add inexact rename detection progress infrastructure

We might spend many seconds doing inexact rename detection
with no output.  It's nice to let the user know that
something is actually happening.

This patch adds the infrastructure, but no callers actually
turn on progress reporting.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.h

@@ -111,6 +111,7 @@ struct diff_options {
 	int rename_score;
 	int rename_limit;
 	int needed_rename_limit;
+	int show_rename_progress;
 	int dirstat_percent;
 	int setup;
 	int abbrev;

diffcore-rename.c

@@ -5,6 +5,7 @@
 #include "diff.h"
 #include "diffcore.h"
 #include "hash.h"
+#include "progress.h"
 
 /* Table of rename/copy destinations */
 
@@ -424,6 +425,7 @@ void diffcore_rename(struct diff_options *options)
 	struct diff_score *mx;
 	int i, j, rename_count;
 	int num_create, num_src, dst_cnt;
+	struct progress *progress = NULL;
 
 	if (!minimum_score)
 		minimum_score = DEFAULT_RENAME_SCORE;
@@ -503,6 +505,12 @@ void diffcore_rename(struct diff_options *options)
 		goto cleanup;
 	}
 
+	if (options->show_rename_progress) {
+		progress = start_progress_delay(
+				"Performing inexact rename detection",
+				rename_dst_nr * rename_src_nr, 50, 1);
+	}
+
 	mx = xcalloc(num_create * NUM_CANDIDATE_PER_DST, sizeof(*mx));
 	for (dst_cnt = i = 0; i < rename_dst_nr; i++) {
 		struct diff_filespec *two = rename_dst[i].two;
@@ -532,7 +540,9 @@ void diffcore_rename(struct diff_options *options)
 			diff_free_filespec_blob(two);
 		}
 		dst_cnt++;
+		display_progress(progress, (i+1)*rename_src_nr);
 	}
+	stop_progress(&progress);
 
 	/* cost matrix sorted by most to least similar pair */
 	qsort(mx, dst_cnt * NUM_CANDIDATE_PER_DST, sizeof(*mx), score_compare);