Add -c/--constraint option to pip-compile

README.md

@@ -98,7 +98,6 @@ dependencies = ["django"]
 
 [project.optional-dependencies]
 dev = ["pytest"]
-
 ```
 
 You can produce your pin files as easily as:

piptools/scripts/compile.py

@@ -326,6 +326,20 @@ def _determine_linesep(
     help="Do not read any config file.",
     is_eager=True,
 )
+@click.option(
+    "-c",
+    "--constraint",
+    type=click.Path(
+        exists=True,
+        file_okay=True,
+        dir_okay=False,
+        readable=True,
+        allow_dash=False,
+        path_type=str,
+    ),
+    multiple=True,
+    help="Constrain versions using the given constraints file; may be used more than once.",
+)
 def cli(
     ctx: click.Context,
     verbose: int,
@@ -366,6 +380,7 @@ def cli(
     unsafe_package: tuple[str, ...],
     config: Path | None,
     no_config: bool,
+    constraint: tuple[str, ...],
 ) -> None:
     """
     Compiles requirements.txt from requirements.in, pyproject.toml, setup.cfg,
@@ -561,6 +576,18 @@ def cli(
                 )
             )
 
+    # Parse all constraints from `--constraint` files
+    for filename in constraint:
+        constraints.extend(
+            parse_requirements(
+                filename,
+                constraint=True,
+                finder=repository.finder,
+                options=repository.options,
+                session=repository.session,
+            )
+        )
+
     if upgrade_packages:
         constraints_file = tempfile.NamedTemporaryFile(mode="wt", delete=False)
         constraints_file.write("\n".join(upgrade_packages))

tests/conftest.py

@@ -10,7 +10,7 @@
 from functools import partial
 from pathlib import Path
 from textwrap import dedent
-from typing import Any
+from typing import Any, cast
 
 import pytest
 import tomli_w
@@ -234,7 +234,7 @@ def runner():
 @pytest.fixture
 def tmpdir_cwd(tmpdir):
     with tmpdir.as_cwd():
-        yield tmpdir
+        yield Path(tmpdir)
 
 
 @pytest.fixture
@@ -455,12 +455,12 @@ def _maker(
         pyproject_param: str, new_default: Any, config_file_name: str = CONFIG_FILE_NAME
     ) -> Path:
         # Make a config file with this one config default override
-        config_path = Path(tmpdir_cwd) / pyproject_param
+        config_path = tmpdir_cwd / pyproject_param
         config_file = config_path / config_file_name
         config_path.mkdir(exist_ok=True)
 
         config_to_dump = {"tool": {"pip-tools": {pyproject_param: new_default}}}
         config_file.write_text(tomli_w.dumps(config_to_dump))
-        return config_file.relative_to(tmpdir_cwd)
+        return cast(Path, config_file.relative_to(tmpdir_cwd))
 
     return _maker

tests/test_cli_compile.py

@@ -3019,6 +3019,38 @@ def test_raise_error_on_invalid_config_option(
     assert "Invalid value for config key 'dry_run': ['invalid', 'value']" in out.stderr
 
 
+@pytest.mark.parametrize("option", ("-c", "--constraint"))
+def test_constraint_option(pip_conf, runner, tmpdir_cwd, make_config_file, option):
+    req_in = tmpdir_cwd / "requirements.in"
+    req_in.write_text("small-fake-a")
+
+    constraints_txt = tmpdir_cwd / "constraints.txt"
+    constraints_txt.write_text("small-fake-a==0.1")
+
+    out = runner.invoke(
+        cli,
+        [
+            req_in.name,
+            option,
+            constraints_txt.name,
+            "--output-file",
+            "-",
+            "--no-header",
+            "--no-emit-options",
+        ],
+    )
+
+    assert out.exit_code == 0
+    assert out.stdout == dedent(
+        """\
+        small-fake-a==0.1
+            # via
+            #   -c constraints.txt
+            #   -r requirements.in
+        """
+    )
+
+
 def test_allow_in_config_pip_sync_option(pip_conf, runner, tmp_path, make_config_file):
     config_file = make_config_file("--ask", True)  # pip-sync's option
 

tests/test_utils.py

@@ -634,6 +634,7 @@ def test_callback_config_file_defaults(pyproject_param, new_default, make_config
         ("trusted_host", "not-a-list"),
         ("annotate", "not-a-bool"),
         ("max_rounds", "not-an-int"),
+        ("constraint", "not-an-list"),
     ),
 )
 def test_callback_config_file_defaults_multi_validate_value(