feat: add --check CLI option

README.md

@@ -101,6 +101,10 @@ Outputs the name of each file right before it is proccessed. This can be useful
 
 Prevent `git commit` if any files are fixed.
 
+### `--check`
+
+Check that files are correctly formatted, but don't format them. This is useful on CI to verify that all changed files in the current branch were correctly formatted.
+
 <!-- Undocumented = Unsupported :D
 
 ### `--config`

bin/pretty-quick.js

@@ -36,6 +36,12 @@ const prettyQuickResult = prettyQuick(
       console.log(`✍️  Fixing up ${chalk.bold(file)}.`);
     },
 
+    onCheckFile: (file, isFormatted) => {
+      if (!isFormatted) {
+        console.log(`⛔️  Check failed: ${chalk.bold(file)}`);
+      }
+    },
+
     onExamineFile: file => {
       console.log(`🔍  Examining ${chalk.bold(file)}.`);
     },
@@ -56,5 +62,10 @@ if (prettyQuickResult.success) {
       '✗ File had to be prettified and prettyQuick was set to bail mode.'
     );
   }
+  if (prettyQuickResult.errors.indexOf('CHECK_FAILED') !== -1) {
+    console.log(
+      '✗ Code style issues found in the above file(s). Forgot to run Prettier?'
+    );
+  }
   process.exit(1); // ensure git hooks abort
 }

src/index.js

@@ -1,5 +1,5 @@
 import scms from './scms';
-import formatFiles from './formatFiles';
+import processFiles from './processFiles';
 import createIgnorer from './createIgnorer';
 import createMatcher from './createMatcher';
 import isSupportedExtension from './isSupportedExtension';
@@ -14,12 +14,14 @@ export default (
     restage = true,
     branch,
     bail,
+    check,
     verbose,
     onFoundSinceRevision,
     onFoundChangedFiles,
     onPartiallyStagedFile,
-    onWriteFile,
     onExamineFile,
+    onCheckFile,
+    onWriteFile,
   } = {}
 ) => {
   const scm = scms(currentDirectory);
@@ -60,7 +62,8 @@ export default (
 
   const failReasons = new Set();
 
-  formatFiles(directory, changedFiles, {
+  processFiles(directory, changedFiles, {
+    check,
     config,
     onWriteFile: file => {
       onWriteFile && onWriteFile(file);
@@ -76,6 +79,12 @@ export default (
         }
       }
     },
+    onCheckFile: (file, isFormatted) => {
+      onCheckFile && onCheckFile(file, isFormatted);
+      if (!isFormatted) {
+        failReasons.add('CHECK_FAILED');
+      }
+    },
     onExamineFile: verbose && onExamineFile,
   });
 

src/processFiles.js

@@ -0,0 +1,36 @@
+import { readFileSync, writeFileSync } from 'fs';
+import * as prettier from 'prettier';
+import { join } from 'path';
+
+export default (
+  directory,
+  files,
+  { check, config, onExamineFile, onCheckFile, onWriteFile } = {}
+) => {
+  for (const relative of files) {
+    onExamineFile && onExamineFile(relative);
+    const file = join(directory, relative);
+    const options = Object.assign(
+      {},
+      prettier.resolveConfig.sync(file, {
+        config,
+        editorconfig: true,
+      }),
+      { filepath: file }
+    );
+    const input = readFileSync(file, 'utf8');
+
+    if (check) {
+      const isFormatted = prettier.check(input, options);
+      onCheckFile && onCheckFile(relative, isFormatted);
+      continue;
+    }
+
+    const output = prettier.format(input, options);
+
+    if (output !== input) {
+      writeFileSync(file, output);
+      onWriteFile && onWriteFile(relative);
+    }
+  }
+};