[PATCH v3 07/10] sparse-index: partially expand directories

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

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 | 57 +++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 50 insertions(+), 7 deletions(-)

diff --git a/sparse-index.c b/sparse-index.c
index 7848910c154..a881f851810 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 +236,52 @@ 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?
+		 *
+		 * Artificially pad the path name with a slash "/" to
+		 * indicate it as a directory, and add an arbitrary file
+		 * name ("-") so we can consider base->buf as a file name
+		 * to match against the cone-mode patterns.
+		 *
+		 * If we compared just "path", then we would expand more
+		 * than we should. Since every file at root is always
+		 * included, we would expand every directory at root at
+		 * least one level deep instead of using sparse directory
+		 * entries.
+		 */
+		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 index.
+		 */
+		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 +293,7 @@ void expand_index(struct index_state *istate, struct pattern_list *pl)
 	struct index_state *full;
 	struct strbuf base = STRBUF_INIT;
 	const char *tr_region;
+	struct modify_index_context ctx;
 
 	/*
 	 * If the index is already full, then keep it full. We will convert
@@ -293,6 +333,9 @@ void expand_index(struct index_state *istate, struct pattern_list *pl)
 	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;
@@ -318,7 +361,7 @@ void expand_index(struct index_state *istate, struct pattern_list *pl)
 		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);
-- 
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