try more url checking

micropip/_utils.py

@@ -316,7 +316,7 @@ def validate_constraints(
         if req.extras:
             messages.append("may not provide [extras]")
 
-        if not (req.url or req.specifier):
+        if not (req.url or len(req.specifier)):
             messages.append("no version or URL")
 
         if req.marker and not req.marker.evaluate(environment):

micropip/transaction.py

@@ -75,22 +75,24 @@ async def add_requirement(self, req: str | Requirement) -> None:
             return await self.add_requirement_inner(req)
 
         try:
-            req = constrain_requirement(Requirement(req), self.constrained_reqs)
-            url = req.url
+            as_req = constrain_requirement(Requirement(req), self.constrained_reqs)
         except InvalidRequirement:
-            url = f"{req}"
+            as_req = None
 
-        if not (url and urlparse(url).path.endswith(".whl")):
-            return await self.add_requirement_inner(
-                req if isinstance(req, Requirement) else Requirement(req)
-            )
+        if as_req:
+            if as_req.name and len(as_req.specifier):
+                return await self.add_requirement_inner(as_req)
+            if as_req.url:
+                req = as_req.url
 
-        if url:
+        if urlparse(req).path.endswith(".whl"):
             # custom download location
-            wheel = WheelInfo.from_url(url)
+            wheel = WheelInfo.from_url(req)
             check_compatible(wheel.filename)
             return await self.add_wheel(wheel, extras=set(), specifier="")
 
+        return await self.add_requirement_inner(Requirement(req))
+
     def check_version_satisfied(self, req: Requirement) -> tuple[bool, str]:
         ver = None
         try: