Merge branch 'ad/bisect-terms'

The use of 'good/bad' in "git bisect" made it confusing to use when
hunting for a state change that is not a regression (e.g. bugfix).
The command learned 'old/new' and then allows the end user to
say e.g. "bisect start --term-old=fast --term=new=slow" to find a
performance regression.

Michael's idea to make 'good/bad' more intelligent does have
certain attractiveness ($gname/272867), and makes some of the work
on this topic a moot point.

* ad/bisect-terms:
bisect: allow setting any user-specified in 'git bisect start'
bisect: add 'git bisect terms' to view the current terms
bisect: add the terms old/new
bisect: sanity check on terms

diff --combined bisect.c
index 041a13d093a21597c60d799c0f6943998f2d6a8a,f7292cbac4def85cdc4394df02567b73ba2cc91d..053d1a2ab91a6c41a0fe957569ff905d12b00bee
--- 1/bisect.c
--- 2/bisect.c
+++ b/bisect.c
@@@ -19,6 -19,7 +19,6 @@@ static struct object_id *current_bad_oi
  
  static const char *argv_checkout[] = {"checkout", "-q", NULL, "--", NULL};
  static const char *argv_show_branch[] = {"show-branch", NULL, NULL};
 -static const char *argv_update_ref[] = {"update-ref", "--no-deref", "BISECT_HEAD", NULL, NULL};
  
  static const char *term_bad;
  static const char *term_good;
@@@ -428,13 -429,10 +428,13 @@@ static int read_bisect_refs(void
        return for_each_ref_in("refs/bisect/", register_ref, NULL);
  }
  
 +static GIT_PATH_FUNC(git_path_bisect_names, "BISECT_NAMES")
 +static GIT_PATH_FUNC(git_path_bisect_expected_rev, "BISECT_EXPECTED_REV")
 +
  static void read_bisect_paths(struct argv_array *array)
  {
        struct strbuf str = STRBUF_INIT;
 -      const char *filename = git_path("BISECT_NAMES");
 +      const char *filename = git_path_bisect_names();
        FILE *fp = fopen(filename, "r");
  
        if (!fp)
@@@ -655,7 -653,7 +655,7 @@@ static void exit_if_skipped_commits(str
  
  static int is_expected_rev(const struct object_id *oid)
  {
 -      const char *filename = git_path("BISECT_EXPECTED_REV");
 +      const char *filename = git_path_bisect_expected_rev();
        struct stat st;
        struct strbuf str = STRBUF_INIT;
        FILE *fp;
@@@ -677,16 -675,34 +677,16 @@@
        return res;
  }
  
 -static void mark_expected_rev(char *bisect_rev_hex)
 -{
 -      int len = strlen(bisect_rev_hex);
 -      const char *filename = git_path("BISECT_EXPECTED_REV");
 -      int fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
 -
 -      if (fd < 0)
 -              die_errno("could not create file '%s'", filename);
 -
 -      bisect_rev_hex[len] = '\n';
 -      write_or_die(fd, bisect_rev_hex, len + 1);
 -      bisect_rev_hex[len] = '\0';
 -
 -      if (close(fd) < 0)
 -              die("closing file %s: %s", filename, strerror(errno));
 -}
 -
 -static int bisect_checkout(char *bisect_rev_hex, int no_checkout)
 +static int bisect_checkout(const unsigned char *bisect_rev, int no_checkout)
  {
 +      char bisect_rev_hex[GIT_SHA1_HEXSZ + 1];
  
 -      mark_expected_rev(bisect_rev_hex);
 +      memcpy(bisect_rev_hex, sha1_to_hex(bisect_rev), GIT_SHA1_HEXSZ + 1);
 +      update_ref(NULL, "BISECT_EXPECTED_REV", bisect_rev, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
  
        argv_checkout[2] = bisect_rev_hex;
        if (no_checkout) {
 -              argv_update_ref[3] = bisect_rev_hex;
 -              if (run_command_v_opt(argv_update_ref, RUN_GIT_CMD))
 -                      die("update-ref --no-deref HEAD failed on %s",
 -                          bisect_rev_hex);
 +              update_ref(NULL, "BISECT_HEAD", bisect_rev, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
        } else {
                int res;
                res = run_command_v_opt(argv_checkout, RUN_GIT_CMD);
@@@ -730,6 -746,11 +730,11 @@@ static void handle_bad_merge_base(void
                                "This means the bug has been fixed "
                                "between %s and [%s].\n",
                                bad_hex, bad_hex, good_hex);
+               } else if (!strcmp(term_bad, "new") && !strcmp(term_good, "old")) {
+                       fprintf(stderr, "The merge base %s is new.\n"
+                               "The property has changed "
+                               "between %s and [%s].\n",
+                               bad_hex, bad_hex, good_hex);
                } else {
                        fprintf(stderr, "The merge base %s is %s.\n"
                                "This means the first '%s' commit is "
@@@ -762,11 -783,11 +767,11 @@@ static void handle_skipped_merge_base(c
  }
  
  /*
-  * "check_merge_bases" checks that merge bases are not "bad".
+  * "check_merge_bases" checks that merge bases are not "bad" (or "new").
   *
-  * - If one is "bad", it means the user assumed something wrong
+  * - If one is "bad" (or "new"), it means the user assumed something wrong
   * and we must exit with a non 0 error code.
-  * - If one is "good", that's good, we have nothing to do.
+  * - If one is "good" (or "old"), that's good, we have nothing to do.
   * - If one is "skipped", we can't know but we should warn.
   * - If we don't know, we should check it out and ask the user to test.
   */
@@@ -788,7 -809,7 +793,7 @@@ static void check_merge_bases(int no_ch
                        handle_skipped_merge_base(mb);
                } else {
                        printf("Bisecting: a merge base must be tested\n");
 -                      exit(bisect_checkout(sha1_to_hex(mb), no_checkout));
 +                      exit(bisect_checkout(mb, no_checkout));
                }
        }
  
@@@ -932,6 -953,7 +937,6 @@@ int bisect_next_all(const char *prefix
        struct commit_list *tried;
        int reaches = 0, all = 0, nr, steps;
        const unsigned char *bisect_rev;
 -      char bisect_rev_hex[GIT_SHA1_HEXSZ + 1];
  
        read_bisect_terms(&term_bad, &term_good);
        if (read_bisect_refs())
@@@ -969,10 -991,11 +974,10 @@@
        }
  
        bisect_rev = revs.commits->item->object.sha1;
 -      memcpy(bisect_rev_hex, sha1_to_hex(bisect_rev), GIT_SHA1_HEXSZ + 1);
  
        if (!hashcmp(bisect_rev, current_bad_oid->hash)) {
                exit_if_skipped_commits(tried, current_bad_oid);
 -              printf("%s is the first %s commit\n", bisect_rev_hex,
 +              printf("%s is the first %s commit\n", sha1_to_hex(bisect_rev),
                        term_bad);
                show_diff_tree(prefix, revs.commits->item);
                /* This means the bisection process succeeded. */
@@@ -985,7 -1008,7 +990,7 @@@
               "(roughly %d step%s)\n", nr, (nr == 1 ? "" : "s"),
               steps, (steps == 1 ? "" : "s"));
  
 -      return bisect_checkout(bisect_rev_hex, no_checkout);
 +      return bisect_checkout(bisect_rev, no_checkout);
  }
  
  static inline int log2i(int n)