fixed an issue with reassigned parameter

Author: Andarist

src/compiler/checker.ts

@@ -28666,7 +28666,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                         const parentType = getTypeForBindingElementParent(parent, CheckMode.Normal);
                         const parentTypeConstraint = parentType && mapType(parentType, getBaseConstraintOrType);
                         links.flags &= ~NodeCheckFlags.InCheckIdentifier;
-                        if (parentTypeConstraint && parentTypeConstraint.flags & TypeFlags.Union && !(parent.kind === SyntaxKind.Parameter && isSymbolAssigned(symbol))) {
+                        if (parentTypeConstraint && parentTypeConstraint.flags & TypeFlags.Union && !(rootDeclaration.kind === SyntaxKind.Parameter && isSymbolAssigned(symbol))) {
                             const pattern = declaration.parent;
                             const narrowedType = getFlowTypeOfReference(pattern, parentTypeConstraint, parentTypeConstraint, /*flowContainer*/ undefined, location.flowNode);
                             if (narrowedType.flags & TypeFlags.Never) {

tests/baselines/reference/dependentDestructuredVariablesFromNestedPatterns.symbols

@@ -111,3 +111,28 @@ async function test3() {
 >p1 : Symbol(p1, Decl(dependentDestructuredVariablesFromNestedPatterns.ts, 29, 10))
 }
 
+function test4([[p1, p1Error]]: [[undefined, Error] | [number, undefined]]) {
+>test4 : Symbol(test4, Decl(dependentDestructuredVariablesFromNestedPatterns.ts, 36, 1))
+>p1 : Symbol(p1, Decl(dependentDestructuredVariablesFromNestedPatterns.ts, 38, 17))
+>p1Error : Symbol(p1Error, Decl(dependentDestructuredVariablesFromNestedPatterns.ts, 38, 20))
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2022.error.d.ts, --, --))
+
+  if (Math.random()) {
+>Math.random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
+>Math : Symbol(Math, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
+
+    p1 = undefined;
+>p1 : Symbol(p1, Decl(dependentDestructuredVariablesFromNestedPatterns.ts, 38, 17))
+>undefined : Symbol(undefined)
+  }
+  if (p1Error) {
+>p1Error : Symbol(p1Error, Decl(dependentDestructuredVariablesFromNestedPatterns.ts, 38, 20))
+
+    return;
+  }
+
+  p1;
+>p1 : Symbol(p1, Decl(dependentDestructuredVariablesFromNestedPatterns.ts, 38, 17))
+}
+

tests/baselines/reference/dependentDestructuredVariablesFromNestedPatterns.types

@@ -122,3 +122,29 @@ async function test3() {
 >p1 : number
 }
 
+function test4([[p1, p1Error]]: [[undefined, Error] | [number, undefined]]) {
+>test4 : ([[p1, p1Error]]: [[undefined, Error] | [number, undefined]]) => void
+>p1 : number | undefined
+>p1Error : Error | undefined
+
+  if (Math.random()) {
+>Math.random() : number
+>Math.random : () => number
+>Math : Math
+>random : () => number
+
+    p1 = undefined;
+>p1 = undefined : undefined
+>p1 : number | undefined
+>undefined : undefined
+  }
+  if (p1Error) {
+>p1Error : Error | undefined
+
+    return;
+  }
+
+  p1;
+>p1 : number | undefined
+}
+

tests/cases/conformance/controlFlow/dependentDestructuredVariablesFromNestedPatterns.ts

@@ -40,3 +40,14 @@ async function test3() {
 
   p1;
 }
+
+function test4([[p1, p1Error]]: [[undefined, Error] | [number, undefined]]) {
+  if (Math.random()) {
+    p1 = undefined;
+  }
+  if (p1Error) {
+    return;
+  }
+
+  p1;
+}