read-tree: add "--super-prefix" option, eliminate global

The "--super-prefix" option to "git" was initially added in [1] for
use with "ls-files"[2], and shortly thereafter "submodule--helper"[3]
and "grep"[4]. It wasn't until [5] that "read-tree" made use of it.

At the time [5] made sense, but since then we've made "ls-files"
recurse in-process in [6], "grep" in [7], and finally
"submodule--helper" in the preceding commits.

Let's also remove it from "read-tree", which allows us to remove the
option to "git" itself.

We can do this because the only remaining user of it is the submodule
API, which will now invoke "read-tree" with its new "--super-prefix"
option. It will only do so when the "submodule_move_head()" function
is called.

That "submodule_move_head()" function was then only invoked by
"read-tree" itself, but now rather than setting an environment
variable to pass "--super-prefix" between cmd_read_tree() we:

- Set a new "super_prefix" in "struct unpack_trees_options". The
  "super_prefixed()" function in "unpack-trees.c" added in [5] will now
  use this, rather than get_super_prefix() looking up the environment
  variable we set earlier in the same process.

- Add the same field to the "struct checkout", which is only needed to
  ferry the "super_prefix" in the "struct unpack_trees_options" all the
  way down to the "entry.c" callers of "submodule_move_head()".

  Those calls which used the super prefix all originated in
  "cmd_read_tree()". The only other caller is the "unlink_entry()"
  caller in "builtin/checkout.c", which now passes a "NULL".

1. 74866d75793 (git: make super-prefix option, 2016-10-07)
2. e77aa336f11 (ls-files: optionally recurse into submodules, 2016-10-07)
3. 89c86265576 (submodule helper: support super prefix, 2016-12-08)
4. 0281e487fd9 (grep: optionally recurse into submodules, 2016-12-16)
5. 3d415425c7b (unpack-trees: support super-prefix option, 2017-01-17)
6. 188dce131fa (ls-files: use repository object, 2017-06-22)
7. f9ee2fcdfa0 (grep: recurse in-process using 'struct repository', 2017-08-02)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 0 insertions, 2 deletions

diff --git a/cache.h b/cache.h
index 07d40b0964..7f7e2b5a38 100644
--- a/cache.h
+++ b/cache.h
@@ -480,7 +480,6 @@ static inline enum object_type object_type(unsigned int mode)
 #define GIT_NAMESPACE_ENVIRONMENT "GIT_NAMESPACE"
 #define GIT_WORK_TREE_ENVIRONMENT "GIT_WORK_TREE"
 #define GIT_PREFIX_ENVIRONMENT "GIT_PREFIX"
-#define GIT_SUPER_PREFIX_ENVIRONMENT "GIT_INTERNAL_SUPER_PREFIX"
 #define DEFAULT_GIT_DIR_ENVIRONMENT ".git"
 #define DB_ENVIRONMENT "GIT_OBJECT_DIRECTORY"
 #define INDEX_ENVIRONMENT "GIT_INDEX_FILE"
@@ -566,7 +565,6 @@ int get_common_dir_noenv(struct strbuf *sb, const char *gitdir);
 int get_common_dir(struct strbuf *sb, const char *gitdir);
 const char *get_git_namespace(void);
 const char *strip_namespace(const char *namespaced_ref);
-const char *get_super_prefix(void);
 const char *get_git_work_tree(void);
 
 /*