Subject: Re: [PATCH v3 05/20] sparse-index: implement ensure_full_index()

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Wed, 17 Mar 2021 14:03:45 +0100

On Tue, Mar 16 2021, Derrick Stolee via GitGitGadget wrote:

> From: Derrick Stolee <[email-masked]>
> [...]
> +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 cache_entry *ce;
> +	size_t len = base->len;
> +
> +	if (S_ISDIR(mode))
> +		return READ_TREE_RECURSIVE;
> +
> +	strbuf_addstr(base, path);
> +
> +	ce = make_cache_entry(istate, mode, oid, base->buf, 0, 0);
> +	ce->ce_flags |= CE_SKIP_WORKTREE;
> +	set_index_entry(istate, istate->cache_nr++, ce);
> +
> +	strbuf_setlen(base, len);
> +	return 0;
> +}
>  
>  void ensure_full_index(struct index_state *istate)
>  {
> -	/* intentionally left blank */
> +	int i;
> +	struct index_state *full;
> +	struct strbuf base = STRBUF_INIT;
> +
> +	if (!istate || !istate->sparse_index)
> +		return;
> +
> +	if (!istate->repo)
> +		istate->repo = the_repository;
> +
> +	trace2_region_enter("index", "ensure_full_index", istate->repo);
> +
> +	/* initialize basics of new index */
> +	full = xcalloc(1, sizeof(struct index_state));
> +	memcpy(full, istate, sizeof(struct index_state));
> +
> +	/* then change the necessary things */
> +	full->sparse_index = 0;
> +	full->cache_alloc = (3 * istate->cache_alloc) / 2;
> +	full->cache_nr = 0;
> +	ALLOC_ARRAY(full->cache, full->cache_alloc);
> +
> +	for (i = 0; i < istate->cache_nr; i++) {
> +		struct cache_entry *ce = istate->cache[i];
> +		struct tree *tree;
> +		struct pathspec ps;
> +
> +		if (!S_ISSPARSEDIR(ce->ce_mode)) {
> +			set_index_entry(full, full->cache_nr++, ce);
> +			continue;
> +		}
> +		if (!(ce->ce_flags & CE_SKIP_WORKTREE))
> +			warning(_("index entry is a directory, but not sparse (%08x)"),
> +				ce->ce_flags);
> +
> +		/* recursively walk into cd->name */
> +		tree = lookup_tree(istate->repo, &ce->oid);
> +
> +		memset(&ps, 0, sizeof(ps));
> +		ps.recursive = 1;
> +		ps.has_wildcard = 1;
> +		ps.max_depth = -1;
> +
> +		strbuf_setlen(&base, 0);
> +		strbuf_add(&base, ce->name, strlen(ce->name));
> +
> +		read_tree_at(istate->repo, tree, &base, &ps,
> +			     add_path_to_index, full);
> +
> +		/* free directory entries. full entries are re-used */
> +		discard_cache_entry(ce);
> +	}
> +
> +	/* Copy back into original index. */
> +	memcpy(&istate->name_hash, &full->name_hash, sizeof(full->name_hash));
> +	istate->sparse_index = 0;
> +	free(istate->cache);
> +	istate->cache = full->cache;
> +	istate->cache_nr = full->cache_nr;
> +	istate->cache_alloc = full->cache_alloc;
> +
> +	strbuf_release(&base);
> +	free(full);
> +
> +	trace2_region_leave("index", "ensure_full_index", istate->repo);
>  }

Not that I mind having added the read_tree_at() again, but just thinking
aloud here.

So we need this loop here because there's nothing like a read_tree_at()
that knows how to start at the non-tree root of the index, and then for
each directory there we're going to perform the equivalent of a
read_tree() there, but we need to set the base for add_path_to_index()
since we started at subdirs, not the root.

That's fine, but grepping around a bit I wonder if we shouldn't
eventually have some slightly fancier API that just works like
read_tree() but takes an optional "start at the index's root" instead.

Well, things that want that usually care about the index-specific bits,
whereas this "I just care about the tree for these" is more of a special
case I guess.