Tab N sets a tab's width in cells, 1 through 16, in every pane, drawn and counted (wrapping, clicks, the cursor); bare Tab says it; the ctl read and a Dump keep it

A session setting, not acme's per window: the width is read by File's pure
width functions (~130 callers that are given no pane), so it is one value,
config.tab_now, that Runtime.apply sets and a new session resets. A file:L:C
column counts runes, as compilers do, and never depended on it.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 22 insertions, 0 deletions

diff --git a/src/config.zig b/src/config.zig
index 375b4c69..89e5f813 100644
--- a/src/config.zig
+++ b/src/config.zig
@@ -61,6 +61,7 @@ pub const leader_path = paths: {
         .Get = null,
         .Putall = null,
         .Incl = null,
+        .Tab = null,
         .ClipYank = "y",
         .ClipYankMain = "Y",
         .ClipPaste = "p",
@@ -405,6 +406,11 @@ pub const PREFIX_W: u16 = 5;
 pub const default_incl = [_][]const u8{ "/usr/include", "/usr/local/include" };
 
 pub const tab_width: u16 = 4;
+/// The width a tab is drawn and counted at now: `Tab N` (Runtime.tab) sets
+/// it, a new session starts it at tab_width. ponytail: one for the process,
+/// as the session's setting is one; per pane would mean handing a pane to
+/// every width function (File.graphemeDisplayWidth and its ~130 callers).
+pub var tab_now: u16 = tab_width;
 comptime {
     if (tab_width == 0) @compileError("config.tab_width must be greater than zero");
 }
@@ -802,6 +808,9 @@ pub const Runtime = struct {
     /// the focused pane's file first, other files only once those run out
     /// that way; `all`, every place in the order it was jumped to.
     jump_scope: JumpScope = .file,
+    /// acme's Tab: a tab's width in cells, in every pane (config.tab_now
+    /// is what the drawing and the column arithmetic read).
+    tab: u16 = tab_width,
 
     pub const ShaderAnimation = enum { off, on, always };
     pub const Placement = enum { acme, pardes };
@@ -999,6 +1008,7 @@ pub const Runtime = struct {
         /// A percentage, 0 through 100.
         inactive_dim,
         grip_width,
+        tab,
         transition: animation.Transition,
         scene: Scene,
         /// A Shadertoy file into the post chain or out of it; `off` empties
@@ -1082,6 +1092,7 @@ pub const Runtime = struct {
         .{ .word = "PagerColor", .action = .{ .toggle = .pager_color }, .doc = "A +Pager keeps its program's colours, on or off; for the next text paged." },
         .{ .word = "TermImages", .action = .{ .choice = .term_images }, .doc = "How a new terminal draws its program's kitty graphics: real, as pixels where it can, or petscii, as glyph art." },
         .{ .word = "JumpScope", .action = .{ .choice = .jump_scope }, .doc = "What Back and Forward keep to: file, the focused pane's file until it runs out that way, or all, every place in order." },
+        .{ .word = "Tab", .action = .tab, .doc = "A tab's width in cells, 1 through 16, in every pane; bare, it says the width." },
     };
 
     pub fn find(name: []const u8) ?Setting {
@@ -1282,6 +1293,13 @@ pub const Runtime = struct {
                 if (percent < 50 or percent > 300) return false;
                 state.grip_width = percent;
             },
+            .tab => {
+                const text = std.mem.trim(u8, argument orelse return false, " \t\r\n");
+                const width = std.fmt.parseInt(u16, text, 10) catch return false;
+                if (width < 1 or width > 16) return false;
+                state.tab = width;
+                tab_now = width;
+            },
             .theme, .font => return false,
         }
         return true;
@@ -1317,6 +1335,7 @@ pub const Runtime = struct {
         return choices(action) orelse switch (action) {
             .inactive_dim, .window_opacity, .window_blur => "0-100 (a percentage)",
             .grip_width => "50-300 (a percentage)",
+            .tab => "1-16 (cells)",
             .tagline_size => std.fmt.comptimePrint("{d}-{d} (a percentage)", .{ tagline_percent_min, tagline_percent_max }),
             .message_ms => std.fmt.comptimePrint("0-{d} (milliseconds)", .{message_ms_max}),
             .shell => "a path of at most 255 bytes; bare, $SHELL, else /bin/sh",
@@ -1479,6 +1498,7 @@ pub const Runtime = struct {
                 try out.print("# {s} unsupported\n", .{setting.word}),
             .motion => try out.print("{s} {s}\n", .{ setting.word, @tagName(state.motion) }),
             .inactive_dim => try out.print("{s} {d}\n", .{ setting.word, state.inactive_dim }),
+            .tab => try out.print("{s} {d}\n", .{ setting.word, state.tab }),
             .grip_width => if (setting.enabled(context.capabilities))
                 try out.print("{s} {d}\n", .{ setting.word, state.grip_width })
             else
@@ -1775,6 +1795,7 @@ pub const Runtime = struct {
                 .motion => "playful",
                 .inactive_dim => "35",
                 .grip_width => "200",
+                .tab => "8",
                 else => null,
             };
             try std.testing.expect(apply(&state, setting, argument));
@@ -1849,6 +1870,7 @@ pub const Runtime = struct {
                 .motion => "Motion playful\n",
                 .inactive_dim => "InactiveDim 35\n",
                 .grip_width => "GripWidth 200\n",
+                .tab => "Tab 8\n",
                 .theme, .font => unreachable,
             };
             try std.testing.expect(std.mem.indexOf(u8, report, expected) != null);