When Building Wheels, Resolve Relative Path Dependencies Correctly

Building wheels unpacks the sdist which includes a copy of the
`pyproject.toml`.  If dependencies are delcared using relative paths
(such as `mymodule = { path = '../mymodule' }`), these relative paths
are not available from the temporary directory created to unpack and
build the wheel.  This fix retains the original path to the project for
those relative dependencies.

Fixes #266.

poetry/factory.py

@@ -30,7 +30,7 @@ class Factory:
     """
 
     def create_poetry(
-        self, cwd=None, io=None
+        self, cwd=None, io=None, original_root=None,
     ):  # type: (Optional[Path], Optional[IO]) -> Poetry
         if io is None:
             io = NullIO()
@@ -57,7 +57,7 @@ def create_poetry(
         name = local_config["name"]
         version = local_config["version"]
         package = ProjectPackage(name, version, version)
-        package.root_dir = poetry_file.parent
+        package.root_dir = original_root or poetry_file.parent
 
         for author in local_config["authors"]:
             package.authors.append(author)

poetry/masonry/builders/complete.py

@@ -43,7 +43,7 @@ def build(self):
 
                 with self.unpacked_tarball(sdist_file) as tmpdir:
                     WheelBuilder.make_in(
-                        Factory().create_poetry(tmpdir),
+                        Factory().create_poetry(tmpdir, original_root=self._poetry.file.path.parent),
                         self._env,
                         self._io,
                         dist_dir,
@@ -52,7 +52,7 @@ def build(self):
         else:
             with self.unpacked_tarball(sdist_file) as tmpdir:
                 WheelBuilder.make_in(
-                    Factory().create_poetry(tmpdir),
+                    Factory().create_poetry(tmpdir, original_root=self._poetry.file.path.parent),
                     self._env,
                     self._io,
                     dist_dir,