fix(test-runner): handle Windows path lists safely

scripts/run_tests_parallel.py

@@ -32,7 +32,7 @@
 
 Environment:
     HERMES_TEST_WORKERS  Override worker count (default: os.cpu_count())
-    HERMES_TEST_PATHS    Override discovery roots (colon-sep, default: 'tests')
+    HERMES_TEST_PATHS    Override discovery roots (path-list, default: 'tests')
 
 Exit code: 0 if every file's pytest exited 0; 1 otherwise.
 """
@@ -364,6 +364,52 @@ def _format_file(file: Path, repo_root: Path) -> str:
         return str(file)
 
 
+def _split_path_list(value: str | None) -> list[str]:
+    """Split a test path-list without shredding Windows drive letters.
+
+    CI still passes repo-relative ``:``-joined paths, so keep supporting
+    colon as the portable generated format. On Windows, user-entered absolute
+    paths should use ``os.pathsep`` (``;``), and a single ``C:\\...`` path must
+    not split at the drive separator.
+    """
+    if not value:
+        return []
+
+    if os.pathsep != ":" and os.pathsep in value:
+        return [part.strip() for part in value.split(os.pathsep) if part.strip()]
+
+    parts: list[str] = []
+    start = 0
+    for idx, char in enumerate(value):
+        if char != ":":
+            continue
+        is_windows_drive = (
+            idx == 1
+            and value[0].isalpha()
+            and idx + 1 < len(value)
+            and value[idx + 1] in {"\\", "/"}
+        )
+        if is_windows_drive:
+            continue
+        parts.append(value[start:idx])
+        start = idx + 1
+    parts.append(value[start:])
+    return [part.strip() for part in parts if part.strip()]
+
+
+def _print_line(msg: str = "", *, file=None) -> None:
+    """Print one line, replacing unencodable glyphs on legacy Windows pipes."""
+    stream = sys.stdout if file is None else file
+    try:
+        print(msg, file=stream, flush=True)
+    except UnicodeEncodeError:
+        encoding = getattr(stream, "encoding", None) or "utf-8"
+        safe = msg.encode(encoding, errors="replace").decode(
+            encoding, errors="replace"
+        )
+        print(safe, file=stream, flush=True)
+
+
 def _print_progress(
     tests_done: int,
     approx_total_tests: int,
@@ -434,7 +480,7 @@ def _print_progress(
             msg = msg[: cols - 1] + "…"
     except OSError:
         pass
-    print(msg, flush=True)
+    _print_line(msg)
 
 
 def _print_inline_failure(
@@ -606,7 +652,7 @@ def main() -> int:
     parser.add_argument(
         "--paths",
         default=os.environ.get("HERMES_TEST_PATHS", ":".join(_DEFAULT_ROOTS)),
-        help="Colon-separated discovery roots (default: 'tests')",
+        help="Path-list discovery roots (default: 'tests')",
     )
     parser.add_argument(
         "--include-integration",
@@ -652,7 +698,7 @@ def main() -> int:
         "--files",
         metavar="LIST",
         help=(
-            "Explicit colon-separated list of test files to run. Bypasses "
+            "Explicit path-list of test files to run. Bypasses "
             "discovery entirely — used by CI matrix jobs that receive their "
             "file list from the generate job."
         ),
@@ -749,15 +795,15 @@ def _is_our_flag(tok: str) -> bool:
 
     # --files: explicit file list from the CI generate job — skip discovery.
     if args.files:
-        files = [repo_root / f for f in args.files.split(":") if f.strip()]
+        files = [repo_root / f for f in _split_path_list(args.files)]
         roots = []
     else:
         # Resolve discovery roots: positional path args override --paths if any
         # were supplied, otherwise --paths (which itself defaults to 'tests').
         if args.paths_positional:
             roots = [repo_root / p for p in args.paths_positional]
         else:
-            roots = [repo_root / p for p in args.paths.split(":") if p]
+            roots = [repo_root / p for p in _split_path_list(args.paths)]
 
         if args.include_integration:
             # Caller takes responsibility — typically used via explicit -k filter.

tests/test_run_tests_parallel.py

@@ -21,12 +21,14 @@
 from __future__ import annotations
 
 import json
+import importlib.util
 import os
 import subprocess
 import sys
 import textwrap
 import time
 from pathlib import Path
+from types import ModuleType
 
 import pytest
 
@@ -38,6 +40,19 @@
 _HANDOFF_DIR.mkdir(exist_ok=True)
 
 
+def _load_runner_module() -> ModuleType:
+    repo_root = Path(__file__).resolve().parent.parent
+    runner = repo_root / "scripts" / "run_tests_parallel.py"
+    spec = importlib.util.spec_from_file_location(
+        "_hermes_run_tests_parallel", runner
+    )
+    assert spec is not None
+    assert spec.loader is not None
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
 def _handoff_path_for(nonce: str) -> Path:
     return _HANDOFF_DIR / f"grandchild-{nonce}.json"
 
@@ -261,6 +276,55 @@ def test_explicit_double_dash_still_works(tmp_path: Path) -> None:
     assert "unrecognized arguments" not in proc.stdout
 
 
+def test_path_list_preserves_windows_drive_letters(monkeypatch) -> None:
+    """Windows absolute paths are not split at the drive separator."""
+    runner = _load_runner_module()
+    monkeypatch.setattr(runner.os, "pathsep", ";")
+
+    assert runner._split_path_list(r"C:\Users\me\repo\tests") == [
+        r"C:\Users\me\repo\tests"
+    ]
+    assert runner._split_path_list(r"C:\repo\tests;D:\other\tests") == [
+        r"C:\repo\tests",
+        r"D:\other\tests",
+    ]
+
+
+def test_path_list_keeps_ci_colon_joined_relative_files(monkeypatch) -> None:
+    """CI-generated repo-relative ``:`` lists keep working on every platform."""
+    runner = _load_runner_module()
+    monkeypatch.setattr(runner.os, "pathsep", ";")
+
+    assert runner._split_path_list("tests/a.py:tests/b.py") == [
+        "tests/a.py",
+        "tests/b.py",
+    ]
+
+
+def test_progress_print_replaces_unencodable_glyphs() -> None:
+    """Legacy Windows pipes should not drop progress callbacks."""
+    runner = _load_runner_module()
+
+    class LegacyPipe:
+        encoding = "cp1252"
+
+        def __init__(self) -> None:
+            self.output = ""
+
+        def write(self, text: str) -> int:
+            text.encode(self.encoding)
+            self.output += text
+            return len(text)
+
+        def flush(self) -> None:
+            pass
+
+    pipe = LegacyPipe()
+    runner._print_line("1✓", file=pipe)
+
+    assert pipe.output == "1?\n"
+
+
 def test_positional_path_not_treated_as_flag(tmp_path: Path) -> None:
     """A positional path arg still overrides discovery (not routed to pytest)."""
     probe_dir = _make_probe_dir(tmp_path)