Shared pattern analysis: add support for pattern variable assignment.

Bug: #50585
Change-Id: I1939c6fd8fac205abeac5b0a9b3da9b3b4adca01
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/274604
Commit-Queue: Paul Berry <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>

Author: stereotype441

pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart

@@ -187,6 +187,14 @@ abstract class FlowAnalysis<Node extends Object, Statement extends Node,
   /// A function parameter is always initialized, so [initialized] is `true`.
   void declare(Variable variable, bool initialized);
 
+  /// Call this method after visiting a variable pattern in a non-assignment
+  /// context (or a wildcard pattern).
+  ///
+  /// [matchedType] should be the static type of the value being matched.
+  /// [staticType] should be the static type of the variable pattern itself.
+  void declaredVariablePattern(
+      {required Type matchedType, required Type staticType});
+
   /// Call this method before visiting the body of a "do-while" statement.
   /// [doStatement] should be the same node that was passed to
   /// [AssignedVariables.endNode] for the do-while statement.
@@ -518,6 +526,15 @@ abstract class FlowAnalysis<Node extends Object, Statement extends Node,
   void parenthesizedExpression(
       Expression outerExpression, Expression innerExpression);
 
+  /// Call this method just after visiting the right hand side of a pattern
+  /// assignment expression, and before visiting the pattern.
+  ///
+  /// [rhs] is the right hand side expression.
+  void patternAssignment_afterRhs(Expression rhs);
+
+  /// Call this method after visiting a pattern assignment expression.
+  void patternAssignment_end();
+
   /// Call this method just after visiting the initializer of a pattern variable
   /// declaration, and before visiting the pattern.
   void patternVariableDeclaration_afterInitializer(Expression initializer);
@@ -746,12 +763,6 @@ abstract class FlowAnalysis<Node extends Object, Statement extends Node,
   /// statement.
   void tryFinallyStatement_finallyBegin(Node body);
 
-  /// Call this method after visiting a variable pattern.
-  ///
-  /// [matchedType] should be the static type of the value being matched.
-  /// [staticType] should be the static type of the variable pattern itself.
-  void variablePattern({required Type matchedType, required Type staticType});
-
   /// Call this method when encountering an expression that reads the value of
   /// a variable.
   ///
@@ -950,6 +961,16 @@ class FlowAnalysisDebug<Node extends Object, Statement extends Node,
         () => _wrapped.declare(variable, initialized));
   }
 
+  @override
+  void declaredVariablePattern(
+      {required Type matchedType, required Type staticType}) {
+    _wrap(
+        'declaredVariablePattern(matchedType: $matchedType, '
+        'staticType: $staticType)',
+        () => _wrapped.declaredVariablePattern(
+            matchedType: matchedType, staticType: staticType));
+  }
+
   @override
   void doStatement_bodyBegin(Statement doStatement) {
     return _wrap('doStatement_bodyBegin($doStatement)',
@@ -1243,6 +1264,17 @@ class FlowAnalysisDebug<Node extends Object, Statement extends Node,
             _wrapped.parenthesizedExpression(outerExpression, innerExpression));
   }
 
+  @override
+  void patternAssignment_afterRhs(Expression rhs) {
+    _wrap('patternAssignment_afterRhs($rhs)',
+        () => _wrapped.patternAssignment_afterRhs(rhs));
+  }
+
+  @override
+  void patternAssignment_end() {
+    _wrap('patternAssignment_end()', () => _wrapped.patternAssignment_end());
+  }
+
   @override
   void patternVariableDeclaration_afterInitializer(Expression initializer) {
     _wrap(
@@ -1405,14 +1437,6 @@ class FlowAnalysisDebug<Node extends Object, Statement extends Node,
         () => _wrapped.tryFinallyStatement_finallyBegin(body));
   }
 
-  @override
-  void variablePattern({required Type matchedType, required Type staticType}) {
-    _wrap(
-        'variablePattern(matchedType: $matchedType, staticType: $staticType)',
-        () => _wrapped.variablePattern(
-            matchedType: matchedType, staticType: staticType));
-  }
-
   @override
   Type? variableRead(Expression expression, Variable variable) {
     return _wrap('variableRead($expression, $variable)',
@@ -3371,6 +3395,25 @@ class _FlowAnalysisImpl<Node extends Object, Statement extends Node,
         promotionKeyStore.keyForVariable(variable), initialized);
   }
 
+  @override
+  void declaredVariablePattern(
+      {required Type matchedType, required Type staticType}) {
+    _PatternContext<Type> context = _stack.last as _PatternContext<Type>;
+    ReferenceWithType<Type>? scrutineeReference = context._scrutineeReference;
+    bool coversMatchedType =
+        typeOperations.isSubtypeOf(matchedType, staticType);
+    if (scrutineeReference != null) {
+      ExpressionInfo<Type> promotionInfo =
+          _current.tryPromoteForTypeCheck(this, scrutineeReference, staticType);
+      _current = promotionInfo.ifTrue;
+      if (!coversMatchedType) {
+        context._unmatched = _join(context._unmatched, promotionInfo.ifFalse);
+      }
+    } else if (!coversMatchedType) {
+      context._unmatched = _join(context._unmatched, _current);
+    }
+  }
+
   @override
   void doStatement_bodyBegin(Statement doStatement) {
     AssignedVariablesNodeInfo info =
@@ -3848,6 +3891,16 @@ class _FlowAnalysisImpl<Node extends Object, Statement extends Node,
     forwardExpression(outerExpression, innerExpression);
   }
 
+  @override
+  void patternAssignment_afterRhs(Expression rhs) {
+    _pushPattern(_getExpressionReference(rhs));
+  }
+
+  @override
+  void patternAssignment_end() {
+    _popPattern(null);
+  }
+
   @override
   void patternVariableDeclaration_afterInitializer(Expression initializer) {
     _pushPattern(_getExpressionReference(initializer));
@@ -4048,24 +4101,6 @@ class _FlowAnalysisImpl<Node extends Object, Statement extends Node,
     context._beforeFinally = _current;
   }
 
-  @override
-  void variablePattern({required Type matchedType, required Type staticType}) {
-    _PatternContext<Type> context = _stack.last as _PatternContext<Type>;
-    ReferenceWithType<Type>? scrutineeReference = context._scrutineeReference;
-    bool coversMatchedType =
-        typeOperations.isSubtypeOf(matchedType, staticType);
-    if (scrutineeReference != null) {
-      ExpressionInfo<Type> promotionInfo =
-          _current.tryPromoteForTypeCheck(this, scrutineeReference, staticType);
-      _current = promotionInfo.ifTrue;
-      if (!coversMatchedType) {
-        context._unmatched = _join(context._unmatched, promotionInfo.ifFalse);
-      }
-    } else if (!coversMatchedType) {
-      context._unmatched = _join(context._unmatched, _current);
-    }
-  }
-
   @override
   Type? variableRead(Expression expression, Variable variable) {
     int variableKey = promotionKeyStore.keyForVariable(variable);
@@ -4510,6 +4545,10 @@ class _LegacyTypePromotion<Node extends Object, Statement extends Node,
   @override
   void declare(Variable variable, bool initialized) {}
 
+  @override
+  void declaredVariablePattern(
+      {required Type matchedType, required Type staticType}) {}
+
   @override
   void doStatement_bodyBegin(Statement doStatement) {}
 
@@ -4778,6 +4817,12 @@ class _LegacyTypePromotion<Node extends Object, Statement extends Node,
     forwardExpression(outerExpression, innerExpression);
   }
 
+  @override
+  void patternAssignment_afterRhs(Expression rhs) {}
+
+  @override
+  void patternAssignment_end() {}
+
   @override
   void patternVariableDeclaration_afterInitializer(Expression initializer) {}
 
@@ -4858,9 +4903,6 @@ class _LegacyTypePromotion<Node extends Object, Statement extends Node,
   @override
   void tryFinallyStatement_finallyBegin(Node body) {}
 
-  @override
-  void variablePattern({required Type matchedType, required Type staticType}) {}
-
   @override
   Type? variableRead(Expression expression, Variable variable) {
     int variableKey = _promotionKeyStore.keyForVariable(variable);