blame: use the fingerprint heuristic to match ignored lines

This commit integrates the fuzzy fingerprint heuristic into
guess_line_blames().

We actually make two passes.  The first pass uses the fuzzy algorithm to
find a match within the current diff chunk.  If that fails, the second
pass searches the entire parent file for the best match.

For an example of scanning the entire parent for a match, consider:

commit-a 30) #include <sys/header_a.h>
commit-b 31) #include <header_b.h>
commit-c 32) #include <header_c.h>

Then commit X alphabetizes them:

commit-X 30) #include <header_b.h>
commit-X 31) #include <header_c.h>
commit-X 32) #include <sys/header_a.h>

If we just check the parent's chunk (i.e. the first pass), we'd get:

commit-b 30) #include <header_b.h>
commit-c 31) #include <header_c.h>
commit-X 32) #include <sys/header_a.h>

That's because commit X actually consists of two chunks: one chunk is
removing sys/header_a.h, then some context, and the second chunk is
adding sys/header_a.h.

If we scan the entire parent file, we get:

commit-b 30) #include <header_b.h>
commit-c 31) #include <header_c.h>
commit-a 32) #include <sys/header_a.h>

Signed-off-by: Barret Rhoden <brho@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/blame.c b/blame.c
index ad8810cb0e049d294d54fe823c93ff5ad170e770..86f6b2bd330f721a22377f0ca053bd413582ef5d 100644 (file)
--- a/blame.c
+++ b/blame.c
@@ -989,12 +989,19 @@ static void fill_origin_fingerprints(struct blame_origin *o, mmfile_t *file)
                return;
        o->num_lines = find_line_starts(&line_starts, o->file.ptr,
                                        o->file.size);
-       /* TODO: Will fill in fingerprints in a future commit */
+       o->fingerprints = xcalloc(sizeof(struct fingerprint), o->num_lines);
+       get_line_fingerprints(o->fingerprints, o->file.ptr, line_starts,
+                             0, o->num_lines);
        free(line_starts);
 }
 
 static void drop_origin_fingerprints(struct blame_origin *o)
 {
+       if (o->fingerprints) {
+               free_line_fingerprints(o->fingerprints, o->num_lines);
+               o->num_lines = 0;
+               FREE_AND_NULL(o->fingerprints);
+       }
 }
 
 /*
@@ -1572,9 +1579,34 @@ static int are_lines_adjacent(struct blame_line_tracker *first,
               first->s_lno + 1 == second->s_lno;
 }
 
+static int scan_parent_range(struct fingerprint *p_fps,
+                            struct fingerprint *t_fps, int t_idx,
+                            int from, int nr_lines)
+{
+       int sim, p_idx;
+       #define FINGERPRINT_FILE_THRESHOLD      10
+       int best_sim_val = FINGERPRINT_FILE_THRESHOLD;
+       int best_sim_idx = -1;
+
+       for (p_idx = from; p_idx < from + nr_lines; p_idx++) {
+               sim = fingerprint_similarity(&t_fps[t_idx], &p_fps[p_idx]);
+               if (sim < best_sim_val)
+                       continue;
+               /* Break ties with the closest-to-target line number */
+               if (sim == best_sim_val && best_sim_idx != -1 &&
+                   abs(best_sim_idx - t_idx) < abs(p_idx - t_idx))
+                       continue;
+               best_sim_val = sim;
+               best_sim_idx = p_idx;
+       }
+       return best_sim_idx;
+}
+
 /*
- * This cheap heuristic assigns lines in the chunk to their relative location in
- * the parent's chunk.  Any additional lines are left with the target.
+ * The first pass checks the blame entry (from the target) against the parent's
+ * diff chunk.  If that fails for a line, the second pass tries to match that
+ * line to any part of parent file.  That catches cases where a change was
+ * broken into two chunks by 'context.'
  */
 static void guess_line_blames(struct blame_origin *parent,
                              struct blame_origin *target,
@@ -1583,11 +1615,22 @@ static void guess_line_blames(struct blame_origin *parent,
 {
        int i, best_idx, target_idx;
        int parent_slno = tlno + offset;
+       int *fuzzy_matches;
 
+       fuzzy_matches = fuzzy_find_matching_lines(parent, target,
+                                                 tlno, parent_slno, same,
+                                                 parent_len);
        for (i = 0; i < same - tlno; i++) {
                target_idx = tlno + i;
-               best_idx = target_idx + offset;
-               if (best_idx < parent_slno + parent_len) {
+               if (fuzzy_matches && fuzzy_matches[i] >= 0) {
+                       best_idx = fuzzy_matches[i];
+               } else {
+                       best_idx = scan_parent_range(parent->fingerprints,
+                                                    target->fingerprints,
+                                                    target_idx, 0,
+                                                    parent->num_lines);
+               }
+               if (best_idx >= 0) {
                        line_blames[i].is_parent = 1;
                        line_blames[i].s_lno = best_idx;
                } else {
@@ -1595,6 +1638,7 @@ static void guess_line_blames(struct blame_origin *parent,
                        line_blames[i].s_lno = target_idx;
                }
        }
+       free(fuzzy_matches);
 }
 
 /*
@@ -2371,6 +2415,12 @@ static void pass_blame(struct blame_scoreboard *sb, struct blame_origin *origin,
                        if (!porigin)
                                continue;
                        pass_blame_to_parent(sb, origin, porigin, 1);
+                       /*
+                        * Preemptively drop porigin so we can refresh the
+                        * fingerprints if we use the parent again, which can
+                        * occur if you ignore back-to-back commits.
+                        */
+                       drop_origin_blob(porigin);
                        if (!origin->suspects)
                                goto finish;
                }

diff --git a/t/t8014-blame-ignore-fuzzy.sh b/t/t8014-blame-ignore-fuzzy.sh
index 8443966152718ba8bd287016ac4e04f71b15c084..6f1a94caef223cf037ab4e79754e27c2c5e53a6a 100755 (executable)
--- a/t/t8014-blame-ignore-fuzzy.sh
+++ b/t/t8014-blame-ignore-fuzzy.sh
@@ -3,9 +3,6 @@
 test_description='git blame ignore fuzzy heuristic'
 . ./test-lib.sh
 
-# short circuit until blame has the fuzzy capabilities
-test_done
-
 pick_author='s/^[0-9a-f^]* *(\([^ ]*\) .*/\1/'
 
 # Each test is composed of 4 variables: