Use workaround to fix build requirements in build isolation, and renable build isolation

snap/snapcraft.yaml

@@ -40,7 +40,6 @@ parts:
   certbot:
     plugin: python
     source: .
-    constraints: [$SNAPCRAFT_PART_SRC/snap-constraints.txt]
     python-packages:
       - git+https://github.com/certbot/python-augeas.git@certbot-patched
       - ./acme
@@ -75,7 +74,7 @@ parts:
     build-packages: [gcc, libffi-dev, libssl-dev, git, libaugeas-dev, python3-dev]
     build-environment:
       - SNAPCRAFT_PYTHON_VENV_ARGS: --system-site-packages
-      - PIP_NO_BUILD_ISOLATION: "no"
+      - PIP_CONSTRAINT: $SNAPCRAFT_PART_SRC/snap-constraints.txt
     override-pull: |
         snapcraftctl pull
         cd $SNAPCRAFT_PART_SRC

tools/pip_install.py

@@ -82,17 +82,18 @@ def merge_requirements(tools_path, requirements, test_constraints, all_constrain
         fd.write(merged_requirements)
 
 
-def call_with_print(command):
+def call_with_print(command, env=None):
+    if not env:
+        env = os.environ
     print(command)
-    subprocess.check_call(command, shell=True)
+    subprocess.check_call(command, shell=True, env=env)
 
 
-def pip_install_with_print(args_str, disable_build_isolation=True):
-    command = ['"', sys.executable, '" -m pip install --disable-pip-version-check ']
-    if disable_build_isolation:
-        command.append('--no-build-isolation ')
-    command.append(args_str)
-    call_with_print(''.join(command))
+def pip_install_with_print(args_str, env=None):
+    if not env:
+        env = os.environ
+    command = ['"', sys.executable, '" -m pip install --disable-pip-version-check ', args_str]
+    call_with_print(''.join(command), env=env)
 
 
 def main(args):
@@ -113,20 +114,22 @@ def main(args):
             else:
                 certbot_normal_processing(tools_path, test_constraints)
 
+            env = os.environ.copy()
+            env["PIP_CONSTRAINT"] = all_constraints
+
             merge_requirements(tools_path, requirements, test_constraints, all_constraints)
             if requirements:  # This branch is executed during the oldest tests
                 # First step, install the transitive dependencies of oldest requirements
                 # in respect with oldest constraints.
-                pip_install_with_print('--constraint "{0}" --requirement "{1}"'
-                                       .format(all_constraints, requirements))
+                pip_install_with_print('--requirement "{0}"'.format(requirements),
+                                       env=env)
                 # Second step, ensure that oldest requirements themselves are effectively
                 # installed using --force-reinstall, and avoid corner cases like the one described
                 # in https://github.com/certbot/certbot/issues/7014.
                 pip_install_with_print('--force-reinstall --no-deps --requirement "{0}"'
                                        .format(requirements))
 
-            pip_install_with_print('--constraint "{0}" {1}'.format(
-                all_constraints, ' '.join(args)))
+            pip_install_with_print(' '.join(args), env=env)
 
 
 if __name__ == '__main__':

tools/pipstrap.py

@@ -35,12 +35,7 @@ def main():
         with open(requirements_filepath, 'w') as f:
             f.write(REQUIREMENTS)
         pip_install_args = '--requirement ' + requirements_filepath
-        # We don't disable build isolation because we may have an older
-        # version of pip that doesn't support the flag disabling it. We
-        # expect these packages to already have usable wheels available
-        # anyway so no building should be required.
-        pip_install.pip_install_with_print(pip_install_args,
-                                           disable_build_isolation=False)
+        pip_install.pip_install_with_print(pip_install_args)
 
 
 if __name__ == '__main__':