Dedupe inherited jsdoc comments

JSDoc on own properties was already deduped, but inherited jsdoc was
incorrectly not deduped.

Fixes #32708

Author: sandersn

src/services/jsDoc.ts

@@ -158,25 +158,6 @@ namespace ts.JsDoc {
         }
     }
 
-    /**
-     * Iterates through 'array' by index and performs the callback on each element of array until the callback
-     * returns a truthy value, then returns that value.
-     * If no such value is found, the callback is applied to each element of array and undefined is returned.
-     */
-    function forEachUnique<T, U>(array: readonly T[] | undefined, callback: (element: T, index: number) => U): U | undefined {
-        if (array) {
-            for (let i = 0; i < array.length; i++) {
-                if (array.indexOf(array[i]) === i) {
-                    const result = callback(array[i], i);
-                    if (result) {
-                        return result;
-                    }
-                }
-            }
-        }
-        return undefined;
-    }
-
     export function getJSDocTagNameCompletions(): CompletionEntry[] {
         return jsDocTagNameCompletionEntries || (jsDocTagNameCompletionEntries = map(jsDocTagNames, tagName => {
             return {

src/services/services.ts

@@ -527,11 +527,11 @@ namespace ts {
 
         let doc = JsDoc.getJsDocCommentsFromDeclarations(declarations);
         if (doc.length === 0 || declarations.some(hasJSDocInheritDocTag)) {
-            for (const declaration of declarations) {
+            forEachUnique(declarations, declaration => {
                 const inheritedDocs = findInheritedJSDocComments(declaration, declaration.symbol.name, checker!); // TODO: GH#18217
                 // TODO: GH#16312 Return a ReadonlyArray, avoid copying inheritedDocs
                 if (inheritedDocs) doc = doc.length === 0 ? inheritedDocs.slice() : inheritedDocs.concat(lineBreakPart(), doc);
-            }
+            });
         }
         return doc;
     }

src/services/utilities.ts

@@ -1458,6 +1458,25 @@ namespace ts {
     export function documentSpansEqual(a: DocumentSpan, b: DocumentSpan): boolean {
         return a.fileName === b.fileName && textSpansEqual(a.textSpan, b.textSpan);
     }
+
+    /**
+     * Iterates through 'array' by index and performs the callback on each element of array until the callback
+     * returns a truthy value, then returns that value.
+     * If no such value is found, the callback is applied to each element of array and undefined is returned.
+     */
+    export function forEachUnique<T, U>(array: readonly T[] | undefined, callback: (element: T, index: number) => U): U | undefined {
+        if (array) {
+            for (let i = 0; i < array.length; i++) {
+                if (array.indexOf(array[i]) === i) {
+                    const result = callback(array[i], i);
+                    if (result) {
+                        return result;
+                    }
+                }
+            }
+        }
+        return undefined;
+    }
 }
 
 // Display-part writer helpers

tests/cases/fourslash/quickInfoInheritedJSDoc.ts

@@ -0,0 +1,14 @@
+/// <reference path='fourslash.ts'/>
+// #32708
+
+////interface I<T> {
+////    /** only once please */
+////    t: T
+////}
+////interface C<T> extends I<T> {
+////    t: T
+////}
+////declare var cnsb: C<number> & C<string> & C<boolean>;
+////cnsb.t/**/
+
+verify.quickInfoAt("", "(property) C<T>.t: never", "only once please");