Do not retry numeric-only getaddrinfo failures

newsfragments/1249.bugfix.rst

@@ -0,0 +1 @@
+`trio.socket.getaddrinfo` no longer retries in a worker thread or calls the custom hostname resolver when the caller already passed both ``AI_NUMERICHOST`` and ``AI_NUMERICSERV``; the ``EAI_NONAME`` error from the non-blocking attempt is raised directly.

src/trio/_socket.py

@@ -207,11 +207,13 @@ async def getaddrinfo(
     # If host and port are numeric, then getaddrinfo doesn't block and we can
     # skip the whole thread thing, which seems worthwhile. So we try first
     # with the _NUMERIC_ONLY flags set, and then only spawn a thread if that
-    # fails with EAI_NONAME:
+    # fails with EAI_NONAME. If the caller already asked for _NUMERIC_ONLY,
+    # a retry would make the exact same call, so let the error propagate:
     def numeric_only_failure(exc: BaseException) -> bool:
         return (
             isinstance(exc, _stdlib_socket.gaierror)
             and exc.errno == _stdlib_socket.EAI_NONAME
+            and flags & _NUMERIC_ONLY != _NUMERIC_ONLY
         )
 
     async with _try_sync(numeric_only_failure):

src/trio/_tests/test_socket.py

@@ -1128,6 +1128,33 @@ async def getnameinfo(
     assert await tsocket.getaddrinfo("host", "port") == "x"
 
 
+async def test_getaddrinfo_numeric_only_flags_skip_resolver() -> None:
+    # If the caller already passed AI_NUMERICHOST|AI_NUMERICSERV, the fast
+    # path call is identical to the one a worker thread or custom resolver
+    # would make, so its EAI_NONAME failure must propagate directly.
+    calls: list[tuple[object, ...]] = []
+
+    class RecordingResolver:
+        async def getaddrinfo(self, *args: object) -> list[object]:
+            calls.append(args)
+            return []
+
+        async def getnameinfo(self, *args: object) -> tuple[str, str]:
+            raise NotImplementedError
+
+    resolver = RecordingResolver()
+    assert await resolver.getaddrinfo(b"example.invalid", 80) == []
+    seen = len(calls)
+    tsocket.set_custom_hostname_resolver(resolver)  # type: ignore[arg-type]
+    try:
+        with pytest.raises(tsocket.gaierror) as excinfo:
+            await tsocket.getaddrinfo("example.invalid", 80, flags=_NUMERIC_ONLY)
+        assert excinfo.value.errno == tsocket.EAI_NONAME
+        assert len(calls) == seen
+    finally:
+        tsocket.set_custom_hostname_resolver(None)
+
+
 async def test_custom_socket_factory() -> None:
     class CustomSocketFactory:
         def socket(