Infer typedef variable declaration to never

src/compiler/checker.ts

@@ -7084,6 +7084,14 @@ namespace ts {
                 return addOptionality(declaredType, isOptional);
             }
 
+            const jsDocTypeDefTag = getJSDocTypedefTag(declaration);
+            // The typedef is attached to a variable declaration, instead of specifying the name in the typedef itself
+            // This means that the variable declared references the typedef and should not be used in regular control
+            // flow of the program, only in jsdoc type references.
+            if (jsDocTypeDefTag && !jsDocTypeDefTag.name && isVariableDeclaration(declaration)) {
+                return neverType;
+            }
+
             if ((noImplicitAny || isInJSFile(declaration)) &&
                 declaration.kind === SyntaxKind.VariableDeclaration && !isBindingPattern(declaration.name) &&
                 !(getCombinedModifierFlags(declaration) & ModifierFlags.Export) && !(declaration.flags & NodeFlags.Ambient)) {

src/compiler/utilitiesPublic.ts

@@ -716,6 +716,11 @@ namespace ts {
         return getFirstJSDocTag(node, isJSDocTemplateTag);
     }
 
+    /** Gets the JSDoc typedef tag for the node if present */
+    export function getJSDocTypedefTag(node: Node): JSDocTypedefTag | undefined {
+        return getFirstJSDocTag(node, isJSDocTypedefTag);
+    }
+
     /** Gets the JSDoc type tag for the node if present and valid */
     export function getJSDocTypeTag(node: Node): JSDocTypeTag | undefined {
         // We should have already issued an error if there were multiple type jsdocs, so just use the first one.

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -3524,6 +3524,8 @@ declare namespace ts {
     function getJSDocReturnTag(node: Node): JSDocReturnTag | undefined;
     /** Gets the JSDoc template tag for the node if present */
     function getJSDocTemplateTag(node: Node): JSDocTemplateTag | undefined;
+    /** Gets the JSDoc typedef tag for the node if present */
+    function getJSDocTypedefTag(node: Node): JSDocTypedefTag | undefined;
     /** Gets the JSDoc type tag for the node if present and valid */
     function getJSDocTypeTag(node: Node): JSDocTypeTag | undefined;
     /**

tests/baselines/reference/api/typescript.d.ts

@@ -3524,6 +3524,8 @@ declare namespace ts {
     function getJSDocReturnTag(node: Node): JSDocReturnTag | undefined;
     /** Gets the JSDoc template tag for the node if present */
     function getJSDocTemplateTag(node: Node): JSDocTemplateTag | undefined;
+    /** Gets the JSDoc typedef tag for the node if present */
+    function getJSDocTypedefTag(node: Node): JSDocTypedefTag | undefined;
     /** Gets the JSDoc type tag for the node if present and valid */
     function getJSDocTypeTag(node: Node): JSDocTypeTag | undefined;
     /**

tests/baselines/reference/jsdocTypeDefNoImplicitAny.symbols

@@ -0,0 +1,9 @@
+=== tests/cases/conformance/jsdoc/index.js ===
+/** @typedef {{foo: number}} */
+export let a;
+>a : Symbol(a, Decl(index.js, 1, 10), Decl(index.js, 0, 4))
+
+/** @typedef {number} */
+let b;
+>b : Symbol(b, Decl(index.js, 3, 3), Decl(index.js, 2, 4))
+

tests/baselines/reference/jsdocTypeDefNoImplicitAny.types

@@ -0,0 +1,9 @@
+=== tests/cases/conformance/jsdoc/index.js ===
+/** @typedef {{foo: number}} */
+export let a;
+>a : never
+
+/** @typedef {number} */
+let b;
+>b : never
+

tests/baselines/reference/jsdocTypedefNoCrash.types

@@ -4,6 +4,6 @@
  * }}
  */
 export const foo = 5;
->foo : 5
+>foo : never
 >5 : 5
 

tests/baselines/reference/jsdocTypedefNoCrash2.types

@@ -7,6 +7,6 @@ export type foo = 5;
  * }}
  */
 export const foo = 5;
->foo : 5
+>foo : never
 >5 : 5
 

tests/cases/conformance/jsdoc/jsdocTypeDefNoImplicitAny.ts

@@ -0,0 +1,9 @@
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+// @noImplicitAny: true
+// @Filename: index.js
+/** @typedef {{foo: number}} */
+export let a;
+/** @typedef {number} */
+let b;

tests/cases/fourslash/jsdocTypedefTagSemanticMeaning1.ts

@@ -9,4 +9,4 @@
 /////** @type {[|T|]} */
 ////const n = [|T|];
 
-verify.singleReferenceGroup("type T = number\nconst T: 1", "T");
+verify.singleReferenceGroup("type T = number\nconst T: never", "T");