macos: configurable undo timeout

macos/Sources/Features/Terminal/BaseTerminalController.swift

@@ -77,7 +77,7 @@ class BaseTerminalController: NSWindowController,
 
     /// The time that undo/redo operations that contain running ptys are valid for.
     var undoExpiration: Duration {
-        .seconds(5)
+        ghostty.config.undoTimeout
     }
 
     /// The undo manager for this controller is the undo manager of the window,

macos/Sources/Ghostty/Ghostty.Config.swift

@@ -506,6 +506,14 @@ extension Ghostty {
             return v;
         }
 
+        var undoTimeout: Duration {
+            guard let config = self.config else { return .seconds(5) }
+            var v: UInt = 0
+            let key = "undo-timeout"
+            _ = ghostty_config_get(config, &v, key, UInt(key.count))
+            return .milliseconds(v)
+        }
+
         var autoUpdate: AutoUpdate? {
             guard let config = self.config else { return nil }
             var v: UnsafePointer<Int8>? = nil

macos/Sources/Helpers/ExpiringUndoManager.swift

@@ -29,6 +29,9 @@ class ExpiringUndoManager: UndoManager {
         expiresAfter duration: Duration,
         handler: @escaping (TargetType) -> Void
     ) {
+        // Ignore instantly expiring undos
+        guard duration.timeInterval > 0 else { return }
+
         let expiringTarget = ExpiringTarget(
             target,
             expiresAfter: duration,

src/config/Config.zig

@@ -1705,6 +1705,52 @@ keybind: Keybinds = .{},
 /// window is ever created. Only implemented on Linux and macOS.
 @"initial-window": bool = true,
 
+/// The duration that undo operations remain available. After this
+/// time, the operation will be removed from the undo stack and
+/// cannot be undone.
+///
+/// The default value is 5 seconds.
+///
+/// This timeout applies per operation, meaning that if you perform
+/// multiple operations, each operation will have its own timeout.
+/// New operations do not reset the timeout of previous operations.
+///
+/// A timeout of zero will effectively disable undo operations. It is
+/// not possible to set an infinite timeout, but you can set a very
+/// large timeout to effectively disable the timeout (on the order of years).
+/// This is highly discouraged, as it will cause the undo stack to grow
+/// indefinitely, memory usage to grow unbounded, and terminal sessions
+/// to never actually quit.
+///
+/// The duration is specified as a series of numbers followed by time units.
+/// Whitespace is allowed between numbers and units. Each number and unit will
+/// be added together to form the total duration.
+///
+/// The allowed time units are as follows:
+///
+///   * `y` - 365 SI days, or 8760 hours, or 31536000 seconds. No adjustments
+///     are made for leap years or leap seconds.
+///   * `d` - one SI day, or 86400 seconds.
+///   * `h` - one hour, or 3600 seconds.
+///   * `m` - one minute, or 60 seconds.
+///   * `s` - one second.
+///   * `ms` - one millisecond, or 0.001 second.
+///   * `us` or `µs` - one microsecond, or 0.000001 second.
+///   * `ns` - one nanosecond, or 0.000000001 second.
+///
+/// Examples:
+///   * `1h30m`
+///   * `45s`
+///
+/// Units can be repeated and will be added together. This means that
+/// `1h1h` is equivalent to `2h`. This is confusing and should be avoided.
+/// A future update may disallow this.
+///
+/// This configuration is only supported on macOS. Linux doesn't
+/// support undo operations at all so this configuration has no
+/// effect.
+@"undo-timeout": Duration = .{ .duration = 5 * std.time.ns_per_s },
+
 /// The position of the "quick" terminal window. To learn more about the
 /// quick terminal, see the documentation for the `toggle_quick_terminal`
 /// binding action.
@@ -6583,7 +6629,7 @@ pub const Duration = struct {
             if (remaining.len == 0) break;
 
             // Find the longest number
-            const number = number: {
+            const number: u64 = number: {
                 var prev_number: ?u64 = null;
                 var prev_remaining: ?[]const u8 = null;
                 for (1..remaining.len + 1) |index| {
@@ -6597,8 +6643,17 @@ pub const Duration = struct {
                 break :number prev_number;
             } orelse return error.InvalidValue;
 
-            // A number without a unit is invalid
-            if (remaining.len == 0) return error.InvalidValue;
+            // A number without a unit is invalid unless the number is
+            // exactly zero. In that case, the unit is unambiguous since
+            // its all the same.
+            if (remaining.len == 0) {
+                if (number == 0) {
+                    value = 0;
+                    break;
+                }
+
+                return error.InvalidValue;
+            }
 
             // Find the longest matching unit. Needs to be the longest matching
             // to distinguish 'm' from 'ms'.
@@ -6808,6 +6863,11 @@ test "parse duration" {
         try std.testing.expectEqual(unit.factor, d.duration);
     }
 
+    {
+        const d = try Duration.parseCLI("0");
+        try std.testing.expectEqual(@as(u64, 0), d.duration);
+    }
+
     {
         const d = try Duration.parseCLI("100ns");
         try std.testing.expectEqual(@as(u64, 100), d.duration);