[PATCH 3/6] sparse-checkout: enable `set` to initialize sparse-checkout mode

["Elijah Newren via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Elijah Newren <newren@xxxxxxxxx>

The previously suggested workflow:
  git sparse-checkout init ...
  git sparse-checkout set ...

Suffered from three problems:
  1) It would delete nearly all files in the first step, then
     restore them in the second.  That was poor performance and
     forced unnecessary rebuilds.
  2) The two-step process resulted in two progress bars, which
     was suboptimal from a UI point of view for wrappers that
     invoked both of these commands but only exposed a single
     command to their end users.
  3) With cone mode, the first step would delete nearly all
     ignored files everywhere, because everything was considered
     to be outside of the specified sparsity paths.  (The user was
     not allowed to specify any sparsity paths in the `init` step.)

Avoid these problems by teaching `set` to understand the extra
parameters that `init` takes and performing any necessary initialization
if not already in a sparse checkout.

Signed-off-by: Elijah Newren <newren@xxxxxxxxx>
---
 builtin/sparse-checkout.c | 52 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index e252b82136e..cf6a6c6c3a7 100644
--- a/builtin/sparse-checkout.c
+++ b/builtin/sparse-checkout.c
@@ -682,17 +682,26 @@ static int sparse_checkout_add(int argc, const char **argv, const char *prefix)
 }
 
 static char const * const builtin_sparse_checkout_set_usage[] = {
-	N_("git sparse-checkout set (--stdin | <patterns>)"),
+	N_("git sparse-checkout set [--cone] [--[no-]sparse-index] (--stdin | <patterns>)"),
 	NULL
 };
 
 static struct sparse_checkout_set_opts {
+	int cone_mode;
+	int sparse_index;
 	int use_stdin;
 } set_opts;
 
 static int sparse_checkout_set(int argc, const char **argv, const char *prefix)
 {
+	int mode, record_mode;
+	const char *default_patterns[] = {"/*", "!/*/"};
+
 	static struct option builtin_sparse_checkout_set_options[] = {
+		OPT_BOOL(0, "cone", &set_opts.cone_mode,
+			 N_("initialize the sparse-checkout in cone mode")),
+		OPT_BOOL(0, "sparse-index", &set_opts.sparse_index,
+			 N_("toggle the use of a sparse index")),
 		OPT_BOOL(0, "stdin", &set_opts.use_stdin,
 			 N_("read patterns from standard in")),
 		OPT_END(),
@@ -700,11 +709,52 @@ static int sparse_checkout_set(int argc, const char **argv, const char *prefix)
 
 	repo_read_index(the_repository);
 
+	set_opts.cone_mode = -1;
+	set_opts.sparse_index = -1;
+
 	argc = parse_options(argc, argv, prefix,
 			     builtin_sparse_checkout_set_options,
 			     builtin_sparse_checkout_set_usage,
 			     PARSE_OPT_KEEP_UNKNOWN);
 
+	/* Determine if we need to record the mode; ensure sparse checkout on */
+	record_mode = (set_opts.cone_mode != -1) || !core_apply_sparse_checkout;
+	core_apply_sparse_checkout = 1;
+
+	/* If not specified, use previous definition of cone mode */
+	if (set_opts.cone_mode == -1 && core_apply_sparse_checkout)
+		set_opts.cone_mode = core_sparse_checkout_cone;
+
+	/* Set cone/non-cone mode appropriately */
+	if (set_opts.cone_mode == 1) {
+		mode = MODE_CONE_PATTERNS;
+		core_sparse_checkout_cone = 1;
+	} else {
+		mode = MODE_ALL_PATTERNS;
+	}
+	if (record_mode && set_config(mode))
+		return 1;
+
+	/* Set sparse-index/non-sparse-index mode if specified */
+	if (set_opts.sparse_index >= 0) {
+		if (set_sparse_index_config(the_repository, set_opts.sparse_index) < 0)
+			die(_("failed to modify sparse-index config"));
+
+		/* force an index rewrite */
+		repo_read_index(the_repository);
+		the_repository->index->updated_workdir = 1;
+	}
+
+	/*
+	 * Cone mode automatically specifies the toplevel directory.  For
+	 * non-cone mode, if nothing is specified, manually select just the
+	 * top-level directory (much as 'init' would do).
+	 */
+	if (!core_sparse_checkout_cone && argc == 0) {
+		argv = default_patterns;
+		argc = 2;
+	}
+
 	return modify_pattern_list(argc, argv, set_opts.use_stdin, REPLACE);
 }
 
-- 
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