Compile with dart2js and dart2wasm (#3737)

_test/build.both.yaml

@@ -0,0 +1,23 @@
+targets:
+  $default:
+    builders:
+      build_web_compilers:entrypoint:
+        options:
+          compilers:
+            dart2wasm:
+            dart2js:
+          loader: .dart.js
+        generate_for:
+          - web/main.dart
+          - web/sub/main.dart
+          - test/configurable_uri_test.dart
+          - test/configurable_uri_test.dart.browser_test.dart
+          - test/hello_world_test.dart
+          - test/hello_world_test.dart.browser_test.dart
+          - test/hello_world_deferred_test.dart
+          - test/hello_world_deferred_test.dart.browser_test.dart
+          - test/hello_world_custom_html_test.dart
+          - test/hello_world_custom_html_test.dart.browser_test.dart
+          - test/other_test.dart.browser_test.dart
+          - test/sub-dir/subdir_test.dart
+          - test/sub-dir/subdir_test.dart.browser_test.dart

_test/test/dart2wasm_integration_test.dart

@@ -59,6 +59,29 @@ void main() {
       );
       await _expectWasCompiledWithDart2Wasm();
     }, onPlatform: {'windows': const Skip('flaky on windows')});
+
+    test('when also enabling dart2js', () async {
+      await expectTestsPass(
+        usePrecompiled: true,
+        buildArgs: [
+          '--release',
+          '--config=both',
+          '--output=${d.sandbox}',
+        ],
+        testArgs: _testArgs,
+      );
+      await _expectWasCompiledWithDart2Wasm();
+
+      await d.dir(
+        'test',
+        [
+          d.file(
+            'hello_world_deferred_test.dart.browser_test.dart2js.js',
+            startsWith('// Generated by dart2js'),
+          ),
+        ],
+      ).validate();
+    }, onPlatform: {'windows': const Skip('flaky on windows')});
   });
 }
 

build_web_compilers/CHANGELOG.md

@@ -1,8 +1,10 @@
-## 4.0.12-wip
+## 4.1.0-wip
 
-- Account for dartdevc snapshot in the Dart SDK changing to an AOT snapshot.
 - Support compiling to WebAssembly by using `dart2wasm` as a value for the
   compiler option.
+- Support compiling with multiple compilers (e.g. `dart2js` and `dart2wasm`)
+  with a new `compilers` option.
+- Account for dartdevc snapshot in the Dart SDK changing to an AOT snapshot.
 - Bump the min sdk to 3.6.0-165.0.dev.
 
 ## 4.0.11

build_web_compilers/README.md

@@ -39,14 +39,35 @@ then all you need is the `dev_dependency` listed above.
 
 ## Configuration
 
-### Configuring the default compiler
-
 By default, this package uses the [Dart development compiler][] (_dartdevc_,
 also known as _DDC_) to compile Dart to JavaScript. In release builds (running
-the build tool with `--release`, the default compiler is `dart2js`).
+the build tool with `--release`), `dart2js` is used as a compiler.
+
+In addition to compiling to JavaScript, this package also supports compiling to
+WebAssembly. Currently, `dart2wasm` needs to be enabled with builder options.
+To understand the impact of these options, be aware of differences between
+compiling to JavaScript and compiling to WebAssembly:
+
+1. Dart has two compilers emitting JavaScript: `dart2js` and `dartdevc` (which
+  supports incremental rebuilds but is typically only used for development).
+  For both JavaScript compilers, `build_web_compilers` generates a primary
+  entrypoint script and additional module files or source maps depending on
+  compiler options.
+2. Compiling with `dart2wasm` generates a WebAssembly module (a `.wasm` file)
+   and a JavaScript module (a `.mjs` file) exporting functions to instantiate
+   that module. `dart2wasm` alone generates no entrypoint file that could be
+   added as a `<script>` tag.
+
+In addition to invoking compilers, `build_web_compilers` can emit an entrypoint
+file suitable for `dart2wasm`. When both `dart2wasm` and a JavaScript compiler
+are enabled, the entrypoint file runs a feature detection for WasmGC and loads
+either the WebAssembly module or the JavaScript file depending on what the
+browser supports.
+
+### Compiler arguments
 
-If you would like to opt into dart2js for all builds, you will need to add a
-`build.yaml` file, which should look roughly like the following:
+To customize compilers, you will need to add a `build.yaml` file configuring
+the `build_web_compilers:entrypoint` builder, similar to the following:
 
 ```yaml
 targets:
@@ -58,28 +79,103 @@ targets:
         - test/**.browser_test.dart
         - web/**.dart
         options:
-          compiler: dart2js
-          # List any dart2js specific args here, or omit it.
-          dart2js_args:
-          - -O2
+          compilers:
+            # All compilers listed here are enabled:
+            dart2js:
+              # List any dart2js specific args here, or omit it.
+              args:
+                - O2
+            dart2wasm:
+              args:
+                - O3
+```
+
+`build_runner` runs development builds by default, but can use builders with a
+different configuration for `--release` builds. For instance, if you wanted to
+compile with `dartdevc` only on development and `dart2js` + `dart2wasm` for
+release builds, you can use this configuration as a starting point:
+
+```yaml
+targets:
+  $default:
+    builders:
+      build_web_compilers:entrypoint:
+        generate_for:
+        - test/**.browser_test.dart
+        - web/**.dart
+        dev_options:
+          compilers:
+            dartdevc:
+        release_options:
+          compilers:
+            dart2js:
+              args:
+                - O2
+            dart2wasm:
+              args:
+                - O3
 ```
 
-In addition to DDC and dart2js, this package also supports the dart2wasm
-compiler for compiling to WebAssembly with a JavaScript loader. It can be
-enabled by using `compiler: dart2wasm` in the build configuration:
+### Customizing emitted file names
+
+The file names emitted by `build_web_compilers` can be changed. The default
+names depend on which compilers are enabled:
+
+1. When only `dart2js` or `dartdevc` is enabled, a single `.dart.js` entrypoint
+   is emitted.
+2. When only `dart2wasm` is enabled, a single `.dart.js` entrypoint (loading
+   a generated `.wasm` module through a `.mjs` helper file) is generated.
+3. When both `dart2wasm` and a JavaScript compiler are enabled, then:
+   - The output of the JavaScript compiler is named `.dart2js.js` or `.ddc.js`
+     depending on the compiler.
+   - `dart2wasm` continues to emit a `.wasm` and a `.mjs` file.
+   - An entrypoint loader named `.dart.js` that loads the appropriate output
+     depending on browser features is generated.
+
+All names can be overridden by using the `loader` option or the `extension`
+flag in compiler options:
 
 ```yaml
 targets:
   $default:
     builders:
       build_web_compilers:entrypoint:
         options:
-          compiler: dart2wasm
-          # List flags that should be forwarded to `dart compile wasm`
-          dart2wasm_args:
-          - -O2
+          loader: .load.js
+          compilers:
+            dart2js:
+              extension: .old.js
+            dart2wasm:
+              extension: .new.mjs
+```
+
+This configuration uses both `dart2js` and `dart2wasm`, but names the final
+entrypoint for a `main.dart` file `main.load.js`. That loader will either load
+a `.new.mjs` file for WebAssembly or a `.old.js` for pure JavaScript.
+
+Note that the `loader` option is ignored when `dart2wasm` is not enabled, as
+it's the compiler requiring an additional loader to be emitted.
+
+### Customizing the WebAssembly loader
+
+In some cases, for instance when targeting Node.JS, the generated loader for
+`dart2wasm` may be unsuitable. The builtin loader can be disabled by setting
+the option to null:
+
+```yaml
+targets:
+  $default:
+    builders:
+      build_web_compilers:entrypoint:
+        options:
+          loader: null
+          compilers:
+            dart2js:
+            dart2wasm:
 ```
 
+In this case, you need to use another builder or a predefined loader instead.
+
 ### Configuring -D environment variables
 
 dartdevc is a modular compiler, so in order to ensure consistent builds
@@ -96,22 +192,71 @@ global_options:
         ANOTHER_VAR: false
 ```
 
-For dart2js, use the `dart2js_args` option. This may be configured globally, or
-per target.
+These may also be specified on the command line with a `--define` argument.
+
+```sh
+webdev serve -- '--define=build_web_compilers:ddc=environment={"SOME_VAR":"changed"}'
+```
+
+For dart2js, use the `args` option within the `dart2js` compiler entry. This
+may be configured globally, or per target.
+
+```yaml
+targets:
+  $default:
+    builders:
+      build_web_compilers:entrypoint:
+        options:
+          compilers:
+            dart2js:
+              args:
+                - -DSOME_VAR=some value
+                - -DANOTHER_VAR=true
+```
+
+To apply variables across multiple compilers, they have to be added to each
+one:
 
 ```yaml
 targets:
   $default:
     builders:
       build_web_compilers:entrypoint:
         options:
+          compilers:
+            dart2js:
+              args:
+                - -DSOME_VAR=some value
+                - -DANOTHER_VAR=true
+            dart2wasm:
+              args:
+                - -DSOME_VAR=some value
+                - -DANOTHER_VAR=true
+```
+
+### Legacy builder options
+
+Previous versions of `build_web_compilers` only supported a single enabled
+compiler that would be enabled with the `compiler` option.
+If you only want to use `dart2js` for all builds, you can use that option:
+
+```yaml
+targets:
+  $default:
+    builders:
+      build_web_compilers:entrypoint:
+        # These are globs for the entrypoints you want to compile.
+        generate_for:
+        - test/**.browser_test.dart
+        - web/**.dart
+        options:
+          compiler: dart2js
+          # List any dart2js specific args here, or omit it.
           dart2js_args:
-          - -DSOME_VAR=some value
-          - -DANOTHER_VAR=true
+          - -O2
 ```
 
-Similarly, options are passed to `dart compile wasm` when using the
-`dart2wasm_args` option:
+Similarly, only compiling with `dart2wasm`:
 
 ```yaml
 targets:
@@ -120,16 +265,15 @@ targets:
       build_web_compilers:entrypoint:
         options:
           compiler: dart2wasm
+          # List flags that should be forwarded to `dart compile wasm`
           dart2wasm_args:
-          - -DSOME_VAR=some value
-          - -DANOTHER_VAR=true
+          - -O2
 ```
 
-These may also be specified on the command line with a `--define` argument.
-
-```sh
-webdev serve -- '--define=build_web_compilers:ddc=environment={"SOME_VAR":"changed"}'
-```
+When no option is set, the `compiler` option is implicitly set to `dart2js` on
+release builds and to `dartdevc` otherwise.
+Note that the `compilers` option takes precedence over the `compiler` option
+when set.
 
 ## Manual Usage
 

build_web_compilers/lib/src/dart2js_bootstrap.dart

@@ -25,14 +25,20 @@ Future<void> bootstrapDart2Js(
   BuildStep buildStep,
   List<String> dart2JsArgs, {
   required bool? nativeNullAssertions,
+  String entrypointExtension = jsEntrypointExtension,
 }) =>
-    _resourcePool.withResource(() => _bootstrapDart2Js(buildStep, dart2JsArgs,
-        nativeNullAssertions: nativeNullAssertions));
+    _resourcePool.withResource(() => _bootstrapDart2Js(
+          buildStep,
+          dart2JsArgs,
+          nativeNullAssertions: nativeNullAssertions,
+          entrypointExtension: entrypointExtension,
+        ));
 
 Future<void> _bootstrapDart2Js(
   BuildStep buildStep,
   List<String> dart2JsArgs, {
   required bool? nativeNullAssertions,
+  required String entrypointExtension,
 }) async {
   var dartEntrypointId = buildStep.inputId;
   var moduleId =
@@ -74,7 +80,7 @@ https://github.com/dart-lang/build/blob/master/docs/faq.md#how-can-i-resolve-ski
     var jsOutputPath = p.withoutExtension(dartUri.scheme == 'package'
             ? 'packages/${dartUri.path}'
             : dartUri.path.substring(1)) +
-        jsEntrypointExtension;
+        entrypointExtension;
     var librariesSpec = p.joinAll([sdkDir, 'lib', 'libraries.json']);
     _validateUserArgs(dart2JsArgs);
     args = dart2JsArgs.toList()
@@ -102,7 +108,7 @@ https://github.com/dart-lang/build/blob/master/docs/faq.md#how-can-i-resolve-ski
         ...args,
       ],
       workingDirectory: scratchSpace.tempDir.path);
-  var jsOutputId = dartEntrypointId.changeExtension(jsEntrypointExtension);
+  var jsOutputId = dartEntrypointId.changeExtension(entrypointExtension);
   var jsOutputFile = scratchSpace.fileFor(jsOutputId);
   if (result.exitCode == 0 && await jsOutputFile.exists()) {
     log.info('${result.stdout}\n${result.stderr}');
@@ -111,7 +117,7 @@ https://github.com/dart-lang/build/blob/master/docs/faq.md#how-can-i-resolve-ski
     var fileGlob = Glob('$dartFile.js*');
     var archive = Archive();
     await for (var jsFile in fileGlob.list(root: rootDir)) {
-      if (jsFile.path.endsWith(jsEntrypointExtension) ||
+      if (jsFile.path.endsWith(entrypointExtension) ||
           jsFile.path.endsWith(jsEntrypointSourceMapExtension)) {
         // These are explicitly output, and are not part of the archive.
         continue;