Add the ability for Pants to provide Python via a union (with a pyenv impl)

src/python/pants/backend/python/dependency_inference/parse_python_dependencies.py

@@ -192,6 +192,7 @@ async def parse_python_dependencies(
                 file,
             ],
             input_digest=input_digest,
+            append_only_caches=python_interpreter.append_only_caches,
             description=f"Determine Python dependencies for {request.source.address}",
             env=parser_script.env,
             level=LogLevel.DEBUG,

src/python/pants/backend/python/goals/run_helper.py

@@ -27,6 +27,7 @@
 from pants.engine.fs import CreateDigest, Digest, FileContent, MergeDigests
 from pants.engine.rules import Get, MultiGet, rule_helper
 from pants.engine.target import TransitiveTargets, TransitiveTargetsRequest
+from pants.util.frozendict import FrozenDict
 
 
 def _in_chroot(relpath: str) -> str:
@@ -113,12 +114,18 @@ async def _create_python_source_run_request(
         **complete_pex_environment.environment_dict(python_configured=venv_pex.python is not None),
         "PEX_EXTRA_SYS_PATH": os.pathsep.join(source_roots),
     }
+    append_only_caches = (
+        FrozenDict({}) if venv_pex.append_only_caches is None else venv_pex.append_only_caches
+    )
 
     return RunRequest(
         digest=merged_digest,
         args=[_in_chroot(venv_pex.pex.argv0)],
         extra_env=extra_env,
-        append_only_caches=complete_pex_environment.append_only_caches,
+        append_only_caches={
+            **complete_pex_environment.append_only_caches,
+            **append_only_caches,
+        },
     )
 
 

src/python/pants/backend/python/providers/BUILD

@@ -0,0 +1,4 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_sources()

src/python/pants/backend/python/providers/pyenv/BUILD

@@ -0,0 +1,12 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_sources()
+python_tests(
+    name="tests",
+    overrides={
+        "rules_integration_test.py": {
+            "timeout": 600,
+        }
+    },
+)

src/python/pants/backend/python/providers/pyenv/register.py

@@ -0,0 +1,9 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+
+from pants.backend.python.providers.pyenv.rules import rules as pyenv_rules
+
+
+def rules():
+    return pyenv_rules()

src/python/pants/backend/python/providers/pyenv/rules.py

@@ -0,0 +1,183 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from textwrap import dedent  # noqa: PNT20
+
+from pants.backend.python.subsystems.setup import PythonSetup
+from pants.backend.python.util_rules.pex import PythonProvider
+from pants.backend.python.util_rules.pex import rules as pex_rules
+from pants.backend.python.util_rules.pex_environment import PythonExecutable
+from pants.core.util_rules.external_tool import (
+    DownloadedExternalTool,
+    ExternalToolRequest,
+    TemplatedExternalTool,
+)
+from pants.core.util_rules.external_tool import rules as external_tools_rules
+from pants.engine.env_vars import EnvironmentVars, EnvironmentVarsRequest
+from pants.engine.fs import CreateDigest, FileContent
+from pants.engine.internals.native_engine import Digest, MergeDigests
+from pants.engine.internals.selectors import Get, MultiGet
+from pants.engine.platform import Platform
+from pants.engine.process import Process, ProcessCacheScope, ProcessResult
+from pants.engine.rules import collect_rules, rule
+from pants.engine.unions import UnionRule
+from pants.option.option_types import StrListOption
+from pants.util.frozendict import FrozenDict
+from pants.util.meta import classproperty
+
+
+class PyenvSubsystem(TemplatedExternalTool):
+    options_scope = "pyenv"
+    name = "pyenv"
+    help = "pyenv (https://github.com/pyenv/pyenv)."
+
+    default_version = "2.3.13"
+    default_url_template = "https://github.com/pyenv/pyenv/archive/refs/tags/v{version}.tar.gz"
+
+    python_configure_opts = StrListOption(
+        help="Flags to use when configuring CPython.",
+        advanced=True,
+    )
+
+    @classproperty
+    def default_known_versions(cls):
+        return [
+            "|".join(
+                (
+                    cls.default_version,
+                    plat,
+                    "9105de5e5cf8dc0eca2a520ed04493d183128d46a2cfb402d4cc271af1bf144b",
+                    "749323",
+                )
+            )
+            for plat in ["macos_arm64", "macos_x86_64", "linux_x86_64", "linux_arm64"]
+        ]
+
+    def generate_exe(self, plat: Platform) -> str:
+        """Returns the path to the tool executable.
+
+        If the downloaded artifact is the executable itself, you can leave this unimplemented.
+
+        If the downloaded artifact is an archive, this should be overridden to provide a
+        relative path in the downloaded archive, e.g. `./bin/protoc`.
+        """
+        return f"./pyenv-{self.version}/bin/pyenv"
+
+
+class PythonToolchainRequest(PythonProvider):
+    pass
+
+
+PYENV_NAMED_CACHE = ".pyenv"
+PYENV_APPEND_ONLY_CACHES = FrozenDict({"pyenv": PYENV_NAMED_CACHE})
+
+
+@rule
+async def get_python(
+    request: PythonToolchainRequest,
+    python_setup: PythonSetup,
+    platform: Platform,
+    pyenv_subsystem: PyenvSubsystem,
+) -> PythonExecutable:
+    env_vars, pyenv = await MultiGet(
+        Get(EnvironmentVars, EnvironmentVarsRequest(["PATH", "LDFLAGS"])),
+        Get(DownloadedExternalTool, ExternalToolRequest, pyenv_subsystem.get_request(platform)),
+    )
+
+    python_to_use = request.interpreter_constraints.minimum_python_version(
+        python_setup.interpreter_versions_universe
+    )
+    if python_to_use is None:
+        raise ValueError(
+            f"Couldn't determine a compatible Interpreter Constraint from {python_setup.interpreter_versions_universe}"
+        )
+
+    which_python_result = await Get(
+        ProcessResult,
+        Process(
+            [pyenv.exe, "latest", "--known", python_to_use],
+            input_digest=pyenv.digest,
+            description=f"Choose specific version for Python {python_to_use}",
+            env={"PATH": env_vars.get("PATH", "")},
+            # Caching the result is OK, since if the user really needs a different patch,
+            # they should list a more precise IC.
+        ),
+    )
+    specific_python = which_python_result.stdout.decode("ascii").strip()
+
+    shim_digest = await Get(
+        Digest,
+        CreateDigest(
+            [
+                FileContent(
+                    "install_python_shim.sh",
+                    dedent(
+                        f"""\
+                        #!/usr/bin/env bash
+                        set -e
+                        DEST=$(realpath {PYENV_NAMED_CACHE}/{specific_python})
+                        if [ ! -d "$DEST" ]; then
+                            export PYENV_ROOT=$(realpath $(mktemp -d -u -p {PYENV_NAMED_CACHE} {specific_python}.XXXXXX))
+                            # export LDFLAGS="$LDFLAGS -Wl,-rpath=PYENV_ROOT/lib"
+                            {pyenv.exe} install {specific_python}
+                            # Removing write perms helps ensure users aren't accidentally modifying Python
+                            # or the site-packages
+                            chmod -R -w "$PYENV_ROOT"/versions/{specific_python}
+                            chmod +w "$PYENV_ROOT"/versions/{specific_python}
+                            ln -s "$PYENV_ROOT"/versions/{specific_python} {PYENV_NAMED_CACHE}/{specific_python}
+                            rm -rf "$PYENV_ROOT"/shims
+                        fi
+                        echo "$DEST"/bin/python
+                        """
+                    ).encode("ascii"),
+                    is_executable=True,
+                )
+            ]
+        ),
+    )
+    digest = await Get(Digest, MergeDigests([shim_digest, pyenv.digest]))
+
+    # NB: We don't cache this process at any level for two reasons:
+    #   1. Several tools (including pex) refer to Python at an absolute path, so a named cache is
+    #   the only way for this to work reasonably well. Since the named cache could be wiped between
+    #   runs (technically during a run, but we can't do anything about that) the
+    #   fastest-yet-still-correct solution is to always run this process and make it bail
+    #   early-and-quickly if the requisite Python already exists.
+    #   2. Pyenv compiles Python using whatever compiler the system is configured to use. Python
+    #   then stores this information so that it cn use the same compiler when compiling extension
+    #   modules. Therefore caching the compiled Python is somewhat unsafe (especially for a remote
+    #   cache).
+    result = await Get(
+        ProcessResult,
+        Process(
+            ["./install_python_shim.sh"],
+            input_digest=digest,
+            description=f"Install Python {python_to_use}",
+            append_only_caches=PYENV_APPEND_ONLY_CACHES,
+            env={
+                "PATH": env_vars.get("PATH", ""),
+                "TMPDIR": "{chroot}/tmpdir",
+                "LDFLAGS": env_vars.get("LDFLAGS", ""),
+                "PYTHON_CONFIGURE_OPTS": " ".join(pyenv_subsystem.python_configure_opts),
+            },
+            # Don't cache, we want this to always be run so that we can assume for the rest of the
+            # session the named_cache destination for this Python is valid, as the Python ecosystem
+            # mainly assumes absolute paths for Python interpreters.
+            cache_scope=ProcessCacheScope.PER_SESSION,
+        ),
+    )
+
+    return PythonExecutable(
+        path=result.stdout.decode("utf-8").splitlines()[-1].strip(),
+        fingerprint=None,
+        append_only_caches=PYENV_APPEND_ONLY_CACHES,
+    )
+
+
+def rules():
+    return (
+        *collect_rules(),
+        *pex_rules(),
+        *external_tools_rules(),
+        UnionRule(PythonProvider, PythonToolchainRequest),
+    )

src/python/pants/backend/python/providers/pyenv/rules_integration_test.py

@@ -0,0 +1,124 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import annotations
+
+import shutil
+from textwrap import dedent
+
+import pytest
+
+from pants.backend.python import target_types_rules
+from pants.backend.python.dependency_inference import rules as dependency_inference_rules
+from pants.backend.python.goals.run_python_source import PythonSourceFieldSet
+from pants.backend.python.goals.run_python_source import rules as run_rules
+from pants.backend.python.providers.pyenv.rules import rules as pyenv_rules
+from pants.backend.python.target_types import PythonSourcesGeneratorTarget
+from pants.build_graph.address import Address
+from pants.core.goals.run import RunRequest
+from pants.engine.process import InteractiveProcess
+from pants.engine.rules import QueryRule
+from pants.engine.target import Target
+from pants.testutil.rule_runner import RuleRunner, mock_console
+
+
+@pytest.fixture
+def rule_runner() -> RuleRunner:
+    return RuleRunner(
+        rules=[
+            *run_rules(),
+            *pyenv_rules(),
+            *dependency_inference_rules.rules(),
+            *target_types_rules.rules(),
+            QueryRule(RunRequest, (PythonSourceFieldSet,)),
+        ],
+        target_types=[
+            PythonSourcesGeneratorTarget,
+        ],
+    )
+
+
+def run_run_request(
+    rule_runner: RuleRunner,
+    target: Target,
+) -> str:
+    args = [
+        "--backend-packages=['pants.backend.python', 'pants.backend.python.providers.pyenv']",
+        "--source-root-patterns=['src']",
+    ]
+    rule_runner.set_options(args, env_inherit={"PATH", "PYENV_ROOT", "HOME"})
+    run_request = rule_runner.request(RunRequest, [PythonSourceFieldSet.create(target)])
+    run_process = InteractiveProcess(
+        argv=run_request.args,
+        env=run_request.extra_env,
+        input_digest=run_request.digest,
+        run_in_workspace=True,
+        immutable_input_digests=run_request.immutable_input_digests,
+        append_only_caches=run_request.append_only_caches,
+    )
+    with mock_console(rule_runner.options_bootstrapper) as mocked_console:
+        exit_code = rule_runner.run_interactive_process(run_process)
+        if exit_code:
+            print(mocked_console[1].get_stderr().strip())
+        return mocked_console[1].get_stdout().strip()
+
+
+@pytest.mark.parametrize("py_version", ["2.7", "3.9"])
+def test_using_pyenv(rule_runner, py_version):
+    rule_runner.write_files(
+        {
+            "src/app.py": dedent(
+                """\
+                import os.path
+                import sys
+                import sysconfig
+
+                print(sysconfig.get_config_var("prefix"))
+                print(sys.version.replace("\\n", " "))
+                """
+            ),
+            "src/BUILD": f"python_sources(interpreter_constraints=['=={py_version}.*'])",
+        }
+    )
+
+    target = rule_runner.get_target(Address("src", relative_file_path="app.py"))
+    stdout = run_run_request(rule_runner, target)
+    named_caches_dir = (
+        rule_runner.options_bootstrapper.bootstrap_options.for_global_scope().named_caches_dir
+    )
+    prefix_dir, version = stdout.splitlines()
+    assert prefix_dir.startswith(f"{named_caches_dir}/pyenv")
+    assert py_version in version
+
+
+def test_venv_pex_reconstruction(rule_runner):
+    """A VenvPex refers to the location of the venv so it doesn't have to re-construct if it exists.
+
+    Part of this location is a hash of the interpreter. Without careful consideration it can be easy
+    for this hash to drift from build-time to run-time. This test validates the assumption that the
+    venv could be reconstructed exactly if the underlying directory was wiped clean.
+    """
+    rule_runner.write_files(
+        {
+            "src/app.py": dedent(
+                """\
+                import pathlib
+                import sys
+
+                in_venv_python_path = pathlib.Path(sys.executable)
+                venv_link = in_venv_python_path.parent.parent
+                venv_location = venv_link.resolve()
+                print(venv_location)
+                """
+            ),
+            "src/BUILD": "python_sources()",
+        }
+    )
+
+    target = rule_runner.get_target(Address("src", relative_file_path="app.py"))
+    stdout1 = run_run_request(rule_runner, target)
+    assert "pex_root/venvs/" in stdout1
+    venv_location = stdout1
+    shutil.rmtree(venv_location)
+    stdout2 = run_run_request(rule_runner, target)
+    assert stdout1 == stdout2