spdx-diff: cli: Change output format to JSON and enfore JSON filename argument

Previously, the tool was printing human-readable text to stdout and generating a JSON file separately.
This change enforces the presence of an explicit argument used as the JSON output filename.

The console output is now also emitted in JSON format to ensure consistency and
 to simplify integration with automated pipelines and tooling.

Signed-off-by: Christophe Guerreiro <christophe.guerreiro@non.se.com>

Author: Christophe Guerreiro

src/spdx_diff/cli.py

@@ -9,7 +9,6 @@
 from argparse import ArgumentParser, ArgumentTypeError, BooleanOptionalAction
 from collections import defaultdict
 from contextlib import redirect_stdout
-from datetime import datetime, timezone
 from typing import Any
 
 from . import __version__
@@ -386,8 +385,15 @@ def write_diff_to_json(
             "changed": dict(sorted(pcfg_diff[2].items())),
         },
     }
-    with output_file.open("w", encoding="utf-8") as f:
-        json.dump(delta, f, indent=2, ensure_ascii=False)
+    # Write the resulting SPDX diff JSON to stdout for piping
+    json.dump(delta, sys.stdout, indent=2, ensure_ascii=False)
+    sys.stdout.write("\n")
+
+    # Write the resulting SPDX diff JSON to file
+    if output_file is not None:
+        _logger.info("Writing diff results to %s", output_file)
+        with output_file.open("w", encoding="utf-8") as f:
+            json.dump(delta, f, indent=2, ensure_ascii=False)
 
 
 def path_is_file(value: str) -> pathlib.Path:
@@ -430,21 +436,13 @@ def main() -> None:
         type=path_is_file,
         help="New SPDX3 JSON file",
     )
-    timestamp = datetime.now(tz=timezone.utc).astimezone().strftime("%Y%m%d-%H%M%S")
-    default_output = f"spdx_diff_{timestamp}.json"
     parser.add_argument(
-        "--output",
+        "--json-output",
         "-o",
         metavar="PATH",
         type=pathlib.Path,
-        default=default_output,
-        help="Optional output file name (JSON)",
-    )
-    parser.add_argument(
-        "--format",
-        choices=["text", "json", "both"],
-        default="both",
-        help="Output format: text (console only), json (file only), or both (default)",
+        default=None,
+        help="JSON Output file name (default: none)",
     )
 
     # Output filtering category options
@@ -511,8 +509,6 @@ def main() -> None:
         pcfg_diff[2],
     )
 
-    if args.format in ["json", "both"]:
-        write_diff_to_json(pkg_diff, cfg_diff, pcfg_light_diff, args.output)
     # Print human readable information on stderr
     with redirect_stdout(sys.stderr):
         if show_packages:
@@ -531,6 +527,7 @@ def main() -> None:
             )
 
 
+    write_diff_to_json(pkg_diff, cfg_diff, pcfg_light_diff, args.json_output)
 
 
 if __name__ == "__main__":