Add some logging to the sys.watchFile and sys.watchDirectory

Author: sheetalkamat

src/compiler/sys.ts

@@ -379,6 +379,9 @@ namespace ts {
     /*@internal*/
     export const ignoredPaths = ["/node_modules/.", "/.git", "/.#"];
 
+    /*@internal*/
+    export let sysLog: (s: string) => void = noop;
+
     /*@internal*/
     export interface RecursiveDirectoryWatcherHost {
         watchDirectory: HostWatchDirectory;
@@ -1053,6 +1056,7 @@ namespace ts {
                  * @param createWatcher
                  */
                 function invokeCallbackAndUpdateWatcher(createWatcher: () => FileWatcher) {
+                    sysLog(`sysLog:: ${fileOrDirectory}:: Changing watcher to ${createWatcher === watchPresentFileSystemEntry ? "Present" : "Missing"}FileSystemEntryWatcher`);
                     // Call the callback for current directory
                     callback("rename", "");
 
@@ -1115,6 +1119,7 @@ namespace ts {
                  * Eg. on linux the number of watches are limited and one could easily exhaust watches and the exception ENOSPC is thrown when creating watcher at that point
                  */
                 function watchPresentFileSystemEntryWithFsWatchFile(): FileWatcher {
+                    sysLog(`sysLog:: ${fileOrDirectory}:: Changing to fsWatchFile`);
                     return fallbackPollingWatchFile(fileOrDirectory, createFileWatcherCallback(callback), pollingInterval);
                 }
 

src/compiler/watchUtilities.ts

@@ -370,6 +370,9 @@ namespace ts {
         const createFileWatcher: CreateFileWatcher<WatchFileHost, PollingInterval, FileWatcherEventKind, never, X, Y> = getCreateFileWatcher(watchLogLevel, watchFile);
         const createFilePathWatcher: CreateFileWatcher<WatchFileHost, PollingInterval, FileWatcherEventKind, Path, X, Y> = watchLogLevel === WatchLogLevel.None ? watchFilePath : createFileWatcher;
         const createDirectoryWatcher: CreateFileWatcher<WatchDirectoryHost, WatchDirectoryFlags, undefined, never, X, Y> = getCreateFileWatcher(watchLogLevel, watchDirectory);
+        if (watchLogLevel === WatchLogLevel.Verbose && sysLog === noop) {
+            sysLog = s => log(s);
+        }
         return {
             watchFile: (host, file, callback, pollingInterval, detailInfo1, detailInfo2) =>
                 createFileWatcher(host, file, callback, pollingInterval, /*passThrough*/ undefined, detailInfo1, detailInfo2, watchFile, log, "FileWatcher", getDetailWatchInfo),