Merge branch 'jh/dirstat' into maint

* jh/dirstat:
  --dirstat: In case of renames, use target filename instead of source filename
  Teach --dirstat not to completely ignore rearranged lines within a file
  --dirstat-by-file: Make it faster and more correct
  --dirstat: Describe non-obvious differences relative to --stat or regular diff

1 files changed, 37 insertions, 5 deletions

diff --git a/diff.c b/diff.c
index 9fa841010..5376d01e1 100644
--- a/diff.c
+++ b/diff.c
@@ -1538,8 +1538,36 @@ static void show_dirstat(struct diff_options *options)
 		struct diff_filepair *p = q->queue[i];
 		const char *name;
 		unsigned long copied, added, damage;
+		int content_changed;
 
-		name = p->one->path ? p->one->path : p->two->path;
+		name = p->two->path ? p->two->path : p->one->path;
+
+		if (p->one->sha1_valid && p->two->sha1_valid)
+			content_changed = hashcmp(p->one->sha1, p->two->sha1);
+		else
+			content_changed = 1;
+
+		if (!content_changed) {
+			/*
+			 * The SHA1 has not changed, so pre-/post-content is
+			 * identical. We can therefore skip looking at the
+			 * file contents altogether.
+			 */
+			damage = 0;
+			goto found_damage;
+		}
+
+		if (DIFF_OPT_TST(options, DIRSTAT_BY_FILE)) {
+			/*
+			 * In --dirstat-by-file mode, we don't really need to
+			 * look at the actual file contents at all.
+			 * The fact that the SHA1 changed is enough for us to
+			 * add this file to the list of results
+			 * (with each file contributing equal damage).
+			 */
+			damage = 1;
+			goto found_damage;
+		}
 
 		if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two)) {
 			diff_populate_filespec(p->one, 0);
@@ -1563,14 +1591,18 @@ static void show_dirstat(struct diff_options *options)
 		/*
 		 * Original minus copied is the removed material,
 		 * added is the new material.  They are both damages
-		 * made to the preimage. In --dirstat-by-file mode, count
-		 * damaged files, not damaged lines. This is done by
-		 * counting only a single damaged line per file.
+		 * made to the preimage.
+		 * If the resulting damage is zero, we know that
+		 * diffcore_count_changes() considers the two entries to
+		 * be identical, but since content_changed is true, we
+		 * know that there must have been _some_ kind of change,
+		 * so we force all entries to have damage > 0.
 		 */
 		damage = (p->one->size - copied) + added;
-		if (DIFF_OPT_TST(options, DIRSTAT_BY_FILE) && damage > 0)
+		if (!damage)
 			damage = 1;
 
+found_damage:
 		ALLOC_GROW(dir.files, dir.nr + 1, dir.alloc);
 		dir.files[dir.nr].name = name;
 		dir.files[dir.nr].changed = damage;