Z arms the view keys until Esc, and zm puts the cursor's column mid-view

Z is helix's sticky view mode: the z keys stay armed after each until Esc,
which leaves the mode and does nothing else (no pane hop). zm is
align_view_middle: an unwrapped view scrolls sideways so the cursor's column
is in its middle.

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

1 files changed, 17 insertions, 4 deletions

diff --git a/src/modal.zig b/src/modal.zig
index 0171da93..16196b4f 100644
--- a/src/modal.zig
+++ b/src/modal.zig
@@ -16,6 +16,7 @@ pub const Normal = struct {
         prefix_next,
         prefix_prev,
         prefix_register,
+        prefix_view_sticky,
 
         goto_file_start,
         goto_last_line,
@@ -38,6 +39,7 @@ pub const Normal = struct {
         view_top,
         view_center,
         view_bottom,
+        view_middle,
         view_scroll_down,
         view_scroll_up,
 
@@ -196,9 +198,12 @@ pub const Normal = struct {
         held_char: u21 = 0,
         /// `"<reg>`: the register the next command names, 0 for none
         register: u21 = 0,
+        /// `Z`: the view keys stay armed until Esc (helix's sticky view)
+        sticky: bool = false,
 
+        /// Drop what is pending; sticky view mode stays armed through it.
         pub fn clear(state: *State) void {
-            state.* = .{};
+            state.* = if (state.sticky) .{ .sticky = true, .prefix = .view } else .{};
         }
     };
 
@@ -254,7 +259,7 @@ pub const Normal = struct {
         view_bottom,
         last_modification,
     };
-    pub const View = enum { top, center, bottom, scroll_down, scroll_up };
+    pub const View = enum { top, center, bottom, middle, scroll_down, scroll_up };
     pub const Find = enum { forward, backward, till_forward, till_backward };
     pub const Line = enum { start, end, first_nonws };
     pub const Page = enum { half_down, half_up, down, up };
@@ -407,7 +412,10 @@ pub const Normal = struct {
 
     pub fn parse(state: *State, key: Input) Result {
         if (key.has(.escape)) {
-            state.clear();
+            // Esc out of sticky view mode leaves that mode and nothing else
+            const sticky = state.sticky;
+            state.* = .{};
+            if (sticky) return .ignored;
             return resultAction(.escape);
         }
 
@@ -448,8 +456,9 @@ pub const Normal = struct {
                 return .ignored;
             },
             .view => {
-                state.prefix = .none;
+                if (!state.sticky) state.prefix = .none;
                 if (key.has(.view_top)) return resultAction(.{ .view = .top });
+                if (key.has(.view_middle)) return resultAction(.{ .view = .middle });
                 if (key.has(.view_center)) return resultAction(.{ .view = .center });
                 if (key.has(.view_bottom)) return resultAction(.{ .view = .bottom });
                 if (key.has(.view_scroll_down)) return resultAction(.{ .view = .scroll_down });
@@ -543,6 +552,10 @@ pub const Normal = struct {
         // Prefix setters retain the count for their continuation.
         if (key.has(.prefix_goto)) return armPrefix(state, .goto, if (counted.explicit) count else 0);
         if (key.has(.prefix_view)) return armPrefix(state, .view, if (counted.explicit) count else 0);
+        if (key.has(.prefix_view_sticky)) {
+            state.sticky = true;
+            return armPrefix(state, .view, 0);
+        }
         if (key.has(.prefix_find_fwd)) return armPrefix(state, .find_fwd, if (counted.explicit) count else 0);
         if (key.has(.prefix_find_back)) return armPrefix(state, .find_back, if (counted.explicit) count else 0);
         if (key.has(.prefix_till_fwd)) return armPrefix(state, .till_fwd, if (counted.explicit) count else 0);