Fine. Don't lookup private fields, methods from other libraries.

Prevent the resolver from considering private identifiers when
collecting applicable extensions for a different library. Previously we
probed members by simple name and could end up touching private
fields/methods like `_foo` across library boundaries, which led to
unnecessary dependency tracking and occasional cache churn (e.g., ID
mismatches) and extra analysis work.

Add an early accessibility guard:
- Skip an extension if the requested `baseName` is not accessible from
  the extension’s library URI.

With this guard in place, the subsequent per-member name equality checks
are redundant and are removed, simplifying the lookup. The result is
correct privacy behavior, fewer spurious lookups, and more stable
analysis results.

Change-Id: I063823f29d820377897a406663fe4d612c493f72
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/445343
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/dart/resolver/applicable_extensions.dart

@@ -133,6 +133,10 @@ extension ExtensionsExtensions on Iterable<ExtensionElement> {
   ) {
     var result = <_NotInstantiatedExtensionWithMember>[];
     for (var extension in this) {
+      if (!baseName.isAccessibleFor(extension.library.uri)) {
+        continue;
+      }
+
       if (baseName.name == '[]') {
         var getter = extension.getMethod('[]');
         var setter = extension.getMethod('[]=');
@@ -150,31 +154,27 @@ extension ExtensionsExtensions on Iterable<ExtensionElement> {
       } else {
         var field = extension.getField(baseName.name);
         if (field != null && !field.isStatic) {
-          if (Name.forElement(field) == baseName) {
-            result.add(
-              _NotInstantiatedExtensionWithMember(
-                // TODO(paulberry): eliminate this cast by changing the
-                // extension to apply only to `Iterable<ExtensionElementImpl>`.
-                extension as ExtensionElementImpl,
-                getter: field.getter,
-                setter: field.setter,
-              ),
-            );
-          }
+          result.add(
+            _NotInstantiatedExtensionWithMember(
+              // TODO(paulberry): eliminate this cast by changing the
+              // extension to apply only to `Iterable<ExtensionElementImpl>`.
+              extension as ExtensionElementImpl,
+              getter: field.getter,
+              setter: field.setter,
+            ),
+          );
         }
 
         var method = extension.getMethod(baseName.name);
         if (method != null && !method.isStatic) {
-          if (Name.forElement(method) == baseName) {
-            result.add(
-              _NotInstantiatedExtensionWithMember(
-                // TODO(paulberry): eliminate this cast by changing the
-                // extension to apply only to `Iterable<ExtensionElementImpl>`.
-                extension as ExtensionElementImpl,
-                getter: method,
-              ),
-            );
-          }
+          result.add(
+            _NotInstantiatedExtensionWithMember(
+              // TODO(paulberry): eliminate this cast by changing the
+              // extension to apply only to `Iterable<ExtensionElementImpl>`.
+              extension as ExtensionElementImpl,
+              getter: method,
+            ),
+          );
         }
       }
     }

pkg/analyzer/test/src/dart/analysis/driver_test.dart

@@ -20519,13 +20519,6 @@ void f() {
       package:test/a.dart
         Object: <null>
         int: <null>
-    instances
-      package:test/a.dart
-        A
-          requestedFields
-            _foo: #M1
-          requestedMethods
-            _foo: <null>
     exportedExtensions
       dart:core: #M9
       package:test/a.dart: #M0
@@ -20561,43 +20554,9 @@ extension A on Object {
       7 +8 UNUSED_IMPORT
 [operation] readLibraryCycleBundle
   package:test/test.dart
-[operation] getErrorsCannotReuse
-  instanceFieldIdMismatch
-    libraryUri: package:test/a.dart
-    interfaceName: A
-    fieldName: _foo
-    expectedId: #M1
-    actualId: #M10
-[operation] analyzeFile
+[operation] getErrorsFromBytes
   file: /home/test/lib/test.dart
   library: /home/test/lib/test.dart
-[stream]
-  ResolvedUnitResult #3
-    path: /home/test/lib/test.dart
-    uri: package:test/test.dart
-    flags: exists isLibrary
-    errors
-      7 +8 UNUSED_IMPORT
-[operation] analyzedLibrary
-  file: /home/test/lib/test.dart
-  requirements
-    topLevels
-      dart:core
-        Object: #M3
-        int: #M4
-      package:test/a.dart
-        Object: <null>
-        int: <null>
-    instances
-      package:test/a.dart
-        A
-          requestedFields
-            _foo: #M10
-          requestedMethods
-            _foo: <null>
-    exportedExtensions
-      dart:core: #M9
-      package:test/a.dart: #M0
 [status] idle
 ''',
     );