Re: [PATCH 5/8] sparse-index: partially expand directories

> From: Derrick Stolee <dstolee@microsoft.com>
> 
> The expand_to_pattern_list() method expands sparse directory entries
> to their list of contained files when either the pattern list is NULL or
> the directory is contained in the new pattern list's cone mode patterns.
> 
> It is possible that the pattern list has a recursive match with a
> directory 'A/B/C/' and so an existing sparse directory 'A/B/' would need
> to be expanded. If there exists a directory 'A/B/D/', then that
> directory should not be expanded and instead we can create a sparse
> directory.
> 
> To implement this, we plug into the add_path_to_index() callback for the
> call to read_tree_at(). Since we now need access to both the index we
> are writing and the pattern list we are comparing, create a 'struct
> modify_index_context' to use as a data transfer object. It is important
> that we use the given pattern list since we will use this pattern list
> to change the sparse-checkout patterns and cannot use
> istate->sparse_checkout_patterns.
> 
> Signed-off-by: Derrick Stolee <derrickstolee@github.com>
> ---
>  sparse-index.c | 46 +++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 39 insertions(+), 7 deletions(-)
> 
> diff --git a/sparse-index.c b/sparse-index.c
> index 79e8ff087bc..3d8eed585b5 100644
> --- a/sparse-index.c
> +++ b/sparse-index.c
> @@ -9,6 +9,11 @@
>  #include "dir.h"
>  #include "fsmonitor.h"
>  
> +struct modify_index_context {
> +	struct index_state *write;
> +	struct pattern_list *pl;
> +};
> +
>  static struct cache_entry *construct_sparse_dir_entry(
>  				struct index_state *istate,
>  				const char *sparse_dir,
> @@ -231,18 +236,41 @@ static int add_path_to_index(const struct object_id *oid,
>  			     struct strbuf *base, const char *path,
>  			     unsigned int mode, void *context)
>  {
> -	struct index_state *istate = (struct index_state *)context;
> +	struct modify_index_context *ctx = (struct modify_index_context *)context;
>  	struct cache_entry *ce;
>  	size_t len = base->len;
>  
> -	if (S_ISDIR(mode))
> -		return READ_TREE_RECURSIVE;
> +	if (S_ISDIR(mode)) {
> +		int dtype;
> +		size_t baselen = base->len;
> +		if (!ctx->pl)
> +			return READ_TREE_RECURSIVE;
>  
> -	strbuf_addstr(base, path);
> +		/*
> +		 * Have we expanded to a point outside of the sparse-checkout?
> +		 */
> +		strbuf_addstr(base, path);
> +		strbuf_add(base, "/-", 2);
> +
> +		if (path_matches_pattern_list(base->buf, base->len,
> +					      NULL, &dtype,
> +					      ctx->pl, ctx->write)) {
> +			strbuf_setlen(base, baselen);
> +			return READ_TREE_RECURSIVE;
> +		}
>  
> -	ce = make_cache_entry(istate, mode, oid, base->buf, 0, 0);
> +		/*
> +		 * The path "{base}{path}/" is a sparse directory. Create the correct
> +		 * name for inserting the entry into the idnex.

> +		 */
> +		strbuf_setlen(base, base->len - 1);
> +	} else {
> +		strbuf_addstr(base, path);
> +	}
> +
> +	ce = make_cache_entry(ctx->write, mode, oid, base->buf, 0, 0);
>  	ce->ce_flags |= CE_SKIP_WORKTREE | CE_EXTENDED;
> -	set_index_entry(istate, istate->cache_nr++, ce);
> +	set_index_entry(ctx->write, ctx->write->cache_nr++, ce);
>  
>  	strbuf_setlen(base, len);
>  	return 0;
> @@ -254,6 +282,7 @@ void expand_to_pattern_list(struct index_state *istate,
>  	int i;
>  	struct index_state *full;
>  	struct strbuf base = STRBUF_INIT;
> +	struct modify_index_context ctx;
>  
>  	/*
>  	 * If the index is already full, then keep it full. We will convert
> @@ -294,6 +323,9 @@ void expand_to_pattern_list(struct index_state *istate,
>  	full->cache_nr = 0;
>  	ALLOC_ARRAY(full->cache, full->cache_alloc);
>  
> +	ctx.write = full;
> +	ctx.pl = pl;
> +
>  	for (i = 0; i < istate->cache_nr; i++) {
>  		struct cache_entry *ce = istate->cache[i];
>  		struct tree *tree;
> @@ -319,7 +351,7 @@ void expand_to_pattern_list(struct index_state *istate,
>  		strbuf_add(&base, ce->name, strlen(ce->name));
>  
>  		read_tree_at(istate->repo, tree, &base, &ps,
> -			     add_path_to_index, full);
> +			     add_path_to_index, &ctx);
>  
>  		/* free directory entries. full entries are re-used */
>  		discard_cache_entry(ce);