feat: add the ability to specify a custom output file extension (#119)

Fixes #91

README.md

@@ -181,6 +181,8 @@ more information.
   extensionless files), but this mapping can be used to override the behavior
   to provide a specific target directory, name, and/or file extension for any
   specific files being converted.
+* `outputFileExtension`: an optional file extension, like `"ts"` or `"jsx"`. If
+  specified, all converted files will have this extension.
 * `jscodeshiftScripts`: an optional array of paths to
   [jscodeshift](https://github.com/facebook/jscodeshift) scripts to run after
   decaffeinate. This is useful to automate any cleanups to convert the output of

src/config/resolveConfig.js

@@ -27,6 +27,7 @@ export default async function resolveConfig(commander) {
     searchDirectory: config.searchDirectory,
     fileFilterFn: config.fileFilterFn,
     customNames: resolveCustomNames(config.customNames),
+    outputFileExtension: config.outputFileExtension || 'js',
     fixImportsConfig: config.fixImportsConfig,
     jscodeshiftScripts: config.jscodeshiftScripts,
     landConfig: config.landConfig,

src/convert.js

@@ -48,15 +48,15 @@ Re-run with the "check" command for more details.`);
     });
 
   await runWithProgressBar(
-    'Renaming files from .coffee to .js...',
+    `Renaming files from .coffee to .${config.outputFileExtension}...`,
     movingCoffeeFiles,
     async function(coffeePath) {
       await move(coffeePath, jsPathFor(coffeePath, config));
     });
 
   let shortDescription = getShortDescription(coffeeFiles);
   let renameCommitMsg =
-    `decaffeinate: Rename ${shortDescription} from .coffee to .js`;
+    `decaffeinate: Rename ${shortDescription} from .coffee to .${config.outputFileExtension}`;
 
   if (movingCoffeeFiles.length > 0) {
     console.log(`Generating the first commit: "${renameCommitMsg}"...`);

src/util/FilePaths.js

@@ -53,7 +53,7 @@ export function jsPathFor(path, config) {
   if (isExtensionless(path)) {
     return path;
   } else {
-    return basePathFor(path) + '.js';
+    return basePathFor(path) + '.' + config.outputFileExtension;
   }
 }
 

test/convert-test.js

@@ -339,6 +339,14 @@ console.log(x);
     });
   });
 
+  it('allows a custom file extension', async function() {
+    await runWithTemplateDir('convert-to-typescript', async function() {
+      await initGitRepo();
+      await runCli('convert');
+      await assertExists('./A.ts');
+    });
+  });
+
   it('handles a missing eslint config', async function() {
     await runWithTemplateDir('simple-success', async function() {
       await initGitRepo();

test/examples/convert-to-typescript/A.coffee

@@ -0,0 +1 @@
+console.log 'This is a file'

test/examples/convert-to-typescript/bulk-decaffeinate.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  outputFileExtension: 'ts',
+};

test/util/FilePaths-test.js

@@ -12,13 +12,17 @@ describe('FilePaths', () => {
   });
 
   it('generates correct js paths', () => {
-    let emptyConfig = {customNames: {}};
+    let emptyConfig = {customNames: {}, outputFileExtension: 'js'};
     assert.equal(FilePaths.jsPathFor('./a/b/foo.coffee', emptyConfig), 'a/b/foo.js');
     assert.equal(FilePaths.jsPathFor('foo.coffee', emptyConfig), 'foo.js');
     assert.equal(FilePaths.jsPathFor('foo.coffee.md', emptyConfig), 'foo.js');
     assert.equal(FilePaths.jsPathFor('foo.cjsx', emptyConfig), 'foo.js');
     assert.equal(FilePaths.jsPathFor('foo', emptyConfig), 'foo');
-    assert.equal(FilePaths.jsPathFor('foo', {customNames: {foo: 'bar'}}), 'bar');
+    assert.equal(
+      FilePaths.jsPathFor('foo', {customNames: {foo: 'bar'}}), 'bar');
+    assert.equal(
+      FilePaths.jsPathFor('foo.coffee', {customNames: {}, outputFileExtension: 'ts'}),
+      'foo.ts');
   });
 
   it('generates correct decaffeinate out paths', () => {