Initial support for code completion in extension type declarations

Change-Id: I6acb71d0ac282135b6527431b162fad9a0dee8f7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/324900
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

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

@@ -94,6 +94,12 @@ final class KeywordSuggestion extends CandidateSuggestion {
     );
   }
 
+  /// Initialize a newly created candidate suggestion to suggest the [keyword].
+  factory KeywordSuggestion.fromPseudoKeyword(String keyword) {
+    return KeywordSuggestion._(
+        completion: keyword, selectionOffset: keyword.length);
+  }
+
   /// Initialize a newly created candidate suggestion to suggest a keyword.
   KeywordSuggestion._(
       {required this.completion, required this.selectionOffset});

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

@@ -246,6 +246,16 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
     }
   }
 
+  @override
+  void visitCompilationUnit(CompilationUnit node) {
+    var followingMember = node.memberAfter(offset);
+    if (_forIncompletePreceedingUnitMember(node, followingMember)) {
+      // The preceeding member is incomplete, so assume that the user is
+      // completing it rather than starting a new member.
+      return;
+    }
+  }
+
   @override
   void visitConditionalExpression(ConditionalExpression node) {
     // TODO(brianwilkerson) Consider adding a location for the condition.
@@ -428,10 +438,11 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
     }
     var name = node.name;
     if (name != null && offset <= name.end) {
-      // TODO(brianwilkerson) We probably need to suggest `on`.
-      // TODO(brianwilkerson) We probably need to suggest `type` when extension
-      //  types are supported.
-      // Don't suggest a name for the extension.
+      keywordHelper.addKeyword(Keyword.ON);
+      if (featureSet.isEnabled(Feature.inline_class)) {
+        keywordHelper.addPseudoKeyword('type');
+      }
+      // TODO(brianwilkerson) Suggest a name for the extension.
       return;
     }
     if (offset <= node.leftBracket.offset) {
@@ -453,6 +464,14 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
     _forExpression(node);
   }
 
+  @override
+  void visitExtensionTypeDeclaration(ExtensionTypeDeclaration node) {
+    if (offset >= node.representation.end &&
+        (offset <= node.leftBracket.offset || node.leftBracket.isSynthetic)) {
+      keywordHelper.addKeyword(Keyword.IMPLEMENTS);
+    }
+  }
+
   @override
   void visitFieldDeclaration(FieldDeclaration node) {
     _forIncompletePreceedingClassMember(node);
@@ -1033,7 +1052,9 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
 
   @override
   void visitTopLevelVariableDeclaration(TopLevelVariableDeclaration node) {
-    if (_forIncompletePreceedingUnitMember(node)) {
+    var unit = node.parent;
+    if (unit is CompilationUnit &&
+        _forIncompletePreceedingUnitMember(unit, node)) {
       return;
     } else if (node.isSingleIdentifier) {
       // The parser recovers from a simple identifier by assuming that it's a
@@ -1123,7 +1144,9 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
       // The order of these conditions is critical. We need to check for an
       // incomplete preceeding member even when the grandparent isn't a single
       // identifier, but want to return only if both conditions are true.
-      if (_forIncompletePreceedingUnitMember(grandparent) &&
+      var unit = grandparent.parent;
+      if (unit is CompilationUnit &&
+          _forIncompletePreceedingUnitMember(unit, grandparent) &&
           grandparent.isSingleIdentifier) {
         return;
       }
@@ -1356,14 +1379,11 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
   /// then the user might be attempting to complete the preceeding member rather
   /// than attempting to prepend something to the given [member], so add the
   /// suggestions appropriate for that situation.
-  bool _forIncompletePreceedingUnitMember(AstNode member) {
-    if (offset <= member.beginToken.end) {
-      var parent = member.parent;
-      if (parent is! CompilationUnit) {
-        return false;
-      }
+  bool _forIncompletePreceedingUnitMember(
+      CompilationUnit parent, AstNode? member) {
+    if (member == null || offset <= member.beginToken.end) {
       var members = parent.sortedDirectivesAndDeclarations;
-      var index = members.indexOf(member);
+      var index = member == null ? members.length : members.indexOf(member);
       if (index <= 0) {
         return false;
       }
@@ -1378,6 +1398,11 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
             keywordHelper.addClassDeclarationKeywords(declaration);
             return true;
           }
+        case ExtensionTypeDeclaration declaration:
+          if (declaration.hasNoBody) {
+            visitExtensionTypeDeclaration(declaration);
+            return true;
+          }
         case ImportDirective directive:
           if (directive.semicolon.isSynthetic) {
             visitImportDirective(directive);
@@ -1569,6 +1594,20 @@ extension on ClassMember {
   }
 }
 
+extension on CompilationUnit {
+  /// Return the member that is immediately after the given [offset] or `null`
+  /// if the offset isn't before a member.
+  AstNode? memberAfter(int offset) {
+    var members = sortedDirectivesAndDeclarations;
+    for (var member in members) {
+      if (offset < member.offset) {
+        return member;
+      }
+    }
+    return null;
+  }
+}
+
 extension on ExpressionStatement {
   /// Return `true` if this statement consists of a single identifier.
   bool get isSingleIdentifier {
@@ -1580,6 +1619,13 @@ extension on ExpressionStatement {
   }
 }
 
+extension on ExtensionTypeDeclaration {
+  /// Return `true` if this class declaration doesn't have a body.
+  bool get hasNoBody {
+    return leftBracket.isSynthetic && rightBracket.isSynthetic;
+  }
+}
+
 extension on FieldDeclaration {
   /// Return `true` if this field declaration consists of a single identifier.
   bool get isSingleIdentifier {

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

@@ -145,6 +145,10 @@ class _KeywordVisitor extends SimpleAstVisitor<void> {
         return;
       }
     }
+    if (previousMember is ExtensionTypeDeclaration) {
+      // Already handled by the in-scope completion pass.
+      return;
+    }
     if (previousMember == null || previousMember is Directive) {
       if (previousMember == null &&
           !node.directives.any((d) => d is LibraryDirective)) {

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

@@ -290,6 +290,9 @@ class KeywordHelper {
   void addExtensionDeclarationKeywords(ExtensionDeclaration node) {
     if (node.onKeyword.isSynthetic) {
       addKeyword(Keyword.ON);
+      if (node.name == null && featureSet.isEnabled(Feature.inline_class)) {
+        addPseudoKeyword('type');
+      }
     }
   }
 
@@ -461,6 +464,11 @@ class KeywordHelper {
     addVariablePatternKeywords();
   }
 
+  /// Add a keyword suggestion to suggest the [keyword].
+  void addPseudoKeyword(String keyword) {
+    collector.addSuggestion(KeywordSuggestion.fromPseudoKeyword(keyword));
+  }
+
   /// Add the keywords that are appropriate when the selection is at the
   /// beginning of a statement. The [node] provides context to determine which
   /// keywords to include.

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

@@ -36,6 +36,8 @@ extension ^
 suggestions
   on
     kind: keyword
+  type
+    kind: keyword
 ''');
   }
 
@@ -49,4 +51,29 @@ suggestions
     kind: keyword
 ''');
   }
+
+  Future<void> test_afterName_beforeEof_partial() async {
+    await computeSuggestions('''
+extension o^
+''');
+    if (isProtocolVersion2) {
+      assertResponse(r'''
+replacement
+  left: 1
+suggestions
+  on
+    kind: keyword
+''');
+    } else {
+      assertResponse(r'''
+replacement
+  left: 1
+suggestions
+  on
+    kind: keyword
+  type
+    kind: keyword
+''');
+    }
+  }
 }

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

@@ -0,0 +1,64 @@
+// Copyright (c) 2023, 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 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../../../../client/completion_driver_test.dart';
+
+void main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(ExtensionTypeDeclarationTest1);
+    defineReflectiveTests(ExtensionTypeDeclarationTest2);
+  });
+}
+
+@reflectiveTest
+class ExtensionTypeDeclarationTest1 extends AbstractCompletionDriverTest
+    with ExtensionTypeDeclarationTestCases {
+  @override
+  TestingCompletionProtocol get protocol => TestingCompletionProtocol.version1;
+}
+
+@reflectiveTest
+class ExtensionTypeDeclarationTest2 extends AbstractCompletionDriverTest
+    with ExtensionTypeDeclarationTestCases {
+  @override
+  TestingCompletionProtocol get protocol => TestingCompletionProtocol.version2;
+}
+
+mixin ExtensionTypeDeclarationTestCases on AbstractCompletionDriverTest {
+  Future<void> test_afterRepresentationField_beforeEof() async {
+    await computeSuggestions('''
+extension type E(int i) ^
+''');
+    assertResponse(r'''
+suggestions
+  implements
+    kind: keyword
+''');
+  }
+
+  Future<void> test_afterRepresentationField_beforeEof_partial() async {
+    await computeSuggestions('''
+extension type E(int i) i^
+''');
+    assertResponse(r'''
+replacement
+  left: 1
+suggestions
+  implements
+    kind: keyword
+''');
+  }
+
+  @FailingTest(reason: 'The AstBuilder drops the incomplete extension type')
+  Future<void> test_afterType_beforeEof() async {
+    await computeSuggestions('''
+extension type ^
+''');
+    assertResponse(r'''
+suggestions
+''');
+  }
+}

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

@@ -21,6 +21,7 @@ import 'enum_test.dart' as enum_;
 import 'extends_clause_test.dart' as extends_clause;
 import 'extension_body_test.dart' as extension_body;
 import 'extension_declaration_test.dart' as extension_declaration;
+import 'extension_type_declaration_test.dart' as extension_type_declaration;
 import 'field_declaration_test.dart' as field_declaration;
 import 'field_formal_parameter_test.dart' as field_formal_parameter;
 import 'for_element_test.dart' as for_element;
@@ -88,6 +89,7 @@ void main() {
     extends_clause.main();
     extension_body.main();
     extension_declaration.main();
+    extension_type_declaration.main();
     field_declaration.main();
     field_formal_parameter.main();
     for_element.main();