[kernel] Adds helper to trim dill files for modular dependencies.

Introduce a helper library to trim components based on what we believe
it is needed for modular bytecode compilation. The script is configured
to accept a set of entry points, so unreachable libraries can be removed
entirely. The contents of the retained libraries is trimmed to remove
method bodies, constructor bodies, and initializers, except for where
they may be needed.


In the near future, this should be expanded to:
* include proper unit testing in the CFE
* review whether additional trimming operations can be made
* consider an explicit representation of trimmed content, to help the
  CFE recover when assumptions are not met (e.g. sentinel markers
  to establish whether a value has been trimmed)
* CFE produces trimmed data directly if needed, without having to first
  produce the full dill.

Tests that specifically stress that we don't over-trim include:
apply_mixin (requires preserving method bodies), const_body (requires
preserving initializers).

TEST=existing and new e2e dynamic module aot tests.

b/394936876

Change-Id: I26db8385bdfe1664b2aea234ec8bb896c7c21230
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418702
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Sigmund Cherem <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: sigmundch

pkg/dynamic_modules/pubspec.yaml

@@ -11,4 +11,7 @@ resolution: workspace
 dev_dependencies:
   args: any
   expect: any
+  front_end: any
+  kernel: any
   lints: any
+  vm: any

pkg/dynamic_modules/test/data/const_body/dynamic_interface.yaml

@@ -0,0 +1,14 @@
+# Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+
+callable:
+  - library: 'shared/shared.dart'
+    class: 'B'
+    member: ''
+    # TODO(sigmund): This should be included by default
+  - library: 'dart:core'
+    class: 'Object'
+  - library: 'dart:core'
+    class: 'pragma'
+    member: '_'

pkg/dynamic_modules/test/data/const_body/main.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../../common/testing.dart' as helper;
+import 'shared/shared.dart';
+
+import 'package:expect/expect.dart';
+
+// Constants with a constructor body can be used from dynamic modules.
+void main() async {
+  final c1 = (await helper.load('entry1.dart'));
+  final c2 = (await helper.load('entry2.dart'));
+
+  Expect.identical((c1 as B).x, 2);
+  Expect.identical(c1, c2);
+  helper.done();
+}

pkg/dynamic_modules/test/data/const_body/modules/entry1.dart

@@ -0,0 +1,8 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../shared/shared.dart';
+
+@pragma('dyn-module:entry-point')
+Object? dynamicModuleEntrypoint() => const B(1);

pkg/dynamic_modules/test/data/const_body/modules/entry2.dart

@@ -0,0 +1,8 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../shared/shared.dart';
+
+@pragma('dyn-module:entry-point')
+Object? dynamicModuleEntrypoint() => const B(1);

pkg/dynamic_modules/test/data/const_body/shared/shared.dart

@@ -0,0 +1,8 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class B {
+  final int x;
+  const B(int y) : x = y + 1;
+}

pkg/dynamic_modules/test/data/shared_const/dynamic_interface.yaml

@@ -3,7 +3,7 @@
 # BSD-style license that can be found in the LICENSE file.
 
 callable:
-  - library: 'main.dart'
+  - library: 'shared/shared.dart'
     class: 'B'
     member: ''
     # TODO(sigmund): This should be included by default

pkg/dynamic_modules/test/data/shared_const/main.dart

@@ -3,20 +3,16 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import '../../common/testing.dart' as helper;
-import 'package:expect/expect.dart';
+import 'shared/shared.dart';
 
-class B {
-  final int x;
-  const B(this.x);
-}
+import 'package:expect/expect.dart';
 
-// Similar to `isolated_shared`, constant canonicalization distinguishes
-// two constnats, even if they are created from a common library that was
-// not part of the original application.
+// Constants are properly canonicalized across dynamic modules.
 void main() async {
   final c1 = (await helper.load('entry1.dart'));
   final c2 = (await helper.load('entry2.dart'));
 
+  Expect.identical((c1 as B).x, 1);
   Expect.identical(c1, c2);
   helper.done();
 }

pkg/dynamic_modules/test/data/shared_const/modules/entry1.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import '../main.dart';
+import '../shared/shared.dart';
 
 @pragma('dyn-module:entry-point')
 Object? dynamicModuleEntrypoint() => const B(1);

pkg/dynamic_modules/test/data/shared_const/modules/entry2.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import '../main.dart';
+import '../shared/shared.dart';
 
 @pragma('dyn-module:entry-point')
 Object? dynamicModuleEntrypoint() => const B(1);