Implement requirement installation for PEP 517 conform packages witho…

…ut setup.py

The idea of this patch is that we build a wheel and install that whell when we install a requirement from
source that does not support setup.py.
Fixes pypa#6222.

news/6222.bugfix

@@ -0,0 +1 @@
+Fixes a bug that prevented installation of packages from source only if those packages depended on PEP 517 conform packages without a ``setup.py``

src/pip/_internal/req/req_install.py

@@ -30,7 +30,7 @@
 from pip._internal.utils.misc import (
     _make_build_dir, ask_path_exists, backup_dir, call_subprocess,
     display_path, dist_in_site_packages, dist_in_usersite, ensure_dir,
-    get_installed_version, redact_password_from_url, rmtree,
+    get_installed_version, redact_password_from_url, rmtree, unpack_file,
 )
 from pip._internal.utils.packaging import get_metadata
 from pip._internal.utils.setuptools_build import SETUPTOOLS_SHIM
@@ -922,6 +922,18 @@ def install(
             self.install_succeeded = True
             return
 
+        if self.use_pep517:
+            self.install_use_pep517(
+                warn_script_location=warn_script_location,
+                use_user_site=use_user_site,
+                pycompile=pycompile,
+                prefix=prefix,
+                root=root,
+                home=home,
+            )
+            self.install_succeed = True
+            return
+
         # Extend the list of global and install options passed on to
         # the setup.py call with the ones from the requirements file.
         # Options specified in requirements file override those
@@ -993,6 +1005,34 @@ def prepend_root(path):
             with open(inst_files_path, 'w') as f:
                 f.write('\n'.join(new_lines) + '\n')
 
+    def install_use_pep517(
+            self, warn_script_location, use_user_site, pycompile, prefix, root, home
+    ):
+        with TempDirectory(kind='wheel') as wheel_dir, TempDirectory(kind='wheel') as build_dir:
+            wheel_name = self.build_wheel_use_pep517(build_dir.path)
+            unpack_file(
+                os.path.join(build_dir.path, wheel_name),
+                wheel_dir.path,
+                'application/zip',
+                None
+            )
+            version = wheel.wheel_version(wheel_dir.path)
+            wheel.check_compatibility(version, self.name)
+            self.move_wheel_files(
+                wheel_dir.path, root=root, prefix=prefix, home=home,
+                warn_script_location=warn_script_location,
+                use_user_site=use_user_site, pycompile=pycompile,
+            )
+            return
+
+    def build_wheel_use_pep517(self, output_directory):
+        self.spin_message = 'Building wheel for %s (PEP 517)' % (self.name,)
+        with self.build_env, indent_log():
+            return self.pep517_backend.build_wheel(
+                output_directory,
+                metadata_directory=self.metadata_directory,
+            )
+
     def get_install_args(
         self,
         global_options,  # type: Sequence[str]