fix(download_lt): emit a warning when no checksum available

CHANGELOG.md

@@ -37,6 +37,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/2.0.0/),
 - Fixed a bug in `LanguageTool._start_server_on_free_port` where `_url` was not updated when retrying on a different port, causing all subsequent server requests to target the wrong (original) port.
 - Fixed a bug in `LanguageTool._query_server` where `RateLimitError` was only raised when the rate-limit response body was invalid JSON, a valid JSON body with status 426 was silently returned as data instead (for now, the body from LanguageTool for rate-limiting responses is "Upgrade Required", which is not valid JSON, but this may change in the future).
 - Fixed a bug in `LanguageTool._terminate_server` where `_RUNNING_SERVER_PROCESSES.remove()` could raise `ValueError` if the server process was not yet in the list or was no longer in it.
+- Fixed a missing warning when downloading a LanguageTool zip file (with `LanguageTool` or `LocalLanguageTool`) without an available SHA-256 checksum. Now a `RuntimeWarning` is emitted in this case.
 
 ### Removed
 - **Breaking:** Removed all functions and classes previously deprecated in v3.3.0:

docs/source/references/env_vars.rst

@@ -48,7 +48,10 @@ resolved in this order:
 3. The bundled ``language_tool_python/_ressources/integrity.toml`` manifest, which
    covers release and archive downloads. Snapshots are not included.
 
-If none of the above resolves to a checksum, the download proceeds without verification.
+If none of the above resolves to a checksum, a ``RuntimeWarning`` is emitted and the
+download proceeds without verification. This is typically the case for snapshots, which
+are absent from the bundled manifest. Provide a checksum via
+``LTP_DOWNLOAD_SHA256_<VERSION>`` to silence the warning and verify the download.
 
 .. list-table::
    :header-rows: 1

src/language_tool_python/download_lt.py

@@ -5,6 +5,7 @@
 import contextlib
 import hashlib
 import importlib.resources
+import inspect
 import logging
 import os
 import re
@@ -83,6 +84,35 @@
 _LTP_JAR_DIR_PATH_ENV_VAR = "LTP_JAR_DIR_PATH"
 _DOWNLOAD_CHUNK_BYTES = 1024 * 1024
 _SAFE_ZIP_EXTRACTOR = SafeZipExtractor()
+_PACKAGE_DIR = Path(__file__).resolve().parent
+
+
+def _external_stacklevel() -> int:
+    """Compute the stacklevel of the first caller located outside this package.
+
+    The call chain leading into a warning here varies in depth depending on how it is
+    reached (e.g. through ``LanguageTool.__init__()`` versus calling
+    ``LocalLanguageTool.download()`` directly), so a hardcoded stacklevel would point
+    to the wrong line, or nothing at all, depending on the caller. Walking the stack
+    until leaving this package keeps the warning attributed to the caller's code.
+
+    :return: The stacklevel to pass to :func:`warnings.warn`, from the perspective of
+        the caller of this function.
+    :rtype: int
+    """
+    frame = inspect.currentframe()
+    try:
+        frame = frame.f_back if frame is not None else None
+        stacklevel = 1
+        while frame is not None:
+            frame_dir = Path(frame.f_code.co_filename).resolve().parent
+            if frame_dir != _PACKAGE_DIR:
+                break
+            frame = frame.f_back
+            stacklevel += 1
+        return stacklevel
+    finally:
+        del frame  # Avoid reference cycles
 
 
 def _loads_manifest(raw_manifest: str) -> object:
@@ -156,7 +186,9 @@
     for the given version. It normalizes the version name to construct the environment
     variable name. If no specific environment variable is found for the version, it
     falls back to a general environment variable or a manifest lookup. If the bypass
-    environment variable is set, it will skip verification and return None.
+    environment variable is set, it will skip verification and return None. If no
+    checksum is configured for the version (typically snapshots, which are absent from
+    the bundled manifest), a RuntimeWarning is emitted before returning None.
 
     :param version_name: The version name of LanguageTool (e.g., '6.0', '20240101', or
         'latest').
@@ -173,7 +205,7 @@
             f"{_LTP_BYPASS_VERIFIED_DOWNLOADS_ENV_VAR}="
             f"false to re-enable verification."
         )
-        warn(err, RuntimeWarning, stacklevel=2)
+        warn(err, RuntimeWarning, stacklevel=_external_stacklevel())
         return None
     suffix = re.sub(r"[^A-Za-z0-9]+", "_", version_name).strip("_").upper()
     version_env_var = f"LTP_DOWNLOAD_SHA256_{suffix}"
@@ -189,6 +221,12 @@
                 err = f"Invalid SHA-256 checksum configured by {source}."
                 raise PathError(err)
             return normalized
+    err = (
+        f"No SHA-256 checksum available for LanguageTool {version_name}. "
+        f"Integrity will not be verified for this download. "
+        f"You can provide one via the {version_env_var} environment variable."
+    )
+    warn(err, RuntimeWarning, stacklevel=_external_stacklevel())
     return None
 
 

tests/unit/test_download_unit.py

@@ -4,6 +4,7 @@
 
 import re
 import subprocess
+import warnings
 from datetime import datetime, timezone
 from typing import TYPE_CHECKING
 
@@ -321,14 +322,29 @@ def test_known_version_returns_hash(self) -> None:
         assert result is not None
         assert len(result) == _SHA256_HEX_LENGTH
 
-    def test_unknown_version_returns_none(
+    def test_unknown_version_returns_none_with_warning(
         self, monkeypatch: pytest.MonkeyPatch
     ) -> None:
-        """A version absent from the manifest returns None."""
+        """A version absent from the manifest returns None and warns about it."""
         monkeypatch.delenv("LTP_BYPASS_VERIFIED_DOWNLOADS", raising=False)
-        result = _dl._get_zip_hash("0.0")
+        monkeypatch.delenv("LTP_DOWNLOAD_SHA256", raising=False)
+        monkeypatch.delenv("LTP_DOWNLOAD_SHA256_0_0", raising=False)
+        with pytest.warns(RuntimeWarning, match="No SHA-256 checksum available"):
+            result = _dl._get_zip_hash("0.0")
         assert result is None
 
+    def test_known_version_emits_no_checksum_warning(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """A version present in the manifest emits no missing-checksum warning."""
+        monkeypatch.delenv("LTP_BYPASS_VERIFIED_DOWNLOADS", raising=False)
+        monkeypatch.delenv("LTP_DOWNLOAD_SHA256", raising=False)
+        monkeypatch.delenv("LTP_DOWNLOAD_SHA256_6_8", raising=False)
+        with warnings.catch_warnings():
+            warnings.simplefilter("error", RuntimeWarning)
+            result = _dl._get_zip_hash("6.8")
+        assert result is not None
+
     def test_invalid_hash_in_env_raises(self, monkeypatch: pytest.MonkeyPatch) -> None:
         """An invalid SHA-256 value in LTP_DOWNLOAD_SHA256 raises PathError."""
         monkeypatch.setenv("LTP_DOWNLOAD_SHA256", "not-a-valid-sha256")