V2 ./pants test.pytest selects interpreter based off of compatibili…

…ty constraints (pantsbuild#7679)

Currently the V2 task will always use the current interpreter to run Pytest, even if the targets have different requirements. Instead, we must support choosing the interpreter for the subprocess based on the targets' compatibility (which falls back to global compatibility if missing).

Note that we let Pex do the intepreter resolution for us to simplify the Pants code. All we have to do is pass the interpreter constraints to PEX, along with exposing the `--python-setup-interpreter-search-paths`, and then Pex will handle the resolution for us.

src/python/pants/backend/python/rules/python_test_runner.py

@@ -4,12 +4,14 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
+import os
 import sys
 from builtins import str
 
 from future.utils import text_type
 
 from pants.backend.python.subsystems.pytest import PyTest
+from pants.backend.python.subsystems.python_setup import PythonSetup
 from pants.engine.fs import Digest, MergedDirectories, Snapshot, UrlToFetch
 from pants.engine.isolated_process import (ExecuteProcessRequest, ExecuteProcessResult,
                                            FallibleExecuteProcessResult)
@@ -26,10 +28,24 @@ class PyTestResult(TestResult):
   pass
 
 
+def parse_interpreter_constraints(python_setup, python_target_adaptors):
+  constraints = {
+    constraint
+    for target_adaptor in python_target_adaptors
+    for constraint in python_setup.compatibility_or_constraints(
+      getattr(target_adaptor, 'compatibility', None)
+    )
+  }
+  constraints_args = []
+  for constraint in sorted(constraints):
+    constraints_args.extend(["--interpreter-constraint", constraint])
+  return constraints_args
+
+
 # TODO: Support deps
 # TODO: Support resources
-@rule(PyTestResult, [TransitiveHydratedTarget, PyTest])
-def run_python_test(transitive_hydrated_target, pytest):
+@rule(PyTestResult, [TransitiveHydratedTarget, PyTest, PythonSetup])
+def run_python_test(transitive_hydrated_target, pytest, python_setup):
   target_root = transitive_hydrated_target.root
 
   # TODO: Inject versions and digests here through some option, rather than hard-coding it.
@@ -50,30 +66,31 @@ def run_python_test(transitive_hydrated_target, pytest):
       for py_req in maybe_python_req_lib.adaptor.requirements:
         all_requirements.append(str(py_req.requirement))
 
-  # TODO: This should be configurable, both with interpreter constraints, and for remote execution.
   # TODO(#7061): This str() can be removed after we drop py2!
   python_binary = text_type(sys.executable)
+  interpreter_constraint_args = parse_interpreter_constraints(
+    python_setup, python_target_adaptors=[target.adaptor for target in all_targets]
+  )
 
   # TODO: This is non-hermetic because the requirements will be resolved on the fly by
   # pex27, where it should be hermetically provided in some way.
   output_pytest_requirements_pex_filename = 'pytest-with-requirements.pex'
   requirements_pex_argv = [
     python_binary,
     './{}'.format(pex_snapshot.files[0]),
-    # TODO(#7061): This text_type() can be removed after we drop py2!
-    '--python', text_type(python_binary),
     '-e', 'pytest:main',
     '-o', output_pytest_requirements_pex_filename,
-    # Sort all user requirement strings to increase the chance of cache hits across invocations.
-  ] + [
+  ] + interpreter_constraint_args + [
     # TODO(#7061): This text_type() wrapping can be removed after we drop py2!
     text_type(req)
+    # Sort all user requirement strings to increase the chance of cache hits across invocations.
     for req in sorted(
         list(pytest.get_requirement_strings())
         + list(all_requirements))
   ]
   requirements_pex_request = ExecuteProcessRequest(
     argv=tuple(requirements_pex_argv),
+    env={'PATH': os.pathsep.join(python_setup.interpreter_search_paths)},
     input_files=pex_snapshot.directory_digest,
     description='Resolve requirements for {}'.format(target_root.address.reference()),
     output_files=(output_pytest_requirements_pex_filename,),
@@ -101,6 +118,7 @@ def run_python_test(transitive_hydrated_target, pytest):
 
   request = ExecuteProcessRequest(
     argv=(python_binary, './{}'.format(output_pytest_requirements_pex_filename)),
+    env={'PATH': os.pathsep.join(python_setup.interpreter_search_paths)},
     input_files=merged_input_files,
     description='Run pytest for {}'.format(target_root.address.reference()),
   )
@@ -119,4 +137,5 @@ def rules():
   return [
       run_python_test,
       optionable_rule(PyTest),
+      optionable_rule(PythonSetup),
     ]

tests/python/pants_test/backend/python/rules/BUILD

@@ -0,0 +1,13 @@
+# Copyright 2019 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_tests(
+  name='python_test_runner',
+  sources=['test_python_test_runner.py'],
+  dependencies=[
+    'src/python/pants/backend/python/rules',
+    'src/python/pants/backend/python/subsystems',
+    'src/python/pants/engine/legacy:structs',
+    'tests/python/pants_test/subsystem:subsystem_utils',
+  ]
+)

tests/python/pants_test/backend/python/rules/test_python_test_runner.py

@@ -0,0 +1,31 @@
+# coding=utf-8
+# Copyright 2019 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+from unittest import TestCase
+
+from pants.backend.python.rules.python_test_runner import parse_interpreter_constraints
+from pants.backend.python.subsystems.python_setup import PythonSetup
+from pants.engine.legacy.structs import PythonTargetAdaptor
+from pants_test.subsystem.subsystem_util import global_subsystem_instance
+
+
+class TestPythonTestRunner(TestCase):
+
+  def test_interpreter_constraints_parsing(self):
+    python_setup = global_subsystem_instance(PythonSetup)
+    target_adaptors = [
+      # NB: This target will use the global --python-setup-interpreter-constraints.
+      PythonTargetAdaptor(compatibility=None),
+      PythonTargetAdaptor(compatibility=["CPython>=400"]),
+    ]
+    self.assertEqual(
+      parse_interpreter_constraints(python_setup, target_adaptors),
+      [
+        "--interpreter-constraint", "CPython>=2.7,<3",
+        "--interpreter-constraint", "CPython>=3.6,<4",
+        "--interpreter-constraint", "CPython>=400"
+      ]
+    )