feat: add defaults keyword for --mixin

CHANGELOG.md

@@ -6,6 +6,12 @@ All notable changes to microbench are documented here.
 
 ### Enhancements
 
+- **`--mixin defaults` keyword** (CLI): `defaults` can be used as a mixin
+  name to expand to the standard default set (`python-info`, `host-info`,
+  `slurm-info`, `loaded-modules`, `working-dir`). This makes it easy to add
+  one or more extra mixins without listing all five defaults explicitly:
+  `microbench --mixin defaults file-hash -- ./job.sh`.
+
 - **`file-hash` mixin — automatic argument file scanning** (CLI): the
   default hash list now includes not only the command executable (`cmd[0]`)
   but also any command-line arguments (`cmd[1:]`) that resolve to existing

docs/cli.md

@@ -133,8 +133,20 @@ mixins with descriptions:
 microbench --show-mixins
 ```
 
-Specifying `--mixin` replaces the defaults entirely. Use `--no-mixin` to
-disable all mixins and record only timing and command fields:
+Specifying `--mixin` replaces the defaults entirely. Use the special name
+`defaults` in a `--mixin` list to include the standard default set, so you
+can extend it without listing all of them explicitly:
+
+```bash
+# Defaults plus file-hash
+microbench --mixin defaults file-hash -- ./job.sh
+
+# Defaults plus git-info and cgroup-limits
+microbench --mixin defaults git-info cgroup-limits -- ./job.sh
+```
+
+Use `--no-mixin` to disable all mixins and record only timing and command
+fields:
 
 ```bash
 # Only Python info — no host info or SLURM

microbench/cli/main.py

@@ -123,7 +123,13 @@ def main(argv=None):
     elif args.no_mixins:
         mixin_names = []
     elif args.mixins is not None:
-        mixin_names = list(dict.fromkeys(args.mixins))
+        expanded = []
+        for name in args.mixins:
+            if name == 'defaults':
+                expanded.extend(_DEFAULT_MIXINS)
+            else:
+                expanded.append(name)
+        mixin_names = list(dict.fromkeys(expanded))
     else:
         mixin_names = list(_DEFAULT_MIXINS)
 

microbench/cli/parser.py

@@ -44,9 +44,11 @@ def _make_mixin_type(mixin_map):
     """Return an argparse type function that normalises and validates mixin names."""
 
     def _parse(value):
+        if value == 'defaults':
+            return 'defaults'
         canonical = _mb_name_to_cli(value) if value.startswith('MB') else value
         if canonical not in mixin_map:
-            valid = ', '.join(sorted(mixin_map))
+            valid = 'defaults, ' + ', '.join(sorted(mixin_map))
             raise argparse.ArgumentTypeError(
                 f'unknown mixin {value!r}. Available: {valid}'
             )
@@ -163,6 +165,8 @@ def _build_parser(mixin_map):
         type=_make_mixin_type(mixin_map),
         help=(
             'One or more mixins to include. Replaces defaults when specified. '
+            'Use the special name "defaults" to include the default set '
+            '(e.g. --mixin defaults file-hash). '
             'Use --show-mixins to list available options. '
             'MB-prefixed names (e.g. MBHostInfo) are also accepted.'
         ),

tests/test_cli.py

@@ -125,6 +125,54 @@ def test_cli_explicit_mixin_replaces_defaults():
     assert 'slurm' not in record
 
 
+def test_cli_mixin_defaults_keyword_alone():
+    """--mixin defaults alone is equivalent to omitting --mixin."""
+    _, record_explicit, _ = _run_main(['--mixin', 'defaults', '--', 'true'])
+    _, record_implicit, _ = _run_main(['--', 'true'])
+
+    for key in ('python', 'host', 'slurm', 'loaded_modules'):
+        assert key in record_explicit
+    assert record_explicit['python']['version'] == record_implicit['python']['version']
+
+
+def test_cli_mixin_defaults_keyword_extends_defaults():
+    """--mixin defaults plus a default mixin on top works."""
+    _, record, _ = _run_main(['--mixin', 'defaults', 'working-dir', '--', 'true'])
+
+    # All defaults present
+    assert 'python' in record
+    assert 'host' in record
+    assert 'slurm' in record
+    assert 'loaded_modules' in record
+    # working-dir is already in defaults, so no duplicate effect needed — just check
+    assert 'working_dir' in record['call']
+
+
+def test_cli_mixin_defaults_keyword_with_extra_mixin():
+    """--mixin defaults file-hash produces defaults plus file-hash."""
+    _, record, _ = _run_main(['--mixin', 'defaults', 'peak-memory', '--', 'true'])
+
+    assert 'python' in record
+    assert 'host' in record
+    # peak-memory records to call.peak_memory_bytes
+    assert 'peak_memory_bytes' in record['call']
+
+
+def test_cli_mixin_defaults_keyword_deduplicates():
+    """Repeating defaults in --mixin does not produce duplicate mixins."""
+    _, record, _ = _run_main(['--mixin', 'defaults', 'defaults', '--', 'true'])
+
+    assert 'python' in record
+    assert 'host' in record
+
+
+def test_cli_mixin_defaults_keyword_invalid_extra():
+    """An unknown mixin alongside defaults exits non-zero."""
+    with pytest.raises(SystemExit) as exc:
+        main(['--mixin', 'defaults', 'no-such-mixin', '--', 'true'])
+    assert exc.value.code != 0
+
+
 def test_cli_outfile(tmp_path):
     """--outfile writes JSONL to the specified file."""
     outfile = tmp_path / 'results.jsonl'