Merge branch 'en/diff-rename-follow-fix' into seen

* en/diff-rename-follow-fix:
  diffcore-rename: fix BUG when break detection and --follow used together

Author: gitster

diffcore-rename.c

@@ -33,7 +33,7 @@ static struct diff_rename_dst *locate_rename_dst(struct diff_filepair *p)
 {
 	/* Lookup by p->ONE->path */
 	int idx = break_idx ? strintmap_get(break_idx, p->one->path) : -1;
-	return (idx == -1) ? NULL : &rename_dst[idx];
+	return (idx == -1 || idx == rename_dst_nr) ? NULL : &rename_dst[idx];
 }
 
 /*
@@ -1669,9 +1669,10 @@ void diffcore_rename_extended(struct diff_options *options,
 			if (DIFF_PAIR_BROKEN(p)) {
 				/* broken delete */
 				struct diff_rename_dst *dst = locate_rename_dst(p);
-				if (!dst)
-					BUG("tracking failed somehow; failed to find associated dst for broken pair");
-				if (dst->is_rename)
+				if (options->single_follow && dst &&
+				    strcmp(dst->p->two->path, p->two->path))
+					dst = NULL;
+				if (dst && dst->is_rename)
 					/* counterpart is now rename/copy */
 					pair_to_free = p;
 			}

t/t4206-log-follow-harder-copies.sh

@@ -54,4 +54,22 @@ test_expect_success 'validate the output.' '
 	compare_diff_patch current expected
 '
 
+test_expect_success 'log --follow -B does not die or use uninitialized memory' '
+	git switch --orphan break_and_follow_are_icky_so_use_both &&
+	printf "%s\n" A B C D E F G H I J K L M N O P Q R S T U V W X Y Z >z &&
+	git add z &&
+	git commit -m "Initial" &&
+
+	test_seq 1 130 >z &&
+	echo lame >somefile &&
+	git add z somefile &&
+	git commit -m "Rewrite z, introduce lame somefile" &&
+
+	echo Content >somefile &&
+	git add somefile &&
+	git commit -m "Rewrite somefile" &&
+
+	git log -B --follow somefile
+'
+
 test_done