apprt: clean up how apprt initializes surfaces

src/App.zig

@@ -129,7 +129,7 @@ pub fn deleteSurface(self: *App, rt_surface: *apprt.Surface) void {
 
 /// The last focused surface. This is only valid while on the main thread
 /// before tick is called.
-pub fn focusedSurface(self: *App) ?*Surface {
+pub fn focusedSurface(self: *const App) ?*Surface {
     const surface = self.focused_surface orelse return null;
     if (!self.hasSurface(surface)) return null;
     return surface;
@@ -214,7 +214,7 @@ fn surfaceMessage(self: *App, surface: *Surface, msg: apprt.surface.Message) !vo
     // Not a problem.
 }
 
-fn hasSurface(self: *App, surface: *Surface) bool {
+fn hasSurface(self: *const App, surface: *const Surface) bool {
     for (self.surfaces.items) |v| {
         if (&v.core_surface == surface) return true;
     }

src/apprt/embedded.zig

@@ -144,8 +144,6 @@ pub const Surface = struct {
     };
 
     pub fn init(self: *Surface, app: *App, opts: Options) !void {
-        const alloc = app.core_app.alloc;
-
         self.* = .{
             .app = app,
             .core_surface = undefined,
@@ -163,24 +161,14 @@ pub const Surface = struct {
         try app.core_app.addSurface(self);
         errdefer app.core_app.deleteSurface(self);
 
-        // Our parent pwd will be tracked here
-        var parent_pwd: ?[]const u8 = null;
-        defer if (parent_pwd) |v| alloc.free(v);
-
         // Shallow copy the config so that we can modify it.
-        var config = app.config.*;
-
-        // Get our previously focused surface
-        const parent = app.core_app.focusedSurface();
-        if (parent) |p| {
-            parent_pwd = try p.pwd(alloc);
-            if (parent_pwd) |v| config.@"working-directory" = v;
-        }
+        var config = try apprt.surface.newConfig(app.core_app, app.config);
+        defer config.deinit();
 
         // Initialize our surface right away. We're given a view that is
         // ready to use.
         try self.core_surface.init(
-            alloc,
+            app.core_app.alloc,
             &config,
             .{ .rt_app = app, .mailbox = &app.core_app.mailbox },
             self,

src/apprt/glfw.zig

@@ -346,24 +346,13 @@ pub const Surface = struct {
         try app.app.addSurface(self);
         errdefer app.app.deleteSurface(self);
 
-        // Our parent pwd will be tracked here
-        const alloc = app.app.alloc;
-        var parent_pwd: ?[]const u8 = null;
-        defer if (parent_pwd) |v| alloc.free(v);
-
-        // Shallow copy the config so that we can modify it.
-        var config = app.config;
-
-        // Get our previously focused surface
-        const parent = app.app.focusedSurface();
-        if (parent) |p| {
-            parent_pwd = try p.pwd(alloc);
-            if (parent_pwd) |v| config.@"working-directory" = v;
-        }
+        // Get our new surface config
+        var config = try apprt.surface.newConfig(app.app, &app.config);
+        defer config.deinit();
 
         // Initialize our surface now that we have the stable pointer.
         try self.core_surface.init(
-            alloc,
+            app.app.alloc,
             &config,
             .{ .rt_app = app, .mailbox = &app.app.mailbox },
             self,

src/apprt/gtk.zig

@@ -722,10 +722,14 @@ pub const Surface = struct {
         try self.app.core_app.addSurface(self);
         errdefer self.app.core_app.deleteSurface(self);
 
+        // Get our new surface config
+        var config = try apprt.surface.newConfig(self.app.core_app, &self.app.config);
+        defer config.deinit();
+
         // Initialize our surface now that we have the stable pointer.
         try self.core_surface.init(
             self.app.core_app.alloc,
-            &self.app.config,
+            &config,
             .{ .rt_app = self.app, .mailbox = &self.app.core_app.mailbox },
             self,
         );

src/apprt/surface.zig

@@ -61,3 +61,24 @@ pub const Mailbox = struct {
         }, timeout);
     }
 };
+
+/// Returns a new config for a surface for the given app that should be
+/// used for any new surfaces. The resulting config should be deinitialized
+/// after the surface is initialized.
+pub fn newConfig(app: *const App, config: *const Config) !Config {
+    // Create a shallow clone
+    var copy = config.shallowClone(app.alloc);
+
+    // Our allocator is our config's arena
+    const alloc = copy._arena.?.allocator();
+
+    // Get our previously focused surface for some inherited values.
+    const prev = app.focusedSurface();
+    if (prev) |p| {
+        if (try p.pwd(alloc)) |pwd| {
+            copy.@"working-directory" = pwd;
+        }
+    }
+
+    return copy;
+}

src/config.zig

@@ -691,6 +691,21 @@ pub const Config = struct {
         }
     }
 
+    /// Create a shallow copy of this config. This will share all the memory
+    /// allocated with the previous config but will have a new arena for
+    /// any changes or new allocations. The config should have `deinit`
+    /// called when it is complete.
+    ///
+    /// Beware: these shallow clones are not meant for a long lifetime,
+    /// they are just meant to exist temporarily for the duration of some
+    /// modifications. It is very important that the original config not
+    /// be deallocated while shallow clones exist.
+    pub fn shallowClone(self: *const Config, alloc_gpa: Allocator) Config {
+        var result = self.*;
+        result._arena = ArenaAllocator.init(alloc_gpa);
+        return result;
+    }
+
     /// Create a copy of this configuration. This is useful as a starting
     /// point for modifying a configuration since a config can NOT be
     /// modified once it is in use by an app or surface.