Check for missing type parameter names in JSDoc template tags (#42017)

* Check for missing type parameter names in JSDoc template tags

Fixes #36692

* Update baselines

Author: RyanCavanaugh

src/compiler/parser.ts

@@ -8043,6 +8043,9 @@ namespace ts {
                 function parseTemplateTagTypeParameter() {
                     const typeParameterPos = getNodePos();
                     const name = parseJSDocIdentifierName(Diagnostics.Unexpected_token_A_type_parameter_name_was_expected_without_curly_braces);
+                    if (nodeIsMissing(name)) {
+                        return undefined;
+                    }
                     return finishNode(factory.createTypeParameterDeclaration(name, /*constraint*/ undefined, /*defaultType*/ undefined), typeParameterPos);
                 }
 
@@ -8051,7 +8054,10 @@ namespace ts {
                     const typeParameters = [];
                     do {
                         skipWhitespace();
-                        typeParameters.push(parseTemplateTagTypeParameter());
+                        const node = parseTemplateTagTypeParameter();
+                        if (node !== undefined) {
+                            typeParameters.push(node);
+                        }
                         skipWhitespaceOrAsterisk();
                     } while (parseOptionalJsdoc(SyntaxKind.CommaToken));
                     return createNodeArray(typeParameters, pos);

src/testRunner/unittests/jsDocParsing.ts

@@ -382,5 +382,9 @@ namespace ts {
             const root = createSourceFile("foo.ts", "/** */var a = true;", ScriptTarget.ES5, /*setParentNodes*/ false);
             root.statements[0].getStart(root, /*includeJsdocComment*/ true);
         });
+        describe("missing type parameter in jsDoc doesn't create a 1-element array", () => {
+            const doc = parseIsolatedJSDocComment("/**\n    @template\n*/");
+            assert.equal((doc?.jsDoc.tags?.[0] as JSDocTemplateTag).typeParameters.length, 0);
+        });
     });
 }

tests/baselines/reference/jsdocTemplateTag3.types

@@ -89,7 +89,7 @@ f({ a: 12  }, undefined, undefined, 101, 'nope');
  * @param {T} x
  */
 function g(x) { }
->g : <(Missing) extends any, T>(x: T) => void
+>g : <T>(x: T) => void
 >x : T