make it work without --use-feature=fast-deps!

src/pip/_internal/operations/prepare.py

@@ -333,19 +333,15 @@ def _fetch_metadata_only(
         self,
         req: InstallRequirement,
     ) -> Optional[BaseDistribution]:
-        # --use-feature=fast-deps must be provided.
-        if not self.use_lazy_wheel:
-            return None
         if self.require_hashes:
             logger.debug(
                 "Metadata-only fetching is not used as hash checking is required",
             )
             return None
         # Try PEP 658 metadata first, then fall back to lazy wheel if unavailable.
-        pep_658_dist = self._fetch_metadata_using_pep_658(req)
-        if pep_658_dist is not None:
-            return pep_658_dist
-        return self._fetch_metadata_using_lazy_wheel(req.link)
+        return self._fetch_metadata_using_pep_658(
+            req
+        ) or self._fetch_metadata_using_lazy_wheel(req.link)
 
     def _fetch_metadata_using_pep_658(
         self,
@@ -355,6 +351,12 @@ def _fetch_metadata_using_pep_658(
         metadata_link = req.link.metadata_link()
         if metadata_link is None:
             return None
+        assert req.req is not None
+        logger.info(
+            "Obtaining dependency information for %s from %s",
+            req.req,
+            metadata_link,
+        )
         metadata_file = get_http_url(
             metadata_link,
             self._download,
@@ -366,7 +368,6 @@ def _fetch_metadata_using_pep_658(
         containing_dir = os.path.dirname(metadata_file.path)
         new_metadata_path = os.path.join(containing_dir, "METADATA")
         os.rename(metadata_file.path, new_metadata_path)
-        assert req.req is not None
         return get_metadata_distribution(
             new_metadata_path,
             req.link.filename,
@@ -378,9 +379,12 @@ def _fetch_metadata_using_lazy_wheel(
         link: Link,
     ) -> Optional[BaseDistribution]:
         """Fetch metadata using lazy wheel, if possible."""
+        # --use-feature=fast-deps must be provided.
+        if not self.use_lazy_wheel:
+            return None
         if link.is_file or not link.is_wheel:
             logger.debug(
-                "Lazy wheel is not used as %r does not points to a remote wheel",
+                "Lazy wheel is not used as %r does not point to a remote wheel",
                 link,
             )
             return None

tests/functional/test_download.py

@@ -1350,34 +1350,22 @@ def download_generated_index(
     def run_for_generated_index(
         packages: Dict[str, List[Package]],
         args: List[str],
-        fast_deps: bool = False,
         allow_error: bool = False,
     ) -> Tuple[TestPipResult, Path]:
         """
         Produce a PyPI directory structure pointing to the specified packages, then
         execute `pip download -i ...` pointing to our generated index.
         """
         index_dir = index_for_packages(packages)
-        pip_args = []
-        if fast_deps:
-            pip_args.append("--use-feature=fast-deps")
-        pip_args.extend(
-            [
-                "download",
-                "-d",
-                str(download_dir),
-                "-i",
-                path_to_url(index_dir),
-            ]
-        )
-        pip_args.extend(args)
-        result = script.pip(
-            *pip_args,
-            # We need allow_stderr_warning=True if fast_deps=True, since that will print
-            # a warning to stderr.
-            allow_stderr_warning=fast_deps,
-            allow_error=allow_error,
-        )
+        pip_args = [
+            "download",
+            "-d",
+            str(download_dir),
+            "-i",
+            path_to_url(index_dir),
+            *args,
+        ]
+        result = script.pip(*pip_args, allow_error=allow_error)
         return (result, download_dir)
 
     return run_for_generated_index
@@ -1413,12 +1401,11 @@ def test_download_metadata(
     requirement_to_download: str,
     expected_outputs: List[str],
 ) -> None:
-    """Verify that when using --use-feature=fast-deps, if a data-dist-info-metadata
-    attribute is present, then it is used instead of the actual dist's METADATA."""
+    """Verify that if a data-dist-info-metadata attribute is present, then it is used
+    instead of the actual dist's METADATA."""
     _, download_dir = download_generated_index(
         _simple_packages,
         [requirement_to_download],
-        fast_deps=True,
     )
     assert sorted(os.listdir(download_dir)) == expected_outputs
 
@@ -1442,7 +1429,6 @@ def test_incorrect_metadata_hash(
     result, _ = download_generated_index(
         _simple_packages,
         [requirement_to_download],
-        fast_deps=True,
         allow_error=True,
     )
     assert result.returncode != 0
@@ -1466,7 +1452,6 @@ def test_metadata_not_found(
     result, _ = download_generated_index(
         _simple_packages,
         [requirement_to_download],
-        fast_deps=True,
         allow_error=True,
     )
     assert result.returncode != 0