feat: generate tslint.json

`init` now generates a tslint.json file which inherits from the default
configuration. This empowers the users to customize if necessary
instead of being overly opinionated.

Fixes: #127
Fixes: #119

src/init.ts

@@ -142,40 +142,48 @@ async function writePackageJson(
   options.logger.dir(preview);
 }
 
+async function generateTsLintConfig(options: Options): Promise<void> {
+  const config = formatJson({extends: 'gts/tslint.json'});
+  return generateConfigFile(options, './tslint.json', config);
+}
+
 async function generateTsConfig(options: Options): Promise<void> {
+  const config = formatJson({
+    extends: './node_modules/gts/tsconfig-google.json',
+    compilerOptions: {rootDir: '.', outDir: 'build'},
+    include: ['src/*.ts', 'src/**/*.ts', 'test/*.ts', 'test/**/*.ts']
+  });
+  return generateConfigFile(options, './tsconfig.json', config);
+}
+
+async function generateConfigFile(
+    options: Options, filename: string, contents: string) {
   let existing;
   try {
-    existing = await read('./tsconfig.json', 'utf8');
+    existing = await read(filename, 'utf8');
   } catch (err) {
     if (err.code === 'ENOENT') {
       /* not found, create it. */
     } else {
-      throw new Error(`Unknown error reading tsconfig.json: ${err.message}`);
+      throw new Error(`Unknown error reading ${filename}: ${err.message}`);
     }
   }
 
-  const tsconfig = formatJson({
-    extends: './node_modules/gts/tsconfig-google.json',
-    compilerOptions: {rootDir: '.', outDir: 'build'},
-    include: ['src/*.ts', 'src/**/*.ts', 'test/*.ts', 'test/**/*.ts']
-  });
-
-  let writeTsConfig = true;
-  if (existing && existing === tsconfig) {
-    options.logger.log('No edits needed in tsconfig.json.');
+  let writeFile = true;
+  if (existing && existing === contents) {
+    options.logger.log(`No edits needed in ${filename}`);
     return;
   } else if (existing) {
-    writeTsConfig = await query(
-        `${chalk.bold('tsconfig.json')} already exists`, 'Overwrite', false,
-        options);
+    writeFile = await query(
+        `${chalk.bold(filename)} already exists`, 'Overwrite', false, options);
   }
 
-  if (writeTsConfig) {
-    options.logger.log('Writing tsconfig.json...');
+  if (writeFile) {
+    options.logger.log(`Writing ${filename}...`);
     if (!options.dryRun) {
-      await write('./tsconfig.json', tsconfig);
+      await write(filename, contents);
     }
-    options.logger.dir(JSON.parse(tsconfig));
+    options.logger.dir(JSON.parse(contents));
   }
 }
 
@@ -213,6 +221,7 @@ export async function init(options: Options): Promise<boolean> {
     options.logger.log('No edits needed in package.json.');
   }
   await generateTsConfig(options);
+  await generateTsLintConfig(options);
 
   // Run `npm install` after initial setup so `npm run check` works right away.
   if (!options.dryRun) {

test/test-kitchen.ts

@@ -85,8 +85,13 @@ test.serial('init', async t => {
         `npx -p ${stagingPath}/gts.tgz --ignore-existing gts init -n`,
         execOpts);
   }
+
+  // Ensure tsconfig.json got generated.
   fs.accessSync(`${stagingPath}/kitchen/tsconfig.json`);
 
+  // Ensure tslint.json got generated.
+  fs.accessSync(`${stagingPath}/kitchen/tslint.json`);
+
   // Compilation shouldn't have happened. Hence no `build` directory.
   const dirContents = fs.readdirSync(`${stagingPath}/kitchen`);
   t.is(dirContents.indexOf('build'), -1);
@@ -130,6 +135,8 @@ test.serial('generated json files should terminate with newline', async t => {
                .endsWith('\n'));
   t.truthy(fs.readFileSync(`${stagingPath}/kitchen/tsconfig.json`, 'utf8')
                .endsWith('\n'));
+  t.truthy(fs.readFileSync(`${stagingPath}/kitchen/tslint.json`, 'utf8')
+               .endsWith('\n'));
 });
 
 test.serial('check before fix', async t => {