard) \"get\""));
    try testing.expectEqual(E.NOENT, wr(p, ctl_node, "get\n").errno());
    try testing.expect(p.paneBySerial(serial) != null);
    try testing.expectEqualStrings("from disk\nunsaved\n", pane.file.?.content);
    try testing.expect(pane_files.dirtyOf(pane));
}

test "exec Save writes the named file through the host" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "one\ntwo\n");
    defer p.deinit();
    const serial = serialOf(p);
    const pane = p.panes[0].?;
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .name), "/tmp/renamed.txt\n").reply.status);
    try testing.expect(pane_files.dirtyOf(pane));
    const saved = wr(p, Node.of(serial, .exec), "Save\n");
    try testing.expectEqual(Status.ok, saved.reply.status);
    try testing.expect(saved.saved);
    p.perform(.{ .save_file = .{ .pane = 0 } });
    try testing.expect(!pane_files.dirtyOf(pane));
    try testing.expectEqualStrings(pane.file.?.content, p.fallback.get("/tmp/renamed.txt").?);
}

test "a pane's own look and exec go to the event reader holding it, which writes them back to act" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "Msg routed\n");
    defer p.deinit();
    const serial = serialOf(p);
    const event = Node.of(serial, .event);
    const h = call(p, .{ .tag = 1, .op = .open, .node = event }).reply.handle;
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(serial, .exec), "Msg routed\n").reply.status);
    // Not done: the reader has it, as it would a middle click.
    const pane = p.panes[0].?;
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "routed") == null);
    const record = call(p, .{ .tag = 2, .op = .read, .node = event, .handle = h, .size = 256 }).bytes;
    try testing.expectEqualStrings("FX0 0 2 10 Msg routed\n", record);
    // Written back, it is done.
    try testing.expectEqual(tree.Status.ok, wr(p, event, record).reply.status);
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "routed") != null);
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(serial, .look), "one.txt:3\n").reply.status);
    try testing.expectEqualStrings("FL0 0 6 9 one.txt:3\n", call(p, .{ .tag = 3, .op = .read, .node = event, .handle = h, .size = 256 }).bytes);
    // The root's is a click at the pane with the keyboard, this one.
    try testing.expectEqual(tree.Status.ok, wr(p, root_exec, "Msg rooted\n").reply.status);
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "rooted") == null);
    try testing.expectEqualStrings("FX0 0 2 10 Msg rooted\n", call(p, .{ .tag = 5, .op = .read, .node = event, .handle = h, .size = 256 }).bytes);
    _ = call(p, .{ .tag = 4, .op = .release, .node = event, .handle = h });
    // With no reader, the root's and the pane's act at once.
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(serial, .exec), "Msg direct\n").reply.status);
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "direct") != null);
}

test "look and exec read back what the last command touched, a ctl write's too" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    var want: [32]u8 = undefined;
    _ = wr(p, root_exec, "Msg first\n");
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{d}\n", .{serial}), rd(p, root_exec, 0, 64).bytes);
    // A pane made through ctl is what both read next, not the Msg's pane.
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(serial, .ctl), "Tty\n").reply.status);
    const made = p.panes[p.active].?.serial;
    try testing.expect(made != serial);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{d}\n", .{made}), rd(p, root_exec, 0, 64).bytes);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{d}\n", .{made}), rd(p, @intFromEnum(tree.TopFile.look), 0, 64).bytes);
    // A ctl write that makes nothing names the pane it ran at.
    try testing.expectEqual(tree.Status.ok, wr(p, @intFromEnum(tree.TopFile.ctl), "Verbose off\n").reply.status);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{d}\n", .{made}), rd(p, root_exec, 0, 64).bytes);
}

test "an error's words give the errno a mount reads: EINVAL for what is malformed, EIO for what failed" {
    // 9ns (cloud9's 9ns/src/nine.zig) maps an error to an errno by its
    // words, and EIO when none of them match: these words must not.
    const addressing = @import("addr.zig");
    const einval = [_][]const u8{ "control message", "invalid", "bad " };
    const other = [_][]const u8{ "interrupt", "shut down", "not exist", "not found", "no such", "exists", "not empty", "not a dir", "is a dir", "permission", "denied", "read-only", "read only", "no space", "not allowed", "not permitted", "cannot", "fid", "busy", "in use", "too long", "not supported", "unsupported" };
    const Case = struct { text: []const u8, malformed: bool };
    for ([_]Case{
        .{ .text = addressing.e_syntax, .malformed = true },
        .{ .text = addressing.e_regexp, .malformed = true },
        .{ .text = e_prompt, .malformed = true },
        .{ .text = addressing.e_no_match, .malformed = false },
        .{ .text = addressing.e_range, .malformed = false },
        .{ .text = addressing.e_order, .malformed = false },
        .{ .text = addressing.e_slow, .malformed = false },
        .{ .text = "/tmp/x.txt: Modified (Exit again to discard)", .malformed = false },
    }) |c| {
        const says_einval = for (einval) |w| {
            if (std.ascii.findIgnoreCase(c.text, w) != null) break true;
        } else false;
        try testing.expectEqual(c.malformed, says_einval);
        for (other) |w| try testing.expect(std.ascii.findIgnoreCase(c.text, w) == null);
    }
}

test "Joincol with no column to the right and Theme with no such theme say so" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const joined = wr(p, root_ctl, "Joincol\n");
    try testing.expectEqual(tree.Status.err, joined.reply.status);
    try testing.expectStringStartsWith(joined.reply.ename, "Joincol: no column to the right");
    const themed = wr(p, root_ctl, "Theme drak\n");
    try testing.expectEqual(E.INVAL, themed.errno());
    try testing.expectStringStartsWith(themed.reply.ename, "bad value in control message; like it: ");
    try testing.expect(std.mem.indexOf(u8, themed.reply.ename, " dark") != null or std.mem.indexOf(u8, themed.reply.ename, ": dark") != null);
    try testing.expect(std.mem.endsWith(u8, themed.reply.ename, "\"Theme drak\""));
    // A click on the word says it on the message row.
    _ = wr(p, Node.of(serialOf(p), .exec), "Theme drak\n");
    const pane = p.panes[p.active].?;
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "no theme \"drak\"") != null);
}

test "a look after Newcol fills the empty column the keyboard is on" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "f.txt", .data = "file\n" });
    var dir: [4096]u8 = undefined;
    const at = dir[0..try tmp.dir.realPath(testing.io, &dir)];
    var line: [4200]u8 = undefined;
    // Newcol makes an empty column and gives its tag the keyboard; no pane
    // has it, so focus reads empty.
    try testing.expectEqual(tree.Status.ok, wr(p, @intFromEnum(tree.TopFile.ctl), "Newcol\n").reply.status);
    try testing.expectEqual(@as(usize, 0), p.col_n[p.ncol - 1]);
    try testing.expectEqualStrings("", rd(p, @intFromEnum(tree.TopFile.focus), 0, 64).bytes);
    try testing.expectEqual(tree.Status.ok, wr(p, @intFromEnum(tree.TopFile.look), try std.fmt.bufPrint(&line, "{s}/f.txt\n", .{at})).reply.status);
    try testing.expectEqual(@as(usize, 1), p.col_n[p.ncol - 1]);
    try testing.expectEqual(p.active, p.col_panes[p.ncol - 1][0]);
}

test "a Restore of a file that is no dump fails the write before any warning, and a failed Dump fails its write" {
    if (comptime !pardes.hosted) return error.SkipZigTest;
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const f = pane_files.fileOf(p.panes[0].?).?;
    f.content = try p.gpa.realloc(f.content, 3);
    @memcpy(f.content, "yy\n");
    f.revision +%= 1; // unsaved: a Restore would warn about it first
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "notes.txt", .data = "just notes\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line_buf: [4200]u8 = undefined;
    const line = try std.fmt.bufPrint(&line_buf, "Restore {s}/notes.txt\n", .{dir});
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const refused = wr(p, root_ctl, line);
    try testing.expectEqual(E.IO, refused.errno());
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, "not a pardes dump") != null);
    try testing.expect(p.restore_req == null);
    try testing.expect(p.panes[0].?.discard_warned == null);

    p.fs.late_failure_len = 0;
    p.dumpFailed("/nowhere/pardes.dump.zon", error.FileNotFound);
    try testing.expectEqualStrings("Dump /nowhere/pardes.dump.zon: FileNotFound", p.fs.late_failure[0..p.fs.late_failure_len]);
}

test "a setting this frontend cannot show says GUI-only, and DumpDir reads back the directory in effect" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    if (!builtins.capabilities.lift) {
        try testing.expectEqualStrings("Lift is GUI-only \"Lift on\"", wr(p, root_ctl, "Lift on\n").reply.ename);
        try testing.expectEqualStrings("GripWidth is GUI-only \"GripWidth 120\"", wr(p, root_ctl, "GripWidth 120\n").reply.ename);
    }
    try testing.expectEqualStrings("unknown control message \"Liftt on\"", wr(p, root_ctl, "Liftt on\n").reply.ename);
    var buf: [900]u8 = undefined;
    if (pardes.dump.directory(&buf, "")) |dir| {
        var want: [920]u8 = undefined;
        const line = try std.fmt.bufPrint(&want, "\nDumpDir {s}\n", .{dir});
        try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 1 << 16).bytes, line) != null);
    }
}

test "Shell refuses a path that is no executable, and bare it goes back to the default" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const refused = wr(p, root_ctl, "Shell /nonexistent/zzsh\n");
    try testing.expectEqual(Status.err, refused.reply.status);
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, "Shell: no shell \"/nonexistent/zzsh\"") != null);
    try testing.expect(th.logHas(p, "no shell \"/nonexistent/zzsh\""));
    try testing.expectEqual(E.IO, wr(p, root_ctl, "Shell /etc\n").errno());
    try testing.expect(th.logHas(p, "Shell: not a shell: /etc is a directory"));
    try testing.expectEqualStrings("", p.settings.shell.requested.get());
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Shell /bin/sh\n").reply.status);
    try testing.expectEqualStrings("/bin/sh", p.settings.shell.requested.get());
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Shell\n").reply.status);
    try testing.expectEqualStrings("", p.settings.shell.requested.get());
    try testing.expect(th.logHas(p, "Shell: the default again, "));
    var want: [300]u8 = undefined;
    try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 8192).bytes, try std.fmt.bufPrint(&want, "Shell {s}\n", .{config.defaultShell()})) != null);
}

test "a builtin that fails a ctl write logs only its err, so the same failure again is counted" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.update(.tick); // the pane's `new` is logged first
    while (p.nextEffect()) |_| {}
    const ctl_node = @intFromEnum(tree.TopFile.ctl);
    for (0..3) |_| try testing.expectEqual(Status.err, wr(p, ctl_node, "Kill zzz\n").reply.status);
    const log = @intFromEnum(tree.TopFile.log);
    const h = call(p, .{ .tag = 1, .op = .open, .node = log }).reply.handle;
    const text = call(p, .{ .tag = 2, .op = .read, .node = log, .handle = h, .size = 1 << 16 }).bytes;
    try testing.expect(std.mem.endsWith(u8, text, "err - ctl: Kill: no running command has that first word \"Kill zzz\" (x3)\n"));
    try testing.expect(std.mem.indexOf(u8, text, "msg - Kill") == null);
    _ = call(p, .{ .tag = 3, .op = .release, .node = log, .handle = h });
}

test "an exec line over the command limit fails the write and says the limit; a builtin's may be longer" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const long = "echo " ++ "y" ** pardes.exec.command_max ++ "\n";
    const refused = wr(p, root_exec, long);
    try testing.expectEqual(E.INVAL, refused.errno());
    try testing.expectEqualStrings(e_too_long, refused.reply.ename);
    try testing.expect(th.logHas(p, "a command line is at most 1024 bytes"));
    try testing.expectEqual(Status.ok, wr(p, root_exec, "Msg " ++ "z" ** 1100 ++ "\n").reply.status);
}

test "Edit's p and = never fail for want of room for +Errors: the text is logged instead" {
    const p = try withFile(testing.allocator, "one\ntwo\n");
    defer p.deinit();
    p.update(.{ .resize = .{ .cols = 80, .rows = 6 } });
    const ctl_node = Node.of(serialOf(p), .ctl);
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "Edit ,p\n").reply.status);
    try testing.expect(th.logHas(p, " one\n") and th.logHas(p, " two\n"));
    p.sync();
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    try testing.expectEqual(@as(usize, 1), count); // the +Errors that had no room is gone
}

test "size sets the screen of a session no frontend is attached to, and only of one" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    try testing.expectEqual(E.INVAL, wr(p, root_ctl, "size 120 40\n").errno()); // a frontend's
    p.unattended = true;
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "size 120 40\n").reply.status);
    try testing.expectEqual(@as(u16, 120), p.screen_w);
    try testing.expectEqual(@as(u16, 40), p.screen_h);
    try testing.expectEqual(E.INVAL, wr(p, root_ctl, "size 120\n").errno());
    try testing.expectEqual(E.INVAL, wr(p, root_ctl, "size\n").errno());
    try testing.expect(std.mem.indexOf(u8, wr(p, root_ctl, "size 5 2\n").reply.ename, "at least 20x6, at most 4096x4096") != null);
    // Too small for the panes it has, each its tag and two rows: refused,
    // the size as it was.
    for (0..4) |_| p.newScratchBelow(p.active);
    p.sync();
    try testing.expect(std.mem.indexOf(u8, wr(p, root_ctl, "size 80 8\n").reply.ename, "too small for the panes") != null);
    try testing.expectEqual(@as(u16, 40), p.screen_h);
}

test "Repl with no such language names a few whole, and where the rest are" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const refused = wr(p, Node.of(serialOf(p), .ctl), "Repl zzlang\n");
    try testing.expectEqual(Status.err, refused.reply.status);
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, "Repl: no language \"zzlang\"; - or one like zig ada bash c c_sharp clojure (") != null);
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, " more: docs/tags.md, Repl)") != null);
}

test "a 10k-line Edit text block is taken in linear time and memory" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    var block: std.ArrayList(u8) = .empty;
    defer block.deinit(gpa);
    try block.appendSlice(gpa, "Edit $a\n");
    for (0..10_000) |i| try block.print(gpa, "line {d} of the block {{ with a brace }}\n", .{i});
    try block.appendSlice(gpa, ".\n");
    const started = std.Io.Clock.awake.now(std.testing.io);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serialOf(p), .ctl), block.items).reply.status);
    const took = started.durationTo(std.Io.Clock.awake.now(std.testing.io)).toNanoseconds();
    try testing.expect(took < std.time.ns_per_s);
    try testing.expect(p.scratch.queryCapacity() < 50 * 1024 * 1024);
    try testing.expectEqual(@as(usize, 10_001), std.mem.count(u8, p.panes[0].?.file.?.content, "\n"));
}

test "a file changed on disk under unsaved edits is not reloaded: it says so, get asks, Save warns once" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const serial = serialOf(p);
    const f = &p.panes[0].?.file.?;
    // Clean, it takes the new text.
    pardes.panes.File.changed(p, 0, "two\n");
    try testing.expectEqualStrings("two\n", f.content);
    var reloaded: [32]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&reloaded, "changed {d} reloaded\n", .{serial})));
    // Edited, it keeps its text and stays dirty.
    _ = wr(p, Node.of(serial, .body), "mine\n");
    pardes.panes.File.changed(p, 0, "three\n");
    try testing.expectEqualStrings("two\nmine\n", f.content);
    try testing.expect(f.revision != f.saved_revision);
    try testing.expect(th.logHas(p, "changed on disk (get reloads it, Save overwrites it)"));
    var want: [32]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "changed {d}\n", .{serial})));
    // Exit and get still ask about the edits.
    try testing.expectEqual(Status.err, wr(p, @intFromEnum(tree.TopFile.ctl), "Exit\n").reply.status);
    try testing.expect(std.mem.indexOf(u8, wr(p, Node.of(serial, .ctl), "get\n").reply.ename, "Modified") != null);
    // Save warns once before overwriting the newer file, then writes.
    const first = wr(p, Node.of(serial, .ctl), "Save\n");
    try testing.expectEqual(Status.err, first.reply.status);
    try testing.expect(std.mem.indexOf(u8, first.reply.ename, "modified on disk since read") != null);
    try testing.expect(wr(p, Node.of(serial, .ctl), "Save\n").saved);
}

test "a looked word is found in its own pane, next place after the dot, wrapping, and opens no pane" {
    const p = try withFile(testing.allocator, "foo x foo y\n");
    defer p.deinit();
    const serial = serialOf(p);
    const look_node = Node.of(serial, .look);
    const dot = Node.of(serial, .dot);
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    for ([_][]const u8{ "          0           3 ", "          6           9 ", "          0           3 " }) |want| {
        try testing.expectEqual(Status.ok, wr(p, look_node, "foo\n").reply.status);
        try testing.expectEqualStrings(want, rd(p, dot, 0, 64).bytes);
    }
    var after: usize = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expectEqual(count, after);
    // LookWord list: the +Search listing, as before.
    try testing.expect(p.executeBuiltinLine(0, "LookWord list"));
    try testing.expectEqual(Status.ok, wr(p, look_node, "foo\n").reply.status);
    after = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expect(after > count);
}

test "each word's /commands description is its own doc comment's first sentence, no citation" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const listed = rd(p, @intFromEnum(tree.TopFile.commands), 0, 1 << 16).bytes;
    for ([_][]const u8{
        "\nRepl arg pane -- Binds this terminal as a language's REPL",
        "\nJoincol root -- Fold the active pane's column into the one on its right, keeping its panes.\n",
        "\nExit root -- acme's Exit: quit, once warnModified has nothing to say.\n",
        "\nKill arg root -- acme's Kill: stop the commands pardes started",
    }) |row| try testing.expect(std.mem.indexOf(u8, listed, row) != null);
    try testing.expect(std.mem.indexOf(u8, listed, ".c:") == null);
    // Every description is the first sentence of the doc comment just
    // above its word's declaration in builtins.zig.
    const source = @embedFile("../builtins.zig");
    var it = std.mem.tokenizeScalar(u8, listed, '\n');
    while (it.next()) |line| {
        const dashes = std.mem.indexOf(u8, line, " -- ") orelse continue;
        const word = line[0 .. std.mem.indexOfScalar(u8, line, ' ').?];
        var needle: [64]u8 = undefined;
        const at = std.mem.indexOf(u8, source, try std.fmt.bufPrint(&needle, "\npub const {s} = struct", .{word})).?;
        const said = std.mem.trimEnd(u8, line[dashes + 4 ..], "…");
        // Its opening words are in the comment block right above.
        const head = said[0..@min(said.len, 10)];
        const block_start = std.mem.lastIndexOf(u8, source[0..at], "\n\n") orelse 0;
        try testing.expect(std.mem.indexOf(u8, source[block_start..at], head) != null);
    }
}

test "Newcol at the column cap fails the write and says the cap" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.update(.{ .resize = .{ .cols = 4000, .rows = 30 } });
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    while (p.ncol < pardes.MAX_COLS) {
        // From the widest column's tag, so no column gets too narrow first.
        p.sync();
        var widest: usize = 0;
        for (0..p.ncol) |c| if (p.col_w[c] > p.col_w[widest]) {
            widest = c;
        };
        pardes.tagline.enterHeader(p, widest);
        try testing.expectEqual(Status.ok, wr(p, root_ctl, "Newcol\n").reply.status);
    }
    const refused = wr(p, root_ctl, "Newcol\n");
    try testing.expectEqual(Status.err, refused.reply.status);
    var want: [64]u8 = undefined;
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, try std.fmt.bufPrint(&want, "no space for a column: {d} max", .{pardes.MAX_COLS})) != null);
    try testing.expect(th.logHas(p, "no space for a column"));
}

test "Save on a terminal asked over 9P is an ask in the log, answered with a path, and not asked twice" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const serial = serialOf(p);
    const id = p.paneBySerial(serial).?;
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .tagexec), "Save\n").reply.status);
    var want: [48]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "ask {d} save path\n", .{serial})));
    try testing.expect(p.panes[id].?.prompt == .save);
    // Again: the one open stands, one ask in the log.
    _ = wr(p, Node.of(serial, .tagexec), "Save\n");
    const log = @intFromEnum(tree.TopFile.log);
    const h = call(p, .{ .tag = 1, .op = .open, .node = log }).reply.handle;
    try testing.expectEqual(@as(usize, 1), std.mem.count(u8, call(p, .{ .tag = 2, .op = .read, .node = log, .handle = h, .size = 1 << 16 }).bytes, "save path\n"));
    _ = call(p, .{ .tag = 3, .op = .release, .node = log, .handle = h });
    // Answered: the path is written to, the prompt goes.
    const answered = wr(p, Node.of(serial, .ctl), "answer /tmp/pardes-ask-save.txt\n");
    try testing.expectEqual(Status.ok, answered.reply.status);
    try testing.expect(p.panes[id].?.prompt == .none);
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "answer {d} /tmp/pardes-ask-save.txt\n", .{serial})));
}