Port TypeScript PR #61788: Fix control flow analysis of aliased discriminants with parenthesized initializers

Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Author: Copilot

internal/checker/flow.go

@@ -1442,26 +1442,32 @@ func (c *Checker) getCandidateDiscriminantPropertyAccess(f *FlowState, expr *ast
 		symbol := c.getResolvedSymbol(expr)
 		if c.isConstantVariable(symbol) {
 			declaration := symbol.ValueDeclaration
+			initializer := getCandidateVariableDeclarationInitializer(declaration)
 			// Given 'const x = obj.kind', allow 'x' as an alias for 'obj.kind'
-			if ast.IsVariableDeclaration(declaration) && declaration.Type() == nil {
-				if initializer := declaration.Initializer(); initializer != nil && ast.IsAccessExpression(initializer) && c.isMatchingReference(f.reference, initializer.Expression()) {
-					return initializer
-				}
+			if initializer != nil && ast.IsAccessExpression(initializer) && c.isMatchingReference(f.reference, initializer.Expression()) {
+				return initializer
 			}
 			// Given 'const { kind: x } = obj', allow 'x' as an alias for 'obj.kind'
 			if ast.IsBindingElement(declaration) && declaration.Initializer() == nil {
-				parent := declaration.Parent.Parent
-				if ast.IsVariableDeclaration(parent) && parent.Type() == nil {
-					if initializer := parent.Initializer(); initializer != nil && (ast.IsIdentifier(initializer) || ast.IsAccessExpression(initializer)) && c.isMatchingReference(f.reference, initializer) {
-						return declaration
-					}
+				initializer = getCandidateVariableDeclarationInitializer(declaration.Parent.Parent)
+				if initializer != nil && (ast.IsIdentifier(initializer) || ast.IsAccessExpression(initializer)) && c.isMatchingReference(f.reference, initializer) {
+					return declaration
 				}
 			}
 		}
 	}
 	return nil
 }
 
+func getCandidateVariableDeclarationInitializer(node *ast.Node) *ast.Node {
+	if ast.IsVariableDeclaration(node) && node.Type() == nil {
+		if initializer := node.Initializer(); initializer != nil {
+			return ast.SkipParentheses(initializer)
+		}
+	}
+	return nil
+}
+
 // An evolving array type tracks the element types that have so far been seen in an
 // 'x.push(value)' or 'x[n] = value' operation along the control flow graph. Evolving
 // array types are ultimately converted into manifest array types (using getFinalArrayType)

testdata/baselines/reference/submodule/conformance/controlFlowAliasing2.errors.txt

@@ -47,9 +47,11 @@ function _tcb1(this: { test: Test }) {
 >_t1 : Symbol(_t1, Decl(controlFlowAliasing2.ts, 16, 7))
 
     (((((this).test)).name));
+>(((this).test)).name : Symbol(TestA.name, Decl(controlFlowAliasing2.ts, 5, 12))
 >(this).test : Symbol(test, Decl(controlFlowAliasing2.ts, 14, 22))
 >this : Symbol(this, Decl(controlFlowAliasing2.ts, 14, 15))
 >test : Symbol(test, Decl(controlFlowAliasing2.ts, 14, 22))
+>name : Symbol(TestA.name, Decl(controlFlowAliasing2.ts, 5, 12))
   }
 
   // Same as above, without the parenthesis
@@ -112,9 +114,11 @@ function _tcb2(this: { test: Test }) {
 >_t1 : Symbol(_t1, Decl(controlFlowAliasing2.ts, 36, 7))
 
     (((((this).test)).name));
+>(((this).test)).name : Symbol(TestA.name, Decl(controlFlowAliasing2.ts, 5, 12))
 >(this).test : Symbol(test, Decl(controlFlowAliasing2.ts, 34, 22))
 >this : Symbol(this, Decl(controlFlowAliasing2.ts, 34, 15))
 >test : Symbol(test, Decl(controlFlowAliasing2.ts, 34, 22))
+>name : Symbol(TestA.name, Decl(controlFlowAliasing2.ts, 5, 12))
   }
 
   // Same as above, without the parenthesis
@@ -175,9 +179,11 @@ function _tcb3(this: { test: Test }) {
 >_t1 : Symbol(_t1, Decl(controlFlowAliasing2.ts, 55, 9))
 
     (((((this).test)).name));
+>(((this).test)).name : Symbol(TestA.name, Decl(controlFlowAliasing2.ts, 5, 12))
 >(this).test : Symbol(test, Decl(controlFlowAliasing2.ts, 54, 22))
 >this : Symbol(this, Decl(controlFlowAliasing2.ts, 54, 15))
 >test : Symbol(test, Decl(controlFlowAliasing2.ts, 54, 22))
+>name : Symbol(TestA.name, Decl(controlFlowAliasing2.ts, 5, 12))
   }
 
   // Same as above, without the parenthesis
@@ -236,9 +242,11 @@ function _tcb4(this: { test: Test }) {
 >_t1 : Symbol(_t1, Decl(controlFlowAliasing2.ts, 74, 9))
 
     (((((this).test)).name));
+>(((this).test)).name : Symbol(TestA.name, Decl(controlFlowAliasing2.ts, 5, 12))
 >(this).test : Symbol(test, Decl(controlFlowAliasing2.ts, 73, 22))
 >this : Symbol(this, Decl(controlFlowAliasing2.ts, 73, 15))
 >test : Symbol(test, Decl(controlFlowAliasing2.ts, 73, 22))
+>name : Symbol(TestA.name, Decl(controlFlowAliasing2.ts, 5, 12))
   }
 
   // Same as above, without the parenthesis