[PATCH 22/27] add: allow operating on a sparse-only index

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

From: Derrick Stolee <dstolee@microsoft.com>

Replace enough callers to ensure_full_index() to instead call
expand_to_path() to reduce how often 'git add' expands a sparse index in
memory (before writing a sparse index again).

One non-obvious case is index_name_pos_also_unmerged() which is only hit
on the Windows platform (in my tests). Use expand_to_path() instead of
ensure_full_index().

Add a test to check that 'git add -A' and 'git add <file>' does not
expand the index at all, as long as <file> is not within a sparse
directory.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 builtin/add.c                            |  3 +++
 dir.c                                    |  8 ++++----
 read-cache.c                             | 10 +++++-----
 sparse-index.c                           | 18 ++++++++++++++----
 t/t1092-sparse-checkout-compatibility.sh | 14 ++++++++++++++
 5 files changed, 40 insertions(+), 13 deletions(-)

diff --git a/builtin/add.c b/builtin/add.c
index a825887c503..b73f8d51de6 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -491,6 +491,9 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 	add_new_files = !take_worktree_changes && !refresh_only && !add_renormalize;
 	require_pathspec = !(take_worktree_changes || (0 < addremove_explicit));
 
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 0;
+
 	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
 
 	/*
diff --git a/dir.c b/dir.c
index c786fa98d0e..21998c7c4b7 100644
--- a/dir.c
+++ b/dir.c
@@ -18,6 +18,7 @@
 #include "ewah/ewok.h"
 #include "fsmonitor.h"
 #include "submodule-config.h"
+#include "sparse-index.h"
 
 /*
  * Tells read_directory_recursive how a file or directory should be treated.
@@ -899,9 +900,9 @@ static int read_skip_worktree_file_from_index(struct index_state *istate,
 {
 	int pos, len;
 
-	ensure_full_index(istate);
-
 	len = strlen(path);
+
+	expand_to_path(istate, path, len, 0);
 	pos = index_name_pos(istate, path, len);
 	if (pos < 0)
 		return -1;
@@ -1707,8 +1708,7 @@ static enum exist_status directory_exists_in_index(struct index_state *istate,
 	if (ignore_case)
 		return directory_exists_in_index_icase(istate, dirname, len);
 
-	ensure_full_index(istate);
-
+	expand_to_path(istate, dirname, len, 0);
 	pos = index_name_pos(istate, dirname, len);
 	if (pos < 0)
 		pos = -pos-1;
diff --git a/read-cache.c b/read-cache.c
index 78910d8f1b7..8c974829497 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -647,7 +647,7 @@ static int index_name_pos_also_unmerged(struct index_state *istate,
 	int pos;
 	struct cache_entry *ce;
 
-	ensure_full_index(istate);
+	expand_to_path(istate, path, namelen, 0);
 
 	pos = index_name_pos(istate, path, namelen);
 	if (pos >= 0)
@@ -724,8 +724,6 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 	int hash_flags = HASH_WRITE_OBJECT;
 	struct object_id oid;
 
-	ensure_full_index(istate);
-
 	if (flags & ADD_CACHE_RENORMALIZE)
 		hash_flags |= HASH_RENORMALIZE;
 
@@ -733,6 +731,8 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		return error(_("%s: can only add regular files, symbolic links or git-directories"), path);
 
 	namelen = strlen(path);
+	expand_to_path(istate, path, namelen, 0);
+
 	if (S_ISDIR(st_mode)) {
 		if (resolve_gitlink_ref(path, "HEAD", &oid) < 0)
 			return error(_("'%s' does not have a commit checked out"), path);
@@ -1104,7 +1104,7 @@ static int has_dir_name(struct index_state *istate,
 	size_t len_eq_last;
 	int cmp_last = 0;
 
-	ensure_full_index(istate);
+	expand_to_path(istate, ce->name, ce->ce_namelen, 0);
 
 	/*
 	 * We are frequently called during an iteration on a sorted
@@ -1349,7 +1349,7 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
 {
 	int pos;
 
-	ensure_full_index(istate);
+	expand_to_path(istate, ce->name, ce->ce_namelen, 0);
 
 	if (option & ADD_CACHE_JUST_APPEND)
 		pos = istate->cache_nr;
diff --git a/sparse-index.c b/sparse-index.c
index bf8dce9a09b..a201f3b905c 100644
--- a/sparse-index.c
+++ b/sparse-index.c
@@ -286,6 +286,7 @@ static int in_expand_to_path = 0;
 void expand_to_path(struct index_state *istate,
 		    const char *path, size_t pathlen, int icase)
 {
+	struct cache_entry *ce = NULL;
 	struct strbuf path_as_dir = STRBUF_INIT;
 	int pos;
 
@@ -320,13 +321,22 @@ void expand_to_path(struct index_state *istate,
 
 	if (pos < 0)
 		pos = -pos - 1;
+	if (pos < istate->cache_nr)
+		ce = istate->cache[pos];
 
 	/*
-	 * Even if the path doesn't exist, if the value isn't exactly a
-	 * sparse-directory entry, then there is no need to expand the
-	 * index.
+	 * If we didn't land on a sparse directory, then there is
+	 * nothing to expand.
 	 */
-	if (istate->cache[pos]->ce_mode != CE_MODE_SPARSE_DIRECTORY)
+	if (ce && !S_ISSPARSEDIR(ce))
+		goto cleanup;
+	/*
+	 * If that sparse directory is not a prefix of the path we
+	 * are looking for, then we don't need to expand.
+	 */
+	if (ce &&
+	    (ce->ce_namelen >= path_as_dir.len ||
+	     strncmp(ce->name, path_as_dir.buf, ce->ce_namelen)))
 		goto cleanup;
 
 	trace2_region_enter("index", "expand_to_path", istate->repo);
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 09650f0755c..ae594ab880c 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -390,6 +390,20 @@ test_expect_success 'sparse-index is expanded and converted back' '
 	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
 		git -C sparse-index -c core.fsmonitor="" reset --hard &&
 	test_region index convert_to_sparse trace2.txt &&
+	test_region index ensure_full_index trace2.txt &&
+
+	rm trace2.txt &&
+	echo >>sparse-index/README.md &&
+	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
+		git -C sparse-index -c core.fsmonitor="" add -A &&
+	test_region index convert_to_sparse trace2.txt &&
+	test_region index ensure_full_index trace2.txt &&
+
+	rm trace2.txt &&
+	echo >>sparse-index/extra.txt &&
+	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
+		git -C sparse-index -c core.fsmonitor="" add extra.txt &&
+	test_region index convert_to_sparse trace2.txt &&
 	test_region index ensure_full_index trace2.txt
 '
 
-- 
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