Warn on all redirects if linkcheck_allowed_redirects is an empty dictionary

CHANGES.rst

@@ -16,6 +16,9 @@ Features added
 * #13332: Add :confval:`doctest_fail_fast` option to exit after the first failed
   test.
   Patch by Till Hoffmann.
+* #13439: linkcheck: Permit warning on every redirect with
+  ``linkcheck_allowed_redirects = {}``.
+  Patch by Adam Turner.
 
 Bugs fixed
 ----------

doc/usage/configuration.rst

@@ -3668,6 +3668,11 @@ and which failures and redirects it ignores.
 
    .. versionadded:: 4.1
 
+   .. versionchanged:: 8.3
+      Setting :confval:`!linkcheck_allowed_redirects` to the empty directory
+      may now be used to warn on all redirects encountered
+      by the *linkcheck* builder.
+
 .. confval:: linkcheck_anchors
    :type: :code-py:`bool`
    :default: :code-py:`True`

sphinx/builders/linkcheck.py

@@ -25,6 +25,7 @@
 
 from sphinx._cli.util.colour import darkgray, darkgreen, purple, red, turquoise
 from sphinx.builders.dummy import DummyBuilder
+from sphinx.errors import ConfigError
 from sphinx.locale import __
 from sphinx.transforms.post_transforms import SphinxPostTransform
 from sphinx.util import logging, requests
@@ -178,7 +179,7 @@ def process_result(self, result: CheckResult) -> None:
                         text = 'with unknown code'
                 linkstat['text'] = text
                 redirection = f'{text} to {result.message}'
-                if self.config.linkcheck_allowed_redirects:
+                if self.config.linkcheck_allowed_redirects is not None:
                     msg = f'redirect  {res_uri} - {redirection}'
                     logger.warning(msg, location=(result.docname, result.lineno))
                 else:
@@ -386,7 +387,7 @@ def __init__(
         )
         self.check_anchors: bool = config.linkcheck_anchors
         self.allowed_redirects: dict[re.Pattern[str], re.Pattern[str]]
-        self.allowed_redirects = config.linkcheck_allowed_redirects
+        self.allowed_redirects = config.linkcheck_allowed_redirects or {}
         self.retries: int = config.linkcheck_retries
         self.rate_limit_timeout = config.linkcheck_rate_limit_timeout
         self._allow_unauthorized = config.linkcheck_allow_unauthorized
@@ -748,20 +749,26 @@ def rewrite_github_anchor(app: Sphinx, uri: str) -> str | None:
 
 
 def compile_linkcheck_allowed_redirects(app: Sphinx, config: Config) -> None:
-    """Compile patterns in linkcheck_allowed_redirects to the regexp objects."""
-    linkcheck_allowed_redirects = app.config.linkcheck_allowed_redirects
-    for url, pattern in list(linkcheck_allowed_redirects.items()):
+    """Compile patterns to the regexp objects."""
+    if config.linkcheck_allowed_redirects is _sentinel_lar:
+        config.linkcheck_allowed_redirects = None
+        return
+    if not isinstance(config.linkcheck_allowed_redirects, dict):
+        raise ConfigError
+    allowed_redirects = {}
+    for url, pattern in config.linkcheck_allowed_redirects.items():
         try:
-            linkcheck_allowed_redirects[re.compile(url)] = re.compile(pattern)
+            allowed_redirects[re.compile(url)] = re.compile(pattern)
         except re.error as exc:
             logger.warning(
                 __('Failed to compile regex in linkcheck_allowed_redirects: %r %s'),
                 exc.pattern,
                 exc.msg,
             )
-        finally:
-            # Remove the original regexp-string
-            linkcheck_allowed_redirects.pop(url)
+    config.linkcheck_allowed_redirects = allowed_redirects
+
+
+_sentinel_lar = object()
 
 
 def setup(app: Sphinx) -> ExtensionMetadata:
@@ -772,7 +779,9 @@ def setup(app: Sphinx) -> ExtensionMetadata:
     app.add_config_value(
         'linkcheck_exclude_documents', [], '', types=frozenset({list, tuple})
     )
-    app.add_config_value('linkcheck_allowed_redirects', {}, '', types=frozenset({dict}))
+    app.add_config_value(
+        'linkcheck_allowed_redirects', _sentinel_lar, '', types=frozenset({dict})
+    )
     app.add_config_value('linkcheck_auth', [], '', types=frozenset({list, tuple}))
     app.add_config_value('linkcheck_request_headers', {}, '', types=frozenset({dict}))
     app.add_config_value('linkcheck_retries', 1, '', types=frozenset({int}))
@@ -799,7 +808,8 @@ def setup(app: Sphinx) -> ExtensionMetadata:
 
     app.add_event('linkcheck-process-uri')
 
-    app.connect('config-inited', compile_linkcheck_allowed_redirects, priority=800)
+    # priority 900 to happen after ``check_confval_types()``
+    app.connect('config-inited', compile_linkcheck_allowed_redirects, priority=900)
 
     # FIXME: Disable URL rewrite handler for github.com. temporarily.
     # See: https://github.com./sphinx-doc/sphinx/issues/9435

tests/test_builders/test_build_linkcheck.py

@@ -10,6 +10,7 @@
 import wsgiref.handlers
 from base64 import b64encode
 from http.server import BaseHTTPRequestHandler
+from io import StringIO
 from queue import Queue
 from typing import TYPE_CHECKING
 from unittest import mock
@@ -27,6 +28,7 @@
     RateLimit,
     compile_linkcheck_allowed_redirects,
 )
+from sphinx.errors import ConfigError
 from sphinx.testing.util import SphinxTestApp
 from sphinx.util import requests
 from sphinx.util._pathlib import _StrPath
@@ -37,6 +39,7 @@
 
 if TYPE_CHECKING:
     from collections.abc import Callable, Iterable
+    from pathlib import Path
     from typing import Any
 
     from urllib3 import HTTPConnectionPool
@@ -752,6 +755,34 @@ def test_follows_redirects_on_GET(app, capsys):
     assert app.warning.getvalue() == ''
 
 
+def test_linkcheck_allowed_redirects_config(
+    make_app: Callable[..., SphinxTestApp], tmp_path: Path
+) -> None:
+    tmp_path.joinpath('conf.py').touch()
+    tmp_path.joinpath('index.rst').touch()
+
+    # ``linkcheck_allowed_redirects = None`` is rejected
+    warning_stream = StringIO()
+    with pytest.raises(ConfigError):
+        make_app(
+            'linkcheck',
+            srcdir=tmp_path,
+            confoverrides={'linkcheck_allowed_redirects': None},
+            warning=warning_stream,
+        )
+    assert strip_escape_sequences(warning_stream.getvalue()).splitlines() == [
+        "WARNING: The config value `linkcheck_allowed_redirects' has type `NoneType'; expected `dict'."
+    ]
+
+    # ``linkcheck_allowed_redirects = {}`` is permitted
+    app = make_app(
+        'linkcheck',
+        srcdir=tmp_path,
+        confoverrides={'linkcheck_allowed_redirects': {}},
+    )
+    assert strip_escape_sequences(app.warning.getvalue()) == ''
+
+
 @pytest.mark.sphinx('linkcheck', testroot='linkcheck-localserver-warn-redirects')
 def test_linkcheck_allowed_redirects(app: SphinxTestApp) -> None:
     with serve_application(app, make_redirect_handler(support_head=False)) as address: