Added support for Pytest config files (#11624)

Closes #11526 : this adds support for a pytest.ini config file and an associated test. Pytest does not offer support for directly specifying a path for a config file, though this can be done indirectly using `--rootdir=path`, which may bring in other issues; however, this can be implemented if need be. 

[ci skip-rust]
[ci skip-build-wheels]

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

@@ -42,7 +42,15 @@
 )
 from pants.core.util_rules.source_files import SourceFiles, SourceFilesRequest
 from pants.engine.addresses import UnparsedAddressInputs
-from pants.engine.fs import AddPrefix, Digest, DigestSubset, MergeDigests, PathGlobs, Snapshot
+from pants.engine.fs import (
+    AddPrefix,
+    Digest,
+    DigestSubset,
+    GlobMatchErrorBehavior,
+    MergeDigests,
+    PathGlobs,
+    Snapshot,
+)
 from pants.engine.process import (
     FallibleProcessResult,
     InteractiveProcess,
@@ -133,6 +141,15 @@ async def setup_pytest_for_target(
         ),
     )
 
+    config_digest_request = Get(
+        Digest,
+        PathGlobs(
+            globs=[pytest.config] if pytest.config else [],
+            glob_match_error_behavior=GlobMatchErrorBehavior.error,
+            description_of_origin="the option `--pytest-config`",
+        ),
+    )
+
     prepared_sources_request = Get(
         PythonSourceFiles, PythonSourceFilesRequest(all_targets, include_files=True)
     )
@@ -161,11 +178,18 @@ async def setup_pytest_for_target(
         SourceFiles, SourceFilesRequest([request.field_set.sources])
     )
 
-    pytest_pex, requirements_pex, prepared_sources, field_set_source_files = await MultiGet(
+    (
+        pytest_pex,
+        requirements_pex,
+        prepared_sources,
+        field_set_source_files,
+        config_digest,
+    ) = await MultiGet(
         pytest_pex_request,
         requirements_pex_request,
         prepared_sources_request,
         field_set_source_files_request,
+        config_digest_request,
     )
 
     pytest_runner_pex = await Get(
@@ -187,6 +211,7 @@ async def setup_pytest_for_target(
             (
                 coverage_config.digest,
                 prepared_sources.source_files.snapshot.digest,
+                config_digest,
                 *(binary.digest for binary in assets),
             )
         ),

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

@@ -52,6 +52,7 @@ def rule_runner() -> RuleRunner:
 SOURCE_ROOT = "tests/python"
 PACKAGE = os.path.join(SOURCE_ROOT, "pants_test")
 GOOD_SOURCE = FileContent(f"{PACKAGE}/test_good.py", b"def test():\n  pass\n")
+GOOD_WITH_PRINT = FileContent(f"{PACKAGE}/test_good.py", b"def test():\n  print('All good!')")
 BAD_SOURCE = FileContent(f"{PACKAGE}/test_bad.py", b"def test():\n  assert False\n")
 PY3_ONLY_SOURCE = FileContent(f"{PACKAGE}/test_py3.py", b"def test() -> None:\n  pass\n")
 LIBRARY_SOURCE = FileContent(f"{PACKAGE}/library.py", b"def add_two(x):\n  return x + 2\n")
@@ -143,6 +144,7 @@ def run_pytest(
     execution_slot_var: Optional[str] = None,
     extra_env_vars: Optional[str] = None,
     env: Optional[Mapping[str, str]] = None,
+    config: Optional[str] = None,
     force: bool = False,
 ) -> TestResult:
     args = [
@@ -162,6 +164,9 @@ def run_pytest(
         args.append("--test-use-coverage")
     if execution_slot_var:
         args.append(f"--pytest-execution-slot-var={execution_slot_var}")
+    if config:
+        rule_runner.create_file(relpath="pytest.ini", contents=config)
+        args.append("--pytest-config=pytest.ini")
     if force:
         args.append("--test-force")
     rule_runner.set_options(args, env=env)
@@ -253,6 +258,13 @@ def test():
     assert f"{PACKAGE}/test_relative_import.py ." in result.stdout
 
 
+def test_respects_config(rule_runner: RuleRunner) -> None:
+    target = create_test_target(rule_runner, [GOOD_WITH_PRINT])
+    result = run_pytest(rule_runner, target, config="[pytest]\naddopts = -s\n")
+    assert result.exit_code == 0
+    assert "All good!" in result.stdout and "Captured" not in result.stdout
+
+
 def test_transitive_dep(rule_runner: RuleRunner) -> None:
     create_python_library(rule_runner, [LIBRARY_SOURCE])
     transitive_dep_fc = FileContent(

src/python/pants/backend/python/subsystems/pytest.py

@@ -3,7 +3,7 @@
 
 from typing import Optional, Tuple, cast
 
-from pants.option.custom_types import shell_str
+from pants.option.custom_types import file_option, shell_str
 from pants.option.subsystem import Subsystem
 
 
@@ -89,6 +89,22 @@ def register_options(cls, register):
                 "to tests under this environment variable name."
             ),
         )
+        register(
+            "--config",
+            type=file_option,
+            default=None,
+            advanced=True,
+            help=(
+                "Path to pytest.ini or alternative Pytest config file.\n\n"
+                "Pytest will attempt to auto-discover the config file,"
+                "meaning that it should typically be an ancestor of your"
+                "tests, such as in the build root.\n\nPants will not automatically"
+                " set --rootdir for you to force Pytest to pick up your config "
+                "file, but you can manually set --rootdir in [pytest].args.\n\n"
+                "Refer to https://docs.pytest.org/en/stable/customize.html#"
+                "initialization-determining-rootdir-and-configfile."
+            ),
+        )
 
     def get_requirement_strings(self) -> Tuple[str, ...]:
         """Returns a tuple of requirements-style strings for Pytest and Pytest plugins."""
@@ -105,3 +121,7 @@ def timeout_default(self) -> Optional[int]:
     @property
     def timeout_maximum(self) -> Optional[int]:
         return cast(Optional[int], self.options.timeout_maximum)
+
+    @property
+    def config(self) -> Optional[str]:
+        return cast(Optional[str], self.options.config)