Write action stdout as an output

action.yml

@@ -39,6 +39,9 @@ outputs:
   exitcode:
     description: "Exit code of Darker"
     value: ${{ steps.darker.outputs.exitcode }}
+  stdout:
+    description: "Standard output of Darker"
+    value: ${{ steps.darker.outputs.stdout }}
 branding:
   color: "black"
   icon: "check-circle"

action/main.py

@@ -19,10 +19,23 @@
 REVISION = os.getenv("INPUT_REVISION") or os.getenv("INPUT_COMMIT_RANGE") or "HEAD^"
 WORKING_DIRECTORY = os.getenv("INPUT_WORKING_DIRECTORY", ".")
 
+
+def set_github_output(key: str, val: str) -> None:
+    """Write a key-value pair to the output file."""
+    with Path(os.environ["GITHUB_OUTPUT"]).open("a", encoding="UTF-8") as f:
+        print(f"{key}={val}", file=f)
+
+
+def exit(exitcode: int) -> None:
+    """Write the exit code to the output file and exit with it."""
+    set_github_output("exitcode", str(exitcode))
+    sys.exit(exitcode)
+
+
 # Check if the working directory exists
 if not os.path.isdir(WORKING_DIRECTORY):
     print(f"::error::Working directory does not exist: {WORKING_DIRECTORY}", flush=True)
-    sys.exit(21)
+    exit(21)
 
 
 def pip_install(*packages):
@@ -87,8 +100,5 @@ def pip_install(*packages):
 )
 print(proc.stdout, end="")
 
-print(f"Writing exitcode={proc.returncode} to {os.environ['GITHUB_OUTPUT']}")
-
-with Path(os.environ["GITHUB_OUTPUT"]).open("a", encoding="UTF-8") as f:
-    print(f"exitcode={proc.returncode}", file=f)
-sys.exit(proc.returncode)
+set_github_output("stdout", f"<<DARKER_ACTION_EOF\n{proc.stdout}\nDARKER_ACTION_EOF")
+exit(proc.returncode)