We allow the user to relocate certain paths out of $GIT_DIR via
environment variables, e.g. GIT_OBJECT_DIRECTORY, GIT_INDEX_FILE and
GIT_GRAFT_FILE. All callers are not supposed to use git_path() or
git_pathdup() to get those paths. Instead they must use
get_object_directory(), get_index_file() and get_graft_file()
respectively. This is inconvenient and could be missed in review
(there's git_path("objects/info/alternates") somewhere in
sha1_file.c).

This patch makes git_path() and git_pathdup() understand those
environment variables. So if you set GIT_OBJECT_DIRECTORY to /foo/bar,
git_path("objects/abc") should return /tmp/bar/abc. The same is done
for the two remaining env variables.

XXX trim consecutive slashes

Signed-off-by: Nguyễn Thái Ngọc Duy <pclo...@gmail.com>
---
 cache.h               |  1 +
 environment.c         |  9 +++++++--
 path.c                | 35 ++++++++++++++++++++++++++++++++---
 t/t0060-path-utils.sh | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 test-path-utils.c     |  7 +++++++
 5 files changed, 95 insertions(+), 5 deletions(-)

diff --git a/cache.h b/cache.h
index ce377e1..cdafbd7 100644
--- a/cache.h
+++ b/cache.h
@@ -584,6 +584,7 @@ extern int fsync_object_files;
 extern int core_preload_index;
 extern int core_apply_sparse_checkout;
 extern int precomposed_unicode;
+extern int git_db_env, git_index_env, git_graft_env;
 
 /*
  * The character that begins a commented line in user-editable file
diff --git a/environment.c b/environment.c
index 0a15349..1d74dde 100644
--- a/environment.c
+++ b/environment.c
@@ -81,6 +81,7 @@ static size_t namespace_len;
 
 static const char *git_dir;
 static char *git_object_dir, *git_index_file, *git_graft_file;
+int git_db_env, git_index_env, git_graft_env;
 
 /*
  * Repository-local GIT_* environment variables; see cache.h for details.
@@ -134,15 +135,19 @@ static void setup_git_env(void)
        if (!git_object_dir) {
                git_object_dir = xmalloc(strlen(git_dir) + 9);
                sprintf(git_object_dir, "%s/objects", git_dir);
-       }
+       } else
+               git_db_env = 1;
        git_index_file = getenv(INDEX_ENVIRONMENT);
        if (!git_index_file) {
                git_index_file = xmalloc(strlen(git_dir) + 7);
                sprintf(git_index_file, "%s/index", git_dir);
-       }
+       } else
+               git_index_env = 1;
        git_graft_file = getenv(GRAFT_ENVIRONMENT);
        if (!git_graft_file)
                git_graft_file = git_pathdup("info/grafts");
+       else
+               git_graft_env = 1;
        if (getenv(NO_REPLACE_OBJECTS_ENVIRONMENT))
                read_replace_refs = 0;
        namespace = expand_namespace(getenv(GIT_NAMESPACE_ENVIRONMENT));
diff --git a/path.c b/path.c
index 24594c4..eda9176 100644
--- a/path.c
+++ b/path.c
@@ -49,10 +49,38 @@ char *mksnpath(char *buf, size_t n, const char *fmt, ...)
        return cleanup_path(buf);
 }
 
+static int dir_prefix(const char *buf, const char *dir)
+{
+       int len = strlen(dir);
+       return !strncmp(buf, dir, len) &&
+               (is_dir_sep(buf[len]) || buf[len] == '\0');
+}
+
+static void replace_dir(char *buf, int len, const char *newdir)
+{
+       int newlen = strlen(newdir);
+       int buflen = strlen(buf);
+       memmove(buf + newlen + 1, buf + len, buflen - len + 1);
+       memcpy(buf, newdir, newlen);
+       buf[newlen] = '/';
+}
+
+static void adjust_git_path(char *buf, int git_dir_len)
+{
+       /* XXX buffer overflow */
+       char *base = buf + git_dir_len;
+       if (git_graft_env && !strcmp(base, "info/grafts"))
+               strcpy(buf, get_graft_file());
+       else if (git_index_env && !strcmp(base, "index"))
+               strcpy(buf, get_index_file());
+       else if (git_db_env && dir_prefix(base, "objects"))
+               replace_dir(buf, git_dir_len + 7, get_object_directory());
+}
+
 static char *vsnpath(char *buf, size_t n, const char *fmt, va_list args)
 {
        const char *git_dir = get_git_dir();
-       size_t len;
+       size_t len, total_len;
 
        len = strlen(git_dir);
        if (n < len + 1)
@@ -60,9 +88,10 @@ static char *vsnpath(char *buf, size_t n, const char *fmt, 
va_list args)
        memcpy(buf, git_dir, len);
        if (len && !is_dir_sep(git_dir[len-1]))
                buf[len++] = '/';
-       len += vsnprintf(buf + len, n - len, fmt, args);
-       if (len >= n)
+       total_len = len + vsnprintf(buf + len, n - len, fmt, args);
+       if (total_len >= n)
                goto bad;
+       adjust_git_path(buf, len);
        return cleanup_path(buf);
 bad:
        strlcpy(buf, bad_path, n);
diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index 07c10c8..7ad2730 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -223,4 +223,52 @@ relative_path "<null>"             "<empty>"       ./
 relative_path "<null>"         "<null>"        ./
 relative_path "<null>"         /foo/a/b        ./
 
+test_expect_success 'git_path info/grafts without GIT_GRAFT_FILE' '
+       test-path-utils git_path info/grafts >actual1 &&
+       echo .git/info/grafts >expect1 &&
+       test_cmp expect1 actual1
+'
+
+test_expect_success 'git_path info/grafts with GIT_GRAFT_FILE' '
+       GIT_GRAFT_FILE=foo test-path-utils git_path info/grafts >actual2 &&
+       echo foo >expect2 &&
+       test_cmp expect2 actual2
+'
+
+test_expect_success 'git_path index' '
+       GIT_INDEX_FILE=foo test-path-utils git_path index >actual &&
+       echo foo >expect &&
+       test_cmp expect actual
+'
+
+test_expect_success 'git_path index/foo' '
+       GIT_INDEX_FILE=foo test-path-utils git_path index/foo >actual &&
+       echo .git/index/foo >expect &&
+       test_cmp expect actual
+'
+
+test_expect_success 'git_path index2' '
+       GIT_INDEX_FILE=foo test-path-utils git_path index2 >actual &&
+       echo .git/index2 >expect &&
+       test_cmp expect actual
+'
+
+test_expect_success 'git_path objects' '
+       GIT_OBJECT_DIRECTORY=foo test-path-utils git_path objects >actual &&
+       echo foo/ >expect &&
+       test_cmp expect actual
+'
+
+test_expect_success 'git_path objects/foo' '
+       GIT_OBJECT_DIRECTORY=foo test-path-utils git_path objects/foo >actual &&
+       echo foo//foo >expect &&
+       test_cmp expect actual
+'
+
+test_expect_success 'git_path objects2' '
+       GIT_OBJECT_DIRECTORY=foo test-path-utils git_path objects2 >actual &&
+       echo .git/objects2 >expect &&
+       test_cmp expect actual
+'
+
 test_done
diff --git a/test-path-utils.c b/test-path-utils.c
index 3dd3744..55e4fe0 100644
--- a/test-path-utils.c
+++ b/test-path-utils.c
@@ -135,6 +135,13 @@ int main(int argc, char **argv)
                return 0;
        }
 
+       if (argc == 3 && !strcmp(argv[1], "git_path")) {
+               int nongit_ok = 0;
+               setup_git_directory_gently(&nongit_ok);
+               puts(git_path("%s", argv[2]));
+               return 0;
+       }
+
        fprintf(stderr, "%s: unknown function name: %s\n", argv[0],
                argv[1] ? argv[1] : "(there was none)");
        return 1;
-- 
1.8.5.1.77.g42c48fa

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