Use r+ with truncation when saving existing files

src/vs/base/node/extfs.ts

@@ -332,15 +332,13 @@ export function mv(source: string, target: string, callback: (error: Error) => v
 //
 // See https://github.com/nodejs/node/blob/v5.10.0/lib/fs.js#L1194
 let canFlush = true;
-export function writeFileAndFlush(path: string, data: string | NodeBuffer, options: { encoding?: string; mode?: number; flag?: string; }, callback: (error: Error) => void): void {
+export function writeFileAndFlush(path: string, data: string | NodeBuffer, options: { mode?: number; flag?: string; }, callback: (error: Error) => void): void {
 	if (!canFlush) {
 		return fs.writeFile(path, data, options, callback);
 	}
 
 	if (!options) {
-		options = { encoding: 'utf8', mode: 0o666, flag: 'w' };
-	} else if (typeof options === 'string') {
-		options = { encoding: <string>options, mode: 0o666, flag: 'w' };
+		options = { mode: 0o666, flag: 'w' };
 	}
 
 	// Open the file with same flags and mode as fs.writeFile()
@@ -350,7 +348,7 @@ export function writeFileAndFlush(path: string, data: string | NodeBuffer, optio
 		}
 
 		// It is valid to pass a fd handle to fs.writeFile() and this will keep the handle open!
-		fs.writeFile(fd, data, options.encoding, (writeError) => {
+		fs.writeFile(fd, data, (writeError) => {
 			if (writeError) {
 				return fs.close(fd, () => callback(writeError)); // still need to close the handle on error!
 			}

src/vs/base/node/pfs.ts

@@ -109,6 +109,10 @@ export function touch(path: string): TPromise<void> {
 	return nfcall(fs.utimes, path, now, now);
 }
 
+export function truncate(path: string, len: number): TPromise<void> {
+	return nfcall(fs.truncate, path, len);
+}
+
 export function readFile(path: string): TPromise<Buffer>;
 export function readFile(path: string, encoding: string): TPromise<string>;
 export function readFile(path: string, encoding?: string): TPromise<Buffer | string> {
@@ -120,12 +124,12 @@ export function readFile(path: string, encoding?: string): TPromise<Buffer | str
 // Therefor we use a Queue on the path that is given to us to sequentialize calls to the same path properly.
 const writeFilePathQueue: { [path: string]: Queue<void> } = Object.create(null);
 
-export function writeFile(path: string, data: string, encoding?: string): TPromise<void>;
-export function writeFile(path: string, data: NodeBuffer, encoding?: string): TPromise<void>;
-export function writeFile(path: string, data: any, encoding: string = 'utf8'): TPromise<void> {
+export function writeFile(path: string, data: string, options?: { mode?: number; flag?: string; }): TPromise<void>;
+export function writeFile(path: string, data: NodeBuffer, options?: { mode?: number; flag?: string; }): TPromise<void>;
+export function writeFile(path: string, data: any, options?: { mode?: number; flag?: string; }): TPromise<void> {
 	let queueKey = toQueueKey(path);
 
-	return ensureWriteFileQueue(queueKey).queue(() => nfcall(extfs.writeFileAndFlush, path, data, encoding));
+	return ensureWriteFileQueue(queueKey).queue(() => nfcall(extfs.writeFileAndFlush, path, data, options));
 }
 
 function toQueueKey(path: string): string {

src/vs/workbench/services/files/node/fileService.ts

@@ -348,30 +348,47 @@ export class FileService implements IFileService {
 
 				// 3.) check to add UTF BOM
 				return addBomPromise.then(addBom => {
-					let writeFilePromise: TPromise<void>;
-
-					// Write fast if we do UTF 8 without BOM
-					if (!addBom && encodingToWrite === encoding.UTF8) {
-						writeFilePromise = pfs.writeFile(absolutePath, value, encoding.UTF8);
-					}
-
-					// Otherwise use encoding lib
-					else {
-						const encoded = encoding.encode(value, encodingToWrite, { addBOM: addBom });
-						writeFilePromise = pfs.writeFile(absolutePath, encoded);
-					}
-
-					// 4.) set contents
-					return writeFilePromise.then(() => {
+					// 4.) set contents and resolve
+					return this.doSetContentsAndResolve(resource, absolutePath, value, addBom, encodingToWrite, { mode: 0o666, flag: 'w' }).then(undefined, error => {
+						// Can't use 'w' for hidden files on Windows (see https://github.com/Microsoft/vscode/issues/931)
+						if (!exists || error.code !== 'EPERM' || !isWindows) {
+							return TPromise.wrapError(error);
+						}
 
-						// 5.) resolve
-						return this.resolve(resource);
+						// 'r+' always works for existing files, but we need to truncate manually
+						// 5.) truncate
+						return pfs.truncate(absolutePath, 0).then(() => {
+							// 6.) set contents and resolve again
+							return this.doSetContentsAndResolve(resource, absolutePath, value, addBom, encodingToWrite, { mode: 0o666, flag: 'r+' });
+						});
 					});
 				});
 			});
 		});
 	}
 
+	private doSetContentsAndResolve(resource: uri, absolutePath: string, value: string, addBOM: boolean, encodingToWrite: string, options: { mode?: number; flag?: string; }): TPromise<IFileStat> {
+		let writeFilePromise: TPromise<void>;
+
+		// Write fast if we do UTF 8 without BOM
+		if (!addBOM && encodingToWrite === encoding.UTF8) {
+			writeFilePromise = pfs.writeFile(absolutePath, value, options);
+		}
+
+		// Otherwise use encoding lib
+		else {
+			const encoded = encoding.encode(value, encodingToWrite, { addBOM });
+			writeFilePromise = pfs.writeFile(absolutePath, encoded, options);
+		}
+
+		// set contents
+		return writeFilePromise.then(() => {
+
+			// resolve
+			return this.resolve(resource);
+		});
+	}
+
 	public createFile(resource: uri, content: string = ''): TPromise<IFileStat> {
 
 		// Create file