Run pip-compile in env python rather than pip-tools python

piptools/scripts/compile.py

@@ -3,9 +3,12 @@
 import itertools
 import os
 import shlex
+import shutil
 import sys
 import tempfile
+import typing
 from pathlib import Path
+from subprocess import run  # nosec
 from typing import IO, Any, BinaryIO, cast
 
 import click
@@ -122,7 +125,65 @@ def _determine_linesep(
 @options.build_deps_for
 @options.all_build_deps
 @options.only_build_deps
+@typing.no_type_check
 def cli(
+    *args,
+    verbose: int,
+    quiet: int,
+    **kwargs,
+):
+    """
+    Compiles requirements.txt from requirements.in, pyproject.toml, setup.cfg,
+    or setup.py specs.
+    """
+    log.verbosity = verbose - quiet
+    current_python = sys.executable
+    log.debug(f"{current_python=}")
+    env_python = shutil.which("python")
+    log.debug(f"{env_python=}")
+    if current_python != env_python:
+        # pip-tools probably installed globally (e.g. via pipx)
+        # install pip-tools in a venv made by env_python and run it there
+        click.echo("Installing pip-tools in temporary venv...", err=True)
+        with tempfile.TemporaryDirectory(prefix="pip-tools-env-") as venv_path:
+            log.debug(f"Installing venv at {venv_path}")
+            run(  # nosec
+                [
+                    env_python,
+                    "-m",
+                    "venv",
+                    venv_path,
+                ],
+                capture_output=(not log.verbosity),
+                check=True,
+            )
+            temp_python = venv_path + "/bin/python"
+            log.debug(f"{temp_python=}")
+            run(  # nosec
+                [
+                    temp_python,
+                    "-m",
+                    "pip",
+                    "install",
+                    "pip-tools",  # TODO fix to this version of pip-tools?
+                ],
+                capture_output=(not log.verbosity),
+                check=True,
+            )
+            env = {**os.environ, "PATH": f"{venv_path}/bin:{os.environ['PATH']}"}
+            run(  # nosec
+                [
+                    "pip-compile",
+                    *sys.argv[1:],
+                ],
+                env=env,
+            )
+    else:
+        # pip-tools running in current env python
+        cli_runner(*args, verbose, quiet, **kwargs)
+
+
+def cli_runner(
     ctx: click.Context,
     color: bool | None,
     verbose: int,

tests/test_cli_compile.py

@@ -6,6 +6,7 @@
 import shutil
 import subprocess
 import sys
+import venv
 from textwrap import dedent
 from unittest import mock
 from unittest.mock import MagicMock
@@ -38,6 +39,12 @@
 )
 
 
+@pytest.fixture(autouse=True)
+def mock_run():
+    with mock.patch("piptools.scripts.compile.run") as mock_run:
+        yield mock_run
+
+
 @pytest.fixture(
     autouse=True,
     params=[
@@ -3771,3 +3778,11 @@ def test_stdout_should_not_be_read_when_stdin_is_not_a_plain_file(
     out = runner.invoke(cli, [req_in.as_posix(), "--output-file", fifo.as_posix()])
 
     assert out.exit_code == 0, out
+
+
+@mock.patch("piptools.scripts.compile.cli_runner")
+def test_pip_compile_run_with_env_python(mock_cli_runner, mock_run, runner, tmpdir):
+    venv.EnvBuilder(with_pip=True, symlinks=True).create(tmpdir)
+    runner.invoke(cli, ["--verbose"], env={"PATH": f"{tmpdir}/bin"})
+    mock_run.assert_called()
+    mock_cli_runner.assert_not_called()