Pre-populate the LOCAL_ENGINE xcconfig value so engine developers dont need to...

Pre-populate the LOCAL_ENGINE xcconfig value so engine developers dont need to fill in different values. (#2716)

sky/build/sdk_xcode_harness/Local.xcconfig → sky/build/sdk_xcode_harness/Local.xcconfig.tmpl

@@ -2,9 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-//
-// This file generated. Do not modify or check into version control.
-//
+// This file is overwritten by `flutter tools`.
+
+LOCAL_ENGINE={{ local_engine }}
 
 DART_SDK_PATH=/path/to/dart/sdk
 FLUTTER_APPLICATION_PATH=path/to/flutter/application

sky/build/sky_ios_sdk.gni

@@ -48,7 +48,6 @@ template("sky_ios_sdk") {
     sources = [
       "//sky/build/sdk_xcode_harness/FlutterApplication",
       "//sky/build/sdk_xcode_harness/FlutterApplication.xcodeproj",
-      "//sky/build/sdk_xcode_harness/Local.xcconfig",
       "//sky/build/sdk_xcode_harness/Runner",
     ]
 
@@ -71,6 +70,17 @@ template("sky_ios_sdk") {
     }
   }
 
+  render_template("local_xcconfig") {
+    template = "//sky/build/sdk_xcode_harness/Local.xcconfig.tmpl"
+    output = "$sdk_dir/Local.xcconfig"
+    stamp_file = "$root_build_dir/expand_local_xcconfig.stamp"
+
+    variables = [
+      "local_engine",
+      rebase_path(root_build_dir, ""),
+    ]
+  }
+
   # All user editable files are copied to the out directory so that developers
   # tinkering on the engine still have a fully functional project harness
   copy("copy_user_editable_files") {
@@ -107,6 +117,7 @@ template("sky_ios_sdk") {
       ":copy_user_editable_files",
       ":flutter_xcconfig",
       ":ios_xcode_scripts",
+      ":local_xcconfig",
     ]
   }