[CFE] Fix expression compilation with extension methods imported via prefix

Fixes #56554

Change-Id: I060a76cc3d3bb946283eff17c8feb93f136a8d8f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/389100
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Jens Johansen <[email protected]>

Author: jensjoha

pkg/front_end/lib/src/base/incremental_compiler.dart

@@ -2049,8 +2049,26 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
           indexedLibrary: null,
           mayImplementRestrictedTypes: false);
 
+      SourceLibraryBuilder? orgDebugLibrary = debugLibrary;
       debugLibrary = debugCompilationUnit.createLibrary();
 
+      // Copy over the prefix namespace for extensions
+      // (`forEachExtensionInScope`) to be found when imported via prefixes.
+      // TODO(johnniwinther): Extensions should be available through
+      // [parentScope].
+      orgDebugLibrary.prefixNameSpace.forEachLocalMember((name, member) {
+        debugLibrary.prefixNameSpace
+            .addLocalMember(name, member, setter: false);
+      });
+      // Does a prefix namespace ever have anything but locals?
+      orgDebugLibrary.prefixNameSpace.forEachLocalSetter((name, member) {
+        debugLibrary.prefixNameSpace.addLocalMember(name, member, setter: true);
+      });
+      orgDebugLibrary.prefixNameSpace.forEachLocalExtension((member) {
+        debugLibrary.prefixNameSpace.addExtension(member);
+      });
+      orgDebugLibrary = null;
+
       HybridFileSystem hfs =
           lastGoodKernelTarget.fileSystem as HybridFileSystem;
       MemoryFileSystem fs = hfs.memory;

pkg/front_end/testcases/expression/evaluate_extension_method_from_import.expression.yaml

@@ -0,0 +1,37 @@
+# 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.
+
+entry_point: a1.dart
+sources:
+  a1.dart: |
+    import 'a2.dart' as ext;
+    import 'a3.dart';
+
+    void stopHere() {
+      final i = 0;
+      print(i.f1());
+      print(i.f2());
+      print(i.f3());
+    }
+
+    extension E1 on int {
+      int f1() => this;
+    }
+  a2.dart: |
+    extension E2 on int {
+      int f2() => this;
+    }
+  a3.dart: |
+    extension E3 on int {
+      int f3() => this;
+    }
+definitions: ["i"]
+# int
+definition_types: ["dart:core", "int", "1", "0"]
+type_definitions: []
+type_bounds: []
+type_defaults: []
+method: "stopHere"
+expression: |
+  i.f1() + i.f2() + i.f3()

pkg/front_end/testcases/expression/evaluate_extension_method_from_import.expression.yaml.expect

@@ -0,0 +1,4 @@
+Errors: {
+}
+method /* from org-dartlang-debug:synthetic_debug_expression */ debugExpr(dart.core::int i) → dynamic
+  return #lib1::E1|f1(i).{dart.core::num::+}(#lib2::E2|f2(i)){(dart.core::num) → dart.core::int}.{dart.core::num::+}(#lib3::E3|f3(i)){(dart.core::num) → dart.core::int};

pkg/front_end/testcases/expression/prefixed_import.expression.yaml

@@ -0,0 +1,22 @@
+# 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.
+
+entry_point: a1.dart
+sources:
+  a1.dart: |
+    import 'a2.dart' as ext;
+
+    void stopHere() {
+      ext.foo();
+    }
+  a2.dart: |
+    void foo() {}
+definitions: []
+definition_types: []
+type_definitions: []
+type_bounds: []
+type_defaults: []
+method: "stopHere"
+expression: |
+  ext.foo()

pkg/front_end/testcases/expression/prefixed_import.expression.yaml.expect

@@ -0,0 +1,4 @@
+Errors: {
+}
+method /* from org-dartlang-debug:synthetic_debug_expression */ debugExpr() → dynamic
+  return #lib1::foo();