sparse-checkout: list directories in cone mode

When core.sparseCheckoutCone is enabled, the 'git sparse-checkout set'
command takes a list of directories as input, then creates an ordered
list of sparse-checkout patterns such that those directories are
recursively included and all sibling entries along the parent directories
are also included. Listing the patterns is less user-friendly than the
directories themselves.

In cone mode, and as long as the patterns match the expected cone-mode
pattern types, change the output of 'git sparse-checkout list' to only
show the directories that created the patterns.

With this change, the following piped commands would not change the
working directory:

	git sparse-checkout list | git sparse-checkout set --stdin

The only time this would not work is if core.sparseCheckoutCone is
true, but the sparse-checkout file contains patterns that do not
match the expected pattern types for cone mode.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-sparse-checkout.txt

@@ -28,7 +28,7 @@ THE FUTURE.
 COMMANDS
 --------
 'list'::
-	Provide a list of the contents in the sparse-checkout file.
+	Describe the patterns in the sparse-checkout file.
 
 'init'::
 	Enable the `core.sparseCheckout` setting. If the
@@ -150,6 +150,15 @@ expecting patterns of these types. Git will warn if the patterns do not match.
 If the patterns do match the expected format, then Git will use faster hash-
 based algorithms to compute inclusion in the sparse-checkout.
 
+In the cone mode case, the `git sparse-checkout list` subcommand will list the
+directories that define the recursive patterns. For the example sparse-checkout
+file above, the output is as follows:
+
+--------------------------
+$ git sparse-checkout list
+A/B/C
+--------------------------
+
 If `core.ignoreCase=true`, then the pattern-matching algorithm will use a
 case-insensitive check. This corrects for case mismatched filenames in the
 'git sparse-checkout set' command to reflect the expected cone in the working

builtin/sparse-checkout.c

@@ -53,6 +53,8 @@ static int sparse_checkout_list(int argc, const char **argv)
 
 	memset(&pl, 0, sizeof(pl));
 
+	pl.use_cone_patterns = core_sparse_checkout_cone;
+
 	sparse_filename = get_sparse_checkout_filename();
 	res = add_patterns_from_file_to_list(sparse_filename, "", 0, &pl, NULL);
 	free(sparse_filename);
@@ -62,6 +64,25 @@ static int sparse_checkout_list(int argc, const char **argv)
 		return 0;
 	}
 
+	if (pl.use_cone_patterns) {
+		int i;
+		struct pattern_entry *pe;
+		struct hashmap_iter iter;
+		struct string_list sl = STRING_LIST_INIT_DUP;
+
+		hashmap_for_each_entry(&pl.recursive_hashmap, &iter, pe, ent) {
+			/* pe->pattern starts with "/", skip it */
+			string_list_insert(&sl, pe->pattern + 1);
+		}
+
+		string_list_sort(&sl);
+
+		for (i = 0; i < sl.nr; i++)
+			printf("%s\n", sl.items[i].string);
+
+		return 0;
+	}
+
 	write_patterns_to_file(stdout, &pl);
 	clear_pattern_list(&pl);
 

t/t1091-sparse-checkout-builtin.sh

@@ -246,6 +246,17 @@ test_expect_success 'cone mode: init and set' '
 	test_cmp expect dir
 '
 
+test_expect_success 'cone mode: list' '
+	cat >expect <<-EOF &&
+		folder1
+		folder2
+	EOF
+	git -C repo sparse-checkout set --stdin <expect &&
+	git -C repo sparse-checkout list >actual 2>err &&
+	test_must_be_empty err &&
+	test_cmp expect actual
+'
+
 test_expect_success 'cone mode: set with nested folders' '
 	git -C repo sparse-checkout set deep deep/deeper1/deepest 2>err &&
 	test_line_count = 0 err &&