Split _setup_isolation for readability

Author: sbidoul

src/pip/_internal/distributions/sdist.py

@@ -32,32 +32,24 @@ def prepare_distribution_metadata(
         # Set up the build isolation, if this requirement should be isolated
         should_isolate = self.req.use_pep517 and build_isolation
         if should_isolate:
-            self._setup_isolation(finder)
+            # Setup an isolated environment and install the build backend static
+            # requirements in it.
+            self._prepare_build_backend(finder)
+            # Check that if the requirement is editable, it either supports PEP 660 or
+            # has a setup.py or a setup.cfg. For regular requirements such a sanity
+            # check is done in load_pyproject_toml. For editables this cannot be done
+            # earlier because we support editable installation of projects with
+            # pyproject.toml with setup.cfg and no setup.py (sigh). And we need to setup
+            # the build backend to verify it supports build_editable. It also can not be
+            # done later, because merely calling get_requires_for_build_wheel() for the
+            # setuptools __legacy__ backend creates the egg-info directory, including
+            # UNKNOWN.egg-info if it is misconfigured, and we don't want that.
+            self.req.isolated_editable_sanity_check()
+            # Install the dynamic build requirements.
+            self._install_build_reqs(finder)
 
         self.req.prepare_metadata()
 
-    def _setup_isolation(self, finder: PackageFinder) -> None:
-        self._prepare_build_backend(finder)
-        # Check that if the requirement is editable, it either supports PEP 660
-        # or has a setup.py or a setup.cfg. This cannot be done earlier because
-        # we need to setup the build backend to verify it supports build_editable,
-        # nor can it be done later, because merely calling _get_build_requires_wheel()
-        # for the setuptools __legacy__ backend creates the egg-info directory,
-        # including UNKNOWN.egg-info if it is misconfigured, and we don't want that.
-        self.req.isolated_editable_sanity_check()
-        # Install any extra build dependencies that the backend requests.
-        # This must be done in a second pass, as the pyproject.toml
-        # dependencies must be installed before we can call the backend.
-        if (
-            self.req.editable
-            and self.req.permit_editable_wheels
-            and self.req.supports_pyproject_editable()
-        ):
-            build_reqs = self._get_build_requires_editable()
-        else:
-            build_reqs = self._get_build_requires_wheel()
-        self._install_build_reqs(finder, build_reqs)
-
     def _prepare_build_backend(self, finder: PackageFinder) -> None:
         # Isolate in a BuildEnvironment and install the build-time
         # requirements.
@@ -102,8 +94,19 @@ def _get_build_requires_editable(self) -> Iterable[str]:
             with backend.subprocess_runner(runner):
                 return backend.get_requires_for_build_editable()
 
-    def _install_build_reqs(self, finder: PackageFinder, reqs: Iterable[str]) -> None:
-        conflicting, missing = self.req.build_env.check_requirements(reqs)
+    def _install_build_reqs(self, finder: PackageFinder) -> None:
+        # Install any extra build dependencies that the backend requests.
+        # This must be done in a second pass, as the pyproject.toml
+        # dependencies must be installed before we can call the backend.
+        if (
+            self.req.editable
+            and self.req.permit_editable_wheels
+            and self.req.supports_pyproject_editable()
+        ):
+            build_reqs = self._get_build_requires_editable()
+        else:
+            build_reqs = self._get_build_requires_wheel()
+        conflicting, missing = self.req.build_env.check_requirements(build_reqs)
         if conflicting:
             self._raise_conflicts("the backend dependencies", conflicting)
         self.req.build_env.install_requirements(