lock: add --output-file

src/pip/_internal/commands/lock.py

@@ -10,7 +10,7 @@
     with_cleanup,
 )
 from pip._internal.cli.status_codes import SUCCESS
-from pip._internal.models.pylock import Pylock
+from pip._internal.models.pylock import Pylock, is_valid_pylock_file_name
 from pip._internal.operations.build.build_tracker import get_build_tracker
 from pip._internal.req.req_install import (
     check_legacy_setup_py_options,
@@ -45,6 +45,18 @@ class LockCommand(RequirementCommand):
       %prog [options] <archive url/path> ..."""
 
     def add_options(self) -> None:
+        self.cmd_opts.add_option(
+            cmdoptions.PipOption(
+                "--output-file",
+                "--output",
+                "-o",
+                dest="output_file",
+                metavar="path",
+                type="path",
+                default="pylock.toml",
+                help="Lock file name (default=pylock.toml). Use - for stdout.",
+            )
+        )
         self.cmd_opts.add_option(cmdoptions.requirements())
         self.cmd_opts.add_option(cmdoptions.constraints())
         self.cmd_opts.add_option(cmdoptions.no_deps())
@@ -131,9 +143,22 @@ def run(self, options: Values, args: List[str]) -> int:
 
         requirement_set = resolver.resolve(reqs, check_supported_wheels=True)
 
-        pyproject_lock = Pylock.from_install_requirements(
-            requirement_set.requirements.values(), base_dir=Path.cwd()
-        )
-        sys.stdout.write(pyproject_lock.as_toml())
+        if options.output_file == "-":
+            base_dir = Path.cwd()
+        else:
+            output_file_path = Path(options.output_file)
+            if not is_valid_pylock_file_name(output_file_path):
+                logger.warning(
+                    "%s is not a valid lock file name.",
+                    output_file_path,
+                )
+            base_dir = output_file_path.parent.absolute()
+        pylock_toml = Pylock.from_install_requirements(
+            requirement_set.requirements.values(), base_dir=base_dir
+        ).as_toml()
+        if options.output_file == "-":
+            sys.stdout.write(pylock_toml)
+        else:
+            output_file_path.write_text(pylock_toml, encoding="utf-8")
 
         return SUCCESS

src/pip/_internal/models/pylock.py

@@ -1,4 +1,5 @@
 import dataclasses
+import re
 from dataclasses import dataclass
 from pathlib import Path
 from typing import Any, Dict, Iterable, List, Optional, Tuple
@@ -11,6 +12,12 @@
 from pip._internal.req.req_install import InstallRequirement
 from pip._internal.utils.urls import url_to_path
 
+PYLOCK_FILE_NAME_RE = re.compile(r"^pylock\.([^.]+)\.toml$")
+
+
+def is_valid_pylock_file_name(path: Path) -> bool:
+    return path.name == "pylock.toml" or bool(re.match(PYLOCK_FILE_NAME_RE, path.name))
+
 
 def _toml_dict_factory(data: Iterable[Tuple[str, Any]]) -> Dict[str, Any]:
     return {key.replace("_", "-"): value for key, value in data if value is not None}