gather requirements first when metadata is available

micropip/transaction.py

@@ -249,15 +249,22 @@ async def add_wheel(
 
         wheel_download_task = asyncio.create_task(wheel.download(self.fetch_kwargs))
         if self.deps:
-            try:
-                await wheel.download_pep658_metadata(self.fetch_kwargs)
-            except OSError:
-                # If something goes wrong while downloading the metadata
-                # we just log the error and continue, as the metadata can be fetched extracted from the wheel.
-                logger.debug("Metadata not available for %s", wheel.name)
-
-            await wheel_download_task
-            await self.gather_requirements(wheel.requires(extras))
+            # Case 1) If metadata file is available,
+            #         we can gather requirements without waiting for the wheel to be downloaded.
+            if wheel.pep658_metadata_available():
+                try:
+                    await wheel.download_pep658_metadata(self.fetch_kwargs)
+                except OSError:
+                    # If something goes wrong while downloading the metadata,
+                    # we have to wait for the wheel to be downloaded.
+                    await wheel_download_task
+                await self.gather_requirements(wheel.requires(extras))
+
+            # Case 2) If metadata file is not available,
+            #         we have to wait for the wheel to be downloaded.
+            else:
+                await wheel_download_task
+                await self.gather_requirements(wheel.requires(extras))
 
         self.wheels.append(wheel)
 

micropip/wheelinfo.py

@@ -146,6 +146,12 @@ async def download(self, fetch_kwargs: dict[str, Any]):
                 )
                 self._metadata = Metadata(zipfile.Path(zf, metadata_path))
 
+    def pep658_metadata_available(self) -> bool:
+        """
+        Check if the wheel's metadata is exposed via PEP 658.
+        """
+        return self.data_dist_info_metadata is not None
+
     async def download_pep658_metadata(
         self,
         fetch_kwargs: dict[str, Any],