Add an option to allow disabling build isolation

src/pip/_internal/cmdoptions.py

@@ -451,6 +451,17 @@ def only_binary():
     help='Ignore the Requires-Python information.'
 )  # type: Any
 
+no_build_isolation = partial(
+    Option,
+    '--no-build-isolation',
+    dest='build_isolation',
+    action='store_false',
+    default=True,
+    help='Disable isolation when building a modern source distribution. '
+         'Build dependencies specified by PEP 518 must be already installed '
+         'if this option is used.'
+)  # type: Any
+
 install_options = partial(
     Option,
     '--install-option',

src/pip/_internal/commands/download.py

@@ -57,6 +57,7 @@ def __init__(self, *args, **kw):
         cmd_opts.add_option(cmdoptions.no_clean())
         cmd_opts.add_option(cmdoptions.require_hashes())
         cmd_opts.add_option(cmdoptions.progress_bar())
+        cmd_opts.add_option(cmdoptions.no_build_isolation())
 
         cmd_opts.add_option(
             '-d', '--dest', '--destination-dir', '--destination-directory',
@@ -201,6 +202,7 @@ def run(self, options, args):
                     download_dir=options.download_dir,
                     wheel_download_dir=None,
                     progress_bar=options.progress_bar,
+                    build_isolation=options.build_isolation,
                 )
 
                 resolver = Resolver(

src/pip/_internal/commands/install.py

@@ -139,6 +139,7 @@ def __init__(self, *args, **kw):
             help='Ignore the installed packages (reinstalling instead).')
 
         cmd_opts.add_option(cmdoptions.ignore_requires_python())
+        cmd_opts.add_option(cmdoptions.no_build_isolation())
 
         cmd_opts.add_option(cmdoptions.install_options())
         cmd_opts.add_option(cmdoptions.global_options())
@@ -260,6 +261,7 @@ def run(self, options, args):
                         download_dir=None,
                         wheel_download_dir=None,
                         progress_bar=options.progress_bar,
+                        build_isolation=options.build_isolation,
                     )
 
                     resolver = Resolver(

src/pip/_internal/commands/wheel.py

@@ -63,7 +63,9 @@ def __init__(self, *args, **kw):
             dest='build_options',
             metavar='options',
             action='append',
-            help="Extra arguments to be supplied to 'setup.py bdist_wheel'.")
+            help="Extra arguments to be supplied to 'setup.py bdist_wheel'.",
+        )
+        cmd_opts.add_option(cmdoptions.no_build_isolation())
         cmd_opts.add_option(cmdoptions.constraints())
         cmd_opts.add_option(cmdoptions.editable())
         cmd_opts.add_option(cmdoptions.requirements())
@@ -158,6 +160,7 @@ def run(self, options, args):
                         download_dir=None,
                         wheel_download_dir=options.wheel_dir,
                         progress_bar=options.progress_bar,
+                        build_isolation=options.build_isolation,
                     )
 
                     resolver = Resolver(

src/pip/_internal/operations/prepare.py

@@ -104,7 +104,7 @@ def dist(self, finder):
         return list(pkg_resources.find_distributions(
             self.req.source_dir))[0]
 
-    def prep_for_dist(self, finder):
+    def prep_for_dist(self, finder, build_isolation):
         # FIXME:https://github.com/pypa/pip/issues/1112
         pass
 
@@ -120,23 +120,23 @@ def dist(self, finder):
             )
         return dist
 
-    def prep_for_dist(self, finder):
+    def prep_for_dist(self, finder, build_isolation):
         # Before calling "setup.py egg_info", we need to set-up the build
         # environment.
-
         build_requirements, isolate = self.req.get_pep_518_info()
+        should_isolate = build_isolation and isolate
 
         if 'setuptools' not in build_requirements:
             logger.warning(
                 "This version of pip does not implement PEP 516, so "
                 "it cannot build a wheel without setuptools. You may need to "
                 "upgrade to a newer version of pip.")
 
-        if not isolate:
+        if not should_isolate:
             self.req.build_env = NoOpBuildEnvironment(no_clean=False)
 
         with self.req.build_env as prefix:
-            if isolate:
+            if should_isolate:
                 _install_build_reqs(finder, prefix, build_requirements)
 
             self.req.run_egg_info()
@@ -157,7 +157,7 @@ class RequirementPreparer(object):
     """
 
     def __init__(self, build_dir, download_dir, src_dir, wheel_download_dir,
-                 progress_bar):
+                 progress_bar, build_isolation):
         super(RequirementPreparer, self).__init__()
 
         self.src_dir = src_dir
@@ -181,6 +181,9 @@ def __init__(self, build_dir, download_dir, src_dir, wheel_download_dir,
 
         self.progress_bar = progress_bar
 
+        # Is build isolation allowed?
+        self.build_isolation = build_isolation
+
     @property
     def _download_should_save(self):
         # TODO: Modify to reduce indentation needed
@@ -306,7 +309,7 @@ def prepare_linked_requirement(self, req, session, finder,
                     (req, exc, req.link)
                 )
             abstract_dist = make_abstract_dist(req)
-            abstract_dist.prep_for_dist(finder)
+            abstract_dist.prep_for_dist(finder, self.build_isolation)
             if self._download_should_save:
                 # Make a .zip of the source_dir we already created.
                 if req.link.scheme in vcs.all_schemes:
@@ -331,7 +334,7 @@ def prepare_editable_requirement(self, req, require_hashes, finder):
             req.update_editable(not self._download_should_save)
 
             abstract_dist = make_abstract_dist(req)
-            abstract_dist.prep_for_dist(finder)
+            abstract_dist.prep_for_dist(finder, self.build_isolation)
 
             if self._download_should_save:
                 req.archive(self.download_dir)

tests/functional/test_wheel.py

@@ -222,3 +222,17 @@ def test_pip_wheel_with_pep518_build_reqs(script, data):
     assert wheel_file_path in result.files_created, result.stdout
     assert "Successfully built pep518" in result.stdout, result.stdout
     assert "Installing build dependencies" in result.stdout, result.stdout
+
+
+@pytest.mark.network
+def test_pip_wheel_with_pep518_build_reqs_no_isolation(script, data):
+    script.pip('install', 'wheel')
+    result = script.pip(
+        'wheel', '--no-index', '-f', data.find_links, '--no-build-isolation',
+        'pep518==3.0',
+    )
+    wheel_file_name = 'pep518-3.0-py%s-none-any.whl' % pyversion[0]
+    wheel_file_path = script.scratch / wheel_file_name
+    assert wheel_file_path in result.files_created, result.stdout
+    assert "Successfully built pep518" in result.stdout, result.stdout
+    assert "Installing build dependencies" not in result.stdout, result.stdout

tests/unit/test_req.py

@@ -39,7 +39,8 @@ def _basic_resolver(self, finder):
             src_dir=os.path.join(self.tempdir, 'src'),
             download_dir=None,
             wheel_download_dir=None,
-            progress_bar="on"
+            progress_bar="on",
+            build_isolation=True,
         )
         return Resolver(
             preparer=preparer, wheel_cache=None,