Simplify GitHub Action entrypoint (#2119)

This commit simplifies entrypoint.sh for GitHub Actions by removing
duplication of args and black_args (cf. #1909).

The reason why #1909 uses the input id black_args is to avoid an overlap
with args, but this naming seems redundant. So let me suggest option
and src, which are consistent with CLI. Backward compatibility is
guaranteed; Users can still use black_args as well.

Commit history pre-merge:
* Simplify GitHub Action entrypoint (#1909)
* Fix prettier
* Emit a warning message when `black_args` is used

  This deprecation should be visible in GitHub Action's UI now.

  Co-authored-by: Shota Ray Imaki <shota.imaki.0801@gmail.com>
  Co-authored-by: Richard Si <63936253+ichard26@users.noreply.github.com>

README.md

@@ -425,15 +425,17 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
       - uses: psf/black@stable
-        with:
-          args: ". --check"
 ```
 
-### Inputs
+You may use `options` (Default is `'--check --diff'`) and `src` (Default is `'.'`) as
+follows:
 
-#### `black_args`
-
-**optional**: Black input arguments. Defaults to `. --check --diff`.
+```yaml
+- uses: psf/black@stable
+  with:
+    options: "--check --verbose"
+    src: "./src"
+```
 
 ## Ignoring unmodified files
 

action.yml

@@ -2,8 +2,18 @@ name: "Black"
 description: "The uncompromising Python code formatter."
 author: "Łukasz Langa and contributors to Black"
 inputs:
+  options:
+    description:
+      "Options passed to black. Use `black --help` to see available options. Default:
+      '--check'"
+    required: false
+    default: "--check --diff"
+  src:
+    description: "Source to run black. Default: '.'"
+    required: false
+    default: "."
   black_args:
-    description: "Black input arguments."
+    description: "[DEPRECATED] Black input arguments."
     required: false
     default: ""
 branding:

action/entrypoint.sh

@@ -1,17 +1,8 @@
-#!/bin/bash
-set -e
+#!/bin/bash -e
 
-# If no arguments are given use current working directory
-black_args=(".")
-if [ "$#" -eq 0 ] && [ "${INPUT_BLACK_ARGS}" != "" ]; then
-  black_args+=(${INPUT_BLACK_ARGS})
-elif [ "$#" -ne 0 ] && [ "${INPUT_BLACK_ARGS}" != "" ]; then
-  black_args+=($* ${INPUT_BLACK_ARGS})
-elif [ "$#" -ne 0 ] && [ "${INPUT_BLACK_ARGS}" == "" ]; then
-  black_args+=($*)
-else
-  # Default (if no args provided).
-  black_args+=("--check" "--diff")
-fi
+if [ -n $INPUT_BLACK_ARGS ]; then
+  echo '::warning::Input `with.black_args` is deprecated. Use `with.options` and `with.src` instead.'
+  black $INPUT_BLACK_ARGS
+  exit $?
 
-sh -c "black . ${black_args[*]}"
+black $INPUT_OPTIONS $INPUT_SRC