Merge branch 'lt/default-abbrev' into maint

* lt/default-abbrev:
  Rename core.abbrevlength back to core.abbrev
  Make the default abbrev length configurable

Documentation/config.txt

@@ -558,6 +558,12 @@ core.sparseCheckout::
 	Enable "sparse checkout" feature. See section "Sparse checkout" in
 	linkgit:git-read-tree[1] for more information.
 
+core.abbrev::
+	Set the length object names are abbreviated to.  If unspecified,
+	many commands abbreviate to 7 hexdigits, which may not be enough
+	for abbreviated object names to stay unique for sufficiently long
+	time.
+
 add.ignore-errors::
 add.ignoreErrors::
 	Tells 'git add' to continue adding files when some files cannot be

builtin/describe.c

@@ -21,7 +21,7 @@ static int debug;	/* Display lots of verbose info */
 static int all;	/* Any valid ref can be used */
 static int tags;	/* Allow lightweight tags */
 static int longformat;
-static int abbrev = DEFAULT_ABBREV;
+static int abbrev = -1; /* unspecified */
 static int max_candidates = 10;
 static struct hash_table names;
 static int have_util;
@@ -420,7 +420,11 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 		OPT_END(),
 	};
 
+	git_config(git_default_config, NULL);
 	argc = parse_options(argc, argv, prefix, options, describe_usage, 0);
+	if (abbrev < 0)
+		abbrev = DEFAULT_ABBREV;
+
 	if (max_candidates < 0)
 		max_candidates = 0;
 	else if (max_candidates > MAX_TAGS)

cache.h

@@ -540,6 +540,7 @@ extern int trust_executable_bit;
 extern int trust_ctime;
 extern int quote_path_fully;
 extern int has_symlinks;
+extern int minimum_abbrev, default_abbrev;
 extern int ignore_case;
 extern int assume_unchanged;
 extern int prefer_symlink_refs;
@@ -759,8 +760,8 @@ static inline unsigned int hexval(unsigned char c)
 }
 
 /* Convert to/from hex/sha1 representation */
-#define MINIMUM_ABBREV 4
-#define DEFAULT_ABBREV 7
+#define MINIMUM_ABBREV minimum_abbrev
+#define DEFAULT_ABBREV default_abbrev
 
 struct object_context {
 	unsigned char tree[20];

config.c

@@ -523,6 +523,14 @@ static int git_default_core_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.abbrev")) {
+		int abbrev = git_config_int(var, value);
+		if (abbrev < minimum_abbrev || abbrev > 40)
+			return -1;
+		default_abbrev = abbrev;
+		return 0;
+	}
+
 	if (!strcmp(var, "core.loosecompression")) {
 		int level = git_config_int(var, value);
 		if (level == -1)

environment.c

@@ -15,6 +15,7 @@ int user_ident_explicitly_given;
 int trust_executable_bit = 1;
 int trust_ctime = 1;
 int has_symlinks = 1;
+int minimum_abbrev = 4, default_abbrev = 7;
 int ignore_case;
 int assume_unchanged;
 int prefer_symlink_refs;