Refuse a Path That Does Not Exist, Rather Than Scanning the Caller's Directory

`discover` reads any argument that is neither a file nor a directory as
`.`, so a typo scanned the caller's directory while the rule set anchored
on the missing path's parent. The run then described one tree and judged it
by another, which is this PR's own subject in a different guise.
A missing path is now refused, naming each one.
Two existing cases passed fake paths as a mocking convenience and were
refused by the new check before reaching the guard they exist to test. They
use real directories now, which preserves what they assert rather than
loosening the check to accommodate them.
Two cases added: a missing path is refused, and an existing one is not.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: ptr727

scripts/prose_lint.py

@@ -1110,6 +1110,14 @@ def main(argv: list[str] | None = None) -> int:
 # Only a repository declares a model, so two of them refuse and anything else resolves to one anchor.
 # TestScanRootDecidesTheRuleSet carries the cases and the reason each one exists.
 scan_paths=a.pathsor ['.']
+# A path that does not exist is refused rather than absorbed.
+# `discover` reads a non-file, non-directory argument as `.`, so a typo scanned the caller's directory while the rule set anchored on the missing path's parent.
+absent= [pforpinscan_pathsifnotPath(p).exists()]
+ifabsent:
+print(f"error: requested path(s) do not exist: {', '.join(sorted(absent))}. Refusing "
+'rather than falling back to the current directory, which would scan one tree and '
+'choose the rule set from another.', file=sys.stderr)
+return2
 git_roots= {foundforfoundin (repo_root(Path(p)) forpinscan_paths) iffound}
 iflen(git_roots) >1:
 print('error: the requested paths span more than one repository ('+

scripts/test_prose_lint.py

@@ -1528,20 +1528,26 @@ def test_a_path_under_no_repository_is_refused_too(self) -> None:
  repository-relative ones, so the scope drops every file and the run exits 0. Testing for
  a *different* root missed this, because there is no root to differ from.
  """
+# A real directory, since a path that does not exist is refused earlier for another reason.
+# That would pass this assertion without ever exercising the diff guard.
+loose=self.tmp/'loose'
+loose.mkdir()
 withmock.patch.object(prose_lint, 'repo_root',
 side_effect=lambdap: '/hub'ifstr(p) =='.'else''), \
 contextlib.redirect_stderr(io.StringIO()) aserr:
-self.assertEqual(2, prose_lint.main(['--diff', 'HEAD', '/tmp/loose']))
+self.assertEqual(2, prose_lint.main(['--diff', 'HEAD', str(loose)]))
 self.assertIn('no git repository', err.getvalue())
 
 deftest_list_files_still_reports_scope_across_repositories(self) ->None:
 """It reports the scan scope and never consults the diff, so the guard must not stop it."""
 clean=self.tmp/'clean.md'
 clean.write_text('fine\n', encoding='utf-8')
+other=self.tmp/'other'
+other.mkdir()
 withmock.patch.object(prose_lint, 'repo_root',
 side_effect=lambdap: '/hub'ifstr(p) =='.'else'/other'), \
 mock.patch.object(prose_lint, 'discover', return_value=[clean]):
-self.assertEqual(0, prose_lint.main(['--list-files', '--diff', 'HEAD', '/other/tree']))
+self.assertEqual(0, prose_lint.main(['--list-files', '--diff', 'HEAD', str(other)]))
 
 deftest_a_matching_repository_is_not_refused(self) ->None:
 """The guard must not reject the ordinary case it sits in front of."""
@@ -1851,6 +1857,26 @@ def test_paths_spanning_two_repositories_refuse_rather_than_pick_one(self) -> No
  [str(self.release), str(self.operational), '--check', 'home-path']))
 self.assertIn('more than one repository', self.err.getvalue())
 
+deftest_a_path_that_does_not_exist_is_refused_rather_than_absorbed(self) ->None:
+"""`discover` reads a non-file, non-directory argument as `.`.
+
+ A typo therefore scanned the caller's directory while the rule set anchored on the missing
+ path's parent, so the run described one tree and judged it by another.
+ """
+withmock.patch.object(prose_lint, 'repo_root', return_value=''):
+self.assertEqual(2, prose_lint.main(
+ [str(self.tmp/'no-such-dir'), '--check', 'home-path']))
+self.assertIn('do not exist', self.err.getvalue())
+
+deftest_an_existing_path_is_not_refused_by_that_check(self) ->None:
+"""The guard must not reject the ordinary case it sits in front of."""
+good=self.tmp/'good.md'
+good.write_text('Nothing here breaks a rule.\n', encoding='utf-8')
+withmock.patch.object(prose_lint, 'repo_root', return_value=''), \
+mock.patch.object(prose_lint, 'discover', return_value=[good]):
+self.assertEqual(0, prose_lint.main([str(good), '--check', 'home-path']))
+self.assertNotIn('do not exist', self.err.getvalue())
+
 deftest_several_paths_under_no_repository_are_not_a_conflict(self) ->None:
 """Only a repository declares a model, so two loose paths are not ambiguous.