built-in add -p: coalesce hunks after splitting them

This is considered "the right thing to do", according to 933e44d3a0
("add -p": work-around an old laziness that does not coalesce hunks,
2011-04-06).

Note: we cannot simply modify the hunks while merging them; Once we
implement hunk editing, we will call `reassemble_patch()` whenever a
hunk is edited, therefore we must not modify the hunks (because the user
might e.g. hit `K` and change their mind whether to stage the previous
hunk).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/add-patch.c b/add-patch.c
index 2d34ddd..c8d84ae 100644 (file)
--- a/add-patch.c
+++ b/add-patch.c
@@ -433,6 +433,55 @@ static void render_diff_header(struct add_p_state *s,
        }
 }
 
+/* Coalesce hunks again that were split */
+static int merge_hunks(struct add_p_state *s, struct file_diff *file_diff,
+                      size_t *hunk_index, struct hunk *merged)
+{
+       size_t i = *hunk_index;
+       struct hunk *hunk = file_diff->hunk + i;
+       /* `header` corresponds to the merged hunk */
+       struct hunk_header *header = &merged->header, *next;
+
+       if (hunk->use != USE_HUNK)
+               return 0;
+
+       *merged = *hunk;
+       /* We simply skip the colored part (if any) when merging hunks */
+       merged->colored_start = merged->colored_end = 0;
+
+       for (; i + 1 < file_diff->hunk_nr; i++) {
+               hunk++;
+               next = &hunk->header;
+
+               /*
+                * Stop merging hunks when:
+                *
+                * - the hunk is not selected for use, or
+                * - the hunk does not overlap with the already-merged hunk(s)
+                */
+               if (hunk->use != USE_HUNK ||
+                   header->new_offset >= next->new_offset ||
+                   header->new_offset + header->new_count < next->new_offset ||
+                   merged->start >= hunk->start ||
+                   merged->end < hunk->start)
+                       break;
+
+               merged->end = hunk->end;
+               merged->colored_end = hunk->colored_end;
+
+               header->old_count = next->old_offset + next->old_count
+                       - header->old_offset;
+               header->new_count = next->new_offset + next->new_count
+                       - header->new_offset;
+       }
+
+       if (i == *hunk_index)
+               return 0;
+
+       *hunk_index = i;
+       return 1;
+}
+
 static void reassemble_patch(struct add_p_state *s,
                             struct file_diff *file_diff, struct strbuf *out)
 {
@@ -443,12 +492,19 @@ static void reassemble_patch(struct add_p_state *s,
        render_diff_header(s, file_diff, 0, out);
 
        for (i = file_diff->mode_change; i < file_diff->hunk_nr; i++) {
+               struct hunk merged = { 0 };
+
                hunk = file_diff->hunk + i;
                if (hunk->use != USE_HUNK)
                        delta += hunk->header.old_count
                                - hunk->header.new_count;
-               else
+               else {
+                       /* merge overlapping hunks into a temporary hunk */
+                       if (merge_hunks(s, file_diff, &i, &merged))
+                               hunk = &merged;
+
                        render_hunk(s, hunk, delta, 0, out);
+               }
        }
 }