Rationalise wheel_dir usage.

We we normalising it right before making it, after passing it
RequirementSet, which means RequirementSet also had to normalise it.

And then we passed it to WheelBuilder which as a result had to
normalise it too.

Instead, pass it as-is to RequirementSet, have that normalise it, and
then pull it back out in WheelBuilder.

pip/commands/wheel.py

@@ -186,11 +186,6 @@ def run(self, options, args):
                     wheel_download_dir=options.wheel_dir
                 )
 
-                # make the wheelhouse
-                options.wheel_dir = normalize_path(options.wheel_dir)
-                if not os.path.exists(options.wheel_dir):
-                    os.makedirs(options.wheel_dir)
-
                 try:
                     populate_requirement_set(
                         requirement_set, args, options, logger, finder,
@@ -203,7 +198,6 @@ def run(self, options, args):
                     wb = WheelBuilder(
                         requirement_set,
                         finder,
-                        options.wheel_dir,
                         build_options=options.build_options or [],
                         global_options=options.global_options or [],
                     )

pip/req/req_set.py

@@ -443,6 +443,11 @@ def prepare_files(self, finder):
         """
         Prepare process. Create temp directories, download and/or unpack files.
         """
+        # make the wheelhouse
+        if self.wheel_download_dir:
+            if not os.path.exists(self.wheel_download_dir):
+                os.makedirs(self.wheel_download_dir)
+
         self._walk_req_to_install(
             functools.partial(self._prepare_file, finder))
 

pip/wheel.py

@@ -543,11 +543,11 @@ def supported(self, tags=None):
 class WheelBuilder(object):
     """Build wheels from a RequirementSet."""
 
-    def __init__(self, requirement_set, finder, wheel_dir, build_options=None,
+    def __init__(self, requirement_set, finder, build_options=None,
                  global_options=None):
         self.requirement_set = requirement_set
         self.finder = finder
-        self.wheel_dir = normalize_path(wheel_dir)
+        self.wheel_dir = requirement_set.wheel_download_dir
         self.build_options = build_options or []
         self.global_options = global_options or []
 

tests/unit/test_wheel.py

@@ -374,17 +374,19 @@ class TestWheelBuilder(object):
     def test_skip_building_wheels(self, caplog):
         with patch('pip.wheel.WheelBuilder._build_one') as mock_build_one:
             wheel_req = Mock(is_wheel=True, editable=False)
-            reqset = Mock(requirements=Mock(values=lambda: [wheel_req]))
-            wb = wheel.WheelBuilder(reqset, Mock(), '/wheel/dir')
+            reqset = Mock(requirements=Mock(values=lambda: [wheel_req]),
+                          wheel_download_dir='/wheel/dir')
+            wb = wheel.WheelBuilder(reqset, Mock())
             wb.build()
             assert "due to already being wheel" in caplog.text()
             assert mock_build_one.mock_calls == []
 
     def test_skip_building_editables(self, caplog):
         with patch('pip.wheel.WheelBuilder._build_one') as mock_build_one:
             editable_req = Mock(editable=True, is_wheel=False)
-            reqset = Mock(requirements=Mock(values=lambda: [editable_req]))
-            wb = wheel.WheelBuilder(reqset, Mock(), '/wheel/dir')
+            reqset = Mock(requirements=Mock(values=lambda: [editable_req]),
+                          wheel_download_dir='/wheel/dir')
+            wb = wheel.WheelBuilder(reqset, Mock())
             wb.build()
             assert "due to being editable" in caplog.text()
             assert mock_build_one.mock_calls == []