checkpatch: skip CamelCase cache for --no-tree without root

Running outside tree (--no-tree) without git root (--root DIR) is not
doable because we have no include/ directory which could be cached.  But
3445686af721 expected that we are always in Linux tree (w/a git).  But
--no-tree does not require --root.  Therefore skip whole caching in that
case.

This fixes perl and find errors when running checkpatch.pl *with*
--no-tree --strict and *without* --root:

    No structs that should be const will be found - file 'scripts/const_structs.checkpatch': No such file or directory
    Use of uninitialized value $root in concatenation (.) or string at scripts/checkpatch.pl line 1213.
    find: `/include': No such file or directory

Link: https://lore.kernel.org/20260810161159.1044160-1-pvorel@suse.cz
Fixes: 3445686af721 ("checkpatch: ignore existing CamelCase uses from include/...")
Signed-off-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 8a7787d228a6..f424dafce5bc 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -1206,6 +1206,8 @@ sub seed_camelcase_includes {
 		my $git_last_include_commit = `${git_command} log --no-merges --pretty=format:"%h%n" -1 -- include`;
 		chomp $git_last_include_commit;
 		$camelcase_cache = ".checkpatch-camelcase.git.$git_last_include_commit";
+	} elsif (not defined $root) {
+		return;
 	} else {
 		my $last_mod_date = 0;
 		$files = `find $root/include -name "*.h"`;