config: grapheme-width-method sets mode 2027

Fixes #1403

This changes the behavior of `grapheme-width-method = unicode` to change
the default state of mode 2027 to true. Prior to this, setting this
config would force grapheme clustering regardless of mode 2027. Now,
this only sets the default and running TUI programs can disable it if
they want.

src/config/Config.zig

@@ -208,7 +208,7 @@ const c = @cImport({
 /// reset, this configuration will be used again.
 ///
 /// This configuration can be changed at runtime but will not affect existing
-/// printed cells. Only new cells will use the new configuration.
+/// terminals. Only new terminals will use the new configuration.
 @"grapheme-width-method": GraphemeWidthMethod = .unicode,
 
 /// A named theme to use. The available themes are currently hardcoded to the

src/terminal/Terminal.zig

@@ -119,9 +119,6 @@ flags: packed struct {
     /// then we want to capture the shift key for the mouse protocol
     /// if the configuration allows it.
     mouse_shift_capture: enum { null, false, true } = .null,
-
-    /// If true, we perform grapheme clustering even if mode 2027 is disabled.
-    default_grapheme_cluster: bool = false,
 } = .{},
 
 /// The event types that can be reported for mouse-related activities.
@@ -746,10 +743,7 @@ pub fn print(self: *Terminal, c: u21) !void {
     // This is MUCH slower than the normal path so the conditional below is
     // purposely ordered in least-likely to most-likely so we can drop out
     // as quickly as possible.
-    if (c > 255 and
+    if (c > 255 and self.modes.get(.grapheme_cluster) and self.screen.cursor.x > 0) grapheme: {
-        (self.modes.get(.grapheme_cluster) or self.flags.default_grapheme_cluster) and
-        self.screen.cursor.x > 0)
-    grapheme: {
         const row = self.screen.getRow(.{ .active = self.screen.cursor.y });
 
         // We need the previous cell to determine if we're at a grapheme
@@ -891,9 +885,7 @@ pub fn print(self: *Terminal, c: u21) !void {
         // If we have grapheme clustering enabled, we don't blindly attach
         // any zero width character to our cells and we instead just ignore
         // it.
-        if (self.modes.get(.grapheme_cluster) or
+        if (self.modes.get(.grapheme_cluster)) return;
-            self.flags.default_grapheme_cluster)
-            return;
 
         // If we're at cell zero, then this is malformed data and we don't
         // print anything or even store this. Zero-width characters are ALWAYS

src/termio/Exec.zig

@@ -135,7 +135,13 @@ pub fn init(alloc: Allocator, opts: termio.Options) !Exec {
     errdefer term.deinit(alloc);
     term.default_palette = opts.config.palette;
     term.color_palette.colors = opts.config.palette;
-    term.flags.default_grapheme_cluster = opts.config.grapheme_width_method == .unicode;
+
+    // Setup our initial grapheme cluster support if enabled. We use a
+    // switch to ensure we get a compiler error if more cases are added.
+    switch (opts.config.grapheme_width_method) {
+        .unicode => term.modes.set(.grapheme_cluster, true),
+        .wcswidth => {},
+    }
 
     // Set the image size limits
     try term.screen.kitty_images.setLimit(alloc, opts.config.image_storage_limit);
@@ -373,8 +379,6 @@ pub fn changeConfig(self: *Exec, config: *DerivedConfig) !void {
     //   - command, working-directory: we never restart the underlying
     //   process so we don't care or need to know about these.
 
-    self.terminal.flags.default_grapheme_cluster = config.grapheme_width_method == .unicode;
-
     // Update the default palette. Note this will only apply to new colors drawn
     // since we decode all palette colors to RGB on usage.
     self.terminal.default_palette = config.palette;