Propagate has_shell_shebang's Read Failures Instead of Swallowing Them

scripts/docker_lint.py

@@ -197,15 +197,19 @@ def has_shell_shebang(root: Path, relative_path: str) -> bool:
     """Report whether a tracked file's shebang directly names bash or sh.
 
     Never follows a tracked symlink: `is_symlink()` uses `lstat`, keeping the target unreached.
+    A read failure raises `CommandFailed` instead of returning `False`.
+    That keeps a tracked file this cannot open from silently dropping out of the target list.
     """
     path = root / relative_path
+    if path.is_symlink():
+        return False
     try:
-        if path.is_symlink():
-            return False
         with path.open("rb") as handle:
             first_line = handle.readline(256)
-    except OSError:
-        return False
+    except OSError as error:
+        raise CommandFailed(
+            f"target discovery failed: could not read {relative_path}: {error}"
+        ) from error
     try:
         text = first_line.decode("utf-8").rstrip("\n")
     except UnicodeDecodeError:

scripts/tests/test_docker_lint.py

@@ -180,6 +180,14 @@ def test_has_shell_shebang_reports_false_for_a_symlink_without_reading_it(self)
         with mock.patch.object(Path, "open", side_effect=AssertionError("symlink target opened")):
             self.assertFalse(docker_lint.has_shell_shebang(self.root, "ops/evil-symlink"))
 
+    def test_has_shell_shebang_raises_rather_than_swallowing_a_read_failure(self) -> None:
+        self.track("ops/unreadable")
+        with (
+            mock.patch.object(Path, "open", side_effect=PermissionError("denied")),
+            self.assertRaisesRegex(docker_lint.CommandFailed, "could not read"),
+        ):
+            docker_lint.has_shell_shebang(self.root, "ops/unreadable")
+
     def test_extensionless_untracked_shebang_script_is_not_picked_up(self) -> None:
         path = self.root / "ops" / "vps-backup-pull"
         path.parent.mkdir(parents=True, exist_ok=True)