Do not narrow using JSDoc type assertion nodes (microsoft#56048)

Author: Andarist

src/compiler/binder.ts

@@ -173,6 +173,7 @@ import {
     isJSDocEnumTag,
     isJSDocTemplateTag,
     isJSDocTypeAlias,
+    isJSDocTypeAssertion,
     isJsonSourceFile,
     isJsxNamespacedName,
     isLeftHandSideExpression,
@@ -1223,6 +1224,10 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
             case SyntaxKind.CallExpression:
                 return hasNarrowableArgument(expr as CallExpression);
             case SyntaxKind.ParenthesizedExpression:
+                if (isJSDocTypeAssertion(expr)) {
+                    return false;
+                }
+                // fallthrough
             case SyntaxKind.NonNullExpression:
                 return isNarrowingExpression((expr as ParenthesizedExpression | NonNullExpression).expression);
             case SyntaxKind.BinaryExpression:

tests/baselines/reference/parenthesizedJSDocCastDoesNotNarrow.errors.txt

@@ -0,0 +1,22 @@
+index.js(12,8): error TS2678: Type '"invalid"' is not comparable to type '"foo" | "bar"'.
+
+
+==== index.js (1 errors) ====
+    let value = "";
+    
+    switch (/** @type {"foo" | "bar"} */ (value)) {
+      case "bar":
+        value;
+        break;
+    
+      case "foo":
+        value;
+        break;
+    
+      case "invalid":
+           ~~~~~~~~~
+!!! error TS2678: Type '"invalid"' is not comparable to type '"foo" | "bar"'.
+        value;
+        break;
+    }
+    

tests/baselines/reference/parenthesizedJSDocCastDoesNotNarrow.symbols

@@ -0,0 +1,28 @@
+//// [tests/cases/compiler/parenthesizedJSDocCastDoesNotNarrow.ts] ////
+
+=== index.js ===
+let value = "";
+>value : Symbol(value, Decl(index.js, 0, 3))
+
+switch (/** @type {"foo" | "bar"} */ (value)) {
+>value : Symbol(value, Decl(index.js, 0, 3))
+
+  case "bar":
+    value;
+>value : Symbol(value, Decl(index.js, 0, 3))
+
+    break;
+
+  case "foo":
+    value;
+>value : Symbol(value, Decl(index.js, 0, 3))
+
+    break;
+
+  case "invalid":
+    value;
+>value : Symbol(value, Decl(index.js, 0, 3))
+
+    break;
+}
+

tests/baselines/reference/parenthesizedJSDocCastDoesNotNarrow.types

@@ -0,0 +1,36 @@
+//// [tests/cases/compiler/parenthesizedJSDocCastDoesNotNarrow.ts] ////
+
+=== index.js ===
+let value = "";
+>value : string
+>"" : ""
+
+switch (/** @type {"foo" | "bar"} */ (value)) {
+>(value) : "foo" | "bar"
+>value : string
+
+  case "bar":
+>"bar" : "bar"
+
+    value;
+>value : string
+
+    break;
+
+  case "foo":
+>"foo" : "foo"
+
+    value;
+>value : string
+
+    break;
+
+  case "invalid":
+>"invalid" : "invalid"
+
+    value;
+>value : string
+
+    break;
+}
+

tests/cases/compiler/parenthesizedJSDocCastDoesNotNarrow.ts

@@ -0,0 +1,22 @@
+// @strict: true
+// @noEmit: true
+// @checkJs: true
+// @allowJs: true
+
+// @filename: index.js
+
+let value = "";
+
+switch (/** @type {"foo" | "bar"} */ (value)) {
+  case "bar":
+    value;
+    break;
+
+  case "foo":
+    value;
+    break;
+
+  case "invalid":
+    value;
+    break;
+}