build: respect config.emit_xcframework for building libghostty-vt.xcframework on Darwin (#12267)

This fixes a hardcoded build issue on macOS where Zig unconditionally
forces xcodebuild -create-xcframework to run during compilation, even
when the caller explicitly specifies that they only want the raw
standard C objects/headers (-Demit-lib-vt).

.github/workflows/test.yml

@@ -340,6 +340,9 @@ jobs:
       - name: Build XCFramework
         run: nix develop -c zig build -Demit-lib-vt
 
+      - name: Verify XCFramework artifact
+        run: test -f zig-out/lib/ghostty-vt.xcframework/Info.plist
+
       - name: Build and Run Example
         run: |
           cd example/${{ matrix.dir }}

build.zig

@@ -155,7 +155,11 @@ pub fn build(b: *std.Build) !void {
     // libghostty-vt xcframework (Apple only, universal binary).
     // Only when building on macOS (not cross-compiling) since
     // xcodebuild is required.
-    if (builtin.os.tag.isDarwin() and config.target.result.os.tag.isDarwin()) {
+    if (config.emit_lib_vt and
+        config.emit_xcframework and
+        builtin.os.tag.isDarwin() and
+        config.target.result.os.tag.isDarwin())
+    {
         const apple_libs = try buildpkg.GhosttyLibVt.initStaticAppleUniversal(
             b,
             &config,
@@ -200,8 +204,9 @@ pub fn build(b: *std.Build) !void {
     }
 
     // macOS only artifacts. These will error if they're initialized for
-    // other targets.
-    if (config.target.result.os.tag.isDarwin() and
+    // other targets. In lib-vt mode emit_xcframework controls the lib-vt
+    // xcframework above, not this one.
+    if (!config.emit_lib_vt and config.target.result.os.tag.isDarwin() and
         (config.emit_xcframework or config.emit_macos_app))
     {
         // Ghostty xcframework

src/build/Config.zig

@@ -444,13 +444,22 @@ pub fn init(b: *std.Build, appVersion: []const u8, libVersion: []const u8) !Conf
         bool,
         "emit-xcframework",
         "Build and install the xcframework for the macOS library.",
-    ) orelse !config.emit_lib_vt and
-        builtin.target.os.tag.isDarwin() and
-        target.result.os.tag == .macos and
-        config.app_runtime == .none and
-        (!config.emit_bench and
-            !config.emit_test_exe and
-            !config.emit_helpgen);
+    ) orelse emit_xcfw: {
+        if (!builtin.target.os.tag.isDarwin() or target.result.os.tag != .macos)
+            break :emit_xcfw false;
+        if (config.emit_lib_vt) {
+            // In lib-vt mode default to whether xcodebuild is available,
+            // since xcodebuild is required to produce the XCFramework.
+            const path = expandPath(b.allocator, "xcodebuild") catch
+                break :emit_xcfw false;
+            defer if (path) |p| b.allocator.free(p);
+            break :emit_xcfw path != null;
+        }
+        break :emit_xcfw config.app_runtime == .none and
+            (!config.emit_bench and
+                !config.emit_test_exe and
+                !config.emit_helpgen);
+    };
 
     config.emit_macos_app = b.option(
         bool,