add a convenience CLI tool for building and testing web engine (flutter/engine#12197)

engine/src/flutter/.cirrus.yml

@@ -41,7 +41,7 @@ task:
         $ENGINE_PATH/src/out/host_debug_unopt/dart-sdk/bin/pub get
         cd $ENGINE_PATH/src/flutter/lib/web_ui
         $ENGINE_PATH/src/out/host_debug_unopt/dart-sdk/bin/pub get
-        CHROME_NO_SANDBOX=true $ENGINE_PATH/src/out/host_debug_unopt/dart-sdk/bin/dart dev/test.dart
+        CHROME_NO_SANDBOX=true $ENGINE_PATH/src/out/host_debug_unopt/dart-sdk/bin/dart dev/felt.dart
       fetch_framework_script: |
         mkdir -p $FRAMEWORK_PATH
         cd $FRAMEWORK_PATH

engine/src/flutter/lib/web_ui/dev/felt

@@ -0,0 +1,47 @@
+#!/bin/bash
+
+# felt: a command-line utility for building and testing Flutter web engine.
+#       It stands for Flutter Engine Local Tester.
+
+FELT_PATH=`which felt`
+if [ -z "$FELT_PATH" ]
+then
+  echo "ERROR: felt is not in your PATH"
+  echo "Fix: add lib/web_ui/dev to your PATH"
+  exit 1
+fi
+
+GCLIENT_PATH=`which gclient`
+if [ -z "$GCLIENT_PATH" ]
+then
+  echo "ERROR: gclient is not in your PATH"
+  echo "Fix: add the path to your installation of depot_tools to your PATH"
+  exit 1
+fi
+
+NINJA_PATH=`which ninja`
+if [ -z "$NINJA_PATH" ]
+then
+  echo "ERROR: ninja is not in your PATH"
+  echo "Fix: add the path to your installation of depot_tools to your PATH"
+  exit 1
+fi
+
+ENGINE_SRC_DIR="$(dirname $(dirname $(dirname $(dirname $(dirname ${FELT_PATH})))))"
+FLUTTER_DIR="${ENGINE_SRC_DIR}/flutter"
+WEB_UI_DIR="${FLUTTER_DIR}/lib/web_ui"
+DEV_DIR="${WEB_UI_DIR}/dev"
+OUT_DIR="${ENGINE_SRC_DIR}/out"
+HOST_DEBUG_UNOPT_DIR="${ENGINE_SRC_DIR}/out/host_debug_unopt"
+DART_SDK_DIR="${ENGINE_SRC_DIR}/out/host_debug_unopt/dart-sdk"
+GN="${FLUTTER_DIR}/tools/gn"
+
+if [ ! -d "${OUT_DIR}" ] || [ ! -d "${HOST_DEBUG_UNOPT_DIR}" ]
+then
+  echo "Compiling the Dart SDK."
+  gclient sync
+  $GN --unoptimized --full-dart-sdk
+  ninja -C $HOST_DEBUG_UNOPT_DIR
+fi
+
+(cd $WEB_UI_DIR && $DART_SDK_DIR/bin/dart dev/felt.dart $@)

engine/src/flutter/lib/web_ui/dev/test_runner.dart

@@ -138,7 +138,10 @@ Future<void> _buildTests() async {
   }
 }
 
-Future<int> _runTestBatch(
+/// Runs a batch of tests.
+///
+/// Unless [expectFailure] is set to false, sets [io.exitCode] to a non-zero value if any tests fail.
+Future<void> _runTestBatch(
   List<String> testFiles, {
     @required int concurrency,
     @required bool expectFailure,
@@ -174,6 +177,4 @@ Future<int> _runTestBatch(
       io.exitCode = 1;
     }
   }
-
-  return io.exitCode;
 }