Do not download editables while preparing requirements

Downloading is done at the end of the download command
just like any other requirement. This is necessary to avoid
archiving editable requirements to a zip file when running
pip wheel.

news/9122.bugfix.rst

@@ -0,0 +1,2 @@
+Fix a regression that made ``pip wheel`` generate zip files of editable
+requirements in the wheel directory.

src/pip/_internal/commands/download.py

@@ -132,7 +132,7 @@ class DownloadCommand(RequirementCommand):
 
         downloaded = []  # type: List[str]
         for req in requirement_set.requirements.values():
-            if not req.editable and req.satisfied_by is None:
+            if req.satisfied_by is None:
                 assert req.name is not None
                 preparer.save_linked_requirement(req)
                 downloaded.append(req.name)

src/pip/_internal/operations/prepare.py

@@ -530,7 +530,7 @@ class RequirementPreparer(object):
         assert self.download_dir is not None
         assert req.link is not None
         link = req.link
-        if link.is_vcs:
+        if link.is_vcs or (link.is_existing_dir() and req.editable):
             # Make a .zip of the source_dir we already created.
             req.archive(self.download_dir)
             return
@@ -576,7 +576,6 @@ class RequirementPreparer(object):
                 req, self.req_tracker, self.finder, self.build_isolation,
             )
 
-            req.archive(self.download_dir)
             req.check_if_exists(self.use_user_site)
 
         return dist

tests/functional/test_download.py

@@ -855,9 +855,9 @@ def test_download_editable(script, data, tmpdir):
     """
     Test 'pip download' of editables in requirement file.
     """
-    editable_path = os.path.join(data.src, 'simplewheel-1.0')
+    editable_path = str(data.src / 'simplewheel-1.0').replace(os.path.sep, "/")
     requirements_path = tmpdir / "requirements.txt"
-    requirements_path.write_text("-e " + str(editable_path.resolve()) + "\n")
+    requirements_path.write_text("-e " + editable_path + "\n")
     download_dir = tmpdir / "download_dir"
     script.pip(
         'download', '--no-deps', '-r', str(requirements_path), '-d', str(download_dir)