Use more descriptive exception when range requests are unsupported

src/pip/_internal/network/lazy_wheel.py

@@ -1,6 +1,6 @@
 """Lazy ZIP over HTTP"""
 
-__all__ = ['dist_from_wheel_url']
+__all__ = ['HTTPRangeRequestUnsupported', 'dist_from_wheel_url']
 
 from bisect import bisect_left, bisect_right
 from contextlib import contextmanager
@@ -23,13 +23,18 @@
     from pip._internal.network.session import PipSession
 
 
+class HTTPRangeRequestUnsupported(RuntimeError):
+    pass
+
+
 def dist_from_wheel_url(name, url, session):
     # type: (str, str, PipSession) -> Distribution
     """Return a pkg_resources.Distribution from the given wheel URL.
 
     This uses HTTP range requests to only fetch the potion of the wheel
     containing metadata, just enough for the object to be constructed.
-    If such requests are not supported, RuntimeError is raised.
+    If such requests are not supported, HTTPRangeRequestUnsupported
+    is raised.
     """
     with LazyZipOverHTTP(url, session) as wheel:
         # For read-only ZIP files, ZipFile only needs methods read,
@@ -45,7 +50,8 @@ class LazyZipOverHTTP(object):
 
     This uses HTTP range requests to lazily fetch the file's content,
     which is supposed to be fed to ZipFile.  If such requests are not
-    supported by the server, raise RuntimeError during initialization.
+    supported by the server, raise HTTPRangeRequestUnsupported
+    during initialization.
     """
 
     def __init__(self, url, session, chunk_size=CONTENT_CHUNK_SIZE):
@@ -60,7 +66,7 @@ def __init__(self, url, session, chunk_size=CONTENT_CHUNK_SIZE):
         self._left = []  # type: List[int]
         self._right = []  # type: List[int]
         if 'bytes' not in head.headers.get('Accept-Ranges', 'none'):
-            raise RuntimeError('range request is not supported')
+            raise HTTPRangeRequestUnsupported('range request is not supported')
         self._check_zip()
 
     @property

src/pip/_internal/resolution/resolvelib/candidates.py

@@ -1,13 +1,15 @@
 import logging
 import sys
 
-from pip._vendor.contextlib2 import suppress
 from pip._vendor.packaging.specifiers import InvalidSpecifier, SpecifierSet
 from pip._vendor.packaging.utils import canonicalize_name
 from pip._vendor.packaging.version import Version
 
 from pip._internal.exceptions import HashError, MetadataInconsistent
-from pip._internal.network.lazy_wheel import dist_from_wheel_url
+from pip._internal.network.lazy_wheel import (
+    HTTPRangeRequestUnsupported,
+    dist_from_wheel_url,
+)
 from pip._internal.req.constructors import (
     install_req_from_editable,
     install_req_from_line,
@@ -308,15 +310,22 @@ def iter_dependencies(self):
             assert self._name is not None
             logger.info('Collecting %s', self._ireq.req or self._ireq)
             # If RuntimeError is raised, fallback to self.dist.
-            with indent_log(), suppress(RuntimeError):
+            with indent_log():
                 logger.info(
                     'Obtaining dependency information from %s %s',
                     self._name, self._version,
                 )
                 url = self._link.url.split('#', 1)[0]
                 session = preparer.downloader._session
-                dist = dist_from_wheel_url(self._name, url, session)
-                self._check_metadata_consistency(dist)
+                try:
+                    dist = dist_from_wheel_url(self._name, url, session)
+                except HTTPRangeRequestUnsupported:
+                    logger.debug(
+                        'Failed to get dependency information '
+                        'using HTTP range requests from %s', url,
+                    )
+                else:
+                    self._check_metadata_consistency(dist)
         return self._iter_dependencies(dist or self.dist)
 
     def _prepare_abstract_distribution(self):

tests/unit/test_network_lazy_wheel.py

@@ -3,7 +3,10 @@
 from pip._vendor.pkg_resources import Requirement
 from pytest import fixture, mark, raises
 
-from pip._internal.network.lazy_wheel import dist_from_wheel_url
+from pip._internal.network.lazy_wheel import (
+    HTTPRangeRequestUnsupported,
+    dist_from_wheel_url,
+)
 from pip._internal.network.session import PipSession
 from tests.lib.requests_mocks import MockResponse
 
@@ -39,7 +42,7 @@ def test_dist_from_wheel_url(session):
 def test_dist_from_wheel_url_no_range(session, monkeypatch):
     """Test handling when HTTP range requests are not supported."""
     monkeypatch.setattr(session, 'head', lambda *a, **kw: MockResponse(b''))
-    with raises(RuntimeError):
+    with raises(HTTPRangeRequestUnsupported):
         dist_from_wheel_url('mypy', MYPY_0_782_WHL, session)