From 7bf532bdfd692a6697031e22c96ffba021baebf5 Mon Sep 17 00:00:00 2001
From: CJ van den Berg <cj@vdbonline.com>
Date: Thu, 27 Nov 2025 16:44:16 +0100
Subject: [PATCH] fix: make helix move_prev_word_start an exact match to real
 helix

---
 src/tui/editor.zig     |  2 +-
 src/tui/mode/helix.zig | 72 +++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/src/tui/editor.zig b/src/tui/editor.zig
index cd094ff..ea2a059 100644
--- a/src/tui/editor.zig
+++ b/src/tui/editor.zig
@@ -2196,7 +2196,7 @@ pub const Editor = struct {
     const cursor_operator_const_arg = *const fn (root: Buffer.Root, cursor: *Cursor, ctx: Context, metrics: Buffer.Metrics) error{Stop}!void;
     pub const cursel_operator_mut_once_arg = *const fn (root: Buffer.Root, cursel: *CurSel, ctx: Context, metrics: Buffer.Metrics) error{Stop}!void;
     const cursor_view_operator_const = *const fn (root: Buffer.Root, cursor: *Cursor, view: *const View, metrics: Buffer.Metrics) error{Stop}!void;
-    const cursel_operator_const = *const fn (root: Buffer.Root, cursel: *CurSel, metrics: Buffer.Metrics) error{Stop}!void;
+    pub const cursel_operator_const = *const fn (root: Buffer.Root, cursel: *CurSel, metrics: Buffer.Metrics) error{Stop}!void;
     const cursor_operator = *const fn (root: Buffer.Root, cursor: *Cursor, allocator: Allocator) error{Stop}!Buffer.Root;
     const cursel_operator = *const fn (root: Buffer.Root, cursel: *CurSel, allocator: Allocator) error{Stop}!Buffer.Root;
     const cursel_operator_mut = *const fn (self: *Self, root: Buffer.Root, cursel: *CurSel, allocator: Allocator) error{Stop}!Buffer.Root;
diff --git a/src/tui/mode/helix.zig b/src/tui/mode/helix.zig
index cceab4e..ee70840 100644
--- a/src/tui/mode/helix.zig
+++ b/src/tui/mode/helix.zig
@@ -13,6 +13,8 @@ const Buffer = @import("Buffer");
 const Cursor = Buffer.Cursor;
 const Selection = Buffer.Selection;
 
+const char_class = Editor.char_class;
+
 const Direction = enum { backwards, forwards };
 
 var commands: Commands = undefined;
@@ -263,12 +265,80 @@ const cmds_ = struct {
     }
     pub const extend_next_long_word_start_meta: Meta = .{ .description = "Extend next long word start", .arguments = &.{.integer} };
 
+    fn is_eol(c: []const u8) bool {
+        return char_class(c) == .eol;
+    }
+
+    fn is_whitespace(c: []const u8) bool {
+        return char_class(c) == .whitespace;
+    }
+
+    fn is_word_boundary(root: Buffer.Root, cursor: Cursor, metrics: Buffer.Metrics, comptime direction: enum { left, right }) bool {
+        const nxt = char_class(switch (direction) {
+            .left => cursor.char_left(root, metrics),
+            .right => cursor.char_right(root, metrics),
+        });
+        const cur = char_class(cursor.char_at(root, metrics));
+        if (cur == .eol) return false;
+        return switch (nxt) {
+            .end, .eol => true,
+            .whitespace => cur != .whitespace,
+            else => nxt != cur,
+        };
+    }
+
+    fn move_cursor_prev_word_start(root: Buffer.Root, cursel: *CurSel, metrics: Buffer.Metrics) error{Stop}!void {
+        var cursor = cursel.cursor;
+        if (is_word_boundary(root, cursor, metrics, .left))
+            cursor.move_left(root, metrics) catch {};
+
+        var sel = Selection.from_cursor_inclusive(&cursor, root, metrics);
+        defer {
+            sel.begin = cursor;
+            cursel.cursor = cursor;
+            cursel.selection = sel;
+        }
+
+        // Consume whitespace
+        while (cursor.test_at(root, is_whitespace, metrics)) {
+            cursor.move_left(root, metrics) catch return;
+            // Stop at beginning of line
+            if (cursor.test_left(root, is_eol, metrics)) return;
+        }
+
+        // Consume word/non-word chars
+        while (!is_word_boundary(root, cursor, metrics, .left)) {
+            cursor.move_left(root, metrics) catch return;
+            // Stop at beginning of line
+            if (cursor.test_left(root, is_eol, metrics)) return;
+        }
+    }
+
+    fn move_cursor_prev_word_start_extend(root: Buffer.Root, cursel: *CurSel, metrics: Buffer.Metrics) error{Stop}!void {
+        var selection = cursel.selection;
+        // check if we already had a selection and extend it
+        defer if (selection) |*pre_sel| {
+            pre_sel.normalize();
+            if (cursel.selection) |*sel| sel.end = pre_sel.end;
+        };
+        try move_cursor_prev_word_start(root, cursel, metrics);
+    }
+
+    fn move_cursels_const_repeat(move: Editor.cursel_operator_const, ctx: Ctx) Result {
+        const mv = tui.mainview() orelse return;
+        const ed = mv.get_active_editor() orelse return;
+        const root = try ed.buf_root();
+        try ed.with_cursels_const_repeat(root, move, ctx);
+        ed.clamp();
+    }
+
     pub fn move_prev_word_start(_: *void, ctx: Ctx) Result {
-        try move_to_word(ctx, move_cursor_word_left_helix, .backwards);
+        try move_cursels_const_repeat(move_cursor_prev_word_start, ctx);
     }
     pub const move_prev_word_start_meta: Meta = .{ .description = "Move previous word start", .arguments = &.{.integer} };
 
     pub fn extend_prev_word_start(_: *void, ctx: Ctx) Result {
+        try move_cursels_const_repeat(move_cursor_prev_word_start_extend, ctx);
         try extend_to_word(ctx, move_cursor_word_left_helix, .backwards);
     }
     pub const extend_prev_word_start_meta: Meta = .{ .description = "Extend previous word start", .arguments = &.{.integer} };