feat: add output-file input for clean Black logging

CHANGES.md

@@ -73,6 +73,8 @@
 - Enable 3.14 base CI (#4804)
 - Enhance GitHub Action `psf/black` to support the `required-version` major-version-only
   "stability" format when using pyproject.toml (#4770)
+- Add `output-file` input to GitHub Action `psf/black` to write formatter output to a
+  file for artifact capture and log cleanliness (#4824)
 - Improve error message for vim plugin users. It now handles independently vim version
 - Vim: Warn on unsupported Vim and Python versions independently (#4772)
 - Vim: Print the import paths when importing black fails (#4675)

action.yml

@@ -35,6 +35,12 @@ inputs:
     description: "Whether to add the output to the workflow summary"
     required: false
     default: true
+  output-file:
+    description: >
+      Optional path to write Black output to a file in addition to stdout. Useful for
+      keeping GitHub Actions logs clean when using --diff or --check.
+    required: false
+    default: ""
 branding:
   color: "black"
   icon: "check-circle"
@@ -75,5 +81,6 @@ runs:
         INPUT_BLACK_ARGS: ${{ inputs.black_args }}
         INPUT_VERSION: ${{ inputs.version }}
         INPUT_USE_PYPROJECT: ${{ inputs.use_pyproject }}
+        OUTPUT_FILE: ${{ inputs.output-file }}
         pythonioencoding: utf-8
       shell: bash

action/main.py

@@ -16,6 +16,7 @@
 BLACK_ARGS = os.getenv("INPUT_BLACK_ARGS", default="")
 VERSION = os.getenv("INPUT_VERSION", default="")
 USE_PYPROJECT = os.getenv("INPUT_USE_PYPROJECT") == "true"
+OUTPUT_FILE = os.getenv("OUTPUT_FILE", default="")
 
 BLACK_VERSION_RE = re.compile(r"^black([^A-Z0-9._-]+.*)$", re.IGNORECASE)
 EXTRAS_RE = re.compile(r"\[.*\]")
@@ -182,5 +183,16 @@ def find_black_version_in_array(array: object) -> Union[str, None]:
         encoding="utf-8",
     )
 shutil.rmtree(ENV_PATH, ignore_errors=True)
+
+# Write output to file if specified
+if OUTPUT_FILE:
+    try:
+        with open(OUTPUT_FILE, "w", encoding="utf-8") as f:
+            f.write(proc.stdout)
+        print(f"Black output written to {OUTPUT_FILE}")
+    except Exception as e:
+        print(f"::error::Failed to write output to {OUTPUT_FILE}: {e}", file=sys.stderr)
+        sys.exit(1)
+
 print(proc.stdout)
 sys.exit(proc.returncode)