Resolve VariablePattern.

Change-Id: Ibfd32610e86aa3396495b3ba7210612a17756fc4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/261782
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/lib/dart/ast/ast.dart

@@ -5420,7 +5420,7 @@ abstract class VariablePattern implements DartPattern {
   /// Return the element associated with this declaration, or `null` if either
   /// the variable name is `_` (in which case no variable is defined) or the AST
   /// structure has not been resolved.
-  VariableElement? get declaredElement;
+  VariablePatternElement? get declaredElement;
 
   /// The 'var' or 'final' keyword used when there is no [type], or `null` if a
   /// type is given.

pkg/analyzer/lib/dart/element/element.dart

@@ -2388,6 +2388,15 @@ abstract class VariableElement implements Element, ConstantEvaluationTarget {
   DartObject? computeConstantValue();
 }
 
+/// A pattern variable.
+///
+/// Clients may not extend, implement or mix-in this class.
+@experimental
+abstract class VariablePatternElement implements LocalVariableElement {
+  /// Aliases of this variable in logical-or patterns.
+  List<VariablePatternElement> get aliases;
+}
+
 /// This class exists to provide non-nullable overrides for existing elements,
 /// as opposite to artificial "multiply defined" element.
 abstract class _ExistingElement implements Element {

pkg/analyzer/lib/src/dart/ast/ast.dart

@@ -13422,7 +13422,7 @@ class VariableDeclarationStatementImpl extends StatementImpl
 @experimental
 class VariablePatternImpl extends DartPatternImpl implements VariablePattern {
   @override
-  VariableElement? declaredElement;
+  VariablePatternElementImpl? declaredElement;
 
   @override
   final Token? keyword;
@@ -13463,7 +13463,9 @@ class VariablePatternImpl extends DartPatternImpl implements VariablePattern {
       DartType matchedType,
       Map<PromotableElement, VariableTypeInfo<AstNode, DartType>> typeInfos,
       MatchContext<AstNode, Expression> context) {
-    // TODO(scheglov) https://github.com/dart-lang/sdk/issues/50066
+    resolverVisitor.analyzeVariablePattern(matchedType, typeInfos, context,
+        this, declaredElement, type?.typeOrThrow,
+        isFinal: keyword?.keyword == Keyword.FINAL);
   }
 
   @override

pkg/analyzer/lib/src/dart/element/element.dart

@@ -6479,6 +6479,14 @@ abstract class VariableElementImpl extends ElementImpl
   DartObject? computeConstantValue() => null;
 }
 
+class VariablePatternElementImpl extends LocalVariableElementImpl
+    implements VariablePatternElement {
+  @override
+  final List<VariablePatternElementImpl> aliases = [];
+
+  VariablePatternElementImpl(super.name, super.offset);
+}
+
 abstract class _ExistingElementImpl extends ElementImpl with _HasLibraryMixin {
   _ExistingElementImpl(super.name, super.offset, {super.reference});
 }

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

@@ -4,6 +4,7 @@
 
 import 'package:analyzer/dart/analysis/features.dart';
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/nullability_suffix.dart';
@@ -1177,6 +1178,22 @@ class ResolutionVisitor extends RecursiveAstVisitor<void> {
     }
   }
 
+  @override
+  void visitVariablePattern(covariant VariablePatternImpl node) {
+    node.type?.accept(this);
+
+    if (node.name.lexeme != '_') {
+      final element = VariablePatternElementImpl(
+        node.name.lexeme,
+        node.name.offset,
+      );
+      node.declaredElement = element;
+      _elementHolder.enclose(element);
+      element.isFinal = node.keyword?.keyword == Keyword.FINAL;
+      element.hasImplicitType = node.type == null;
+    }
+  }
+
   /// Builds the label elements associated with [labels] and stores them in the
   /// element holder.
   void _buildLabelElements(

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

@@ -1140,7 +1140,11 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
 
   @override
   void setVariableType(PromotableElement variable, DartType type) {
-    throw UnimplementedError('TODO(paulberry)');
+    if (variable is LocalVariableElementImpl) {
+      variable.type = type;
+    } else {
+      throw UnimplementedError('TODO(paulberry)');
+    }
   }
 
   void setWriteElement(Expression node, Element? element) {
@@ -1241,7 +1245,8 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
 
   @override
   DartType variableTypeFromInitializerType(DartType type) {
-    throw UnimplementedError('TODO(paulberry)');
+    // TODO(scheglov) https://github.com/dart-lang/sdk/issues/50078
+    return type;
   }
 
   @override

pkg/analyzer/test/src/dart/resolution/postfix_pattern_test.dart

@@ -82,16 +82,18 @@ ExtractorPattern
 
   test_inside_ifStatement_case() async {
     await assertNoErrorsInCode(r'''
-void f(x) {
+void f(int? x) {
   if (x case var y!) {}
 }
 ''');
     final node = findNode.caseClause('case').pattern;
-    assertParsedNodeText(node, r'''
+    assertResolvedNodeText(node, r'''
 PostfixPattern
   operand: VariablePattern
     keyword: var
     name: y
+    declaredElement: hasImplicitType y@34
+      type: int
   operator: !
 ''');
   }
@@ -252,13 +254,14 @@ void f(x) {
 }
 ''');
     final node = findNode.switchPatternCase('case').pattern;
-    assertParsedNodeText(node, r'''
+    assertResolvedNodeText(node, r'''
 ParenthesizedPattern
   leftParenthesis: (
   pattern: PostfixPattern
     operand: ConstantPattern
       expression: IntegerLiteral
         literal: 0
+        staticType: int
     operator: !
   rightParenthesis: )
 ''');
@@ -444,16 +447,18 @@ ExtractorPattern
 
   test_inside_ifStatement_case() async {
     await assertNoErrorsInCode(r'''
-void f(x) {
+void f(int? x) {
   if (x case var y?) {}
 }
 ''');
     final node = findNode.caseClause('case').pattern;
-    assertParsedNodeText(node, r'''
+    assertResolvedNodeText(node, r'''
 PostfixPattern
   operand: VariablePattern
     keyword: var
     name: y
+    declaredElement: hasImplicitType y@34
+      type: int
   operator: ?
 ''');
   }
@@ -614,13 +619,14 @@ void f(x) {
 }
 ''');
     final node = findNode.switchPatternCase('case').pattern;
-    assertParsedNodeText(node, r'''
+    assertResolvedNodeText(node, r'''
 ParenthesizedPattern
   leftParenthesis: (
   pattern: PostfixPattern
     operand: ConstantPattern
       expression: IntegerLiteral
         literal: 0
+        staticType: int
     operator: ?
   rightParenthesis: )
 ''');