[wkrd] Workaround package index after PEP 625

Since PEP 625, sdist filenames replace . and - in the project name by
_, such as e.g. zc.buildout==3.0.1 yielding zc_buildout-3.0.1.tar.gz.

However, when looking up available dists in a package index, when an
sdist with such a normalized filename is found, setuptools interprets
the filename by replacing _ with - and uses that as the dist's name;
e.g. zc_buildout-3.0.1.tar.gz yields zc-buildout. This causes lookups
for the name with . (e.g.: zc.buildout) to fail.

Workaround by also looking up the name with . replaced by _, and then
fixing the names of found dists back to expected name.

src/zc/buildout/easy_install.py

@@ -538,13 +538,31 @@ class Installer(object):
                                 return max(dists)
 
         # initialize out index for this project:
-        if index.obtain(requirement) is None:
+        index.obtain(requirement) # ignore result
+        # setuptools may get mixed-up between . and - in project names
+        # due to . and - being turned into _ in sdist archive names, but
+        # _ in archive names being translated to - during index lookup.
+        # See https://github.com/buildout/buildout/issues/647
+
+        dists = [d for d in index[requirement.key] if d in requirement]
+
+        # Workaround by also looking up the name with - instead of .
+        # and fixing the name of dists found back to . instead of -.
+        wkrd_key = requirement.key.replace('.', '-')
+        if wkrd_key != requirement.key:
+            dists.extend(
+                d.clone(project_name=requirement.project_name)
+                for d in index[wkrd_key]
+                if d.key == wkrd_key # for thoroughness
+                and d.version in requirement
+            )
+
+        if not dists:
             # Nothing is available.
             return None
 
-        # Filter the available dists for the requirement and source flag
-        dists = [dist for dist in index[requirement.key]
-                      if dist in requirement and filter_precedence(dist)]
+        # Filter the available dists for the source flag.
+        dists = [dist for dist in dists if filter_precedence(dist)]
 
         # If we prefer final dists, filter for final and use the
         # result if it is non empty.