diff-lib: fix leaking diffopts in do_diff_cache()

In `do_diff_cache()` we initialize a new `rev_info` and then overwrite
its `diffopt` with a user-provided set of options. This can leak memory
because `repo_init_revisions()` may end up allocating memory for the
`diffopt` itself depending on the configuration. And since that field is
overwritten we won't ever free it.

Plug the memory leak by releasing the diffopts before we overwrite them.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

diff-lib.c

@@ -661,6 +661,7 @@ int do_diff_cache(const struct object_id *tree_oid, struct diff_options *opt)
 
 	repo_init_revisions(opt->repo, &revs, NULL);
 	copy_pathspec(&revs.prune_data, &opt->pathspec);
+	diff_free(&revs.diffopt);
 	revs.diffopt = *opt;
 	revs.diffopt.no_free = 1;
 

t/t7610-mergetool.sh

@@ -10,6 +10,7 @@ Testing basic merge tool invocation'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 # All the mergetool test work by checking out a temporary branch based