Fixed an issue with destructured bindings from a generic union constraint not being narrowed correctly (#50221)

Author: Andarist

src/compiler/checker.ts

@@ -25924,10 +25924,11 @@ namespace ts {
                         if (!(links.flags & NodeCheckFlags.InCheckIdentifier)) {
                             links.flags |= NodeCheckFlags.InCheckIdentifier;
                             const parentType = getTypeForBindingElementParent(parent, CheckMode.Normal);
+                            const parentTypeConstraint = parentType && mapType(parentType, getBaseConstraintOrType);
                             links.flags &= ~NodeCheckFlags.InCheckIdentifier;
-                            if (parentType && parentType.flags & TypeFlags.Union && !(parent.kind === SyntaxKind.Parameter && isSymbolAssigned(symbol))) {
+                            if (parentTypeConstraint && parentTypeConstraint.flags & TypeFlags.Union && !(parent.kind === SyntaxKind.Parameter && isSymbolAssigned(symbol))) {
                                 const pattern = declaration.parent;
-                                const narrowedType = getFlowTypeOfReference(pattern, parentType, parentType, /*flowContainer*/ undefined, location.flowNode);
+                                const narrowedType = getFlowTypeOfReference(pattern, parentTypeConstraint, parentTypeConstraint, /*flowContainer*/ undefined, location.flowNode);
                                 if (narrowedType.flags & TypeFlags.Never) {
                                     return neverType;
                                 }

tests/baselines/reference/dependentDestructuredVariables.errors.txt

@@ -1,5 +1,5 @@
-tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts(314,5): error TS7022: 'value1' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
-tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts(314,5): error TS7031: Binding element 'value1' implicitly has an 'any' type.
+tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts(334,5): error TS7022: 'value1' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
+tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts(334,5): error TS7031: Binding element 'value1' implicitly has an 'any' type.
 
 
 ==== tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts (2 errors) ====
@@ -39,6 +39,26 @@ tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts(314,5): er
         }
     }
 
+    // repro #50206
+    function f13<T extends Action>({ kind, payload }: T) {
+        if (kind === 'A') {
+            payload.toFixed();
+        }
+        if (kind === 'B') {
+            payload.toUpperCase();
+        }
+    }
+    
+    function f14<T extends Action>(t: T) {
+        const { kind, payload } = t;
+        if (kind === 'A') {
+            payload.toFixed();
+        }
+        if (kind === 'B') {
+            payload.toUpperCase();
+        }
+    }
+    
     type Action2 =
         | { kind: 'A', payload: number | undefined }
         | { kind: 'B', payload: string | undefined };

tests/baselines/reference/dependentDestructuredVariables.js

@@ -35,6 +35,26 @@ function f12({ kind, payload }: Action) {
     }
 }
 
+// repro #50206
+function f13<T extends Action>({ kind, payload }: T) {
+    if (kind === 'A') {
+        payload.toFixed();
+    }
+    if (kind === 'B') {
+        payload.toUpperCase();
+    }
+}
+
+function f14<T extends Action>(t: T) {
+    const { kind, payload } = t;
+    if (kind === 'A') {
+        payload.toFixed();
+    }
+    if (kind === 'B') {
+        payload.toUpperCase();
+    }
+}
+
 type Action2 =
     | { kind: 'A', payload: number | undefined }
     | { kind: 'B', payload: string | undefined };
@@ -420,6 +440,24 @@ function f12({ kind, payload }) {
             payload; // never
     }
 }
+// repro #50206
+function f13({ kind, payload }) {
+    if (kind === 'A') {
+        payload.toFixed();
+    }
+    if (kind === 'B') {
+        payload.toUpperCase();
+    }
+}
+function f14(t) {
+    const { kind, payload } = t;
+    if (kind === 'A') {
+        payload.toFixed();
+    }
+    if (kind === 'B') {
+        payload.toUpperCase();
+    }
+}
 function f20({ kind, payload }) {
     if (payload) {
         if (kind === 'A') {
@@ -662,6 +700,8 @@ type Action = {
 declare function f10({ kind, payload }: Action): void;
 declare function f11(action: Action): void;
 declare function f12({ kind, payload }: Action): void;
+declare function f13<T extends Action>({ kind, payload }: T): void;
+declare function f14<T extends Action>(t: T): void;
 type Action2 = {
     kind: 'A';
     payload: number | undefined;