feat: replace occurrences of {} in formatter command with filepath

README.md

@@ -61,7 +61,7 @@ For detailed information run:
 The command expects a shell command to run a formatter, and one or more file
 patterns to identify which files should be formatted. For example:
 
-    $ git-format-staged --formatter 'prettier --stdin' 'src/*.js'
+    $ git-format-staged --formatter 'prettier --stdin --stdin-filepath "{}"' 'src/*.js'
 
 That will format all files under `src/` and its subdirectories using
 `prettier`. The file pattern is tested against staged files using Python's
@@ -84,6 +84,16 @@ git-format-staged never operates on files that are excluded from version
 control. So it is not necessary to explicitly exclude stuff like
 `node_modules/`.
 
+The formatter command may include a placeholder, `{}`, which will be replaced
+with the path of the file that is being formatted. This is useful if your
+formatter needs to know the file extension to determine how to format or to
+lint each file. For example:
+
+    $ git-format-staged -f 'prettier --stdin --stdin-filepath "{}"' '*.js' '*.css'
+
+Do not attempt to read or write to `{}` in your formatter command! The
+placeholder exists only for referencing the file name and path.
+
 ### Check staged changes with a linter without formatting
 
 Perhaps you do not want to reformat files automatically; but you do want to

git-format-staged

@@ -60,7 +60,7 @@ def format_staged_files(file_patterns, formatter, git_root, update_working_tree=
 # Returns hash of the new object if formatting produced any changes.
 def format_file_in_index(formatter, diff_entry, update_working_tree=True, write=True):
     orig_hash = diff_entry['dst_hash']
-    new_hash = format_object(formatter, orig_hash)
+    new_hash = format_object(formatter, orig_hash, diff_entry['src_path'])
 
     # If the new hash is the same then the formatter did not make any changes.
     if not write or new_hash == orig_hash:
@@ -77,16 +77,17 @@ def format_file_in_index(formatter, diff_entry, update_working_tree=True, write=
 
     return new_hash
 
+file_path_placeholder = re.compile('\{\}')
 
 # Run formatter on a git blob identified by its hash. Writes output to a new git
 # blob, and returns the hash of the new blob.
-def format_object(formatter, object_hash):
+def format_object(formatter, object_hash, file_path):
     get_content = subprocess.Popen(
             ['git', 'cat-file', '-p', object_hash],
             stdout=subprocess.PIPE
             )
     format_content = subprocess.Popen(
-            formatter,
+            re.sub(file_path_placeholder, file_path, formatter),
             shell=True,
             stdin=get_content.stdout,
             stdout=subprocess.PIPE
@@ -214,7 +215,7 @@ if __name__ == '__main__':
     parser.add_argument(
             '--formatter', '-f',
             required=True,
-            help='Shell command to format files, will run once per file. (Example: "prettier --stdin")'
+            help='Shell command to format files, will run once per file. Occurrences of the placeholder `{}` will be replaced with a path to the file being formatted. (Example: "prettier --stdin --stdin-filepath \'{}\'")'
             )
     parser.add_argument(
             '--no-update-working-tree',

test/git-format-staged_test.js

@@ -503,6 +503,35 @@ test('messages from formatter command can be redirected to stderr', async t => {
   t.regex(stderr, /Parsing error: Unexpected token/)
 })
 
+test('replaces placeholder in the formatter command with name of file to be formatted', async t => {
+  const r = repo(t)
+  await setContent(r, 'index.js', '')
+  await stage(r, 'index.js')
+  await formatStaged(r, '--formatter "echo {}" "*.js"')
+  contentIs(t, await getStagedContent(r, 'index.js'), 'index.js')
+})
+
+test('replaces multiple filename placeholders', async t => {
+  const r = repo(t)
+  await setContent(r, 'index.js', '')
+  await stage(r, 'index.js')
+  await formatStaged(r, '--formatter "echo {} {}" "*.js"')
+  contentIs(t, await getStagedContent(r, 'index.js'), 'index.js index.js')
+})
+
+test('replaces filename placeholders with relative path to files in subdirectories', async t => {
+  const r = repo(t)
+  await fileInTree(r, 'test/testIndex.js', 'function test () {}')
+  await setContent(r, 'test/testIndex.js', '')
+  await stage(r, 'test/testIndex.js')
+  await formatStaged(r, '--formatter "echo {}" "*.js"')
+  contentIs(
+    t,
+    await getStagedContent(r, 'test/testIndex.js'),
+    'test/testIndex.js'
+  )
+})
+
 function contentIs (t: ExecutionContext<>, actual: string, expected: string) {
   t.is(trim(actual), trim(expected))
 }