minstall: rework root elevation prompt for extensibility and behavior

There's a couple issues with the current approach:
- pkexec is an unusual elevation method, the standard is sudo
- it tries to elevate even in automated workflows
- the user may not want to automatically rerun as root, that might be
  badly behaved

Do some upfront checks instead, first to make sure it even makes sense
to try becoming root, and then to ask the user "do you really want
this". Also check for a couple common approaches to root elevation,
including doas.

Fixes #7345
Fixes #7809

1 files changed, 16 insertions, 6 deletions

diff --git a/mesonbuild/minstall.py b/mesonbuild/minstall.py
index 9ba36cb..ab797b5 100644
--- a/mesonbuild/minstall.py
+++ b/mesonbuild/minstall.py
@@ -556,13 +556,23 @@ class Installer:
                     self.log('Preserved {} unchanged files, see {} for the full list'
                              .format(self.preserved_file_count, os.path.normpath(self.lf.name)))
         except PermissionError:
-            if shutil.which('pkexec') is not None and 'PKEXEC_UID' not in os.environ and destdir == '':
-                print('Installation failed due to insufficient permissions.')
-                print('Attempting to use polkit to gain elevated privileges...')
-                os.execlp('pkexec', 'pkexec', sys.executable, main_file, *sys.argv[1:],
-                          '-C', os.getcwd(), '--no-rebuild')
-            else:
+            if is_windows() or destdir != '' or not os.isatty(sys.stdout.fileno()) or not os.isatty(sys.stderr.fileno()):
+                # can't elevate to root except in an interactive unix environment *and* when not doing a destdir install
                 raise
+            rootcmd = os.environ.get('MESON_ROOT_CMD') or shutil.which('sudo') or shutil.which('doas')
+            pkexec = shutil.which('pkexec')
+            if rootcmd is None and pkexec is not None and 'PKEXEC_UID' not in os.environ:
+                rootcmd = pkexec
+
+            if rootcmd is not None:
+                print('Installation failed due to insufficient permissions.')
+                ans = input(f'Attempt to use {rootcmd} to gain elevated privileges? [y/n] ')
+                if ans not in {'y', 'n'}:
+                    raise MesonException('Answer not one of [y/n]')
+                elif ans == 'y':
+                    os.execlp(rootcmd, rootcmd, sys.executable, main_file, *sys.argv[1:],
+                              '-C', os.getcwd(), '--no-rebuild')
+            raise
 
     def do_strip(self, strip_bin: T.List[str], fname: str, outname: str) -> None:
         self.log(f'Stripping target {fname!r}.')