blame: compute abbreviation width that ensures uniqueness

Julia Lawall noticed that in linux-next repository the commit object
60d5c9f5 (shown with the default abbreviation width baked into "git
blame") in output from

$ git blame -L 3675,3675 60d5c9f5b -- \
drivers/staging/brcm80211/brcmfmac/wl_iw.c

is no longer unique in the repository, which results in "short SHA1
60d5c9f5 is ambiguous".

Compute the minimum abbreviation width that ensures uniqueness when
the user did not specify the --abbrev option to avoid this.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/blame.c b/builtin/blame.c
index 3e1f7e1e453f6ecc28fb910686c6580e77929556..f13ec327f6707ec832214ff4ffca7d630048ca94 100644 (file)
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -1828,6 +1828,16 @@ static int read_ancestry(const char *graft_file)
        return 0;
 }
 
+static int update_auto_abbrev(int auto_abbrev, struct origin *suspect)
+{
+       const char *uniq = find_unique_abbrev(suspect->commit->object.sha1,
+                                             auto_abbrev);
+       int len = strlen(uniq);
+       if (auto_abbrev < len)
+               return len;
+       return auto_abbrev;
+}
+
 /*
  * How many columns do we need to show line numbers in decimal?
  */
@@ -1850,12 +1860,16 @@ static void find_alignment(struct scoreboard *sb, int *option)
        int longest_dst_lines = 0;
        unsigned largest_score = 0;
        struct blame_entry *e;
+       int compute_auto_abbrev = (abbrev < 0);
+       int auto_abbrev = default_abbrev;
 
        for (e = sb->ent; e; e = e->next) {
                struct origin *suspect = e->suspect;
                struct commit_info ci;
                int num;
 
+               if (compute_auto_abbrev)
+                       auto_abbrev = update_auto_abbrev(auto_abbrev, suspect);
                if (strcmp(suspect->path, sb->path))
                        *option |= OUTPUT_SHOW_NAME;
                num = strlen(suspect->path);
@@ -1883,6 +1897,10 @@ static void find_alignment(struct scoreboard *sb, int *option)
        max_orig_digits = lineno_width(longest_src_lines);
        max_digits = lineno_width(longest_dst_lines);
        max_score_digits = lineno_width(largest_score);
+
+       if (compute_auto_abbrev)
+               /* one more abbrev length is needed for the boundary commit */
+               abbrev = auto_abbrev + 1;
 }
 
 /*
@@ -2360,10 +2378,9 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 parse_done:
        argc = parse_options_end(&ctx);
 
-       if (abbrev == -1)
-               abbrev = default_abbrev;
-       /* one more abbrev length is needed for the boundary commit */
-       abbrev++;
+       if (0 < abbrev)
+               /* one more abbrev length is needed for the boundary commit */
+               abbrev++;
 
        if (revs_file && read_ancestry(revs_file))
                die_errno("reading graft file '%s' failed", revs_file);