Bug 1675675 - Only put mach_bootstrap paths in PYTHONPATH for mach python --no-virtualenv. r=firefox-build-system-reviewers,rstewart

With PYTHONPATH containing other directories, such as the python ones,
bad things can happen when the python script that is being run then
goes on to subprocess.Popen a python process for a different virtualenv,
or a different version, or whatever.

Differential Revision: https://phabricator.services.mozilla.com/D96155

build/mach_bootstrap.py

@@ -177,6 +177,13 @@ def search_path(mozilla_dir, packages_txt):
             yield path
 
 
+def mach_sys_path(mozilla_dir):
+    return [
+        os.path.join(mozilla_dir, path)
+        for path in search_path(mozilla_dir, "build/mach_virtualenv_packages.txt")
+    ]
+
+
 def bootstrap(topsrcdir, mozilla_dir=None):
     if mozilla_dir is None:
         mozilla_dir = topsrcdir
@@ -198,10 +205,7 @@ def bootstrap(topsrcdir, mozilla_dir=None):
     # case. For default behavior, we educate users and give them an opportunity
     # to react. We always exit after creating the directory because users don't
     # like surprises.
-    sys.path[0:0] = [
-        os.path.join(mozilla_dir, path)
-        for path in search_path(mozilla_dir, "build/mach_virtualenv_packages.txt")
-    ]
+    sys.path[0:0] = mach_sys_path(mozilla_dir)
     import mach.base
     import mach.main
     from mach.util import setenv

python/mach_commands.py

@@ -61,8 +61,10 @@ class MachCommands(MachCommandBase):
         }
 
         if no_virtualenv:
+            from mach_bootstrap import mach_sys_path
+
             python_path = sys.executable
-            append_env["PYTHONPATH"] = os.pathsep.join(sys.path)
+            append_env["PYTHONPATH"] = os.pathsep.join(mach_sys_path(self.topsrcdir))
         else:
             self.activate_virtualenv()
             python_path = self.virtualenv_manager.python_path