const std = @import("std");
const config = @import("pardes_config");
const tracy = @import("tracy.zig");
const grammar_manifest = @import("grammar_manifest.zig");
const look = @import("look.zig");
const regexp = @import("regexp.zig");
const c_heap = @import("c_heap");
const diff = @import("diff.zig");

test {
    _ = diff;
}

pub const enabled = config.syntax_highlighting;
const zig_grammar = config.syntax_zig_grammar;
const minimal_grammars = config.syntax_minimal_grammars;
const full_grammars = config.syntax_full_grammars;

const ts = if (enabled) @import("tree-sitter") else struct {
    pub const Language = opaque {};
    pub const Query = opaque {};
    pub const Parser = opaque {};
    pub const QueryCursor = opaque {};
};
const ts_queries = if (enabled) @import("ts_queries") else struct {};

const LanguageFn = *const fn () callconv(.c) *const ts.Language;

pub const Syn = enum(u8) { none, keyword, string, number, comment };

const Spec = struct {
    name: []const u8,
    exts: []const []const u8,
    language: *const fn () callconv(.c) *const ts.Language,
    query_src: []const u8,
    /// helix's textobjects.scm for the grammar (vendor/queries), "" for none
    objects_src: []const u8 = "",
    objects: ?*ts.Query = null,
    objects_failed: bool = false,
    selected: ?Selected = null,
    capture_styles: [256]u8 = undefined,
};

fn grammarSelected(comptime g: grammar_manifest.Grammar) bool {
    return switch (g.tier) {
        .zig => zig_grammar,
        .minimal => minimal_grammars,
        .full => full_grammars,
    };
}

fn specCount() comptime_int {
    var count = 0;
    for (grammar_manifest.all) |g| {
        if (grammarSelected(g)) count += 1;
    }
    return count;
}
const typst_supplement =
    \\
    \\(call item: (ident) @keyword)
    \\(call item: (field field: (ident) @keyword))
    \\"#" @keyword
    \\
;

fn querySrc(comptime g: grammar_manifest.Grammar) []const u8 {
    const base = @field(ts_queries, g.name ++ "_highlights");
    const source = if (comptime std.mem.eql(u8, g.name, "typst")) base ++ typst_supplement else base;
    return comptime colorQuery(source);
}

fn colorQuery(comptime source: []const u8) []const u8 {
    @setEvalBranchQuota(2_000_000);
    var result: [source.len]u8 = undefined;
    var written: usize = 0;
    var at: usize = 0;
    while (at < source.len) {
        while (at < source.len) {
            if (std.ascii.isWhitespace(source[at])) {
                at += 1;
            } else if (source[at] == ';') {
                while (at < source.len and source[at] != '\n') at += 1;
            } else break;
        }
        const begin = at;
        var depth: usize = 0;
        var colored = false;
        var complete = false;
        while (at < source.len) {
            const byte = source[at];
            if (complete and (byte == '(' or byte == '[' or byte == '"')) break;
            if (byte == ';') {
                while (at < source.len and source[at] != '\n') at += 1;
                continue;
            }
            if (byte == '"') {
                at += 1;
                while (at < source.len) : (at += 1) {
                    if (source[at] == '\\') {
                        at += 1;
                    } else if (source[at] == '"') {
                        at += 1;
                        break;
                    }
                }
                if (depth == 0) complete = true;
                continue;
            }
            if (byte == '(' or byte == '[') depth += 1;
            if (byte == ')' or byte == ']') {
                depth -= 1;
                if (depth == 0) complete = true;
            }
            if (byte == '@') {
                const name = at + 1;
                at = name;
                while (at < source.len and (std.ascii.isAlphanumeric(source[at]) or
                    source[at] == '_' or source[at] == '.' or source[at] == '-')) at += 1;
                colored = colored or synFor(source[name..at]) != .none;
                continue;
            }
            at += 1;
        }
        if (colored) {
            @memcpy(result[written..][0 .. at - begin], source[begin..at]);
            written += at - begin;
        }
    }
    const filtered = result[0..written].*;
    return &filtered;
}

fn initSpecs() [specCount()]Spec {
    var out: [specCount()]Spec = undefined;
    var i = 0;
    inline for (grammar_manifest.all) |g| {
        if (grammarSelected(g)) {
            out[i] = .{
                .name = g.name,
                .exts = g.exts,
                .language = @extern(LanguageFn, .{ .name = "tree_sitter_" ++ g.name }),
                .query_src = querySrc(g),
                .objects_src = @field(ts_queries, g.name ++ "_textobjects"),
            };
            i += 1;
        }
    }
    return out;
}

var specs = initSpecs();

/// What tree-sitter allocates from, the runtime and every grammar's external
/// scanner (build.zig compiles them to use the runtime's allocator):
/// `start`'s allocator, through the shared C heap.
var syntax_allocator: std.mem.Allocator = undefined;
const syntax_heap = c_heap.Heap(&syntax_allocator);
var syntax_started = false;

extern fn ts_set_allocator(
    new_malloc: ?*const fn (size: usize) callconv(.c) ?*anyopaque,
    new_calloc: ?*const fn (nmemb: usize, size: usize) callconv(.c) ?*anyopaque,
    new_realloc: ?*const fn (ptr: ?*anyopaque, size: usize) callconv(.c) ?*anyopaque,
    new_free: ?*const fn (ptr: ?*anyopaque) callconv(.c) void,
) void;

pub fn start(gpa: std.mem.Allocator) void {
    if (comptime enabled) {
        std.debug.assert(!syntax_started);
        stop();
        syntax_allocator = gpa;
        syntax_started = true;
        ts_set_allocator(syntax_heap.malloc, syntax_heap.calloc, syntax_heap.realloc, syntax_heap.free);
    }
}

pub fn stop() void {
    if (comptime enabled) {
        for (&specs) |*spec| {
            if (spec.selected) |selected| {
                selected.cursor.destroy();
                selected.parser.destroy();
                selected.query.destroy();
            }
            spec.selected = null;
            if (spec.objects) |q| q.destroy();
            spec.objects = null;
            spec.objects_failed = false;
        }
        dropDiffPieces();
        ts_set_allocator(null, null, null, null);
        syntax_started = false;
        syntax_allocator = undefined;
    }
}

const Selected = struct {
    name: []const u8,
    lang: *const ts.Language,
    query: *ts.Query,
    parser: *ts.Parser,
    cursor: *ts.QueryCursor,
    capture_styles: []u8,
};

fn ensure(spec: *Spec) !Selected {
    if (spec.selected) |selected| return selected;
    const lang = spec.language();
    var error_offset: u32 = 0;
    const query = try ts.Query.create(lang, spec.query_src, &error_offset);
    errdefer query.destroy();
    if (query.captureCount() > spec.capture_styles.len) return error.TooManyCaptures;
    const capture_styles = spec.capture_styles[0..query.captureCount()];
    for (capture_styles, 0..) |*style, id| {
        const name = query.captureNameForId(@intCast(id)) orelse "";
        style.* = @intFromEnum(synFor(name));
        if (style.* == 0) query.disableCapture(name);
    }
    const parser = ts.Parser.create();
    errdefer parser.destroy();
    try parser.setLanguage(lang);
    const selected: Selected = .{
        .name = spec.name,
        .lang = lang,
        .query = query,
        .parser = parser,
        .cursor = ts.QueryCursor.create(),
        .capture_styles = capture_styles,
    };
    spec.selected = selected;
    return selected;
}

fn forExt(ext: []const u8) !?Selected {
    for (&specs) |*spec| {
        for (spec.exts) |choice| {
            if (std.ascii.eqlIgnoreCase(ext, choice)) return try ensure(spec);
        }
    }
    return null;
}

fn forLang(name: []const u8) !?Selected {
    const canonical = if (grammar_manifest.byName(name)) |i| grammar_manifest.all[i].name else name;
    for (&specs) |*spec| {
        if (std.ascii.eqlIgnoreCase(canonical, spec.name)) return try ensure(spec);
    }
    return null;
}
fn runQuery(styles: []u8, sel: Selected, tree: *ts.Tree, base: usize) void {
    const cursor = sel.cursor;
    cursor.exec(sel.query, tree.rootNode());
    while (cursor.nextMatch()) |match| {
        for (match.captures) |cap| {
            const style = sel.capture_styles[cap.index];
            if (style == 0) continue;
            const b = @min(base + cap.node.startByte(), styles.len);
            const end = @min(base + @as(usize, cap.node.endByte()), styles.len);
            if (end > b) @memset(styles[b..end], style);
        }
    }
}

fn synFor(name: []const u8) Syn {
    for ([_]struct { []const u8, Syn }{
        .{ "comment", .comment },
        .{ "string", .string },
        .{ "character", .string },
        .{ "number", .number },
        .{ "numeric", .number },
        .{ "float", .number },
        .{ "boolean", .number },
        .{ "keyword", .keyword },
        .{ "include", .keyword },
        .{ "conditional", .keyword },
        .{ "repeat", .keyword },
        .{ "title", .keyword },
        .{ "uri", .string },
        .{ "reference", .number },
        .{ "heading", .keyword },
        .{ "strong", .comment },
        .{ "bold", .comment },
        .{ "emphasis", .number },
        .{ "italic", .number },
        .{ "literal", .string },
        .{ "raw", .string },
    }) |m| {
        if (std.mem.indexOf(u8, name, m[0]) != null) return m[1];
    }
    return .none;
}
pub fn highlightFileRange(gpa: std.mem.Allocator, path: []const u8, content: []const u8, start_raw: usize, end_raw: usize) ![]u8 {
    const zone = tracy.zone(@src(), "highlightFileRange");
    defer zone.end();
    if (!enabled) return &.{};
    const selected = (try forExt(std.fs.path.extension(path))) orelse return &.{};
    const start_byte = @min(start_raw, content.len);
    const end_byte = @max(start_byte, @min(end_raw, content.len));
    const source = content[start_byte..end_byte];
    const styles = try gpa.alloc(u8, source.len);
    @memset(styles, 0);
    paint(styles, source, selected);
    return styles;
}

/// Source spans are independent of editor rows. Locations output uses the same
/// declarations as sticky editor headers. Byte ends are exclusive; rows are
/// zero-based and inclusive, including the last signature/opening-brace row.
pub const ContextDeclaration = struct {
    start_byte: usize,
    end_byte: usize,
    start_line: usize,
    end_line: usize,
    header_end_byte: usize,
    header_end_line: usize,
};

pub fn supportsPath(path: []const u8) bool {
    if (!enabled) return false;
    const ext = std.fs.path.extension(path);
    for (specs) |spec| for (spec.exts) |choice| {
        if (std.ascii.eqlIgnoreCase(ext, choice)) return true;
    };
    return false;
}

/// A whole file's parse, kept by the file for the keys that walk its nodes
/// (helix's Alt-o and kin). Opaque outside this file; null without a grammar.
pub fn parseTree(path: []const u8, content: []const u8) ?*anyopaque {
    if (!enabled) return null;
    const selected = (forExt(std.fs.path.extension(path)) catch return null) orelse return null;
    const tree = selected.parser.parseString(content, null) orelse return null;
    return @ptrCast(tree);
}

pub fn freeTree(tree: *anyopaque) void {
    if (!enabled) return;
    const t: *ts.Tree = @ptrCast(@alignCast(tree));
    t.destroy();
}

/// Where a node walk goes from a range (helix object.rs and movement.rs).
pub const NodeWalk = @import("modal.zig").Normal.NodeWalk;
pub const Span = struct { from: usize, to: usize };

/// The spans `walk` takes the byte range [from, to) to, into `out`; `at` is
/// the range's cursor. None when the tree has nothing to say there.
pub fn walkNodes(tree_ptr: *anyopaque, walk: NodeWalk, from: usize, to: usize, at: usize, out: []Span) usize {
    if (!enabled or out.len == 0) return 0;
    const tree: *const ts.Tree = @ptrCast(@alignCast(tree_ptr));
    const lo: u32 = @intCast(@min(from, std.math.maxInt(u32)));
    const hi: u32 = @intCast(@min(to, std.math.maxInt(u32)));
    if (walk == .parent_end or walk == .parent_start) {
        var node = tree.rootNode().namedDescendantForByteRange(lo, hi) orelse return 0;
        if (walk == .parent_end) {
            out[0] = .{ .from = node.endByte(), .to = node.endByte() };
            return 1;
        }
        // already at the node's lo: its first ancestor that starts earlier
        if (node.startByte() == at) {
            const first = node.startByte();
            while (node.startByte() >= first or !node.isNamed()) node = node.parent() orelse break;
        }
        out[0] = .{ .from = node.startByte(), .to = node.startByte() };
        return 1;
    }
    var cursor = tree.walk();
    defer cursor.destroy();
    // helix TreeCursor.reset_to_byte_range: the smallest node holding the range
    while (true) {
        const node = cursor.node();
        if (lo < node.startByte() or hi > node.endByte()) {
            _ = cursor.gotoParent();
            break;
        }
        if (cursor.gotoFirstChildForByte(lo) == null) break;
    }
    switch (walk) {
        .expand => while (cursor.node().startByte() == lo and cursor.node().endByte() == hi) {
            if (!cursor.gotoParent()) break;
        },
        .shrink => _ = cursor.gotoFirstChild(),
        .next_sibling => while (!cursor.gotoNextSibling()) {
            if (!cursor.gotoParent()) break;
        },
        .prev_sibling => while (!cursor.gotoPreviousSibling()) {
            if (!cursor.gotoParent()) break;
        },
        .all_siblings, .all_children => {
            if (walk == .all_siblings) {
                while (true) {
                    if (!cursor.gotoParent()) return 0;
                    if (cursor.node().childCount() > 1) break;
                }
            }
            // the named children, or nothing to say
            var n: usize = 0;
            if (!cursor.gotoFirstChild()) return 0;
            while (true) {
                const child = cursor.node();
                if (child.isNamed() and n < out.len) {
                    out[n] = .{ .from = child.startByte(), .to = child.endByte() };
                    n += 1;
                }
                if (!cursor.gotoNextSibling()) break;
            }
            return n;
        },
        .parent_end, .parent_start => unreachable,
    }
    const node = cursor.node();
    out[0] = .{ .from = node.startByte(), .to = node.endByte() };
    return 1;
}


/// helix's textobjects, which its `]f`, `mif` and kin select: the name a
/// query's captures begin with (`function.around`, `test.inside`).
pub const Object = @import("modal.zig").Normal.Object;

fn objectName(o: Object) []const u8 {
    return if (o == .xml_element) "xml-element" else @tagName(o);
}

/// The grammar's textobject query for `path`, compiled the first time; null
/// when the grammar has none.
fn objectQuery(path: []const u8) ?*ts.Query {
    const ext = std.fs.path.extension(path);
    for (&specs) |*spec| for (spec.exts) |choice| {
        if (!std.ascii.eqlIgnoreCase(ext, choice)) continue;
        if (spec.objects) |q| return q;
        if (spec.objects_src.len == 0 or spec.objects_failed) return null;
        var error_offset: u32 = 0;
        spec.objects = ts.Query.create(spec.language(), spec.objects_src, &error_offset) catch {
            spec.objects_failed = true;
            return null;
        };
        return spec.objects;
    };
    return null;
}

fn captureId(q: *const ts.Query, name: []const u8) ?u32 {
    for (0..q.captureCount()) |i| if (std.mem.eql(u8, q.captureNameForId(@intCast(i)) orelse "", name)) return @intCast(i);
    return null;
}

/// A match's `capture`, as one span over all its nodes (helix's grouped
/// capture), when the match's `#eq?` and `#match?` hold.
fn matchSpan(q: *const ts.Query, match: anytype, capture: u32, text: []const u8) ?Span {
    var span: ?Span = null;
    for (match.captures) |c| if (c.index == capture) {
        const s: Span = .{ .from = c.node.startByte(), .to = c.node.endByte() };
        span = if (span) |old| .{ .from = @min(old.from, s.from), .to = @max(old.to, s.to) } else s;
    };
    var found = span orelse return null;
    // a node that takes its line's newline (this zig grammar's comments)
    // is the line without it, as helix's grammars have it
    if (found.to > found.from + 1 and found.to <= text.len and text[found.to - 1] == '\n') found.to -= 1;
    const steps = q.predicatesForPattern(match.pattern_index);
    var i: usize = 0;
    while (i < steps.len) {
        var end = i;
        while (end < steps.len and steps[end].type != .done) end += 1;
        const pred = steps[i..end];
        i = end + 1;
        if (pred.len != 3 or pred[0].type != .string or pred[1].type != .capture) continue;
        const op = q.stringValueForId(pred[0].value_id) orelse continue;
        const subject = for (match.captures) |c| {
            if (c.index == pred[1].value_id) break text[@min(c.node.startByte(), text.len)..@min(c.node.endByte(), text.len)];
        } else continue;
        const want = if (pred[2].type == .string) q.stringValueForId(pred[2].value_id) orelse continue else for (match.captures) |c| {
            if (c.index == pred[2].value_id) break text[@min(c.node.startByte(), text.len)..@min(c.node.endByte(), text.len)];
        } else continue;
        if (std.mem.eql(u8, op, "eq?")) {
            if (!std.mem.eql(u8, subject, want)) return null;
        } else if (std.mem.eql(u8, op, "match?")) {
            var re = regexp.Regex.compile(want) catch continue;
            if ((re.find(subject, 0, subject.len, subject.len) catch null) == null) return null;
        }
    }
    return found;
}

/// `mi`/`ma`: the smallest `object.inside` (or `.around`) holding byte `at`
/// (helix textobject_treesitter). None without a query or such an object.
pub fn objectAt(path: []const u8, tree_ptr: *anyopaque, text: []const u8, object: Object, around: bool, at: usize) ?Span {
    if (!enabled) return null;
    const q = objectQuery(path) orelse return null;
    var buf: [32]u8 = undefined;
    const want = std.fmt.bufPrint(&buf, "{s}.{s}", .{ objectName(object), if (around) "around" else "inside" }) catch return null;
    const capture = captureId(q, want) orelse return null;
    const tree: *const ts.Tree = @ptrCast(@alignCast(tree_ptr));
    const cursor = ts.QueryCursor.create();
    defer cursor.destroy();
    cursor.exec(q, tree.rootNode());
    var best: ?Span = null;
    while (cursor.nextMatch()) |match| {
        const s = matchSpan(q, match, capture, text) orelse continue;
        if (!(s.from <= at and at < s.to)) continue;
        if (best == null or s.to - s.from < best.?.to - best.?.from) best = s;
    }
    const s = best orelse return null;
    if (s.from >= text.len or s.to >= text.len) return null;
    return s;
}

/// `]f`/`[f` and kin: the next object starting after byte `at`, or the
/// previous one ending before it (helix goto_treesitter_object), from the
/// first of `.movement`, `.around`, `.inside` the query names.
pub fn objectNext(path: []const u8, tree_ptr: *anyopaque, text: []const u8, object: Object, forward: bool, at: usize) ?Span {
    if (!enabled) return null;
    const q = objectQuery(path) orelse return null;
    var buf: [32]u8 = undefined;
    const capture = for ([_][]const u8{ "movement", "around", "inside" }) |kind| {
        const want = std.fmt.bufPrint(&buf, "{s}.{s}", .{ objectName(object), kind }) catch return null;
        if (captureId(q, want)) |id| break id;
    } else return null;
    const tree: *const ts.Tree = @ptrCast(@alignCast(tree_ptr));
    const cursor = ts.QueryCursor.create();
    defer cursor.destroy();
    cursor.exec(q, tree.rootNode());
    var best: ?Span = null;
    while (cursor.nextMatch()) |match| {
        const s = matchSpan(q, match, capture, text) orelse continue;
        if (forward) {
            if (s.from <= at) continue;
            if (best == null or s.from < best.?.from or (s.from == best.?.from and s.to > best.?.to)) best = s;
        } else {
            if (s.to >= at) continue;
            if (best == null or s.to > best.?.to or (s.to == best.?.to and s.from < best.?.from)) best = s;
        }
    }
    const s = best orelse return null;
    if (s.from >= text.len or s.to >= text.len) return null;
    return s;
}

test "every vendored textobject query compiles against its grammar" {
    if (!enabled) return;
    var failed: usize = 0;
    for (&specs) |*spec| {
        if (spec.objects_src.len == 0) continue;
        var error_offset: u32 = 0;
        const q = ts.Query.create(spec.language(), spec.objects_src, &error_offset) catch {
            std.debug.print("textobjects for {s} do not compile (offset {d})\n", .{ spec.name, error_offset });
            failed += 1;
            continue;
        };
        q.destroy();
    }
    try std.testing.expectEqual(@as(usize, 0), failed);
}

/// Owned source analysis. Both slices use the allocator passed to analyzeSource.
/// The parsed tree is released before returning; callers can cache this result.
pub const SourceAnalysis = struct {
    declarations: []ContextDeclaration = &.{},
    colors: []u8 = &.{},

    pub fn deinit(self: *SourceAnalysis, gpa: std.mem.Allocator) void {
        gpa.free(self.declarations);
        gpa.free(self.colors);
        self.* = .{};
    }
};

pub fn analyzeSource(gpa: std.mem.Allocator, path: []const u8, content: []const u8, want_declarations: bool, want_colors: bool) !SourceAnalysis {
    if (!enabled or content.len == 0 or (!want_declarations and !want_colors)) return .{};
    const selected = (try forExt(std.fs.path.extension(path))) orelse return .{};
    const tree = selected.parser.parseString(content, null) orelse return .{};
    defer tree.destroy();
    var result: SourceAnalysis = .{};
    errdefer result.deinit(gpa);
    if (want_declarations) result.declarations = try declarationsFromTree(gpa, content, tree);
    if (want_colors) {
        result.colors = try gpa.alloc(u8, content.len);
        @memset(result.colors, 0);
        paintTree(result.colors, content, selected, tree);
    }
    return result;
}

pub fn contextDeclarations(gpa: std.mem.Allocator, path: []const u8, content: []const u8) ![]ContextDeclaration {
    const analysis = try analyzeSource(gpa, path, content, true, false);
    return analysis.declarations;
}

fn declarationsFromTree(gpa: std.mem.Allocator, content: []const u8, tree: *ts.Tree) ![]ContextDeclaration {
    var result: std.ArrayList(ContextDeclaration) = .empty;
    errdefer result.deinit(gpa);
    // The cursor retains its ancestor stack: sibling visits do not repeatedly
    // reconstruct parents in broad syntax trees. Preorder preserves source order.
    var cursor = tree.rootNode().walk();
    defer cursor.destroy();
    while (true) {
        const node = cursor.node();
        if (node.isNamed()) if (contextSpan(node, content)) |span| {
            if (result.items.len == 0 or result.items[result.items.len - 1].start_line != span.start_line or
                result.items[result.items.len - 1].end_line != span.end_line)
                try result.append(gpa, span);
        };
        if (cursor.gotoFirstChild()) continue;
        while (!cursor.gotoNextSibling()) {
            if (!cursor.gotoParent()) return result.toOwnedSlice(gpa);
        }
    }
}

fn contextSpan(node: ts.Node, source: []const u8) ?ContextDeclaration {
    const kind = node.kind();
    var body: ?ts.Node = null;
    var accepted = false;
    if (std.mem.eql(u8, kind, "Decl")) {
        // Zig's FnProto excludes its body: the surrounding Decl owns both.
        accepted = childOfKind(node, "FnProto") != null;
        body = childOfKind(node, "Block");
        if (body == null) return null;
    } else if (std.mem.eql(u8, kind, "ContainerDecl") or std.mem.eql(u8, kind, "TestDecl")) {
        accepted = true;
        body = childOfKind(node, "Block");
    } else {
        const kinds = [_][]const u8{
            "function_definition",   "function_declaration", "function_item",         "function",                "method_definition",
            "method_declaration",    "method",               "singleton_method",      "constructor_declaration", "destructor_definition",
            "class_definition",      "class_declaration",    "class_specifier",       "class",                   "singleton_class",
            "object_declaration",    "struct_item",          "struct_specifier",      "struct_declaration",      "union_specifier",
            "union_item",            "union_declaration",    "enum_item",             "enum_specifier",          "enum_declaration",
            "interface_declaration", "trait_item",           "trait_definition",      "impl_item",               "mod_item",
            "module_definition",     "module_declaration",   "module",                "namespace_definition",    "namespace_declaration",
            "record_declaration",    "type_declaration",     "extension_declaration", "protocol_declaration",
        };
        for (kinds) |candidate| if (std.mem.eql(u8, kind, candidate)) {
            accepted = true;
            break;
        };
        body = node.childByFieldName("body");
    }
    if (!accepted) return null;
    var owner = node;
    if (std.mem.eql(u8, kind, "ContainerDecl")) {
        // A multiline `const Name = struct` starts at the binding, not at the
        // struct token. Stop at real scopes so returned anonymous containers
        // do not inherit an enclosing function's signature.
        var ancestor = node.parent();
        while (ancestor) |parent| {
            const parent_kind = parent.kind();
            if (std.mem.eql(u8, parent_kind, "VarDecl")) {
                owner = parent;
                break;
            }
            if (std.mem.eql(u8, parent_kind, "Block") or std.mem.eql(u8, parent_kind, "Decl") or
                std.mem.eql(u8, parent_kind, "ContainerDecl") or std.mem.eql(u8, parent_kind, "FnProto") or
                std.mem.eql(u8, parent_kind, "ContainerField") or std.mem.eql(u8, parent_kind, "ParamDecl")) break;
            ancestor = parent.parent();
        }
    }
    const beginning = owner.startPoint();
    const end = node.endPoint();
    if (beginning.row >= end.row) return null;
    var header_end: usize = node.startByte();
    if (body) |block| {
        header_end = block.startByte();
        // Indentation grammars start their body at its first statement.
        if (header_end < source.len and source[header_end] == '{') {
            header_end += 1;
        } else {
            while (header_end > node.startByte() and std.ascii.isWhitespace(source[header_end - 1])) header_end -= 1;
        }
    } else {
        // Containers often expose their braces directly, without a body node.
        var i: u32 = 0;
        while (i < node.childCount()) : (i += 1) {
            const child = node.child(i) orelse continue;
            if (std.mem.eql(u8, child.kind(), "{")) {
                header_end = child.endByte();
                break;
            }
        }
        // Ruby and similar grammars have a body_statement without a field.
        if (header_end == node.startByte()) {
            header_end = std.mem.indexOfScalarPos(u8, source, header_end, '\n') orelse source.len;
        }
    }
    const line_start = @as(usize, owner.startByte()) - beginning.column;
    const header_line = beginning.row + std.mem.count(u8, source[line_start..@min(header_end, source.len)], "\n");
    const header_line_end = std.mem.indexOfScalarPos(u8, source, @min(header_end, source.len), '\n') orelse source.len;
    return .{
        .start_byte = line_start,
        .end_byte = node.endByte(),
        .start_line = beginning.row,
        .end_line = end.row - @as(usize, if (end.column == 0) 1 else 0),
        .header_end_byte = header_line_end,
        .header_end_line = header_line,
    };
}

fn paint(styles: []u8, source: []const u8, selected: Selected) void {
    const tree = selected.parser.parseString(source, null) orelse return;
    defer tree.destroy();
    paintTree(styles, source, selected, tree);
}

fn paintTree(styles: []u8, source: []const u8, selected: Selected, tree: *ts.Tree) void {
    runQuery(styles, selected, tree, 0);
    if (std.mem.eql(u8, selected.name, "markdown")) {
        inject(styles, source, tree.rootNode(), true);
    } else if (std.mem.eql(u8, selected.name, "typst")) {
        inject(styles, source, tree.rootNode(), false);
    }
}

test "syntax context nested Zig containers and multiline function signatures" {
    if (!enabled) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const source =
        "pub const Outer = struct {\n" ++
        "    const Inner = struct {\n" ++
        "        pub fn run(\n" ++
        "            value: u32,\n" ++
        "        ) void {\n" ++
        "            const ignored = .{\n" ++
        "                value,\n" ++
        "            };\n" ++
        "        }\n" ++
        "    };\n" ++
        "};\n";
    const declarations = try contextDeclarations(gpa, "nested.zig", source);
    defer gpa.free(declarations);
    try std.testing.expectEqual(@as(usize, 3), declarations.len);
    try std.testing.expectEqual(@as(usize, 0), declarations[0].start_line);
    try std.testing.expectEqual(@as(usize, 10), declarations[0].end_line);
    try std.testing.expectEqual(@as(usize, 1), declarations[1].start_line);
    try std.testing.expectEqual(@as(usize, 2), declarations[2].start_line);
    try std.testing.expectEqual(@as(usize, 4), declarations[2].header_end_line);
    try std.testing.expectEqual(@as(usize, 8), declarations[2].end_line);
    try std.testing.expectEqualStrings("        pub fn run(\n            value: u32,\n        ) void {", source[declarations[2].start_byte..declarations[2].header_end_byte]);
    const unsupported = try contextDeclarations(gpa, "notes.unknown", source);
    defer gpa.free(unsupported);
    try std.testing.expectEqual(@as(usize, 0), unsupported.len);
}

test "syntax context Python class and function body excludes first statement" {
    if (!enabled or !full_grammars) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const source = "class Outer:\n    def run(\n        self, value,\n    ):\n        return value\n";
    const declarations = try contextDeclarations(gpa, "nested.py", source);
    defer gpa.free(declarations);
    try std.testing.expectEqual(@as(usize, 2), declarations.len);
    try std.testing.expectEqual(@as(usize, 0), declarations[0].header_end_line);
    try std.testing.expectEqual(@as(usize, 3), declarations[1].header_end_line);
}

test "syntax context multiline bindings and C++ namespaces preserve declaration starts" {
    if (!enabled) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const zig_source = "const Outer =\n    struct {\n        field: u8,\n    };\n";
    const zig_declarations = try contextDeclarations(gpa, "nested.zig", zig_source);
    defer gpa.free(zig_declarations);
    try std.testing.expectEqual(@as(usize, 1), zig_declarations.len);
    try std.testing.expectEqual(@as(usize, 0), zig_declarations[0].start_line);
    try std.testing.expectEqual(@as(usize, 1), zig_declarations[0].header_end_line);
    if (!minimal_grammars and !full_grammars) return;
    const cpp_source = "namespace example {\nstruct Outer {\n    int run() {\n        return 1;\n    }\n};\n}\n";
    const cpp_declarations = try contextDeclarations(gpa, "nested.cpp", cpp_source);
    defer gpa.free(cpp_declarations);
    try std.testing.expectEqual(@as(usize, 3), cpp_declarations.len);
    for (cpp_declarations, 0..) |declaration, row| {
        try std.testing.expectEqual(row, declaration.start_line);
        try std.testing.expectEqual(row, declaration.header_end_line);
    }
}

test "syntax context Rust modules impls and methods remain nested" {
    if (!enabled or !full_grammars) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const source = "mod outer {\n    impl Example {\n        fn run(&self) {\n            work();\n        }\n    }\n}\n";
    const declarations = try contextDeclarations(gpa, "nested.rs", source);
    defer gpa.free(declarations);
    try std.testing.expectEqual(@as(usize, 3), declarations.len);
    for (declarations, 0..) |declaration, row| {
        try std.testing.expectEqual(row, declaration.start_line);
        try std.testing.expectEqual(row, declaration.header_end_line);
        try std.testing.expectEqual(@as(usize, 6) - row, declaration.end_line);
    }
}

pub fn highlightLocations(gpa: std.mem.Allocator, content: []const u8, start_byte_raw: usize, end_byte_raw: usize) ![]u8 {
    const tz = tracy.zone(@src(), "highlightLocations");
    defer tz.end();
    const start_byte = @min(start_byte_raw, content.len);
    const end_byte = @max(start_byte, @min(end_byte_raw, content.len));
    const source = content[start_byte..end_byte];
    if (!enabled) return &.{};
    const styles = try gpa.alloc(u8, source.len);
    errdefer gpa.free(styles);
    @memset(styles, 0);
    var memo_ext: []const u8 = "\x00";
    var memo: ?Selected = null;
    var painted = false;

    var offset: usize = 0;
    var lines = std.mem.splitScalar(u8, source, '\n');
    while (lines.next()) |line| {
        defer offset += line.len + 1;
        const code = codeAfterLocation(line) orelse continue;
        const ext = std.fs.path.extension(code.path);
        if (!std.mem.eql(u8, ext, memo_ext)) {
            memo_ext = ext;
            memo = forExt(ext) catch null;
        }
        const selected = memo orelse continue;
        paint(styles[offset + code.at ..][0..code.text.len], code.text, selected);
        painted = true;
    }
    if (!painted) {
        gpa.free(styles);
        return &.{};
    }
    return styles;
}

/// Formatted results carry the exact source boundary independently of their
/// padded location column. This also colors context whose location is hidden.
/// Consecutive source rows share one parse, retaining multiline syntax.
pub fn highlightLocationRows(gpa: std.mem.Allocator, content: []const u8, rows: anytype) ![]u8 {
    if (!enabled or content.len == 0 or rows.len == 0) return &.{};
    const styles = try gpa.alloc(u8, content.len);
    errdefer gpa.free(styles);
    @memset(styles, 0);
    const code = try gpa.alloc(u8, content.len);
    defer gpa.free(code);
    const colors = try gpa.alloc(u8, content.len);
    defer gpa.free(colors);
    const SourceRow = struct { index: usize, start: usize, len: usize };
    const sources = try gpa.alloc(SourceRow, rows.len);
    defer gpa.free(sources);
    var source_count: usize = 0;
    var offset: usize = 0;
    for (rows, 0..) |row, index| {
        if (offset >= content.len) break;
        const end = std.mem.indexOfScalarPos(u8, content, offset, '\n') orelse content.len;
        const source_start = offset + @min(row.code_start, end - offset);
        var address_only = false;
        if (comptime @hasField(@TypeOf(row), "location_end")) {
            address_only = row.location_end > 0 and source_start == end;
        }
        if (!address_only) {
            sources[source_count] = .{ .index = index, .start = source_start, .len = end - source_start };
            source_count += 1;
        }
        offset = @min(end + 1, content.len);
    }
    var painted = false;
    var first: usize = 0;
    while (first < source_count) {
        const first_row = rows[sources[first].index];
        var end = first + 1;
        while (end < source_count) : (end += 1) {
            const row = rows[sources[end].index];
            const previous = rows[sources[end - 1].index];
            if (!std.mem.eql(u8, row.path, first_row.path) or row.at.line != previous.at.line +| 1) break;
        }
        const language = (forExt(std.fs.path.extension(first_row.path)) catch null);
        if (language) |selected| {
            var code_len: usize = 0;
            for (sources[first..end]) |source| {
                @memcpy(code[code_len..][0..source.len], content[source.start..][0..source.len]);
                code_len += source.len;
                if (code_len < code.len) {
                    code[code_len] = '\n';
                    code_len += 1;
                }
            }
            if (code_len > 0) {
                @memset(colors[0..code_len], 0);
                paint(colors[0..code_len], code[0..code_len], selected);
                painted = true;
                var at: usize = 0;
                for (sources[first..end]) |source| {
                    @memcpy(styles[source.start..][0..source.len], colors[at..][0..source.len]);
                    at += source.len + 1;
                }
            }
        }
        first = end;
    }
    // A shown context range can begin inside a comment/string whose opener was
    // omitted. Formatter snapshots from the complete source take precedence,
    // including zero styles that remove misleading fragment-parser captures.
    if (comptime @hasField(@TypeOf(rows[0]), "colors")) {
        offset = 0;
        for (rows) |row| {
            if (offset >= content.len) break;
            const end = std.mem.indexOfScalarPos(u8, content, offset, '\n') orelse content.len;
            const source_start = offset + @min(row.code_start, end - offset);
            const len = @min(row.colors.len, end - source_start);
            if (len > 0) {
                @memcpy(styles[source_start..][0..len], row.colors[0..len]);
                painted = true;
            }
            offset = @min(end + 1, content.len);
        }
    }
    // Declaration context is intentionally muted by the output painter. Keep
    // its source in parsing groups, then remove every syntax/style flag after
    // complete-source snapshots have been applied.
    if (comptime @hasField(@TypeOf(rows[0]), "declaration")) {
        offset = 0;
        for (rows) |row| {
            if (offset >= content.len) break;
            const end = std.mem.indexOfScalarPos(u8, content, offset, '\n') orelse content.len;
            if (row.declaration) {
                const source_start = offset + @min(row.code_start, end - offset);
                @memset(styles[source_start..end], 0);
            }
            offset = @min(end + 1, content.len);
        }
    }
    if (!painted) {
        gpa.free(styles);
        return &.{};
    }
    return styles;
}

fn codeAfterLocation(line: []const u8) ?struct { path: []const u8, at: usize, text: []const u8 } {
    const token_end = std.mem.indexOfAny(u8, line, " \t") orelse return null;
    if (token_end == 0) return null;
    const token = line[0..token_end];
    const target = look.parsePathLine(token);
    if (target.end != token.len) return null;
    if (target.at.line == 0) return null;
    const at = token_end + 1;
    if (at >= line.len) return null;
    return .{ .path = target.path, .at = at, .text = line[at..] };
}

test "syntax formatted locations color hidden context and preserve multiline source" {
    if (!enabled or (!minimal_grammars and !full_grammars)) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const Row = struct { path: []const u8, code_start: usize, at: look.Spot };
    const first = "a path.c:1   \t/* open";
    const second = "             \t| comment body";
    const third = "a path.c:3   \t*/ int value = 42;";
    const content = first ++ "\n" ++ second ++ "\n" ++ third ++ "\n";
    const rows = [_]Row{
        .{ .path = "a path.c", .code_start = "a path.c:1   \t".len, .at = .{ .line = 1 } },
        .{ .path = "a path.c", .code_start = "             \t| ".len, .at = .{ .line = 2 } },
        .{ .path = "a path.c", .code_start = "a path.c:3   \t".len, .at = .{ .line = 3 } },
    };
    const styles = try highlightLocationRows(gpa, content, &rows);
    defer gpa.free(styles);
    const body = std.mem.indexOf(u8, content, "comment body").?;
    try std.testing.expectEqual(@intFromEnum(Syn.comment), styles[body]);
    try std.testing.expectEqual(@intFromEnum(Syn.none), styles[body - 1]);
    const number = std.mem.indexOf(u8, content, "42").?;
    try std.testing.expectEqual(@intFromEnum(Syn.number), styles[number]);
    try std.testing.expectEqual(@intFromEnum(Syn.none), styles[0]);
}

test "syntax formatted locations separate alignment from Markdown indentation" {
    if (!enabled or !full_grammars) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const Row = struct { path: []const u8, code_start: usize, at: look.Spot };
    const content = "short.md:1          \t# Heading\n" ++ "longer path.md:5   \t    # Code\n";
    const rows = [_]Row{
        .{ .path = "short.md", .code_start = "short.md:1          \t".len, .at = .{ .line = 1 } },
        .{ .path = "longer path.md", .code_start = "longer path.md:5   \t".len, .at = .{ .line = 5 } },
    };
    const styles = try highlightLocationRows(gpa, content, &rows);
    defer gpa.free(styles);
    try std.testing.expectEqual(@intFromEnum(Syn.keyword), styles[std.mem.indexOf(u8, content, "Heading").?]);
    try std.testing.expectEqual(@intFromEnum(Syn.string), styles[std.mem.indexOf(u8, content, "Code").?]);
}
fn inject(styles: []u8, source: []const u8, node: ts.Node, markdown: bool) void {
    const kind = node.kind();
    if (markdown and std.mem.eql(u8, kind, "inline")) {
        const begin: usize = node.startByte();
        const end: usize = node.endByte();
        if (begin >= end or end > source.len) return;
        const text = source[begin..end];
        // Every colored inline capture requires one of these delimiters.
        if (std.mem.indexOfAny(u8, text, "*_`[<\\\r\n") == null) return;
        const selected = (forLang("markdown_inline") catch return) orelse return;
        const tree = selected.parser.parseString(text, null) orelse return;
        defer tree.destroy();
        runQuery(styles, selected, tree, begin);
        return;
    }
    if (std.mem.eql(u8, kind, if (markdown) "fenced_code_block" else "raw_blck")) {
        const lang = if (markdown) blk: {
            const info = childOfKind(node, "info_string") orelse return;
            break :blk childOfKind(info, "language") orelse return;
        } else node.childByFieldName("lang") orelse return;
        const content = childOfKind(node, if (markdown) "code_fence_content" else "blob") orelse return;
        const selected = (forLang(source[lang.startByte()..lang.endByte()]) catch return) orelse return;
        const begin: usize = content.startByte();
        const end: usize = content.endByte();
        if (begin > end or end > source.len) return;
        const tree = selected.parser.parseString(source[begin..end], null) orelse return;
        defer tree.destroy();
        @memset(styles[begin..end], 0);
        runQuery(styles, selected, tree, begin);
        return;
    }
    var i: u32 = 0;
    const count = node.childCount();
    while (i < count) : (i += 1) {
        if (node.child(i)) |child| inject(styles, source, child, markdown);
    }
}

fn childOfKind(node: ts.Node, kind: []const u8) ?ts.Node {
    var i: u32 = 0;
    const count = node.childCount();
    while (i < count) : (i += 1) {
        if (node.child(i)) |c| {
            if (std.mem.eql(u8, c.kind(), kind)) return c;
        }
    }
    return null;
}

/// A diff line's style byte carries whether the line was added or removed
/// over its syntax style (the low bits), so the painter can tint its row
/// and mark its prefix.
pub const diff_added: u8 = 0x80;
pub const diff_removed: u8 = 0x40;
pub const syn_bits: u8 = 0x3f;

/// A file section's hunks are parsed together, each side as one text, in
/// pieces: a piece takes whole hunks until it holds `diff_piece_lines`
/// lines, and a hunk longer than `diff_piece_cut` is cut there, counted
/// from the section's first hunk. So a view parses about what a file's
/// view does (its rows and a margin), however many small hunks it shows,
/// and a 20k-line new file is parsed where it is shown, not whole. A string
/// or comment across a cut colours as a fragment would.
const diff_piece_lines = 40;
const diff_piece_cut = 80;

/// Painted hunk pieces, keyed by their bytes and language: scrolling back
/// over a hunk, or a terminal repainting the same output every frame,
/// parses nothing again. Freed by `stop`.
const DiffPiece = struct { hash: u64, styles: []u8, used: u64 };
var diff_pieces: [96]?DiffPiece = @splat(null);
var diff_clock: u64 = 0;

fn dropDiffPieces() void {
    for (&diff_pieces) |*slot| {
        if (slot.*) |piece| syntax_allocator.free(piece.styles);
        slot.* = null;
    }
    diff_clock = 0;
}

/// The styles of `content[start..end)` read as a unified diff: headers
/// muted, `@@` lines as keywords, and each hunk's code in the language of
/// the file its section names. A hunk's old side (context and removed
/// lines) and new side (context and added lines) are each parsed whole, so
/// a string or comment that spans lines colours as it does in the file.
/// Added and removed lines carry `diff_added`/`diff_removed`. A file in no
/// language pardes knows keeps the plain colours: added lines as strings,
/// removed ones as numbers.
pub fn highlightDiff(gpa: std.mem.Allocator, content: []const u8, start_raw: usize, end_raw: usize) ![]u8 {
    return highlightDiffRows(gpa, content, start_raw, end_raw, false);
}

/// The same for a terminal's rows, where a row the terminal wrapped
/// continues the diff line above it.
pub fn highlightDiffRows(gpa: std.mem.Allocator, content: []const u8, start_raw: usize, end_raw: usize, continued_rows: bool) ![]u8 {
    const tz = tracy.zone(@src(), "highlightDiff");
    defer tz.end();
    const start_byte = @min(start_raw, content.len);
    const end_byte = @max(start_byte, @min(end_raw, content.len));
    const styles = try gpa.alloc(u8, end_byte - start_byte);
    errdefer gpa.free(styles);
    @memset(styles, 0);
    const Window = struct {
        styles: []u8,
        start: usize,
        fn put(w: @This(), at: usize, bytes: []const u8) void {
            const lo = @max(at, w.start);
            const hi = @min(at + bytes.len, w.start + w.styles.len);
            if (lo < hi) @memcpy(w.styles[lo - w.start .. hi - w.start], bytes[lo - at .. hi - at]);
        }
        fn fill(w: @This(), at: usize, len: usize, style: u8) void {
            const lo = @max(at, w.start);
            const hi = @min(at + len, w.start + w.styles.len);
            if (lo < hi) @memset(w.styles[lo - w.start .. hi - w.start], style);
        }
    };
    const window: Window = .{ .styles = styles, .start = start_byte };

    var walk: diff.Walk = .{ .continued_rows = continued_rows };
    // The run of hunk lines not painted yet, with each line's kind.
    var piece_start: ?usize = null;
    var piece_end: usize = 0;
    var piece_path: []const u8 = "";
    var kinds: [diff_piece_cut]diff.Kind = undefined;
    var nkinds: usize = 0;
    var at = diff.anchorBefore(content, start_byte);
    while (true) {
        const nl = std.mem.indexOfScalarPos(u8, content, at, '\n') orelse content.len;
        const got = walk.step(content[at..nl]);
        const body = switch (got.kind) {
            .context, .added, .removed, .no_newline => true,
            // The next hunk of the section goes on in the same piece.
            .hunk => piece_start != null and nkinds < diff_piece_lines,
            else => false,
        };
        if (piece_start) |ps| if (!body or nkinds == diff_piece_cut) {
            if (piece_end >= start_byte) try paintDiffPiece(gpa, window, content[ps..piece_end], ps, kinds[0..nkinds], piece_path);
            piece_start = null;
            nkinds = 0;
        };
        if (at >= end_byte and piece_start == null) break;
        if (body and (piece_start != null or got.kind != .hunk)) {
            if (piece_start == null) {
                piece_start = at;
                piece_path = walk.path();
            }
            kinds[nkinds] = got.kind;
            nkinds += 1;
            piece_end = nl;
        } else if (nl >= start_byte) {
            const style: Syn = switch (got.kind) {
                .hunk => .keyword,
                .meta, .old_path, .new_path => .comment,
                else => .none,
            };
            if (style != .none) window.fill(at, nl - at, @intFromEnum(style));
        }
        if (nl >= content.len) break;
        at = nl + 1;
    }
    if (piece_start) |ps| if (piece_end >= start_byte)
        try paintDiffPiece(gpa, window, content[ps..piece_end], ps, kinds[0..nkinds], piece_path);
    return styles;
}

fn paintDiffPiece(gpa: std.mem.Allocator, window: anytype, bytes: []const u8, at: usize, kinds: []const diff.Kind, path: []const u8) !void {
    const selected: ?Selected = if (enabled and syntax_started) (forExt(std.fs.path.extension(path)) catch null) else null;
    if (selected) |sel| {
        const hash = std.hash.Wyhash.hash(std.hash.Wyhash.hash(0, sel.name), bytes);
        diff_clock += 1;
        for (&diff_pieces) |*slot| if (slot.*) |*piece| if (piece.hash == hash and piece.styles.len == bytes.len) {
            piece.used = diff_clock;
            return window.put(at, piece.styles);
        };
        const colored = try syntax_allocator.alloc(u8, bytes.len);
        errdefer syntax_allocator.free(colored);
        try paintHunk(gpa, colored, bytes, kinds, sel);
        window.put(at, colored);
        var oldest: usize = 0;
        for (&diff_pieces, 0..) |*slot, i| {
            const piece = slot.* orelse {
                oldest = i;
                break;
            };
            if (diff_pieces[oldest]) |o| if (piece.used < o.used) {
                oldest = i;
            };
        }
        if (diff_pieces[oldest]) |old| syntax_allocator.free(old.styles);
        diff_pieces[oldest] = .{ .hash = hash, .styles = colored, .used = diff_clock };
        return;
    }
    // No language: each line in one colour, as diffs were always shown.
    var lines = std.mem.splitScalar(u8, bytes, '\n');
    var offset: usize = 0;
    for (kinds) |kind| {
        const line = lines.next() orelse break;
        const style: u8 = switch (kind) {
            .added => @intFromEnum(Syn.string) | diff_added,
            .removed => @intFromEnum(Syn.number) | diff_removed,
            .no_newline => @intFromEnum(Syn.comment),
            .hunk => @intFromEnum(Syn.keyword),
            else => 0,
        };
        if (style != 0) window.fill(at + offset, line.len, style);
        offset += line.len + 1;
    }
}

/// One piece's styles: its old side and its new side each parsed as one
/// text, and every line's code coloured from its side, behind its
/// one-character prefix. A `@@` line between its hunks is in neither.
fn paintHunk(gpa: std.mem.Allocator, out: []u8, bytes: []const u8, kinds: []const diff.Kind, sel: Selected) !void {
    @memset(out, 0);
    const old_src = try gpa.alloc(u8, bytes.len);
    defer gpa.free(old_src);
    const new_src = try gpa.alloc(u8, bytes.len);
    defer gpa.free(new_src);
    var old_len: usize = 0;
    var new_len: usize = 0;
    var lines = std.mem.splitScalar(u8, bytes, '\n');
    for (kinds) |kind| {
        const line = lines.next() orelse break;
        const code = line[codeStart(line, kind)..];
        // A row a terminal wrapped goes on the line above, as it was printed.
        const joined = continuesRow(line, kind);
        if (kind == .context or kind == .removed) {
            if (joined and old_len > 0) old_len -= 1;
            @memcpy(old_src[old_len..][0..code.len], code);
            old_len += code.len;
            old_src[old_len] = '\n';
            old_len += 1;
        }
        if (kind == .context or kind == .added) {
            if (joined and new_len > 0) new_len -= 1;
            @memcpy(new_src[new_len..][0..code.len], code);
            new_len += code.len;
            new_src[new_len] = '\n';
            new_len += 1;
        }
    }
    // A side is parsed only when a line takes its colours from it: the old
    // side for removed lines, the new side for added lines, and context
    // from the new side, else from the old. A piece that only adds or only
    // removes is one parse.
    var removes = false;
    var adds = false;
    for (kinds) |kind| {
        removes = removes or kind == .removed;
        adds = adds or kind == .added;
    }
    const context_new = adds or !removes;
    const old_colors = try gpa.alloc(u8, old_len);
    defer gpa.free(old_colors);
    @memset(old_colors, 0);
    if (!context_new or removes) paint(old_colors, old_src[0..old_len], sel);
    const new_colors = try gpa.alloc(u8, new_len);
    defer gpa.free(new_colors);
    @memset(new_colors, 0);
    if (context_new) paint(new_colors, new_src[0..new_len], sel);

    lines = std.mem.splitScalar(u8, bytes, '\n');
    var offset: usize = 0;
    var old_at: usize = 0;
    var new_at: usize = 0;
    for (kinds) |kind| {
        const line = lines.next() orelse break;
        defer offset += line.len + 1;
        const skip = codeStart(line, kind);
        const code_len = line.len - skip;
        const dst = out[offset + skip ..][0..code_len];
        if (continuesRow(line, kind)) {
            if ((kind == .context or kind == .removed) and old_at > 0) old_at -= 1;
            if ((kind == .context or kind == .added) and new_at > 0) new_at -= 1;
        }
        switch (kind) {
            .removed => @memcpy(dst, old_colors[old_at..][0..code_len]),
            .added => @memcpy(dst, new_colors[new_at..][0..code_len]),
            .context => @memcpy(dst, if (context_new) new_colors[new_at..][0..code_len] else old_colors[old_at..][0..code_len]),
            .no_newline => @memset(out[offset..][0..line.len], @intFromEnum(Syn.comment)),
            .hunk => @memset(out[offset..][0..line.len], @intFromEnum(Syn.keyword)),
            else => {},
        }
        if (kind == .context or kind == .removed) old_at += code_len + 1;
        if (kind == .context or kind == .added) new_at += code_len + 1;
        const flag: u8 = switch (kind) {
            .added => diff_added,
            .removed => diff_removed,
            else => 0,
        };
        if (flag != 0) for (out[offset..][0..line.len]) |*b| {
            b.* |= flag;
        };
    }
}

fn continuesRow(line: []const u8, kind: diff.Kind) bool {
    return line.len > 0 and codeStart(line, kind) == 0 and
        (kind == .context or kind == .added or kind == .removed);
}

/// Where a hunk line's code starts: past its prefix, which a blank context
/// line (its space stripped) and a terminal's wrapped row have none of.
fn codeStart(line: []const u8, kind: diff.Kind) usize {
    if (line.len == 0) return 0;
    return switch (kind) {
        .context => @intFromBool(line[0] == ' '),
        .added => @intFromBool(line[0] == '+'),
        .removed => @intFromBool(line[0] == '-'),
        else => 0,
    };
}

test "syntax a results row is coloured by the file its location names" {
    if (!enabled) return;
    start(std.testing.allocator);
    defer stop();
    const gpa = std.testing.allocator;
    const content =
        "src/a.zig:1:1 const S = struct {};\n" ++
        "src/b.md:2:1 # heading\n" ++
        "just some prose with a colon: here\n" ++
        "src/c.zig:3:1\n";
    const styles = try highlightLocations(gpa, content, 0, content.len);
    defer gpa.free(styles);
    try std.testing.expectEqual(content.len, styles.len);
    for (styles[0.."src/a.zig:1:1".len]) |b| try std.testing.expectEqual(@as(u8, 0), b);
    const zig_kw = std.mem.indexOf(u8, content, "struct").?;
    try std.testing.expectEqual(@intFromEnum(Syn.keyword), styles[zig_kw]);
    try std.testing.expectEqual(@intFromEnum(Syn.keyword), styles[zig_kw + 5]);
    const prose = std.mem.indexOf(u8, content, "just some prose").?;
    for (styles[prose .. prose + 14]) |b| try std.testing.expectEqual(@as(u8, 0), b);
    const bare = std.mem.indexOf(u8, content, "src/c.zig").?;
    for (styles[bare..]) |b| try std.testing.expectEqual(@as(u8, 0), b);
}

test "syntax a buffer with no locations in it keeps no highlights at all" {
    if (!enabled) return;
    start(std.testing.allocator);
    defer stop();
    const content = "nothing has been said yet\n0: save: AccessDenied  (x2)\n";
    const styles = try highlightLocations(std.testing.allocator, content, 0, content.len);
    defer std.testing.allocator.free(styles);
    try std.testing.expectEqual(@as(usize, 0), styles.len);
}

test "syntax codeAfterLocation takes whole-token locations and nothing else" {
    const got = codeAfterLocation("src/x.zig:7:2-9 fn main() void {") orelse
        return error.ShouldBeALocation;
    try std.testing.expectEqualStrings("src/x.zig", got.path);
    try std.testing.expectEqualStrings("fn main() void {", got.text);
    try std.testing.expect(codeAfterLocation("main.zig some words") == null);
    try std.testing.expect(codeAfterLocation("note: this is prose") == null);
    try std.testing.expect(codeAfterLocation("src/x.zig:7:2x rest") == null);
    try std.testing.expect(codeAfterLocation("src/x.zig:7:2") == null);
    try std.testing.expect(codeAfterLocation("") == null);
    try std.testing.expect(codeAfterLocation("   leading space") == null);
}

test "syntax default full grammar set highlights Typst source" {
    if (!enabled or !full_grammars) return;
    start(std.testing.allocator);
    defer stop();

    const source = "// note\n#let answer = 42\n#let text = \"hello\"\n";
    const styles = try highlightFileRange(std.testing.allocator, "paper.typst", source, 0, source.len);
    defer std.testing.allocator.free(styles);

    const comment_at = std.mem.indexOf(u8, source, "// note").?;
    const keyword_at = std.mem.indexOf(u8, source, "let").?;
    const number_at = std.mem.indexOf(u8, source, "42").?;
    const string_at = std.mem.indexOf(u8, source, "\"hello\"").?;
    try std.testing.expectEqual(Syn.comment, @as(Syn, @enumFromInt(styles[comment_at])));
    try std.testing.expectEqual(Syn.keyword, @as(Syn, @enumFromInt(styles[keyword_at])));
    try std.testing.expectEqual(Syn.number, @as(Syn, @enumFromInt(styles[number_at])));
    try std.testing.expectEqual(Syn.string, @as(Syn, @enumFromInt(styles[string_at])));

    const short_ext = try highlightFileRange(std.testing.allocator, "paper.typ", source, 0, source.len);
    defer std.testing.allocator.free(short_ext);
    try std.testing.expectEqual(Syn.keyword, @as(Syn, @enumFromInt(short_ext[keyword_at])));
}

test "syntax Typst markup constructs paint and raw blocks inject their language" {
    if (!enabled or !full_grammars) return;
    start(std.testing.allocator);
    defer stop();

    const source =
        \\// note
        \\= Heading Title
        \\Some *bold* text with `raw` inline.
        \\#import "mod.typ": helper
        \\#let answer = 42
        \\#emit(7, "arg")
        \\```zig
        \\fn widget() u8 { return 99; }
        \\```
        \\
    ;
    const styles = try highlightFileRange(std.testing.allocator, "paper.typ", source, 0, source.len);
    defer std.testing.allocator.free(styles);

    const synAt = struct {
        fn f(s: []const u8, src: []const u8, needle: []const u8, offset: usize) Syn {
            return @enumFromInt(s[std.mem.indexOf(u8, src, needle).? + offset]);
        }
    }.f;
    try std.testing.expectEqual(Syn.keyword, synAt(styles, source, "= Heading", 0));
    try std.testing.expectEqual(Syn.keyword, synAt(styles, source, "Heading", 0));
    try std.testing.expectEqual(Syn.comment, synAt(styles, source, "bold", 0));
    try std.testing.expectEqual(Syn.string, synAt(styles, source, "raw` inline", 0));
    try std.testing.expectEqual(Syn.keyword, synAt(styles, source, "emit", 0));
    try std.testing.expectEqual(Syn.keyword, synAt(styles, source, "#emit", 0));
    try std.testing.expectEqual(Syn.string, synAt(styles, source, "```zig", 0));
    try std.testing.expectEqual(Syn.string, synAt(styles, source, "```zig", 3));
    try std.testing.expectEqual(Syn.keyword, synAt(styles, source, "fn widget", 0));
    try std.testing.expectEqual(Syn.number, synAt(styles, source, "99", 0));
    try std.testing.expectEqual(Syn.none, synAt(styles, source, "widget", 0));

    try std.testing.expectEqual(Syn.comment, synAt(styles, source, "// note", 0));
    try std.testing.expectEqual(Syn.keyword, synAt(styles, source, "import", 0));
    try std.testing.expectEqual(Syn.keyword, synAt(styles, source, "let", 0));
    try std.testing.expectEqual(Syn.number, synAt(styles, source, "42", 0));
    try std.testing.expectEqual(Syn.string, synAt(styles, source, "\"arg\"", 0));
}

test "syntax markdown highlights markup, injects inline spans and fenced code blocks" {
    if (!enabled or !full_grammars) return;
    start(std.testing.allocator);
    defer stop();

    const source =
        "# Heading *slant* Title\n" ++
        "\n" ++
        "Prose with **stout** and *lean* plus `snippet` inline.\n" ++
        "\n" ++
        "```zig\n" ++
        "fn gadget() u8 { return 77; }\n" ++
        "```\n";
    const styles = try highlightFileRange(std.testing.allocator, "doc.md", source, 0, source.len);
    defer std.testing.allocator.free(styles);

    const synAt = struct {
        fn f(s: []const u8, src: []const u8, needle: []const u8, offset: usize) Syn {
            return @enumFromInt(s[std.mem.indexOf(u8, src, needle).? + offset]);
        }
    }.f;
    try std.testing.expectEqual(Syn.keyword, synAt(styles, source, "Title", 0));
    try std.testing.expectEqual(Syn.number, synAt(styles, source, "slant", 0));
    try std.testing.expectEqual(Syn.comment, synAt(styles, source, "stout", 0));
    try std.testing.expectEqual(Syn.number, synAt(styles, source, "lean", 0));
    try std.testing.expectEqual(Syn.string, synAt(styles, source, "snippet", 0));
    try std.testing.expectEqual(Syn.string, synAt(styles, source, "```zig", 0));
    try std.testing.expectEqual(Syn.keyword, synAt(styles, source, "fn gadget", 0));
    try std.testing.expectEqual(Syn.number, synAt(styles, source, "77", 0));
    try std.testing.expectEqual(Syn.none, synAt(styles, source, "gadget", 0));
}

test "syntax inline fast path agrees with full Markdown query" {
    if (!enabled or !full_grammars) return;
    start(std.testing.allocator);
    defer stop();
    const selected = (try forLang("markdown_inline")).?;
    const check = struct {
        fn compare(sel: Selected, source: []const u8) !void {
            const tree = sel.parser.parseString(source, null) orelse return error.ParseFailed;
            defer tree.destroy();
            const expected = try std.testing.allocator.alloc(u8, source.len);
            defer std.testing.allocator.free(expected);
            const actual = try std.testing.allocator.alloc(u8, source.len);
            defer std.testing.allocator.free(actual);
            for ([_]Syn{ .none, .keyword }) |background| {
                @memset(expected, @intFromEnum(background));
                @memset(actual, @intFromEnum(background));
                runQuery(expected, sel, tree, 0);
                inject(actual, source, tree.rootNode(), true);
                if (!std.mem.eql(u8, expected, actual)) std.debug.print("inline mismatch: {s}\n", .{source});
                try std.testing.expectEqualSlices(u8, expected, actual);
            }
        }
    }.compare;
    for ([_][]const u8{
        "",                                         "plain prose",
        "ação Ελληνικά 日本語 🙂",
        "123 456",                                  "tabs\tand spaces",
        "'quoted' (parentheses) \"double quotes\"", "https://example.org a@b.org",
        "&amp; &#10; &#x20;",                       "~~struck~~ $formula$",
        "*emphasis* __strong__",                    "**bold** _emphasis_",
        "`code` and ``a`b``",                       "[text](target \"title\")",
        "![description](image)",                    "[shortcut] [reference][label]",
        "[[wiki|text]]",                            "<https://example.org> <a@b.org>",
        "<i>text</i>",                              "\\*escaped\\*",
        "soft\nline",                               "hard  \nline",
        "hard\\\nline",                             "tab\t\nline",
        "hard  \r\nline",                           "hard  \rline",
        "**broken",                                 "[broken](",
        "`broken",
    }) |source| try check(selected, source);
    for (0..128) |byte| {
        const char: u8 = @intCast(byte);
        const source = [_]u8{ char, 'a', 'b', char, ' ', char, char, 'c', char, char };
        try check(selected, &source);
    }
}

test "syntax plain Markdown keeps block styles without starting the inline parser" {
    if (!enabled or !full_grammars) return;
    start(std.testing.allocator);
    defer stop();
    const source = "# Heading\n\nPlain prose.\n\n    indented code\n";
    const styles = try highlightFileRange(std.testing.allocator, "a.md", source, 0, source.len);
    defer std.testing.allocator.free(styles);
    try std.testing.expectEqual(@intFromEnum(Syn.keyword), styles[2]);
    try std.testing.expectEqual(@intFromEnum(Syn.none), styles[std.mem.indexOf(u8, source, "Plain").?]);
    try std.testing.expectEqual(@intFromEnum(Syn.string), styles[std.mem.indexOf(u8, source, "indented").?]);
    for (specs) |spec| {
        if (std.mem.eql(u8, spec.name, "markdown_inline")) try std.testing.expect(spec.selected == null);
    }
}

test "syntax highlightDiff colors unified diff lines by prefix" {
    const diff_text =
        "diff --git a/x b/x\n" ++
        "--- a/x\n" ++
        "+++ b/x\n" ++
        "@@ -1,2 +1,2 @@\n" ++
        " context\n" ++
        "-old line\n" ++
        "+new line\n";
    const styles = try highlightDiff(std.testing.allocator, diff_text, 0, diff_text.len);
    defer std.testing.allocator.free(styles);
    try std.testing.expectEqual(Syn.comment, diffSynAt(styles, diff_text, "diff --git", 0));
    try std.testing.expectEqual(Syn.comment, diffSynAt(styles, diff_text, "--- a/x", 0));
    try std.testing.expectEqual(Syn.comment, diffSynAt(styles, diff_text, "+++ b/x", 0));
    try std.testing.expectEqual(Syn.keyword, diffSynAt(styles, diff_text, "@@ -1,2", 0));
    try std.testing.expectEqual(Syn.none, diffSynAt(styles, diff_text, " context", 0));
    // A file in no known language: each line in one colour, and tinted.
    try std.testing.expectEqual(Syn.number, diffSynAt(styles, diff_text, "-old line", 0));
    try std.testing.expectEqual(Syn.string, diffSynAt(styles, diff_text, "+new line", 0));
    try std.testing.expect(styles[std.mem.indexOf(u8, diff_text, "-old line").?] & diff_removed != 0);
    try std.testing.expect(styles[std.mem.indexOf(u8, diff_text, "+new line").? + 4] & diff_added != 0);
    try std.testing.expect(styles[std.mem.indexOf(u8, diff_text, " context").?] & (diff_added | diff_removed) == 0);
}

fn diffSynAt(styles: []const u8, text: []const u8, needle: []const u8, offset: usize) Syn {
    return @enumFromInt(styles[std.mem.indexOf(u8, text, needle).? + offset] & syn_bits);
}

test "syntax a Zig hunk is coloured as Zig, each side parsed whole" {
    if (!enabled) return;
    start(std.testing.allocator);
    defer stop();
    const diff_text =
        "diff --git a/src/shape.zig b/src/shape.zig\n" ++
        "index 1111111..2222222 100644\n" ++
        "--- a/src/shape.zig\n" ++
        "+++ b/src/shape.zig\n" ++
        "@@ -1,6 +1,6 @@\n" ++
        " const Shape = struct {\n" ++
        "-    side: u8 = 7,\n" ++
        "+    side: u16 = 42,\n" ++
        "     const note =\n" ++
        "-        \\\\old words defer\n" ++
        "+        \\\\new words defer\n" ++
        "     ;\n" ++
        " };\n";
    const styles = try highlightDiff(std.testing.allocator, diff_text, 0, diff_text.len);
    defer std.testing.allocator.free(styles);
    try std.testing.expectEqual(Syn.keyword, diffSynAt(styles, diff_text, "struct", 0));
    try std.testing.expectEqual(Syn.number, diffSynAt(styles, diff_text, "7,", 0));
    try std.testing.expectEqual(Syn.number, diffSynAt(styles, diff_text, "42", 0));
    // A multiline string, told apart only by parsing the side it is on:
    // `defer` inside it is no keyword.
    try std.testing.expectEqual(Syn.string, diffSynAt(styles, diff_text, "old words defer", 10));
    try std.testing.expectEqual(Syn.string, diffSynAt(styles, diff_text, "new words defer", 10));
    // The prefix is no code: it carries the tint alone.
    const added = std.mem.indexOf(u8, diff_text, "+    side").?;
    try std.testing.expectEqual(diff_added, styles[added]);
    try std.testing.expect(styles[std.mem.indexOf(u8, diff_text, "42").?] & diff_added != 0);
    try std.testing.expect(styles[std.mem.indexOf(u8, diff_text, "7,").?] & diff_removed != 0);
    try std.testing.expectEqual(Syn.comment, diffSynAt(styles, diff_text, "index 111", 0));

    // A window in the middle is coloured as the whole is.
    const from = std.mem.indexOf(u8, diff_text, "     const note").?;
    const part = try highlightDiff(std.testing.allocator, diff_text, from, diff_text.len);
    defer std.testing.allocator.free(part);
    try std.testing.expectEqualSlices(u8, styles[from..], part);
}

test "syntax a Python hunk is coloured as Python" {
    if (!enabled or !full_grammars) return;
    start(std.testing.allocator);
    defer stop();
    const diff_text =
        "--- a/tool.py\n" ++
        "+++ b/tool.py\n" ++
        "@@ -1,3 +1,4 @@\n" ++
        " def run(n):\n" ++
        "-    return n\n" ++
        "+    # doubled now\n" ++
        "+    return n * 2\n" ++
        " \n";
    const styles = try highlightDiff(std.testing.allocator, diff_text, 0, diff_text.len);
    defer std.testing.allocator.free(styles);
    try std.testing.expectEqual(Syn.keyword, diffSynAt(styles, diff_text, "def", 0));
    try std.testing.expectEqual(Syn.keyword, diffSynAt(styles, diff_text, "return n\n", 0));
    try std.testing.expectEqual(Syn.comment, diffSynAt(styles, diff_text, "# doubled", 2));
    try std.testing.expectEqual(Syn.number, diffSynAt(styles, diff_text, "2\n", 0));
}

test "syntax a deleted file's lines are coloured in its language" {
    if (!enabled) return;
    start(std.testing.allocator);
    defer stop();
    const diff_text =
        "diff --git a/gone.zig b/gone.zig\n" ++
        "deleted file mode 100644\n" ++
        "--- a/gone.zig\n" ++
        "+++ /dev/null\n" ++
        "@@ -1,2 +0,0 @@\n" ++
        "-const Gone = enum { a };\n" ++
        "-// the end\n";
    const styles = try highlightDiff(std.testing.allocator, diff_text, 0, diff_text.len);
    defer std.testing.allocator.free(styles);
    try std.testing.expectEqual(Syn.keyword, diffSynAt(styles, diff_text, "enum", 0));
    try std.testing.expectEqual(Syn.comment, diffSynAt(styles, diff_text, "// the end", 3));
    try std.testing.expect(styles[std.mem.indexOf(u8, diff_text, "enum").?] & diff_removed != 0);
    try std.testing.expectEqual(Syn.comment, diffSynAt(styles, diff_text, "deleted file", 0));
}

test "syntax a hunk in no known language keeps the line colours" {
    if (!enabled) return;
    start(std.testing.allocator);
    defer stop();
    const diff_text =
        "--- a/notes.unknownext\n" ++
        "+++ b/notes.unknownext\n" ++
        "@@ -1 +1 @@\n" ++
        "-const struct 1\n" ++
        "+const struct 2\n";
    const styles = try highlightDiff(std.testing.allocator, diff_text, 0, diff_text.len);
    defer std.testing.allocator.free(styles);
    try std.testing.expectEqual(Syn.number, diffSynAt(styles, diff_text, "struct 1", 0));
    try std.testing.expectEqual(Syn.string, diffSynAt(styles, diff_text, "struct 2", 0));
    try std.testing.expectEqual(Syn.string, diffSynAt(styles, diff_text, "+const struct 2", 0));
}

test "syntax git diff output in a command pane is told and coloured by its rows" {
    if (!enabled) return;
    start(std.testing.allocator);
    defer stop();
    // A command pane's rows: its command line, then git's output, with one
    // long added line the terminal wrapped onto a second row.
    const rows = [_][]const u8{
        "git diff",
        "diff --git a/main.zig b/main.zig",
        "--- a/main.zig",
        "+++ b/main.zig",
        "@@ -1,2 +1,2 @@",
        " pub fn main() void {",
        "+    const answer: u32 = 42; // the ",
        "wrapped rest",
        "-    return;",
        "",
    };
    try std.testing.expect(diff.looksLikeDiff(&rows));
    try std.testing.expect(!diff.looksLikeDiff(rows[5..]));
    const text = try std.mem.join(std.testing.allocator, "\n", &rows);
    defer std.testing.allocator.free(text);
    const styles = try highlightDiffRows(std.testing.allocator, text, 0, text.len, true);
    defer std.testing.allocator.free(styles);
    try std.testing.expectEqual(Syn.none, diffSynAt(styles, text, "git diff", 0));
    try std.testing.expectEqual(Syn.keyword, diffSynAt(styles, text, "fn main", 0));
    try std.testing.expectEqual(Syn.number, diffSynAt(styles, text, "42", 0));
    // The wrapped row stays an added line, and inside the comment.
    try std.testing.expect(styles[std.mem.indexOf(u8, text, "wrapped rest").?] & diff_added != 0);
    try std.testing.expectEqual(Syn.comment, diffSynAt(styles, text, "wrapped rest", 0));
    try std.testing.expect(styles[std.mem.indexOf(u8, text, "return").?] & diff_removed != 0);
}

test "syntax a section's small hunks share one parse" {
    if (!enabled) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const diff_text =
        "--- a/x.zig\n+++ b/x.zig\n" ++
        "@@ -1 +1 @@\n-const a = 1;\n+const a = 2;\n" ++
        "@@ -10 +10 @@\n-const b = 1;\n+const b = 2;\n" ++
        "@@ -20 +20 @@\n-const c = 1;\n+const c = 2;\n" ++
        "--- a/y.zig\n+++ b/y.zig\n" ++
        "@@ -1 +1 @@\n-const d = 1;\n+const d = 2;\n";
    const styles = try highlightDiff(gpa, diff_text, 0, diff_text.len);
    defer gpa.free(styles);
    var cached: usize = 0;
    for (diff_pieces) |slot| cached += @intFromBool(slot != null);
    try std.testing.expectEqual(@as(usize, 2), cached); // x.zig's three hunks, and y.zig's
    try std.testing.expectEqual(Syn.keyword, diffSynAt(styles, diff_text, "@@ -10", 0));
    try std.testing.expectEqual(Syn.number, diffSynAt(styles, diff_text, "2;\n@@ -20", 0));
    try std.testing.expect(styles[std.mem.indexOf(u8, diff_text, "@@ -10").?] & (diff_added | diff_removed) == 0);
}

test "syntax a hunk painted once is kept, and a long one is parsed in pieces" {
    if (!enabled) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    var text: std.Io.Writer.Allocating = .init(gpa);
    defer text.deinit();
    const n = diff_piece_cut * 20 + 10;
    try text.writer.print("--- /dev/null\n+++ b/big.zig\n@@ -0,0 +1,{d} @@\n", .{n});
    for (0..n) |i| try text.writer.print("+const v{d} = {d};\n", .{ i, i });
    const content = text.written();
    const at = std.mem.indexOf(u8, content, "+const v1000 ").?;
    const window = try highlightDiff(gpa, content, at, at + 200);
    defer gpa.free(window);
    try std.testing.expectEqual(Syn.number, @as(Syn, @enumFromInt(window["+const v1000 = ".len] & syn_bits)));
    var cached: usize = 0;
    for (diff_pieces) |slot| if (slot) |piece| {
        cached += 1;
        // One piece of many, not the whole hunk.
        try std.testing.expect(piece.styles.len < content.len / 4);
    };
    try std.testing.expectEqual(@as(usize, 1), cached);
    const again = try highlightDiff(gpa, content, at, at + 200);
    defer gpa.free(again);
    try std.testing.expectEqualSlices(u8, window, again);
    cached = 0;
    for (diff_pieces) |slot| cached += @intFromBool(slot != null);
    try std.testing.expectEqual(@as(usize, 1), cached);
}

test "syntax result fragments preserve source indentation and inline markup" {
    if (!enabled) return;
    start(std.testing.allocator);
    defer stop();
    const fixtures = [_]struct { path: []const u8, source: []const u8 }{
        .{ .path = "a.zig", .source = "    const number = 42; // note" },
        .{ .path = "a.md", .source = "# Heading *slant*" },
        .{ .path = "a.md", .source = "**bold** and `code`" },
        .{ .path = "a.md", .source = "    # this is indented code" },
        .{ .path = "a.md", .source = "\t# tab-indented code" },
        .{ .path = "a.py", .source = "    return \"hello\"" },
    };
    for (fixtures) |fixture| {
        const expected = try highlightFileRange(std.testing.allocator, fixture.path, fixture.source, 0, fixture.source.len);
        defer std.testing.allocator.free(expected);
        const row = try std.fmt.allocPrint(std.testing.allocator, "{s}:12:3-9 {s}", .{ fixture.path, fixture.source });
        defer std.testing.allocator.free(row);
        const actual = try highlightLocations(std.testing.allocator, row, 0, row.len);
        defer std.testing.allocator.free(actual);
        if (expected.len == 0) {
            try std.testing.expectEqual(@as(usize, 0), actual.len);
            continue;
        }
        const code_at = row.len - fixture.source.len;
        try std.testing.expectEqualSlices(u8, expected, actual[code_at..]);
        for (actual[0..code_at]) |style| try std.testing.expectEqual(@as(u8, 0), style);
    }
}

test "syntax query filtering preserves upstream colors" {
    if (!enabled) return;
    var allocator: std.heap.DebugAllocator(.{ .stack_trace_frames = 0, .safety = true }) = .init;
    defer if (allocator.deinit() != .ok) @panic("leaked syntax query allocations");
    start(allocator.allocator());
    defer stop();
    const source = "// comment\n# Heading *inline*\nconst value = 42;\nif (true) { return \"quoted\"; }\n/* multi\nline */\n";
    inline for (grammar_manifest.all) |grammar| {
        if (comptime grammarSelected(grammar)) {
            const selected = (try forLang(grammar.name)).?;
            const raw_source = @field(ts_queries, grammar.name ++ "_highlights") ++
                (if (comptime std.mem.eql(u8, grammar.name, "typst")) typst_supplement else "");
            var error_offset: u32 = 0;
            const raw_query = try ts.Query.create(selected.lang, raw_source, &error_offset);
            defer raw_query.destroy();
            var reference = selected;
            reference.query = raw_query;
            reference.capture_styles = try std.testing.allocator.alloc(u8, raw_query.captureCount());
            defer std.testing.allocator.free(reference.capture_styles);
            for (reference.capture_styles, 0..) |*style, id| style.* = @intFromEnum(synFor(raw_query.captureNameForId(@intCast(id)) orelse ""));
            const tree = selected.parser.parseString(source, null) orelse return error.ParseFailed;
            defer tree.destroy();
            var expected: [source.len]u8 = @splat(0);
            var actual: [source.len]u8 = @splat(0);
            runQuery(&expected, reference, tree, 0);
            runQuery(&actual, selected, tree, 0);
            if (!std.mem.eql(u8, &expected, &actual)) std.debug.print("query mismatch: {s}\n", .{grammar.name});
            try std.testing.expectEqualSlices(u8, &expected, &actual);
        }
    }
}

test "syntax Zig keyword captures cover both bytes beyond line ten thousand" {
    if (!enabled) return;
    start(std.testing.allocator);
    defer stop();
    const code = "pub fn main() void {\n    if (true) return;\n}\n";
    const source = try std.testing.allocator.alloc(u8, 10_001 + code.len);
    defer std.testing.allocator.free(source);
    @memset(source[0..10_001], '\n');
    @memcpy(source[10_001..], code);
    const styles = try highlightFileRange(std.testing.allocator, "a.zig", source, 10_001, source.len);
    defer std.testing.allocator.free(styles);
    for ([_][]const u8{ "fn", "if" }) |keyword| {
        const at = std.mem.indexOf(u8, code, keyword).?;
        try std.testing.expectEqual(@intFromEnum(Syn.keyword), styles[at]);
        try std.testing.expectEqual(@intFromEnum(Syn.keyword), styles[at + 1]);
    }
}

test "syntax allocator switching clears default-runtime caches" {
    if (!enabled) return;
    const source = "fn main() void {}";
    const initial = try highlightFileRange(std.testing.allocator, "a.zig", source, 0, source.len);
    std.testing.allocator.free(initial);
    start(std.testing.allocator);
    const custom = try highlightFileRange(std.testing.allocator, "a.zig", source, 0, source.len);
    std.testing.allocator.free(custom);
    stop();
    const restored = try highlightFileRange(std.testing.allocator, "a.zig", source, 0, source.len);
    defer std.testing.allocator.free(restored);
    defer stop();
    try std.testing.expectEqual(@intFromEnum(Syn.keyword), restored[0]);
    try std.testing.expectEqual(@intFromEnum(Syn.keyword), restored[1]);
}

test "syntax location context snapshots retain omitted multiline comment scope" {
    if (!enabled or (!minimal_grammars and !full_grammars)) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const source = "/* documentation\nconst int value = 42;\n*/\n";
    const source_colors = try highlightFileRange(gpa, "a.c", source, 0, source.len);
    defer gpa.free(source_colors);
    const code = "const int value = 42;";
    const source_start = std.mem.indexOf(u8, source, code).?;
    const Row = struct { path: []const u8, code_start: usize, at: look.Spot, colors: []const u8 };
    const content = "| \t" ++ code ++ "\n";
    const rows = [_]Row{.{
        .path = "a.c",
        .code_start = "| \t".len,
        .at = .{ .line = 2 },
        .colors = source_colors[source_start..][0..code.len],
    }};
    const styles = try highlightLocationRows(gpa, content, &rows);
    defer gpa.free(styles);
    for (styles[rows[0].code_start..][0..code.len]) |style|
        try std.testing.expectEqual(@intFromEnum(Syn.comment), style);
    try std.testing.expectEqual(@intFromEnum(Syn.none), styles[0]);
}

test "syntax declaration locations clear snapshots without muting ordinary context" {
    if (!enabled) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const header = "pub fn run() void {";
    const content = "| \t" ++ header ++ "\n| \t    const value = 42;\nfile.zig:3\t}\n";
    const snapshots = [_]u8{0xff} ** header.len;
    const Row = struct {
        path: []const u8 = "file.zig",
        code_start: usize,
        at: look.Spot,
        colors: []const u8 = &.{},
        declaration: bool = false,
    };
    const rows = [_]Row{
        .{ .code_start = 3, .at = .{ .line = 1 }, .colors = &snapshots, .declaration = true },
        .{ .code_start = 3, .at = .{ .line = 2 } },
        .{ .code_start = "file.zig:3\t".len, .at = .{ .line = 3 } },
    };
    const styles = try highlightLocationRows(gpa, content, &rows);
    defer gpa.free(styles);
    for (styles[3..][0..header.len]) |style| try std.testing.expectEqual(@as(u8, 0), style);
    try std.testing.expectEqual(@intFromEnum(Syn.number), styles[std.mem.indexOf(u8, content, "42").?]);
}

test "syntax stacked addresses do not split multiline source groups" {
    if (!enabled or (!minimal_grammars and !full_grammars)) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const Row = struct { path: []const u8 = "a.c", code_start: usize, location_end: usize, at: look.Spot };
    const content = "a.c:1:1\n/* open\na.c:2:1\nint value = 42;\na.c:3:1\n*/ int other = 7;\n";
    const rows = [_]Row{
        .{ .code_start = 7, .location_end = 7, .at = .{ .line = 1 } },
        .{ .code_start = 0, .location_end = 0, .at = .{ .line = 1 } },
        .{ .code_start = 7, .location_end = 7, .at = .{ .line = 2 } },
        .{ .code_start = 0, .location_end = 0, .at = .{ .line = 2 } },
        .{ .code_start = 7, .location_end = 7, .at = .{ .line = 3 } },
        .{ .code_start = 0, .location_end = 0, .at = .{ .line = 3 } },
    };
    const styles = try highlightLocationRows(gpa, content, &rows);
    defer gpa.free(styles);
    try std.testing.expectEqual(@intFromEnum(Syn.comment), styles[std.mem.indexOf(u8, content, "42").?]);
    try std.testing.expectEqual(@intFromEnum(Syn.number), styles[std.mem.indexOf(u8, content, "7;").?]);
    for ([_][]const u8{ "a.c:1:1", "a.c:2:1", "a.c:3:1" }) |label| {
        const at = std.mem.indexOf(u8, content, label).?;
        for (styles[at..][0..label.len]) |style| try std.testing.expectEqual(@intFromEnum(Syn.none), style);
    }
}

test "syntax source analysis preserves declarations and injected colors" {
    if (!enabled) return;
    const gpa = std.testing.allocator;
    start(gpa);
    defer stop();
    const Fixture = struct { path: []const u8, source: []const u8 };
    for ([_]Fixture{
        .{ .path = "a.zig", .source = "const Outer = struct {\n // comment\n const Inner = struct {\n pub fn run(\n x: u32,\n ) u32 { return x; }\n };\n};\n" },
        .{ .path = "a.cpp", .source = "namespace Outer {\nstruct Inner {\nint run(\n int x\n) { return x; }\n};\n}\n" },
        .{ .path = "a.rs", .source = "mod outer {\nstruct Inner {}\nimpl Inner {\nfn run(\n &self\n) {}\n}\n}\n" },
        .{ .path = "a.js", .source = "function outer() {\nclass Inner {\nrun(\n x\n) { return x; }\n}\n}\n" },
        .{ .path = "a.py", .source = "class Outer:\n    class Inner:\n        def run(\n            self, x\n        ):\n            return x\n" },
        .{ .path = "a.md", .source = "# Heading\n\n```zig\npub fn run() void {}\n```\n" },
        .{ .path = "a.typst", .source = "= Heading\n\n```zig\npub fn run() void {}\n```\n" },
    }) |fixture| {
        if (!supportsPath(fixture.path)) continue;
        var analysis = try analyzeSource(gpa, fixture.path, fixture.source, true, true);
        defer analysis.deinit(gpa);
        const colors = try highlightFileRange(gpa, fixture.path, fixture.source, 0, fixture.source.len);
        defer gpa.free(colors);
        try std.testing.expectEqualSlices(u8, colors, analysis.colors);

        // Compare the previous named-node walk to the cursor walk, including
        // source ordering, wrapper deduplication and inclusive declaration ends.
        const selected = (try forExt(std.fs.path.extension(fixture.path))).?;
        const tree = selected.parser.parseString(fixture.source, null).?;
        defer tree.destroy();
        var reference: std.ArrayList(ContextDeclaration) = .empty;
        defer reference.deinit(gpa);
        var node = tree.rootNode();
        walk: while (true) {
            if (contextSpan(node, fixture.source)) |span| {
                if (reference.items.len == 0 or reference.items[reference.items.len - 1].start_line != span.start_line or
                    reference.items[reference.items.len - 1].end_line != span.end_line)
                    try reference.append(gpa, span);
            }
            if (node.namedChild(0)) |child| {
                node = child;
                continue;
            }
            while (node.nextNamedSibling() == null) node = node.parent() orelse break :walk;
            node = node.nextNamedSibling().?;
        }
        try std.testing.expectEqual(reference.items.len, analysis.declarations.len);
        for (reference.items, analysis.declarations) |old, new| try std.testing.expect(std.meta.eql(old, new));

        var declarations_only = try analyzeSource(gpa, fixture.path, fixture.source, true, false);
        defer declarations_only.deinit(gpa);
        try std.testing.expectEqual(@as(usize, 0), declarations_only.colors.len);
        try std.testing.expectEqual(analysis.declarations.len, declarations_only.declarations.len);
        var colors_only = try analyzeSource(gpa, fixture.path, fixture.source, false, true);
        defer colors_only.deinit(gpa);
        try std.testing.expectEqual(@as(usize, 0), colors_only.declarations.len);
        try std.testing.expectEqualSlices(u8, analysis.colors, colors_only.colors);
    }
    var unsupported = try analyzeSource(gpa, "a.unknown", "text", true, true);
    unsupported.deinit(gpa);
    try std.testing.expectEqual(@as(usize, 0), unsupported.declarations.len);
    try std.testing.expectEqual(@as(usize, 0), unsupported.colors.len);
}