Add typedef declaration space, unify typedef name gathering (#18172)

* Add typedef declaration space, unify typedef name gathering, strengthen errorUnusedLocal

* Bonus round: make jsdoc presence way mroe typesafe

* Be exhaustive in nameForNamelessJSDocTypedef

* Remove nonrequired casts

* Replace more casts with guards

* Cannot be internal

* Debug.fail returns never, assert never no longer needs unreachable throw to satisfy checker

* Rename type

* Add replacement message as in 18287

src/services/classifier.ts

@@ -699,7 +699,8 @@ namespace ts {
                 // specially.
                 const docCommentAndDiagnostics = parseIsolatedJSDocComment(sourceFile.text, start, width);
                 if (docCommentAndDiagnostics && docCommentAndDiagnostics.jsDoc) {
-                    docCommentAndDiagnostics.jsDoc.parent = token;
+                    // TODO: This should be predicated on `token["kind"]` being compatible with `HasJSDoc["kind"]`
+                    docCommentAndDiagnostics.jsDoc.parent = token as HasJSDoc;
                     classifyJSDocComment(docCommentAndDiagnostics.jsDoc);
                     return;
                 }

src/services/completions.ts

@@ -1739,7 +1739,7 @@ namespace ts.Completions {
 
     /** Get the corresponding JSDocTag node if the position is in a jsDoc comment */
     function getJsDocTagAtPosition(node: Node, position: number): JSDocTag | undefined {
-        const { jsDoc } = getJsDocHavingNode(node);
+        const { jsDoc } = getJsDocHavingNode(node) as JSDocContainer;
         if (!jsDoc) return undefined;
 
         for (const { pos, end, tags } of jsDoc) {

src/services/navigationBar.ts

@@ -263,13 +263,15 @@ namespace ts.NavigationBar {
                 break;
 
             default:
-                forEach(node.jsDoc, jsDoc => {
-                    forEach(jsDoc.tags, tag => {
-                        if (tag.kind === SyntaxKind.JSDocTypedefTag) {
-                            addLeafNode(tag);
-                        }
+                if (hasJSDocNodes(node)) {
+                    forEach(node.jsDoc, jsDoc => {
+                        forEach(jsDoc.tags, tag => {
+                            if (tag.kind === SyntaxKind.JSDocTypedefTag) {
+                                addLeafNode(tag);
+                            }
+                        });
                     });
-                });
+                }
 
                 forEachChild(node, addChildrenRecursively);
         }

src/services/services.ts

@@ -2111,7 +2111,7 @@ namespace ts {
             }
 
             forEachChild(node, walk);
-            if (node.jsDoc) {
+            if (hasJSDocNodes(node)) {
                 for (const jsDoc of node.jsDoc) {
                     forEachChild(jsDoc, walk);
                 }