dir: check for single file cone patterns

The sparse checkout documentation states that the cone mode pattern set
is limited to patterns that either recursively include directories or
patterns that match all files in a directory. In the sparse checkout
file, the former manifest in the form:

    /A/B/C/

while the latter become a pair of patterns either in the form:

    /A/B/
    !/A/B/*/

or in the special case of matching the toplevel files:

    /*
    !/*/

The 'add_pattern_to_hashsets()' function contains checks which serve to
disable cone-mode when non-cone patterns are encountered. However, these
do not catch when the pattern list attempts to match a single file or
directory, e.g. a pattern in the form:

    /A/B/C

This causes sparse-checkout to exhibit unexpected behaviour when such a
pattern is in the sparse-checkout file and cone mode is enabled.
Concretely, with the pattern like the above, sparse-checkout, in
non-cone mode, will only include the directory or file located at
'/A/B/C'. However, with cone mode enabled, sparse-checkout will instead
just manifest the toplevel files but not any file located at '/A/B/C'.

Relatedly, issues occur when supplying the same kind of filter when
partial cloning with '--filter=sparse:oid=<oid>'. 'upload-pack' will
correctly just include the objects that match the non-cone pattern
matching. Which means that checking out the newly cloned repo with the
same filter, but with cone mode enabled, fails due to missing objects.

To fix these issues, add a cone mode pattern check that asserts that
every pattern is either a directory match or the pattern '/*'. Add a
test to verify the new pattern check and modify another to reflect that
non-directory patterns are caught earlier.

Signed-off-by: William Sprent <williams@unity3d.com>
Acked-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

dir.c

@@ -732,6 +732,13 @@ static void add_pattern_to_hashsets(struct pattern_list *pl, struct path_pattern
 		goto clear_hashmaps;
 	}
 
+	if (!(given->flags & PATTERN_FLAG_MUSTBEDIR) &&
+	    strcmp(given->pattern, "/*")) {
+		/* Not a cone pattern. */
+		warning(_("unrecognized pattern: '%s'"), given->pattern);
+		goto clear_hashmaps;
+	}
+
 	prev = given->pattern;
 	cur = given->pattern + 1;
 	next = given->pattern + 2;

t/t1091-sparse-checkout-builtin.sh

@@ -238,7 +238,7 @@ test_expect_success 'cone mode: match patterns' '
 test_expect_success 'cone mode: warn on bad pattern' '
 	test_when_finished mv sparse-checkout repo/.git/info/ &&
 	cp repo/.git/info/sparse-checkout . &&
-	echo "!/deep/deeper/*" >>repo/.git/info/sparse-checkout &&
+	echo "!/deep/deeper/*/" >>repo/.git/info/sparse-checkout &&
 	git -C repo read-tree -mu HEAD 2>err &&
 	test_i18ngrep "unrecognized negative pattern" err
 '
@@ -667,6 +667,15 @@ test_expect_success 'pattern-checks: starting "*"' '
 	check_read_tree_errors repo "a deep" "disabling cone pattern matching"
 '
 
+test_expect_success 'pattern-checks: non directory pattern' '
+	cat >repo/.git/info/sparse-checkout <<-\EOF &&
+	/deep/deeper1/a
+	EOF
+	check_read_tree_errors repo deep "disabling cone pattern matching" &&
+	check_files repo/deep deeper1 &&
+	check_files repo/deep/deeper1 a
+'
+
 test_expect_success 'pattern-checks: contained glob characters' '
 	for c in "[a]" "\\" "?" "*"
 	do