Pass required information to cov_to_lint.py

Now that we run linters for a baseline on `rev1` in a temporary clone
of the repository, `cov_to_lint.py` needs to find the pre-generated
coverage files. For that, we pass the original repository root path and
the revision being linted as environment variables.

src/darker/linting.py

@@ -20,6 +20,7 @@
 """
 
 import logging
+import os
 import shlex
 from collections import defaultdict
 from contextlib import contextmanager
@@ -36,6 +37,7 @@
     git_clone_local,
     git_get_content_at_revision,
     git_get_root,
+    git_rev_parse,
     shlex_join,
 )
 from darker.highlighting import colorize
@@ -119,6 +121,24 @@ def get(self, new_location: MessageLocation) -> MessageLocation:
         return NO_MESSAGE_LOCATION
 
 
+def make_linter_env(root: Path, revision: str) -> Dict[str, str]:
+    """Populate environment variables for running linters
+
+    :param root: The path to the root of the Git repository
+    :param revision: The commit hash of the Git revision being linted, or ``"WORKTREE"``
+                     if the working tree is being linted
+    :return: The environment variables dictionary to pass to the linter
+
+    """
+    return {
+        **os.environ,
+        "DARKER_LINT_ORIG_REPO": str(root),
+        "DARKER_LINT_REV_COMMIT": (
+            "WORKTREE" if revision == "WORKTREE" else revision[:7]
+        ),
+    }
+
+
 def _strict_nonneg_int(text: str) -> int:
     """Strict parsing of strings to non-negative integers
 
@@ -229,12 +249,14 @@ def _check_linter_output(
     cmdline: Union[str, List[str]],
     root: Path,
     paths: Collection[Path],
+    env: Dict[str, str],
 ) -> Generator[IO[str], None, None]:
     """Run a linter as a subprocess and return its standard output stream
 
     :param cmdline: The command line for running the linter
     :param root: The common root of all files to lint
     :param paths: Paths of files to check, relative to ``root``
+    :param env: Environment variables to pass to the linter
     :return: The standard output stream of the linter subprocess
 
     """
@@ -249,6 +271,7 @@ def _check_linter_output(
         stdout=PIPE,
         encoding="utf-8",
         cwd=root,
+        env=env,
     ) as linter_process:
         # condition needed for MyPy (see https://stackoverflow.com/q/57350490/15770)
         if linter_process.stdout is None:
@@ -260,13 +283,14 @@ def run_linter(  # pylint: disable=too-many-locals
     cmdline: Union[str, List[str]],
     root: Path,
     paths: Collection[Path],
+    env: Dict[str, str],
 ) -> Dict[MessageLocation, LinterMessage]:
     """Run the given linter and return linting errors falling on changed lines
 
     :param cmdline: The command line for running the linter
     :param root: The common root of all files to lint
     :param paths: Paths of files to check, relative to ``root``
-    :param revrange: The Git revision rango to compare
+    :param env: Environment variables to pass to the linter
     :return: The number of modified lines with linting errors from this linter
 
     """
@@ -278,7 +302,7 @@ def run_linter(  # pylint: disable=too-many-locals
     else:
         linter = cmdline[0]
         cmdline_str = shlex_join(cmdline)
-    with _check_linter_output(cmdline, root, paths) as linter_stdout:
+    with _check_linter_output(cmdline, root, paths, env) as linter_stdout:
         for line in linter_stdout:
             (location, message) = _parse_linter_line(linter, line, root)
             if location is NO_MESSAGE_LOCATION or location.path in missing_files:
@@ -334,6 +358,7 @@ def run_linters(
             linter_cmdlines,
             root,
             paths,
+            make_linter_env(root, "WORKTREE"),
         )
         return _print_new_linter_messages(
             baseline={},
@@ -343,9 +368,17 @@ def run_linters(
         )
     git_paths = {(root / path).relative_to(git_root) for path in paths}
     baseline = _get_messages_from_linters_for_baseline(
-        linter_cmdlines, git_root, git_paths, revrange.rev1
+        linter_cmdlines,
+        git_root,
+        git_paths,
+        revrange.rev1,
+    )
+    messages = _get_messages_from_linters(
+        linter_cmdlines,
+        git_root,
+        git_paths,
+        make_linter_env(git_root, "WORKTREE"),
     )
-    messages = _get_messages_from_linters(linter_cmdlines, git_root, git_paths)
     files_with_messages = {location.path for location in messages}
     diff_line_mapping = _create_line_mapping(git_root, files_with_messages, revrange)
     return _print_new_linter_messages(baseline, messages, diff_line_mapping, use_color)
@@ -355,19 +388,20 @@ def _get_messages_from_linters(
     linter_cmdlines: Iterable[Union[str, List[str]]],
     root: Path,
     paths: Collection[Path],
+    env: Dict[str, str],
 ) -> Dict[MessageLocation, List[LinterMessage]]:
     """Run given linters for the given directory and return linting errors
 
     :param linter_cmdlines: The command lines for running the linters
     :param root: The common root of all files to lint
     :param paths: Paths of files to check, relative to ``root``
-    :param revrange: The Git revision rango to compare
+    :param env: The environment variables to pass to the linter
     :return: Linter messages
 
     """
     result = defaultdict(list)
     for cmdline in linter_cmdlines:
-        for message_location, message in run_linter(cmdline, root, paths).items():
+        for message_location, message in run_linter(cmdline, root, paths, env).items():
             result[message_location].append(message)
     return result
 
@@ -429,7 +463,13 @@ def _get_messages_from_linters_for_baseline(
     """
     with TemporaryDirectory() as tmp_path:
         clone_root = git_clone_local(root, revision, Path(tmp_path))
-        result = _get_messages_from_linters(linter_cmdlines, clone_root, paths)
+        rev1_commit = git_rev_parse(revision, root)
+        result = _get_messages_from_linters(
+            linter_cmdlines,
+            clone_root,
+            paths,
+            make_linter_env(root, rev1_commit),
+        )
         fix_py37_win_tempdir_permissions(tmp_path)
     return result
 

src/darker/tests/test_linting.py

@@ -11,7 +11,12 @@
 
 from darker import linting
 from darker.git import WORKTREE, RevisionRange
-from darker.linting import DiffLineMapping, LinterMessage, MessageLocation
+from darker.linting import (
+    DiffLineMapping,
+    LinterMessage,
+    MessageLocation,
+    make_linter_env,
+)
 from darker.tests.helpers import raises_if_exception
 from darker.utils import WINDOWS
 
@@ -169,7 +174,10 @@ def test_require_rev2_worktree(rev2, expect):
 def test_check_linter_output(tmp_path, cmdline, expect):
     """``_check_linter_output()`` runs linter and returns the stdout stream"""
     with linting._check_linter_output(
-        cmdline, tmp_path, {Path("first.py"), Path("the  2nd.py")}
+        cmdline,
+        tmp_path,
+        {Path("first.py"), Path("the  2nd.py")},
+        make_linter_env(tmp_path, "WORKTREE"),
     ) as stdout:
         lines = list(stdout)