Add layout dialog helper.

src/SettingsDialog.zig

@@ -33,6 +33,7 @@ const gtk = @import("gtk");
 
 const Layouts = @import("Layouts.zig");
 const PaletteEditor = @import("PaletteEditor.zig");
+const PathEntry = @import("PathEntry.zig");
 const Settings = @import("Settings.zig");
 const appearance = @import("appearance.zig");
 
@@ -64,6 +65,10 @@ const plain_label = "Plain terminal";
 /// be reading freed memory at the next keystroke.
 const ParamField = struct {
     name: []u8,
+
+    /// The text box holding the value. For a directory parameter it is the one
+    /// inside a `PathEntry`, which frees itself with its widgets — so a row
+    /// rebuilt for a different layout leaves nothing of it behind to track.
     entry: *gtk.Entry,
 };
 
@@ -553,9 +558,33 @@ fn fillParams(
         const field = try self.alloc.create(ParamField);
         errdefer self.alloc.destroy(field);
 
+        var hint_buf: [128]u8 = undefined;
+        const placeholder: ?[*:0]const u8 =
+            std.fmt.bufPrintZ(&hint_buf, "{{{{{s}}}}}", .{param.name}) catch null;
+        const value = valueOf(values, param.name) orelse param.default;
+
+        // The same two shapes the layout prompt offers, for the same reason: a
+        // startup entry names the same directories, and picking one out of a
+        // chooser here is worth as much as it is there.
+        const entry, const widget = switch (param.type) {
+            .string => blk: {
+                const e = gtk.Entry.new();
+                e.setPlaceholderText(placeholder);
+                e.as(gtk.Widget).setHexpand(1);
+                setEntryText(e, value);
+                break :blk .{ e, e.as(gtk.Widget) };
+            },
+            .directory => blk: {
+                const path = try PathEntry.create(self.alloc);
+                path.setPlaceholderText(placeholder);
+                path.setText(value);
+                break :blk .{ path.entry, path.widget() };
+            },
+        };
+
         field.* = .{
             .name = try self.alloc.dupe(u8, param.name),
-            .entry = gtk.Entry.new(),
+            .entry = entry,
         };
         errdefer self.alloc.free(field.name);
 
@@ -568,12 +597,6 @@ fn fillParams(
         label.as(gtk.Widget).addCssClass("playpen-dialog-sublabel");
         grid.attach(label.as(gtk.Widget), 0, @intCast(i), 1, 1);
 
-        var hint_buf: [128]u8 = undefined;
-        field.entry.setPlaceholderText(
-            std.fmt.bufPrintZ(&hint_buf, "{{{{{s}}}}}", .{param.name}) catch null,
-        );
-        field.entry.as(gtk.Widget).setHexpand(1);
-        setEntryText(field.entry, valueOf(values, param.name) orelse param.default);
         _ = gtk.Editable.signals.changed.connect(
             field.entry,
             *StartupRow,
@@ -581,7 +604,7 @@ fn fillParams(
             row,
             .{},
         );
-        grid.attach(field.entry.as(gtk.Widget), 1, @intCast(i), 1, 1);
+        grid.attach(widget, 1, @intCast(i), 1, 1);
 
         try row.params.append(self.alloc, field);
     }