Enable reading file/directory list from stdin

This adds the `--stdin` flag, which makes jscodeshift read the list of
files and directories to process from standard input instead of command
line arguments.

Given that jscodeshift is getting input from multiple sources (file
list, transformer code, source code), there are obviously multiple
options for what should be accepted on the standard input.

My more longer term idea is to be able to accept any of these on stdin.
The first step is the file/directory list. I decided to add the
`--stdin` flag instead of reading from stdin by default, to require the
user to be explicit about their intention.

In the future I could imagine the other inputs being provided on stdin
by using `-` as argument value. This is in-line with other commands,
like `cat`. E.g. reading the transform from stdin could be done via
`--transform -`. Similarly getting the source code from stdin could be
done by passing `-` as a single positional argument.

bin/__tests__/jscodeshift-test.js

@@ -26,6 +26,10 @@ var testUtils = require('../../utils/testUtils');
 var createTransformWith = testUtils.createTransformWith;
 var createTempFileWith = testUtils.createTempFileWith;
 
+function readFile(path) {
+  return fs.readFileSync(path).toString();
+}
+
 function run(args, stdin, cwd) {
   return new Promise(resolve => {
     var jscodeshift = child_process.spawn(
@@ -64,19 +68,37 @@ describe('jscodeshift CLI', () => {
       run(['-t', transformA, sourceA, sourceB]).then(
         out => {
           expect(out[1]).toBe('');
-          expect(fs.readFileSync(sourceA).toString()).toBe('transforma');
-          expect(fs.readFileSync(sourceB).toString()).toBe('transformb\n');
+          expect(readFile(sourceA)).toBe('transforma');
+          expect(readFile(sourceB)).toBe('transformb\n');
         }
       ),
       run(['-t', transformB, sourceC]).then(
         out => {
           expect(out[1]).toBe('');
-          expect(fs.readFileSync(sourceC).toString()).toBe(sourceC);
+          expect(readFile(sourceC)).toBe(sourceC);
         }
       )
     ]);
   });
 
+  it('takes file list from stdin if --stdin is set', () => {
+    var sourceA = createTempFileWith('a');
+    var sourceB = createTempFileWith('b\n');
+    var sourceC = createTempFileWith('c');
+    var transformA = createTransformWith(
+      'return "transform" + fileInfo.source;'
+    );
+
+    return run(['--stdin', '-t', transformA], [sourceA, sourceB, sourceC].join('\n')).then(
+      out => {
+        expect(out[1]).toBe('');
+        expect(readFile(sourceA)).toBe('transforma');
+        expect(readFile(sourceB)).toBe('transformb\n');
+        expect(readFile(sourceC)).toBe('transformc');
+      }
+    );
+  });
+
   it('does not transform files in a dry run', () => {
     var source = createTempFileWith('a');
     var transform = createTransformWith(
@@ -300,4 +322,5 @@ describe('jscodeshift CLI', () => {
       );
     });
   })
+
 });

bin/jscodeshift.js

@@ -101,12 +101,17 @@ const parser = require('../src/argsParser')
         ].join('\n');
       },
     },
+    stdin: {
+      help: 'read file/directory list from stdin',
+      flag: true,
+      default: false,
+    },
   });
 
 let options, positionalArguments;
 try {
   ({options, positionalArguments} = parser.parse());
-  if (positionalArguments.length === 0) {
+  if (positionalArguments.length === 0 && !options.stdin) {
     process.stderr.write(
       'Error: You have to provide at least one file/directory to transform.' +
       '\n\n---\n\n' +
@@ -120,8 +125,18 @@ try {
   process.exit(exitCode);
 }
 
-Runner.run(
-  /^https?/.test(options.transform) ? options.transform : path.resolve(options.transform),
-  positionalArguments,
-  options
-);
+function run(paths, options) {
+	Runner.run(
+		/^https?/.test(options.transform) ? options.transform : path.resolve(options.transform),
+		paths,
+		options
+	);
+}
+
+if (options.stdin) {
+  let buffer = '';
+  process.stdin.on('data', data => buffer += data);
+  process.stdin.on('end', () => run(buffer.split('\n'), options));
+} else {
+  run(positionalArguments, options);
+}

src/argsParser.js

@@ -56,8 +56,10 @@ function getHelpText(options) {
 Usage: jscodeshift [OPTION]... PATH...
   or:  jscodeshift [OPTION]... -t TRANSFORM_PATH PATH...
   or:  jscodeshift [OPTION]... -t URL PATH...
+  or:  jscodeshift [OPTION]... --stdin < file_list.txt
 
 Apply transform logic in TRANSFORM_PATH (recursively) to every PATH.
+If --stdin is set, each line of the standard input is used as a path.
 
 Options:
 "..." behind an option means that it can be supplied multiple times.