libghostty: expose row cell styling bit (#12837)

Add a render row-cells data key for querying whether the current cell
has explicit styling. This lets consumers avoid fetching a raw cell or
full style snapshot when all they need is the cell's HasStyling bit.

The new key is appended to the existing enum for ABI safety and is
served by the existing row-cells getter path. Existing data keys and
function exports are unchanged.

This was identified as an allocation hot-spot in Go renderers.

include/ghostty/vt/render.h

@@ -607,6 +607,13 @@ typedef enum GHOSTTY_ENUM_TYPED {
    *  GHOSTTY_RENDER_STATE_ROW_DATA_SELECTION once per row and applying that
    *  range directly, avoiding one C API call per cell for selection state. */
   GHOSTTY_RENDER_STATE_ROW_CELLS_DATA_SELECTED = 7,
+
+  /** Whether the cell has any explicit styling (bool).
+   *  This is equivalent to querying the raw cell's
+   *  GHOSTTY_CELL_DATA_HAS_STYLING value, but avoids materializing the raw
+   *  GhosttyCell for renderers that only need to know whether fetching the
+   *  full style is necessary. */
+  GHOSTTY_RENDER_STATE_ROW_CELLS_DATA_HAS_STYLING = 8,
   GHOSTTY_RENDER_STATE_ROW_CELLS_DATA_MAX_VALUE = GHOSTTY_ENUM_MAX_VALUE,
 } GhosttyRenderStateRowCellsData;
 

src/terminal/c/render.zig

@@ -466,6 +466,7 @@ pub const RowCellsData = enum(c_int) {
     bg_color = 5,
     fg_color = 6,
     selected = 7,
+    has_styling = 8,
 
     /// Output type expected for querying the data of the given kind.
     pub fn OutType(comptime self: RowCellsData) type {
@@ -476,7 +477,7 @@ pub const RowCellsData = enum(c_int) {
             .graphemes_len => u32,
             .graphemes_buf => u32,
             .bg_color, .fg_color => colorpkg.RGB.C,
-            .selected => bool,
+            .selected, .has_styling => bool,
         };
     }
 };
@@ -571,6 +572,7 @@ fn rowCellsGetTyped(
             x >= sel[0] and x <= sel[1]
         else
             false,
+        .has_styling => out.* = cell.hasStyling(),
     }
 
     return .success;
@@ -1193,6 +1195,67 @@ test "render: row cells get selected" {
     try testing.expect(selected);
 }
 
+test "render: row cells get has_styling" {
+    var terminal: terminal_c.Terminal = null;
+    try testing.expectEqual(Result.success, terminal_c.new(
+        &lib.alloc.test_allocator,
+        &terminal,
+        .{
+            .cols = 10,
+            .rows = 3,
+            .max_scrollback = 10_000,
+        },
+    ));
+    defer terminal_c.free(terminal);
+
+    const input = "A\x1b[31mB";
+    terminal_c.vt_write(terminal, input, input.len);
+
+    var state: RenderState = null;
+    try testing.expectEqual(Result.success, new(
+        &lib.alloc.test_allocator,
+        &state,
+    ));
+    defer free(state);
+
+    try testing.expectEqual(Result.success, update(state, terminal));
+
+    var it: RowIterator = null;
+    try testing.expectEqual(Result.success, row_iterator_new(
+        &lib.alloc.test_allocator,
+        &it,
+    ));
+    defer row_iterator_free(it);
+
+    var cells: RowCells = null;
+    try testing.expectEqual(Result.success, row_cells_new(
+        &lib.alloc.test_allocator,
+        &cells,
+    ));
+    defer row_cells_free(cells);
+
+    try testing.expectEqual(Result.success, get(state, .row_iterator, @ptrCast(&it)));
+    try testing.expect(row_iterator_next(it));
+    try testing.expectEqual(Result.success, row_get(it, .cells, @ptrCast(&cells)));
+
+    var has_styling = true;
+    try testing.expectEqual(Result.success, row_cells_select(cells, 0));
+    try testing.expectEqual(Result.success, row_cells_get(cells, .has_styling, @ptrCast(&has_styling)));
+    try testing.expect(!has_styling);
+
+    try testing.expectEqual(Result.success, row_cells_select(cells, 1));
+    try testing.expectEqual(Result.success, row_cells_get(cells, .has_styling, @ptrCast(&has_styling)));
+    try testing.expect(has_styling);
+
+    has_styling = false;
+    var written: usize = 0;
+    const keys = [_]RowCellsData{.has_styling};
+    var values = [_]?*anyopaque{@ptrCast(&has_styling)};
+    try testing.expectEqual(Result.success, row_cells_get_multi(cells, keys.len, &keys, &values, &written));
+    try testing.expectEqual(keys.len, written);
+    try testing.expect(has_styling);
+}
+
 test "render: row iterator next" {
     var terminal: terminal_c.Terminal = null;
     try testing.expectEqual(Result.success, terminal_c.new(