diff: export diffstat interface

Make the diffstat interface (namely, the diffstat_t struct and
compute_diffstat) no longer be internal to diff.c and allow it to be used
by other parts of git.

This is helpful for code that may want to easily extract information
from files using the diff machinery, while flushing it differently from
how the show_* functions used by diff_flush() do it. One example is the
builtin implementation of git-add--interactive's status.

Signed-off-by: Daniel Ferreira <bnmvco@gmail.com>
Signed-off-by: Slavica Djukic <slawica92@hotmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

diff.c

@@ -2489,22 +2489,6 @@ static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 	}
 }
 
-struct diffstat_t {
-	int nr;
-	int alloc;
-	struct diffstat_file {
-		char *from_name;
-		char *name;
-		char *print_name;
-		const char *comments;
-		unsigned is_unmerged:1;
-		unsigned is_binary:1;
-		unsigned is_renamed:1;
-		unsigned is_interesting:1;
-		uintmax_t added, deleted;
-	} **files;
-};
-
 static struct diffstat_file *diffstat_add(struct diffstat_t *diffstat,
 					  const char *name_a,
 					  const char *name_b)
@@ -6251,12 +6235,7 @@ void diff_flush(struct diff_options *options)
 	    dirstat_by_line) {
 		struct diffstat_t diffstat;
 
-		memset(&diffstat, 0, sizeof(struct diffstat_t));
-		for (i = 0; i < q->nr; i++) {
-			struct diff_filepair *p = q->queue[i];
-			if (check_pair_status(p))
-				diff_flush_stat(p, options, &diffstat);
-		}
+		compute_diffstat(options, &diffstat, q);
 		if (output_format & DIFF_FORMAT_NUMSTAT)
 			show_numstat(&diffstat, options);
 		if (output_format & DIFF_FORMAT_DIFFSTAT)
@@ -6589,6 +6568,20 @@ static int is_submodule_ignored(const char *path, struct diff_options *options)
 	return ignored;
 }
 
+void compute_diffstat(struct diff_options *options,
+		      struct diffstat_t *diffstat,
+		      struct diff_queue_struct *q)
+{
+	int i;
+
+	memset(diffstat, 0, sizeof(struct diffstat_t));
+	for (i = 0; i < q->nr; i++) {
+		struct diff_filepair *p = q->queue[i];
+		if (check_pair_status(p))
+			diff_flush_stat(p, options, diffstat);
+	}
+}
+
 void diff_addremove(struct diff_options *options,
 		    int addremove, unsigned mode,
 		    const struct object_id *oid,

diff.h

@@ -244,6 +244,22 @@ void diff_emit_submodule_error(struct diff_options *o, const char *err);
 void diff_emit_submodule_pipethrough(struct diff_options *o,
 				     const char *line, int len);
 
+struct diffstat_t {
+	int nr;
+	int alloc;
+	struct diffstat_file {
+		char *from_name;
+		char *name;
+		char *print_name;
+		const char *comments;
+		unsigned is_unmerged:1;
+		unsigned is_binary:1;
+		unsigned is_renamed:1;
+		unsigned is_interesting:1;
+		uintmax_t added, deleted;
+	} **files;
+};
+
 enum color_diff {
 	DIFF_RESET = 0,
 	DIFF_CONTEXT = 1,
@@ -333,6 +349,9 @@ void diff_change(struct diff_options *,
 
 struct diff_filepair *diff_unmerge(struct diff_options *, const char *path);
 
+void compute_diffstat(struct diff_options *options, struct diffstat_t *diffstat,
+		      struct diff_queue_struct *q);
+
 #define DIFF_SETUP_REVERSE      	1
 #define DIFF_SETUP_USE_SIZE_CACHE	4