Merge branch 'jk/ambiguous-short-object-names'

When given an abbreviated object name that is not (or more
realistically, "no longer") unique, we gave a fatal error
"ambiguous argument".  This error is now accompanied by hints that
lists the objects that begins with the given prefix.  During the
course of development of this new feature, numerous minor bugs were
uncovered and corrected, the most notable one of which is that we
gave "short SHA1 xxxx is ambiguous." twice without good reason.

* jk/ambiguous-short-object-names:
get_short_sha1: make default disambiguation configurable
get_short_sha1: list ambiguous objects on error
for_each_abbrev: drop duplicate objects
sha1_array: let callbacks interrupt iteration
get_short_sha1: mark ambiguity error for translation
get_short_sha1: NUL-terminate hex prefix
get_short_sha1: refactor init of disambiguation code
get_short_sha1: parse tags when looking for treeish
get_sha1: propagate flags to child functions
get_sha1: avoid repeating ourselves via ONLY_TO_DIE
get_sha1: detect buggy calls with multiple disambiguators

diff --combined cache.h
index 6fc0e5ae68a6965c8be3b822400145095b56f755,f346c01708d1a190700f4895d6975d86c1b551b4..1604e2987852ce54fa1b27067d8f5decde4c292d
--- 1/cache.h
--- 2/cache.h
+++ b/cache.h
@@@ -367,9 -367,8 +367,9 @@@ extern void free_name_hash(struct index
  #define rename_cache_entry_at(pos, new_name) rename_index_entry_at(&the_index, (pos), (new_name))
  #define remove_cache_entry_at(pos) remove_index_entry_at(&the_index, (pos))
  #define remove_file_from_cache(path) remove_file_from_index(&the_index, (path))
 -#define add_to_cache(path, st, flags) add_to_index(&the_index, (path), (st), (flags), 0)
 -#define add_file_to_cache(path, flags) add_file_to_index(&the_index, (path), (flags), 0)
 +#define add_to_cache(path, st, flags) add_to_index(&the_index, (path), (st), (flags))
 +#define add_file_to_cache(path, flags) add_file_to_index(&the_index, (path), (flags))
 +#define chmod_cache_entry(ce, flip) chmod_index_entry(&the_index, (ce), (flip))
  #define refresh_cache(flags) refresh_index(&the_index, (flags), NULL, NULL, NULL)
  #define ce_match_stat(ce, st, options) ie_match_stat(&the_index, (ce), (st), (options))
  #define ce_modified(ce, st, options) ie_modified(&the_index, (ce), (st), (options))
@@@ -526,10 -525,9 +526,10 @@@ extern void verify_non_filename(const c
  extern int path_inside_repo(const char *prefix, const char *path);
  
  #define INIT_DB_QUIET 0x0001
 +#define INIT_DB_EXIST_OK 0x0002
  
 -extern int set_git_dir_init(const char *git_dir, const char *real_git_dir, int);
 -extern int init_db(const char *template_dir, unsigned int flags);
 +extern int init_db(const char *git_dir, const char *real_git_dir,
 +                 const char *template_dir, unsigned int flags);
  
  extern void sanitize_stdfds(void);
  extern int daemonize(void);
@@@ -589,10 -587,9 +589,10 @@@ extern int remove_file_from_index(struc
  #define ADD_CACHE_IGNORE_ERRORS       4
  #define ADD_CACHE_IGNORE_REMOVAL 8
  #define ADD_CACHE_INTENT 16
 -extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags, int force_mode);
 -extern int add_file_to_index(struct index_state *, const char *path, int flags, int force_mode);
 +extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 +extern int add_file_to_index(struct index_state *, const char *path, int flags);
  extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
 +extern int chmod_index_entry(struct index_state *, struct cache_entry *ce, char flip);
  extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
  extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
  extern int index_name_is_other(const struct index_state *, const char *, int);
@@@ -1206,6 -1203,11 +1206,11 @@@ struct object_context 
  #define GET_SHA1_FOLLOW_SYMLINKS 0100
  #define GET_SHA1_ONLY_TO_DIE    04000
  
+ #define GET_SHA1_DISAMBIGUATORS \
+       (GET_SHA1_COMMIT | GET_SHA1_COMMITTISH | \
+       GET_SHA1_TREE | GET_SHA1_TREEISH | \
+       GET_SHA1_BLOB)
+ 
  extern int get_sha1(const char *str, unsigned char *sha1);
  extern int get_sha1_commit(const char *str, unsigned char *sha1);
  extern int get_sha1_committish(const char *str, unsigned char *sha1);
@@@ -1220,6 -1222,8 +1225,8 @@@ extern int get_oid(const char *str, str
  typedef int each_abbrev_fn(const unsigned char *sha1, void *);
  extern int for_each_abbrev(const char *prefix, each_abbrev_fn, void *);
  
+ extern int set_disambiguate_hint_config(const char *var, const char *value);
+ 
  /*
   * Try to read a SHA1 in hexadecimal format from the 40 characters
   * starting at hex.  Write the 20-byte result to sha1 in binary form.
@@@ -1357,7 -1361,6 +1364,7 @@@ struct checkout 
                 not_new:1,
                 refresh_cache:1;
  };
 +#define CHECKOUT_INIT { NULL, "" }
  
  #define TEMPORARY_FILENAME_LENGTH 25
  extern int checkout_entry(struct cache_entry *ce, const struct checkout *state, char *topath);
@@@ -1862,7 -1865,7 +1869,7 @@@ void packet_trace_identity(const char *
   * return 0 if success, 1 - if addition of a file failed and
   * ADD_FILES_IGNORE_ERRORS was specified in flags
   */
 -int add_files_to_cache(const char *prefix, const struct pathspec *pathspec, int flags, int force_mode);
 +int add_files_to_cache(const char *prefix, const struct pathspec *pathspec, int flags);
  
  /* diff.c */
  extern int diff_auto_refresh_index;