Flake8 output file support.

src/python/pants/backend/python/lint/flake8/rules.py

@@ -15,14 +15,14 @@
 from pants.backend.python.subsystems import python_native_code, subprocess_environment
 from pants.backend.python.subsystems.subprocess_environment import SubprocessEncodingEnvironment
 from pants.backend.python.target_types import PythonInterpreterCompatibility, PythonSources
-from pants.core.goals.lint import LintRequest, LintResult, LintResults
+from pants.core.goals.lint import LintRequest, LintResult, LintResultFile, LintResults
 from pants.core.util_rules import determine_source_files, strip_source_roots
 from pants.core.util_rules.determine_source_files import (
     AllSourceFilesRequest,
     SourceFiles,
     SpecifiedSourceFilesRequest,
 )
-from pants.engine.fs import Digest, MergeDigests, PathGlobs, Snapshot
+from pants.engine.fs import Digest, MergeDigests, PathGlobs, Snapshot, SnapshotSubset
 from pants.engine.process import FallibleProcessResult, Process
 from pants.engine.rules import SubsystemRule, rule
 from pants.engine.selectors import Get, MultiGet
@@ -51,10 +51,14 @@ class Flake8Partition:
     interpreter_constraints: PexInterpreterConstraints
 
 
-def generate_args(*, specified_source_files: SourceFiles, flake8: Flake8) -> Tuple[str, ...]:
+def generate_args(
+    *, specified_source_files: SourceFiles, flake8: Flake8, output_file: Optional[str]
+) -> Tuple[str, ...]:
     args = []
     if flake8.options.config is not None:
         args.append(f"--config={flake8.options.config}")
+    if output_file:
+        args.append(f"--output-file={output_file}")
     args.extend(flake8.options.args)
     args.extend(specified_source_files.files)
     return tuple(args)
@@ -117,19 +121,37 @@ async def flake8_lint_partition(
     address_references = ", ".join(
         sorted(field_set.address.reference() for field_set in partition.field_sets)
     )
-
+    output_path = flake8.output_file_path
+    flake8_args = generate_args(
+        specified_source_files=specified_source_files,
+        flake8=flake8,
+        output_file=output_path.name if output_path else None,
+    )
     process = requirements_pex.create_process(
         python_setup=python_setup,
         subprocess_encoding_environment=subprocess_encoding_environment,
         pex_path="./flake8.pex",
-        pex_args=generate_args(specified_source_files=specified_source_files, flake8=flake8),
+        pex_args=flake8_args,
+        output_files=(output_path.name,) if output_path else None,
         input_digest=input_digest,
         description=(
             f"Run Flake8 on {pluralize(len(partition.field_sets), 'target')}: {address_references}."
         ),
     )
     result = await Get(FallibleProcessResult, Process, process)
-    return LintResult.from_fallible_process_result(result, linter_name="Flake8")
+    results_file = None
+
+    if output_path:
+        report_file_snapshot = await Get(
+            Snapshot, SnapshotSubset(result.output_digest, PathGlobs([output_path.name]))
+        )
+        if report_file_snapshot.is_empty or len(report_file_snapshot.files) != 1:
+            raise Exception(f"Unexpected report file snapshot: {report_file_snapshot}")
+        results_file = LintResultFile(output_path=output_path, digest=report_file_snapshot.digest)
+
+    return LintResult.from_fallible_process_result(
+        result, linter_name="Flake8", results_file=results_file
+    )
 
 
 @rule(desc="Lint using Flake8")

src/python/pants/backend/python/lint/flake8/rules_integration_test.py

@@ -9,7 +9,7 @@
 from pants.base.specs import FilesystemLiteralSpec, OriginSpec, SingleAddress
 from pants.core.goals.lint import LintResults
 from pants.engine.addresses import Address
-from pants.engine.fs import FileContent
+from pants.engine.fs import DigestContents, FileContent
 from pants.engine.rules import RootRule
 from pants.engine.selectors import Params
 from pants.engine.target import TargetWithOrigin
@@ -78,13 +78,15 @@ def test_passing_source(self) -> None:
         assert len(result) == 1
         assert result[0].exit_code == 0
         assert result[0].stdout.strip() == ""
+        assert result[0].results_file is None
 
     def test_failing_source(self) -> None:
         target = self.make_target_with_origin([self.bad_source])
         result = self.run_flake8([target])
         assert len(result) == 1
         assert result[0].exit_code == 1
         assert "bad.py:1:1: F401" in result[0].stdout
+        assert result[0].results_file is None
 
     def test_mixed_sources(self) -> None:
         target = self.make_target_with_origin([self.good_source, self.bad_source])
@@ -173,3 +175,14 @@ def test_3rdparty_plugin(self) -> None:
         assert len(result) == 1
         assert result[0].exit_code == 1
         assert "bad.py:1:1: PB11" in result[0].stdout
+
+    def test_output_file(self) -> None:
+        target = self.make_target_with_origin([self.bad_source])
+        result = self.run_flake8([target], additional_args=["--flake8-output-file=report.txt"])
+        assert len(result) == 1
+        assert result[0].exit_code == 1
+        assert result[0].stdout.strip() == ""
+        assert result[0].results_file is not None
+        output_files = self.request_single_product(DigestContents, result[0].results_file.digest)
+        assert len(output_files) == 1
+        assert "bad.py:1:1: F401" in output_files[0].content.decode()

src/python/pants/backend/python/lint/flake8/subsystem.py

@@ -1,6 +1,9 @@
 # Copyright 2019 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
+from pathlib import Path
+from typing import Optional
+
 from pants.backend.python.subsystems.python_tool_base import PythonToolBase
 from pants.option.custom_types import file_option, shell_str
 
@@ -34,3 +37,16 @@ def register_options(cls, register):
             advanced=True,
             help="Path to `.flake8` or alternative Flake8 config file",
         )
+        register(
+            "--output-file",
+            type=str,
+            metavar="filename",
+            default=None,
+            advanced=True,
+            help="Redirect report to a file.",
+        )
+
+    @property
+    def output_file_path(self) -> Optional[Path]:
+        output_file = self.options.output_file
+        return Path(output_file) if output_file else None

src/python/pants/core/goals/lint.py

@@ -3,7 +3,8 @@
 
 import itertools
 from dataclasses import dataclass
-from typing import Iterable
+from pathlib import Path
+from typing import Iterable, Optional
 
 from pants.core.goals.style_request import StyleRequest
 from pants.core.util_rules.filter_empty_sources import (
@@ -12,6 +13,7 @@
 )
 from pants.engine.collection import Collection
 from pants.engine.console import Console
+from pants.engine.fs import Digest, DirectoryToMaterialize, Workspace
 from pants.engine.goal import Goal, GoalSubsystem
 from pants.engine.process import FallibleProcessResult
 from pants.engine.rules import goal_rule
@@ -21,16 +23,27 @@
 from pants.util.strutil import strip_v2_chroot_path
 
 
+@dataclass(frozen=True)
+class LintResultFile:
+    output_path: Path
+    digest: Digest
+
+
 @dataclass(frozen=True)
 class LintResult:
     exit_code: int
     stdout: str
     stderr: str
     linter_name: str
+    results_file: Optional[LintResultFile]
 
     @staticmethod
     def from_fallible_process_result(
-        process_result: FallibleProcessResult, *, linter_name: str, strip_chroot_path: bool = False
+        process_result: FallibleProcessResult,
+        *,
+        linter_name: str,
+        strip_chroot_path: bool = False,
+        results_file: Optional[LintResultFile] = None,
     ) -> "LintResult":
         def prep_output(s: bytes) -> str:
             return strip_v2_chroot_path(s) if strip_chroot_path else s.decode()
@@ -40,7 +53,19 @@ def prep_output(s: bytes) -> str:
             stdout=prep_output(process_result.stdout),
             stderr=prep_output(process_result.stderr),
             linter_name=linter_name,
+            results_file=results_file,
+        )
+
+    def materialize(self, console: Console, workspace: Workspace) -> None:
+        if not self.results_file:
+            return
+        output_path = self.results_file.output_path
+        workspace.materialize_directory(
+            DirectoryToMaterialize(
+                self.results_file.digest, path_prefix=output_path.parent.as_posix(),
+            )
         )
+        console.print_stdout(f"Wrote {self.linter_name} report to: {output_path.as_posix()}")
 
 
 class LintResults(Collection[LintResult]):
@@ -94,6 +119,7 @@ class Lint(Goal):
 @goal_rule
 async def lint(
     console: Console,
+    workspace: Workspace,
     targets_with_origins: TargetsWithOrigins,
     options: LintOptions,
     union_membership: UnionMembership,
@@ -145,6 +171,7 @@ async def lint(
             console.print_stderr(result.stderr)
         if result != sorted_results[-1]:
             console.print_stderr("")
+        result.materialize(console, workspace)
         if result.exit_code != 0:
             exit_code = result.exit_code
 

src/python/pants/core/goals/lint_test.py

@@ -12,6 +12,7 @@
     FieldSetsWithSourcesRequest,
 )
 from pants.engine.addresses import Address
+from pants.engine.fs import Workspace
 from pants.engine.target import (
     FieldSetWithOrigin,
     Sources,
@@ -57,6 +58,7 @@ def lint_results(self) -> LintResults:
                     self.stdout(addresses),
                     "",
                     linter_name=self.linter_name,
+                    results_file=None,
                 )
             ]
         )
@@ -131,20 +133,22 @@ def make_target_with_origin(address: Optional[Address] = None) -> TargetWithOrig
             origin=SingleAddress(directory=address.spec_path, name=address.target_name),
         )
 
-    @staticmethod
     def run_lint_rule(
+        self,
         *,
         lint_request_types: List[Type[LintRequest]],
         targets: List[TargetWithOrigin],
         per_target_caching: bool,
         include_sources: bool = True,
     ) -> Tuple[int, str]:
         console = MockConsole(use_colors=False)
+        workspace = Workspace(self.scheduler)
         union_membership = UnionMembership({LintRequest: lint_request_types})
         result: Lint = run_rule(
             lint,
             rule_args=[
                 console,
+                workspace,
                 TargetsWithOrigins(targets),
                 create_goal_subsystem(LintOptions, per_target_caching=per_target_caching),
                 union_membership,