sparse-index: create expand_to_pattern_list()

In order to allow modifying the sparse-checkout cone using a sparse
index without expanding to a full one, we need to be able to replace
sparse directory entries with their contained files and subdirectories
so other code paths can discover those cache entries and write the
corresponding files to disk before committing the index.

We already have logic in ensure_full_index() that expands the index
entries, so we will use that as our base. Create
expand_to_pattern_list() which takes a pattern list, but for now mostly
ignores it. The current implementation is only correct when the pattern
list is NULL as that does the same as ensure_full_index(). In fact,
ensure_full_index() is converted to a shim over
expand_to_pattern_list().

A future update will actually implement expand_to_pattern_list() to its
full capabilities. For now, it is created and documented. We also start
using doc-style comments in sparse-index.h.

Signed-off-by: Derrick Stolee <[email protected]>

Author: derrickstolee

sparse-index.c

@@ -239,20 +239,42 @@ static int add_path_to_index(const struct object_id *oid,
 	return 0;
 }
 
-void ensure_full_index(struct index_state *istate)
+void expand_to_pattern_list(struct index_state *istate,
+			      struct pattern_list *pl)
 {
 	int i;
 	struct index_state *full;
 	struct strbuf base = STRBUF_INIT;
 
+	/*
+	 * If the index is already full, then keep it full. We will convert
+	 * it to a sparse index on write, if possible.
+	 */
 	if (!istate || !istate->sparse_index)
 		return;
 
+	/*
+	 * If our index is sparse, but our new pattern set does not use
+	 * cone mode patterns, then we need to expand the index before we
+	 * continue. A NULL pattern set indicates a full expansion to a
+	 * full index.
+	 */
+	if (pl && !pl->use_cone_patterns)
+		pl = NULL;
+
+	/*
+	 * A NULL pattern set indicates we are expanding a full index, so
+	 * we use a special region name that indicates the full expansion.
+	 * This is used by test cases, but also helps to differentiate the
+	 * two cases.
+	 */
+	trace2_region_enter("index",
+			    pl ? "expand_to_pattern_list" : "ensure_full_index",
+			    istate->repo);
+
 	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));
@@ -313,7 +335,14 @@ void ensure_full_index(struct index_state *istate)
 	cache_tree_free(&istate->cache_tree);
 	cache_tree_update(istate, 0);
 
-	trace2_region_leave("index", "ensure_full_index", istate->repo);
+	trace2_region_leave("index",
+			    pl ? "expand_to_pattern_list" : "ensure_full_index",
+			    istate->repo);
+}
+
+void ensure_full_index(struct index_state *istate)
+{
+	expand_to_pattern_list(istate, NULL);
 }
 
 /*

sparse-index.h

@@ -5,7 +5,7 @@ struct index_state;
 #define SPARSE_INDEX_MEMORY_ONLY (1 << 0)
 int convert_to_sparse(struct index_state *istate, int flags);
 
-/*
+/**
  * Some places in the codebase expect to search for a specific path.
  * This path might be outside of the sparse-checkout definition, in
  * which case a sparse-index may not contain a path for that index.
@@ -21,4 +21,18 @@ void expand_to_path(struct index_state *istate,
 struct repository;
 int set_sparse_index_config(struct repository *repo, int enable);
 
+struct pattern_list;
+
+/**
+ * Scan the given index and compare its entries to the given pattern list.
+ * If the index is sparse and the pattern list uses cone mode patterns,
+ * then modify the index to contain the all of the file entries within that
+ * new pattern list. This expands sparse directories only as far as needed.
+ *
+ * If the pattern list is NULL or does not use cone mode patterns, then the
+ * index is expanded to a full index.
+ */
+void expand_to_pattern_list(struct index_state *istate,
+			      struct pattern_list *pl);
+
 #endif