feat: add middle-click action configuration (#12478)

This PR addresses
https://github.com/ghostty-org/ghostty/discussions/12108 implemented
similarly to https://github.com/ghostty-org/ghostty/pull/8254 to allow
middle click + TrackPoint scrolling on MacOS. `primary-paste` naming
comes from `gtk_enable_primary_paste`.

The following configuration values for `middle-click-action` are
provided:
- `primary-paste` - Paste from the selection (or system) clipboard per
`copy-on-select`.
- `ignore` - Do nothing, ignore the middle click.

Tested locally on macOS with Zig 0.15.2 using `zig build
-Doptimize=ReleaseFast`.

Thank you!

src/Surface.zig

@@ -311,6 +311,7 @@ const DerivedConfig = struct {
     clipboard_codepoint_map: configpkg.Config.RepeatableClipboardCodepointMap,
     copy_on_select: configpkg.CopyOnSelect,
     right_click_action: configpkg.RightClickAction,
+    middle_click_action: configpkg.MiddleClickAction,
     confirm_close_surface: configpkg.ConfirmCloseSurface,
     cursor_click_to_move: bool,
     desktop_notifications: bool,
@@ -389,6 +390,7 @@ const DerivedConfig = struct {
             .clipboard_codepoint_map = try config.@"clipboard-codepoint-map".clone(alloc),
             .copy_on_select = config.@"copy-on-select",
             .right_click_action = config.@"right-click-action",
+            .middle_click_action = config.@"middle-click-action",
             .confirm_close_surface = config.@"confirm-close-surface",
             .cursor_click_to_move = config.@"cursor-click-to-move",
             .desktop_notifications = config.@"desktop-notifications",
@@ -4014,16 +4016,19 @@ pub fn mouseButtonCallback(
     // copy-on-select targets the system clipboard, middle-click reads from
     // that instead. Falls back to the standard clipboard on platforms that
     // do not support the selection clipboard.
-    if (button == .middle and action == .press) {
-        const clipboard: apprt.Clipboard = switch (self.config.copy_on_select) {
-            .clipboard => .standard,
-            .true, .false => if (self.rt_surface.supportsClipboard(.selection))
-                .selection
-            else
-                .standard,
-        };
-        _ = try self.startClipboardRequest(clipboard, .{ .paste = {} });
-    }
+    if (button == .middle and action == .press) switch (self.config.middle_click_action) {
+        .ignore => {},
+        .@"primary-paste" => {
+            const clipboard: apprt.Clipboard = switch (self.config.copy_on_select) {
+                .clipboard => .standard,
+                .true, .false => if (self.rt_surface.supportsClipboard(.selection))
+                    .selection
+                else
+                    .standard,
+            };
+            _ = try self.startClipboardRequest(clipboard, .{ .paste = {} });
+        },
+    };
 
     // Right-click down selects word for context menus. If the apprt
     // doesn't implement context menus this can be a bit weird but they

src/config.zig

@@ -23,6 +23,7 @@ pub const Command = Config.Command;
 pub const ConfirmCloseSurface = Config.ConfirmCloseSurface;
 pub const CopyOnSelect = Config.CopyOnSelect;
 pub const RightClickAction = Config.RightClickAction;
+pub const MiddleClickAction = Config.MiddleClickAction;
 pub const CustomShaderAnimation = Config.CustomShaderAnimation;
 pub const FontSyntheticStyle = Config.FontSyntheticStyle;
 pub const FontShapingBreak = Config.FontShapingBreak;

src/config/Config.zig

@@ -2404,11 +2404,12 @@ keybind: Keybinds = .{},
 /// The value `clipboard` will always copy text to the selection clipboard
 /// as well as the system clipboard.
 ///
-/// Middle-click paste is always enabled even if this is `false`. The
-/// clipboard it pastes from follows this setting: with `true` (or `false`)
-/// it reads from the selection clipboard (falling back to the system
-/// clipboard on platforms without a selection clipboard); with `clipboard`
-/// it reads from the system clipboard.
+/// Middle-click primary paste (see `middle-click-action`) is enabled by
+/// default even if this is `false`. The clipboard it pastes from follows
+/// this setting: with `true` (or `false`) it reads from the selection
+/// clipboard (falling back to the system clipboard on platforms without a
+/// selection clipboard); with `clipboard` it reads from the system
+/// clipboard.
 ///
 /// The default value is true on Linux and macOS.
 @"copy-on-select": CopyOnSelect = switch (builtin.os.tag) {
@@ -2430,6 +2431,16 @@ keybind: Keybinds = .{},
 /// The default value is `context-menu`.
 @"right-click-action": RightClickAction = .@"context-menu",
 
+/// The action to take when the user middle-clicks on the terminal surface.
+///
+/// Valid values:
+///   * `primary-paste` - Paste from the selection (or system) clipboard per
+///      `copy-on-select`.
+///   * `ignore` - Do nothing, ignore the middle click.
+///
+/// The default value is `primary-paste`.
+@"middle-click-action": MiddleClickAction = .@"primary-paste",
+
 /// The time in milliseconds between clicks to consider a click a repeat
 /// (double, triple, etc.) or an entirely new single click. A value of zero will
 /// use a platform-specific default. The default on macOS is determined by the
@@ -8653,6 +8664,15 @@ pub const RightClickAction = enum {
     @"context-menu",
 };
 
+/// Options for middle-click actions.
+pub const MiddleClickAction = enum {
+    /// Paste from the selection/standard clipboard per `copy-on-select`.
+    @"primary-paste",
+
+    /// No action is taken on middle click.
+    ignore,
+};
+
 /// Shell integration values
 pub const ShellIntegration = enum {
     none,