Backspace in a line's leading blanks goes back to the previous indent stop

helix's delete_char_backward dedents: when everything before the cursor on its
line is blank, it deletes back to the previous multiple of the indent width,
a whole unit when already on one (a tab before the cursor still goes alone).
pardes deleted one space, so O<backspace> under an indented line left three
of four, which is where helix-golf's function_into_class ended up.

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

1 files changed, 13 insertions, 2 deletions

diff --git a/src/edit.zig b/src/edit.zig
index 2dc79ab5..5ba46ca7 100644
--- a/src/edit.zig
+++ b/src/edit.zig
@@ -694,8 +694,19 @@ pub fn insertKey(p: *Pardes, t: *Text, key: Key) void {
         Key.backspace => {
             if (t.cur_col > 0) {
                 const line = modal.lineSlice(text, c.row);
-                const prev = modal.prevGrapheme(line, c.col);
-                const new = modal.deleteChar(p.gpa, text, .{ .row = c.row, .col = prev }) catch return;
+                var prev = modal.prevGrapheme(line, c.col);
+                // in leading blanks, back to the previous indent stop (helix
+                // dedent): a whole unit when on one, else the part past it
+                const lead = line[0..@min(c.col, line.len)];
+                if (std.mem.indexOfNone(u8, lead, " \t") == null and prev < line.len and line[prev] != '\t') {
+                    var width: usize = 0;
+                    for (lead) |ch| width += if (ch == '\t') modal.INDENT_W else 1;
+                    var drop = width % modal.INDENT_W;
+                    if (drop == 0) drop = modal.INDENT_W;
+                    prev = c.col;
+                    while (drop > 0 and prev > 0 and line[prev - 1] == ' ') : (drop -= 1) prev -= 1;
+                }
+                const new = modal.deleteSpan(p.gpa, text, .{ .row = c.row, .col = prev }, c) catch return;
                 setEditText(p, t, new);
                 t.cur_col = @intCast(prev);
                 t.cur_pinned = true;