gh-109276: libregrtest: WASM use stdout for JSON

On Emscripten and WASI, or if --python command line is used,
libregrtest now writes JSON into stdout, instead of using a name
file.

Author: vstinner

Lib/test/libregrtest/run_workers.py

@@ -21,7 +21,7 @@
 from .runtests import RunTests, JsonFile, JsonFileType
 from .single import PROGRESS_MIN_TIME
 from .utils import (
-    StrPath, StrJSON, TestName, MS_WINDOWS, TMP_PREFIX,
+    StrPath, StrJSON, TestName, MS_WINDOWS,
     format_duration, print_warning, count, plural)
 from .worker import create_worker_process, USE_PROCESS_GROUP
 
@@ -225,16 +225,9 @@ def create_stdout(self, stack: contextlib.ExitStack) -> TextIO:
     def create_json_file(self, stack: contextlib.ExitStack) -> tuple[JsonFile, TextIO | None]:
         """Create JSON file."""
 
-        json_file_use_filename = self.runtests.json_file_use_filename()
-        if json_file_use_filename:
-            # create an empty file to make the creation atomic
-            # (to prevent races with other worker threads)
-            prefix = TMP_PREFIX + 'json_'
-            json_fd, json_filename = tempfile.mkstemp(prefix=prefix)
-            os.close(json_fd)
-
-            stack.callback(os_helper.unlink, json_filename)
-            json_file = JsonFile(json_filename, JsonFileType.FILENAME)
+        json_file_use_stdout = self.runtests.json_file_use_stdout()
+        if json_file_use_stdout:
+            json_file = JsonFile(None, JsonFileType.STDOUT)
             json_tmpfile = None
         else:
             json_tmpfile = tempfile.TemporaryFile('w+', encoding='utf8')
@@ -300,11 +293,14 @@ def read_stdout(self, stdout_file: TextIO) -> str:
                               f"Cannot read process stdout: {exc}", None)
 
     def read_json(self, json_file: JsonFile, json_tmpfile: TextIO | None,
-                  stdout: str) -> TestResult:
+                  stdout: str) -> tuple[TestResult, str]:
         try:
             if json_tmpfile is not None:
                 json_tmpfile.seek(0)
                 worker_json: StrJSON = json_tmpfile.read()
+            elif json_file.file_type == JsonFileType.STDOUT:
+                stdout, _, worker_json = stdout.rpartition("\n")
+                stdout = stdout.rstrip()
             else:
                 with json_file.open(encoding='utf8') as json_fp:
                     worker_json: StrJSON = json_fp.read()
@@ -319,14 +315,16 @@ def read_json(self, json_file: JsonFile, json_tmpfile: TextIO | None,
             raise WorkerError(self.test_name, "empty JSON", stdout)
 
         try:
-            return TestResult.from_json(worker_json)
+            result = TestResult.from_json(worker_json)
         except Exception as exc:
             # gh-101634: Catch UnicodeDecodeError if stdout cannot be
             # decoded from encoding
             err_msg = f"Failed to parse worker process JSON: {exc}"
             raise WorkerError(self.test_name, err_msg, stdout,
                               state=State.MULTIPROCESSING_ERROR)
 
+        return (result, stdout)
+
     def _runtest(self, test_name: TestName) -> MultiprocessResult:
         with contextlib.ExitStack() as stack:
             stdout_file = self.create_stdout(stack)
@@ -341,7 +339,7 @@ def _runtest(self, test_name: TestName) -> MultiprocessResult:
             if retcode is None:
                 raise WorkerError(self.test_name, None, stdout, state=State.TIMEOUT)
 
-            result = self.read_json(json_file, json_tmpfile, stdout)
+            result, stdout = self.read_json(json_file, json_tmpfile, stdout)
 
         if retcode != 0:
             raise WorkerError(self.test_name, f"Exit code {retcode}", stdout)

Lib/test/libregrtest/runtests.py

@@ -15,12 +15,17 @@ class JsonFileType:
     UNIX_FD = "UNIX_FD"
     WINDOWS_HANDLE = "WINDOWS_HANDLE"
     FILENAME = "FILENAME"
+    STDOUT = "STDOUT"
 
 
 @dataclasses.dataclass(slots=True, frozen=True)
 class JsonFile:
-    # See RunTests.json_file_use_filename()
-    file: int | StrPath
+    # file type depends on file_type:
+    # - UNIX_FD: file descriptor (int)
+    # - WINDOWS_HANDLE: handle (int)
+    # - FILENAME: filename (str)
+    # - STDOUT: use process stdout (None)
+    file: int | StrPath | None
     file_type: str
 
     def configure_subprocess(self, popen_kwargs: dict) -> None:
@@ -33,9 +38,6 @@ def configure_subprocess(self, popen_kwargs: dict) -> None:
                 startupinfo = subprocess.STARTUPINFO()
                 startupinfo.lpAttributeList = {"handle_list": [self.file]}
                 popen_kwargs['startupinfo'] = startupinfo
-            case JsonFileType.FILENAME:
-                # Filename: nothing to do to
-                pass
 
     @contextlib.contextmanager
     def inherit_subprocess(self):
@@ -49,6 +51,9 @@ def inherit_subprocess(self):
             yield
 
     def open(self, mode='r', *, encoding):
+        if self.file_type == JsonFileType.STDOUT:
+            raise ValueError("for STDOUT file type, just use sys.stdout")
+
         file = self.file
         if self.file_type == JsonFileType.WINDOWS_HANDLE:
             import msvcrt
@@ -123,11 +128,13 @@ def as_json(self) -> StrJSON:
     def from_json(worker_json: StrJSON) -> 'RunTests':
         return json.loads(worker_json, object_hook=_decode_runtests)
 
-    def json_file_use_filename(self) -> bool:
-        # json_file type depends on the platform:
-        # - Unix: file descriptor (int)
-        # - Windows: handle (int)
-        # - Emscripten/WASI or if --python is used: filename (str)
+    def json_file_use_stdout(self) -> bool:
+        # Use STDOUT in two cases:
+        #
+        # - If --python command line option is used;
+        # - On Emscripten and WASI.
+        #
+        # On other platforms, UNIX_FD, WINDOWS_HANDLE or FILENAME can be used.
         return (
             bool(self.python_cmd)
             or support.is_emscripten

Lib/test/libregrtest/worker.py

@@ -7,7 +7,7 @@
 from test.support import os_helper
 
 from .setup import setup_process, setup_test_dir
-from .runtests import RunTests, JsonFile
+from .runtests import RunTests, JsonFile, JsonFileType
 from .single import run_single_test
 from .utils import (
     StrPath, StrJSON, FilterTuple,
@@ -67,10 +67,6 @@ def worker_process(worker_json: StrJSON) -> NoReturn:
     runtests = RunTests.from_json(worker_json)
     test_name = runtests.tests[0]
     match_tests: FilterTuple | None = runtests.match_tests
-    # json_file type depends on the platform:
-    # - Unix: file descriptor (int)
-    # - Windows: handle (int)
-    # - Emscripten/WASI or if --python is used: filename (str)
     json_file: JsonFile = runtests.json_file
 
     setup_test_dir(runtests.test_dir)
@@ -85,8 +81,12 @@ def worker_process(worker_json: StrJSON) -> NoReturn:
 
     result = run_single_test(test_name, runtests)
 
-    with json_file.open('w', encoding='utf-8') as json_fp:
-        result.write_json_into(json_fp)
+    if json_file.file_type == JsonFileType.STDOUT:
+        print()
+        result.write_json_into(sys.stdout)
+    else:
+        with json_file.open('w', encoding='utf-8') as json_fp:
+            result.write_json_into(json_fp)
 
     sys.exit(0)