Find tagless JSDoc as preceding token (#39912)

Author: andrewbranch

src/services/utilities.ts

@@ -1217,6 +1217,10 @@ namespace ts {
         }
 
         const children = n.getChildren(sourceFile);
+        if (children.length === 0) {
+            return n;
+        }
+
         const candidate = findRightmostChildNodeWithTokens(children, /*exclusiveStartPosition*/ children.length, sourceFile);
         return candidate && findRightmostToken(candidate, sourceFile);
     }

tests/cases/fourslash/completionsAfterJSDoc.ts

@@ -0,0 +1,17 @@
+/// <reference path="fourslash.ts" />
+
+////export interface Foo {
+////  /** JSDoc */
+////  /**/foo(): void;
+////}
+
+// Should not crash, #35632
+verify.completions({
+  marker: "",
+  isNewIdentifierLocation: true,
+  exact: [{
+    name: "readonly",
+    kind: "keyword",
+    sortText: completion.SortText.GlobalsOrKeywords
+  }]
+});