Resolution is valid unless it is invalidated

src/compiler/moduleNameResolver.ts

@@ -1127,21 +1127,4 @@ namespace ts {
     function toSearchResult<T>(value: T | undefined): SearchResult<T> {
         return value !== undefined ? { value } : undefined;
     }
-
-    /** Calls `callback` on `directory` and every ancestor directory it has, returning the first defined result. */
-    function forEachAncestorDirectory<T>(directory: string, callback: (directory: string) => SearchResult<T>): SearchResult<T> {
-        while (true) {
-            const result = callback(directory);
-            if (result !== undefined) {
-                return result;
-            }
-
-            const parentPath = getDirectoryPath(directory);
-            if (parentPath === directory) {
-                return undefined;
-            }
-
-            directory = parentPath;
-        }
-    }
 }

src/compiler/resolutionCache.ts

@@ -184,9 +184,9 @@ namespace ts {
 
             const seenNamesInFile = createMap<true>();
             for (const name of names) {
-                // check if this is a duplicate entry in the list
                 let resolution = resolutionsInFile.get(name);
-                if (!moduleResolutionIsValid(resolution, name)) {
+                // Resolution is valid if it is present and not invalidated
+                if (!resolution || resolution.isInvalidated) {
                     const existingResolution = resolution;
                     const resolutionInDirectory = perDirectoryResolution.get(name);
                     if (resolutionInDirectory) {
@@ -221,25 +221,6 @@ namespace ts {
 
             return resolvedModules;
 
-            function moduleResolutionIsValid(resolution: T, name: string): boolean {
-                // This is already calculated resolution in this round of synchronization
-                if (seenNamesInFile.has(name)) {
-                    return true;
-                }
-
-                if (!resolution || resolution.isInvalidated) {
-                    return false;
-                }
-
-                const result = getResult(resolution);
-                if (result) {
-                    return true;
-                }
-                // consider situation if we have no candidate locations as valid resolution.
-                // after all there is no point to invalidate it if we have no idea where to look for the module.
-                return resolution.failedLookupLocations.length === 0;
-            }
-
             function resolutionIsEqualTo(oldResolution: T, newResolution: T): boolean {
                 if (oldResolution === newResolution) {
                     return true;

src/compiler/utilities.ts

@@ -3609,6 +3609,23 @@ namespace ts {
     export function closeFileWatcherOf<T extends { watcher: FileWatcher; }>(objWithWatcher: T) {
         objWithWatcher.watcher.close();
     }
+
+    /** Calls `callback` on `directory` and every ancestor directory it has, returning the first defined result. */
+    export function forEachAncestorDirectory<T>(directory: string, callback: (directory: string) => T): T {
+        while (true) {
+            const result = callback(directory);
+            if (result !== undefined) {
+                return result;
+            }
+
+            const parentPath = getDirectoryPath(directory);
+            if (parentPath === directory) {
+                return undefined;
+            }
+
+            directory = parentPath;
+        }
+    }
 }
 
 namespace ts {