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sparse-index: implement ensure_full_index()

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We will mark an in-memory index_state as having sparse directory entries
with the sparse_index bit. These currently cannot exist, but we will add
a mechanism for collapsing a full index to a sparse one in a later
change. That will happen at write time, so we must first allow parsing
the format before writing it.

Commands or methods that require a full index in order to operate can
call ensure_full_index() to expand that index in-memory. This requires
parsing trees using that index's repository.

Sparse directory entries have a specific 'ce_mode' value. The macro
S_ISSPARSEDIR(ce->ce_mode) can check if a cache_entry 'ce' has this type.
This ce_mode is not possible with the existing index formats, so we don't
also verify all properties of a sparse-directory entry, which are:

 1. ce->ce_mode == 0040000
 2. ce->flags & CE_SKIP_WORKTREE is true
 3. ce->name[ce->namelen - 1] == '/' (ends in dir separator)
 4. ce->oid references a tree object.

These are all semi-enforced in ensure_full_index() to some extent. Any
deviation will cause a warning at minimum or a failure in the worst
case.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Derrick Stolee
2021-03-30 13:10:48 +00:00
committed by Junio C Hamano
parent 3964fc2aae
commit 4300f8442a
3 changed files with 118 additions and 2 deletions
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13
cache.h
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@ -204,6 +204,8 @@ struct cache_entry {
#error "CE_EXTENDED_FLAGS out of range"
#endif
#define S_ISSPARSEDIR(m) ((m) == S_IFDIR)
/* Forward structure decls */
struct pathspec;
struct child_process;
@ -319,7 +321,14 @@ struct index_state {
drop_cache_tree : 1,
updated_workdir : 1,
updated_skipworktree : 1,
fsmonitor_has_run_once : 1;
fsmonitor_has_run_once : 1,
/*
* sparse_index == 1 when sparse-directory
* entries exist. Requires sparse-checkout
* in cone mode.
*/
sparse_index : 1;
struct hashmap name_hash;
struct hashmap dir_hash;
struct object_id oid;
@ -722,6 +731,8 @@ int read_index_from(struct index_state *, const char *path,
const char *gitdir);
int is_index_unborn(struct index_state *);
void ensure_full_index(struct index_state *istate);
/* For use with `write_locked_index()`. */
#define COMMIT_LOCK (1 << 0)
#define SKIP_IF_UNCHANGED (1 << 1)