commit c852d166c02ca93e1753f67ee56b6dd3ba296ab7
Author: Edward Thomson <ethomson@edwardthomson.com>
Date:   Fri Jul 14 17:05:21 2023 +0100

    diff: provide a delta free function, use it in merge
    
    `git_diff_merge` needs to free the old deltas, which are created and
    managed differently for parsed vs generated deltas. Provide a function
    to free them and use it in the diff merge functionality.

diff --git a/src/libgit2/diff.h b/src/libgit2/diff.h
index f21b2764505e..2cd4feccb816 100644
--- a/src/libgit2/diff.h
+++ b/src/libgit2/diff.h
@@ -47,6 +47,7 @@ struct git_diff {
 	int (*entrycomp)(const void *a, const void *b);
 
 	int (*patch_fn)(git_patch **out, git_diff *diff, size_t idx);
+	void (*free_deltas_fn)(git_diff *diff);
 	void (*free_fn)(git_diff *diff);
 };
 
diff --git a/src/libgit2/diff_generate.c b/src/libgit2/diff_generate.c
index 78fe510e7482..6d52f34c24ae 100644
--- a/src/libgit2/diff_generate.c
+++ b/src/libgit2/diff_generate.c
@@ -424,15 +424,23 @@ static void diff_set_ignore_case(git_diff *diff, bool ignore_case)
 	git_vector_sort(&diff->deltas);
 }
 
+static void diff_generated_free_deltas(git_diff *d)
+{
+	git_diff_generated *diff = (git_diff_generated *)d;
+
+	git_vector_free_deep(&diff->base.deltas);
+	git_pool_clear(&diff->base.pool);
+}
+
 static void diff_generated_free(git_diff *d)
 {
 	git_diff_generated *diff = (git_diff_generated *)d;
 
+	diff_generated_free_deltas(d);
+
 	git_attr_session__free(&diff->base.attrsession);
-	git_vector_free_deep(&diff->base.deltas);
 
 	git_pathspec__vfree(&diff->pathspec);
-	git_pool_clear(&diff->base.pool);
 
 	git__memzero(diff, sizeof(*diff));
 	git__free(diff);
@@ -459,6 +467,7 @@ static git_diff_generated *diff_generated_alloc(
 	diff->base.old_src = old_iter->type;
 	diff->base.new_src = new_iter->type;
 	diff->base.patch_fn = git_patch_generated_from_diff;
+	diff->base.free_deltas_fn = diff_generated_free_deltas;
 	diff->base.free_fn = diff_generated_free;
 	git_attr_session__init(&diff->base.attrsession, repo);
 	memcpy(&diff->base.opts, &dflt, sizeof(git_diff_options));
diff --git a/src/libgit2/diff_parse.c b/src/libgit2/diff_parse.c
index 04603969e408..c95b4c51dbe1 100644
--- a/src/libgit2/diff_parse.c
+++ b/src/libgit2/diff_parse.c
@@ -11,7 +11,7 @@
 #include "patch.h"
 #include "patch_parse.h"
 
-static void diff_parsed_free(git_diff *d)
+static void diff_parsed_free_deltas(git_diff *d)
 {
 	git_diff_parsed *diff = (git_diff_parsed *)d;
 	git_patch *patch;
@@ -24,6 +24,13 @@ static void diff_parsed_free(git_diff *d)
 
 	git_vector_free(&diff->base.deltas);
 	git_pool_clear(&diff->base.pool);
+}
+
+static void diff_parsed_free(git_diff *d)
+{
+	git_diff_parsed *diff = (git_diff_parsed *)d;
+
+	diff_parsed_free_deltas(d);
 
 	git__memzero(diff, sizeof(*diff));
 	git__free(diff);
@@ -43,6 +50,7 @@ static git_diff_parsed *diff_parsed_alloc(git_oid_t oid_type)
 	diff->base.pfxcomp = git__prefixcmp;
 	diff->base.entrycomp = git_diff__entry_cmp;
 	diff->base.patch_fn = git_patch_parsed_from_diff;
+	diff->base.free_deltas_fn = diff_parsed_free_deltas;
 	diff->base.free_fn = diff_parsed_free;
 
 	if (git_diff_options_init(&diff->base.opts, GIT_DIFF_OPTIONS_VERSION) < 0) {
diff --git a/src/libgit2/diff_tform.c b/src/libgit2/diff_tform.c
index a651d47b861d..65181b13d40b 100644
--- a/src/libgit2/diff_tform.c
+++ b/src/libgit2/diff_tform.c
@@ -174,27 +174,30 @@ int git_diff__merge(
 			break;
 	}
 
-	if (!error) {
-		onto->deltas = onto_new;
-		onto->pool = onto_pool;
-
-		if ((onto->opts.flags & GIT_DIFF_REVERSE) != 0)
-			onto->old_src = from->old_src;
-		else
-			onto->new_src = from->new_src;
-
-		/* prefix strings also come from old pool, so recreate those.*/
-		onto->opts.old_prefix =
-			git_pool_strdup_safe(&onto->pool, onto->opts.old_prefix);
-		onto->opts.new_prefix =
-			git_pool_strdup_safe(&onto->pool, onto->opts.new_prefix);
-	} else {
-		/* In the case of an error, it is safe to perform a free the objects of the vector. */
+	if (error) {
 		git_vector_free_deep(&onto_new);
 		git_pool_clear(&onto_pool);
+
+		return error;
 	}
 
-	return error;
+	onto->free_deltas_fn(onto);
+
+	onto->deltas = onto_new;
+	onto->pool = onto_pool;
+
+	if ((onto->opts.flags & GIT_DIFF_REVERSE) != 0)
+		onto->old_src = from->old_src;
+	else
+		onto->new_src = from->new_src;
+
+	/* prefix strings also come from old pool, so recreate those.*/
+	onto->opts.old_prefix =
+		git_pool_strdup_safe(&onto->pool, onto->opts.old_prefix);
+	onto->opts.new_prefix =
+		git_pool_strdup_safe(&onto->pool, onto->opts.new_prefix);
+
+	return 0;
 }
 
 int git_diff_merge(git_diff *onto, const git_diff *from)

--- a/src/libgit2/diff_tform.c
+++ b/src/libgit2/diff_tform.c
@@ -174,27 +174,28 @@ int git_diff__merge(
                        break;
        }
 
-       if (!error) {
-               onto->deltas = onto_new;
-               onto->pool = onto_pool;
-
-               if ((onto->opts.flags & GIT_DIFF_REVERSE) != 0)
-                       onto->old_src = from->old_src;
-               else
-                       onto->new_src = from->new_src;
-
-               /* prefix strings also come from old pool, so recreate those.*/
-               onto->opts.old_prefix =
-                       git_pool_strdup_safe(&onto->pool, onto->opts.old_prefix);
-               onto->opts.new_prefix =
-                       git_pool_strdup_safe(&onto->pool, onto->opts.new_prefix);
-       } else {
-               /* In the case of an error, it is safe to perform a free the objects of the vector. */
+       if (error) {
                git_vector_free_deep(&onto_new);
                git_pool_clear(&onto_pool);
+
+               return error;
        }
+       onto->opts.old_prefix =
+               git_pool_strdup_safe(&onto_pool, onto->opts.old_prefix);
+       onto->opts.new_prefix =
+               git_pool_strdup_safe(&onto_pool, onto->opts.new_prefix);
 
-       return error;
+       onto->free_deltas_fn(onto);
+
+       onto->deltas = onto_new;
+       onto->pool = onto_pool;
+
+       if ((onto->opts.flags & GIT_DIFF_REVERSE) != 0)
+               onto->old_src = from->old_src;
+       else
+               onto->new_src = from->new_src;
+
+       return 0;
 }