Re: [PATCH 04/20] sparse-index: add guard to ensure full index

>
> From: Derrick Stolee <dstolee@microsoft.com>
>
> Upcoming changes will introduce modifications to the index format that
> allow sparse directories. It will be useful to have a mechanism for
> converting those sparse index files into full indexes by walking the
> tree at those sparse directories. Name this method ensure_full_index()
> as it will guarantee that the index is fully expanded.
>
> This method is not implemented yet, and instead we focus on the
> scaffolding to declare it and call it at the appropriate time.
>
> Add a 'command_requires_full_index' member to struct repo_settings. This
> will be an indicator that we need the index in full mode to do certain
> index operations. This starts as being true for every command, then we
> will set it to false as some commands integrate with sparse indexes.
>
> If 'command_requires_full_index' is true, then we will immediately
> expand a sparse index to a full one upon reading from disk. This
> suffices for now, but we will want to add more callers to
> ensure_full_index() later.

> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  Makefile        |  1 +
>  repo-settings.c |  8 ++++++++
>  repository.c    | 11 ++++++++++-
>  repository.h    |  2 ++
>  sparse-index.c  |  8 ++++++++
>  sparse-index.h  |  7 +++++++
>  6 files changed, 36 insertions(+), 1 deletion(-)
>  create mode 100644 sparse-index.c
>  create mode 100644 sparse-index.h
>
> diff --git a/Makefile b/Makefile
> index 5a239cac20e3..3bf61699238d 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -980,6 +980,7 @@ LIB_OBJS += setup.o
>  LIB_OBJS += shallow.o
>  LIB_OBJS += sideband.o
>  LIB_OBJS += sigchain.o
> +LIB_OBJS += sparse-index.o
>  LIB_OBJS += split-index.o
>  LIB_OBJS += stable-qsort.o
>  LIB_OBJS += strbuf.o
> diff --git a/repo-settings.c b/repo-settings.c
> index f7fff0f5ab83..d63569e4041e 100644
> --- a/repo-settings.c
> +++ b/repo-settings.c
> @@ -77,4 +77,12 @@ void prepare_repo_settings(struct repository *r)
>                 UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_KEEP);
>
>         UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_DEFAULT);
> +
> +       /*
> +        * This setting guards all index reads to require a full index
> +        * over a sparse index. After suitable guards are placed in the
> +        * codebase around uses of the index, this setting will be
> +        * removed.
> +        */
> +       r->settings.command_requires_full_index = 1;
>  }
> diff --git a/repository.c b/repository.c
> index c98298acd017..a8acae002f71 100644
> --- a/repository.c
> +++ b/repository.c
> @@ -10,6 +10,7 @@
>  #include "object.h"
>  #include "lockfile.h"
>  #include "submodule-config.h"
> +#include "sparse-index.h"
>
>  /* The main repository */
>  static struct repository the_repo;
> @@ -261,6 +262,8 @@ void repo_clear(struct repository *repo)
>
>  int repo_read_index(struct repository *repo)
>  {
> +       int res;
> +
>         if (!repo->index)
>                 repo->index = xcalloc(1, sizeof(*repo->index));
>
> @@ -270,7 +273,13 @@ int repo_read_index(struct repository *repo)
>         else if (repo->index->repo != repo)
>                 BUG("repo's index should point back at itself");
>
> -       return read_index_from(repo->index, repo->index_file, repo->gitdir);
> +       res = read_index_from(repo->index, repo->index_file, repo->gitdir);
> +
> +       prepare_repo_settings(repo);
> +       if (repo->settings.command_requires_full_index)
> +               ensure_full_index(repo->index);
> +
> +       return res;
>  }
>
>  int repo_hold_locked_index(struct repository *repo,
> diff --git a/repository.h b/repository.h
> index b385ca3c94b6..e06a23015697 100644
> --- a/repository.h
> +++ b/repository.h
> @@ -41,6 +41,8 @@ struct repo_settings {
>         enum fetch_negotiation_setting fetch_negotiation_algorithm;
>
>         int core_multi_pack_index;
> +
> +       unsigned command_requires_full_index:1;
>  };
>
>  struct repository {
> diff --git a/sparse-index.c b/sparse-index.c
> new file mode 100644
> index 000000000000..82183ead563b
> --- /dev/null
> +++ b/sparse-index.c
> @@ -0,0 +1,8 @@
> +#include "cache.h"
> +#include "repository.h"
> +#include "sparse-index.h"
> +
> +void ensure_full_index(struct index_state *istate)
> +{
> +       /* intentionally left blank */
> +}
> diff --git a/sparse-index.h b/sparse-index.h
> new file mode 100644
> index 000000000000..09a20d036c46
> --- /dev/null
> +++ b/sparse-index.h
> @@ -0,0 +1,7 @@
> +#ifndef SPARSE_INDEX_H__
> +#define SPARSE_INDEX_H__
> +
> +struct index_state;
> +void ensure_full_index(struct index_state *istate);
> +
> +#endif
> --
> gitgitgadget
>