git hooks: Check that you are not committing to submodules by accident.

And also for a dangerous setting in the configuration that hides the
changes from you.

Change-Id: I99bad8024baf7048696d9602e857c253c20cb5c2
Reviewed-on: https://gerrit.libreoffice.org/63389
Tested-by: Jenkins
Reviewed-by: Jan Holesovsky <kendy@collabora.com>

.git-hooks/pre-commit

@@ -212,6 +212,57 @@ sub check_style($)
     }
 }
 
+sub check_submodules($)
+{
+    my ($h) = @_;
+
+    my $toplevel = `git rev-parse --show-toplevel`;
+    chomp $toplevel;
+
+    # trick to get a list of submodules - directly read from the .gitmodules
+    open(SUBMODULES, "git config --file '$toplevel'/.gitmodules --get-regexp path | awk '{ print \$2 }' |" ) ||  die "Cannot run git config on the .gitmodules.";
+    while (<SUBMODULES>)
+    {
+        chomp;
+
+        my $ignore = `git config submodule.$_.ignore`;
+        chomp $ignore;
+        if ($ignore eq 'all')
+        {
+            print <<EOM;
+Error: Your git configuration has submodule.$_.ignore set to 'all'.
+
+This is dangerous and can lead to accidentally pushing unwanted changes to
+submodules.
+
+To fix it, please do:
+
+  git config --unset submodule.$_.ignore
+
+EOM
+            exit(1);
+        }
+
+        my $diff = `git diff --cached --name-only -z $h -- $_`;
+        chomp $diff;
+        if ($diff ne '')
+        {
+            print <<EOM;
+Error: You are trying to commit changes to submodule $_ from the main repo.
+
+Please do not do that, commit only to the submodule, the git hook on the
+server will make sure the appropriate change is mirrored in the main repo.
+
+To remove the change, you can do:
+
+  git submodule update $_
+
+EOM
+            exit(1);
+        }
+    }
+}
+
 # Do the work :-)
 
 # Initial commit: diff against an empty tree object
@@ -282,6 +333,9 @@ check_style($against);
 # catch missing author info
 check_author();
 
+# catch commits to the submodules
+check_submodules($against);
+
 # all OK
 exit( 0 );
 # vi:set shiftwidth=4 expandtab: