Completion. Issue 54231. Fix suggesting through import prefix, when there is another identifier after it.

Bug: https://github.com/dart-lang/sdk/issues/54231
Change-Id: I06a5eb3763814fde99e2e2ba583679cc27c1a4b6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/355546
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analysis_server/lib/src/services/completion/dart/declaration_helper.dart

@@ -133,6 +133,22 @@ class DeclarationHelper {
     }
   }
 
+  /// Add suggestions for declarations through [prefixElement].
+  void addDeclarationsThroughImportPrefix(PrefixElement prefixElement) {
+    for (var importElement in prefixElement.imports) {
+      var importedLibrary = importElement.importedLibrary;
+      if (importedLibrary == null) {
+        continue;
+      }
+
+      _addDeclarationsImportedFrom(
+        library: importedLibrary,
+        namespace: importElement.namespace,
+        prefix: null,
+      );
+    }
+  }
+
   /// Add any fields that can be initialized in the initializer list of the
   /// given [constructor]. If a [fieldToInclude] is provided, then it should not
   /// be skipped because the cursor is inside that field's name.

pkg/analysis_server/lib/src/services/completion/dart/in_scope_completion_pass.dart

@@ -1525,6 +1525,22 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
 
   @override
   void visitNamedType(NamedType node) {
+    var importPrefix = node.importPrefix;
+    var prefixElement = importPrefix?.element;
+
+    // `prefix.x^ print(0);` is recovered as `prefix.x print; (0);`.
+    if (prefixElement is PrefixElement) {
+      if (node.parent case VariableDeclarationList variableList) {
+        if (variableList.parent case VariableDeclarationStatement statement) {
+          if (statement.semicolon.isSynthetic) {
+            declarationHelper()
+                .addDeclarationsThroughImportPrefix(prefixElement);
+            return;
+          }
+        }
+      }
+    }
+
     _forTypeAnnotation(node);
   }
 

pkg/analysis_server/test/services/completion/dart/location/property_access_expression_test.dart

@@ -55,6 +55,31 @@ suggestions
 ''');
   }
 
+  Future<void> test_afterIdentifier_beforeIdentifier_partial() async {
+    newFile('$testPackageLibPath/a.dart', r'''
+void v01() {}
+void g01() {}
+''');
+
+    // There should be no `void`, we use `v` to verify this.
+    await computeSuggestions('''
+import 'a.dart' as prefix;
+
+void f() {
+  prefix.v^
+  print(0);
+}
+''');
+
+    assertResponse(r'''
+replacement
+  left: 1
+suggestions
+  v01
+    kind: functionInvocation
+''');
+  }
+
   Future<void> test_afterIdentifier_partial() async {
     await computeSuggestions('''
 class A { foo() {bar.as^}}