[3.9] bpo-46105: Honor spec when generating requirement specs with urls and extras. (GH-30151). (GH-30157)

(cherry picked from commit 109d96602199a91e94eb14b8cb3720841f22ded7)

Co-authored-by: Jason R. Coombs <jaraco@jaraco.com>

1 files changed, 12 insertions, 3 deletions

diff --git a/Lib/importlib/metadata.py b/Lib/importlib/metadata.py
index c6c7d31..594986c 100644
--- a/Lib/importlib/metadata.py
+++ b/Lib/importlib/metadata.py
@@ -344,17 +344,26 @@ class Distribution:
         def make_condition(name):
             return name and 'extra == "{name}"'.format(name=name)
 
-        def parse_condition(section):
+        def quoted_marker(section):
             section = section or ''
             extra, sep, markers = section.partition(':')
             if extra and markers:
-                markers = '({markers})'.format(markers=markers)
+                markers = f'({markers})'
             conditions = list(filter(None, [markers, make_condition(extra)]))
             return '; ' + ' and '.join(conditions) if conditions else ''
 
+        def url_req_space(req):
+            """
+            PEP 508 requires a space between the url_spec and the quoted_marker.
+            Ref python/importlib_metadata#357.
+            """
+            # '@' is uniquely indicative of a url_req.
+            return ' ' * ('@' in req)
+
         for section, deps in sections.items():
             for dep in deps:
-                yield dep + parse_condition(section)
+                space = url_req_space(dep)
+                yield dep + space + quoted_marker(section)
 
 
 class DistributionFinder(MetaPathFinder):