Make the default abbrev length configurable

The default of 7 comes from fairly early in git development, when
seven hex digits was a lot (it covers about 250+ million hash
values). Back then I thought that 65k revisions was a lot (it was what
we were about to hit in BK), and each revision tends to be about 5-10
new objects or so, so a million objects was a big number.

These days, the kernel isn't even the largest git project, and even
the kernel has about 220k revisions (_much_ bigger than the BK tree
ever was) and we are approaching two million objects. At that point,
seven hex digits is still unique for a lot of them, but when we're
talking about just two orders of magnitude difference between number
of objects and the hash size, there _will_ be collisions in truncated
hash values. It's no longer even close to unrealistic - it happens all
the time.

We should both increase the default abbrev that was unrealistically
small, _and_ add a way for people to set their own default per-project
in the git config file.

This is the first step to first make it configurable; the default of 7
is not raised yet.

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

diff --git a/Documentation/config.txt b/Documentation/config.txt
index c5e183516a104e6efb7ed597fb4498d75560ab68..30afde98ae753fca6838381abff756048e70409a 100644 (file)
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -567,6 +567,12 @@ core.sparseCheckout::
        Enable "sparse checkout" feature. See section "Sparse checkout" in
        linkgit:git-read-tree[1] for more information.
 
+core.abbrevLength::
+       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

diff --git a/builtin/describe.c b/builtin/describe.c
index 342129fdbdc534bdf9277de710f8e7b7ba11c5c4..95915960d46a2e6b6f222da07b99bcaa428dde42 100644 (file)
--- a/builtin/describe.c
+++ b/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)

diff --git a/cache.h b/cache.h
index d83d68c859904fadbe2501cabd8575be09131d7b..8d73d88962f3f1be42fa4fddb69b115b6dbf0a76 100644 (file)
--- a/cache.h
+++ b/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;
@@ -758,8 +759,8 @@ 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];

diff --git a/config.c b/config.c
index 625e0518767712583f917762634c2fc852c4d2eb..e8a6e56795e3d1e72cab9bb522bd03bdcdb5bdca 100644 (file)
--- a/config.c
+++ b/config.c
@@ -531,6 +531,14 @@ static int git_default_core_config(const char *var, const char *value)
                return 0;
        }
 
+       if (!strcmp(var, "core.abbrevlength")) {
+               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)

diff --git a/environment.c b/environment.c
index 9564475f429312a467a020106f7443112367d5da..f2d90a807b7d50cc3fb6dd7a5c017d0dbc2937dc 100644 (file)
--- a/environment.c
+++ b/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;