diff: add option to skip resolving diff statuses

By default, `diffcore_std()` resolves the statuses for queued diff file
pairs by calling `diff_resolve_rename_copy()`. If status information is
already manually set, invoking `diffcore_std()` may change the status
value.

Introduce the `skip_resolving_statuses` diff option that prevents
`diffcore_std()` from resolving file pair statuses when enabled.

Signed-off-by: Justin Tobler <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jltobler

diff.c

@@ -7085,7 +7085,7 @@ void diffcore_std(struct diff_options *options)
 		diffcore_order(options->orderfile);
 	if (options->rotate_to)
 		diffcore_rotate(options);
-	if (!options->found_follow)
+	if (!options->found_follow && !options->skip_resolving_statuses)
 		/* See try_to_follow_renames() in tree-diff.c */
 		diff_resolve_rename_copy();
 	diffcore_apply_filter(options);

diff.h

@@ -353,6 +353,14 @@ struct diff_options {
 	/* to support internal diff recursion by --follow hack*/
 	int found_follow;
 
+	/*
+	 * By default, diffcore_std() resolves the statuses for queued diff file
+	 * pairs by calling diff_resolve_rename_copy(). If status information
+	 * has already been manually set, this option prevents diffcore_std()
+	 * from resetting statuses.
+	 */
+	int skip_resolving_statuses;
+
 	/* Callback which allows tweaking the options in diff_setup_done(). */
 	void (*set_default)(struct diff_options *);