Bugfix: downloaded files may not match all environments

When Morgan mirrors packages, it chooses the most recent version
that satisfies the requirement strings, and the environments.
However, when matching environments, it would select files (and
therefore version) that matches at least one of the Python versions
of the environments, which could lead to Morgan choosing versions
that do not support all of the Python versions.

This commit fixes this bug by requiring the selected versions match
ALL of the Python versions defined in the environments. This could
potentially lead to Morgan not finding matches at all, but this
would be fixed in a subsequent release by treating each environment
independently of the others.

morgan/__about__.py

@@ -1 +1 @@
-__version__ = "0.13.1"
+__version__ = "0.13.2"

morgan/__init__.py

@@ -7,18 +7,18 @@
 import re
 import tarfile
 import traceback
-from typing import Iterable, Tuple, Dict
 import urllib.parse
 import urllib.request
 import zipfile
+from typing import Dict, Iterable, Tuple
 
 import packaging.requirements
-import packaging.version
-import packaging.utils
-import packaging.tags
 import packaging.specifiers
+import packaging.tags
+import packaging.utils
+import packaging.version
 
-from morgan import server, configurator, metadata
+from morgan import configurator, metadata, server
 from morgan.__about__ import __version__
 
 PYPI_ADDRESS = "https://pypi.org/simple/"
@@ -156,6 +156,9 @@ def _mirror(
                 # for any of our environments and don't return an error
                 return None
 
+        if len(files) == 0:
+            raise Exception(f"No files match requirement {requirement}")
+
         # download all files
         depdict = {}
         for file in files:
@@ -221,35 +224,39 @@ def _filter_files(
                 files))
 
         if len(files) == 0:
-            print("Skipping {}, no version matches requirement".format(
-                requirement.name))
+            print(f"Skipping {requirement}, no version matches requirement")
             return None
 
-        latest_version = files[0]["version"]
+        # Now we only have files that satisfy the requirement, and we need to
+        # filter out files that do not match our environments.
         files = list(filter(
-            lambda file: file["version"] == latest_version, files))
+            lambda file: self._matches_environments(file), files))
+
+        if len(files) == 0:
+            print(f"Skipping {requirement}, no file matches environments")
 
-        # now we only have files from the latest version that satisfies the
-        # requirement. we need to filter out files that do not match any of
-        # our environments
+        # Only keep files from the latest version that satisifies all
+        # specifiers and environments
+        latest_version = files[0]["version"]
         files = list(filter(
-            lambda file: self._should_download(file), files))
+            lambda file: file["version"] == latest_version, files))
 
         return files
 
-    def _should_download(self, fileinfo: dict) -> bool:
+    def _matches_environments(self, fileinfo: dict) -> bool:
         if fileinfo.get("requires-python", None):
+            # The Python versions in all of our environments must be supported
+            # by this file in order to match
             spec_set = packaging.specifiers.SpecifierSet(
                 fileinfo["requires-python"])
-            supported = False
             for supported_python in self._supported_pyversions:
-                if spec_set.contains(supported_python):
-                    supported = True
-                    break
-            if not supported:
-                return False
+                if not spec_set.contains(supported_python):
+                    # file does not support the Python version of one of our
+                    # environments, reject it
+                    return False
 
         if fileinfo.get("tags", None):
+            # At least one of the tags must match ALL of our environments
             for tag in fileinfo["tags"]:
                 (intrp_name, intrp_ver) = parse_interpreter(tag.interpreter)
                 if intrp_name not in ("py", "cp"):
@@ -264,7 +271,10 @@ def _should_download(self, fileinfo: dict) -> bool:
                 else:
                     for platformre in self._supported_platforms:
                         if platformre.fullmatch(tag.platform):
+                            # tag matched, accept this file
                             return True
+
+            # none of the tags matched, reject this file
             return False
 
         return True
@@ -447,7 +457,7 @@ def main():
     parser.add_argument(
         "command",
         choices=["generate_env", "generate_reqs", "mirror", "serve",
-            "copy_server", "version"],
+                 "copy_server", "version"],
         help="Command to execute")
 
     args = parser.parse_args()
@@ -465,5 +475,6 @@ def main():
     elif args.command == "version":
         print("Morgan v{}".format(__version__))
 
+
 if __name__ == "__main__":
     main()