sparse-checkout: cone mode does not recognize "**"

When core.sparseCheckoutCone is enabled, the 'git sparse-checkout set'
command creates a restricted set of possible patterns that are used
by a custom algorithm to quickly match those patterns.

If a user manually edits the sparse-checkout file, then they could
create patterns that do not match these expectations. The cone-mode
matching algorithm can return incorrect results. The solution is to
detect these incorrect patterns, warn that we do not recognize them,
and revert to the standard algorithm.

Check each pattern for the "**" substring, and revert to the old
logic if seen. While technically a "/<dir>/**" pattern matches
the meaning of "/<dir>/", it is not one that would be written by
the sparse-checkout builtin in cone mode. Attempting to accept that
pattern change complicates the logic and instead we punt and do
not accept any instance of "**".

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

dir.c

@@ -651,11 +651,16 @@ static void add_pattern_to_hashsets(struct pattern_list *pl, struct path_pattern
 		return;
 	}
 
+	if (strstr(given->pattern, "**")) {
+		/* Not a cone pattern. */
+		warning(_("unrecognized pattern: '%s'"), given->pattern);
+		goto clear_hashmaps;
+	}
+
 	if (given->patternlen > 2 &&
 	    !strcmp(given->pattern + given->patternlen - 2, "/*")) {
 		if (!(given->flags & PATTERN_FLAG_NEGATIVE)) {
 			/* Not a cone pattern. */
-			pl->use_cone_patterns = 0;
 			warning(_("unrecognized pattern: '%s'"), given->pattern);
 			goto clear_hashmaps;
 		}

t/t1091-sparse-checkout-builtin.sh

@@ -305,4 +305,38 @@ test_expect_success 'different sparse-checkouts with worktrees' '
 	check_files worktree a deep
 '
 
+check_read_tree_errors () {
+	REPO=$1
+	FILES=$2
+	ERRORS=$3
+	git -C $REPO read-tree -mu HEAD 2>err &&
+	if test -z "$ERRORS"
+	then
+		test_must_be_empty err
+	else
+		test_i18ngrep "$ERRORS" err
+	fi &&
+	check_files $REPO $FILES
+}
+
+test_expect_success 'pattern-checks: /A/**' '
+	cat >repo/.git/info/sparse-checkout <<-\EOF &&
+	/*
+	!/*/
+	/folder1/**
+	EOF
+	check_read_tree_errors repo "a folder1" "disabling cone pattern matching"
+'
+
+test_expect_success 'pattern-checks: /A/**/B/' '
+	cat >repo/.git/info/sparse-checkout <<-\EOF &&
+	/*
+	!/*/
+	/deep/**/deepest
+	EOF
+	check_read_tree_errors repo "a deep" "disabling cone pattern matching" &&
+	check_files repo/deep "deeper1" &&
+	check_files repo/deep/deeper1 "deepest"
+'
+
 test_done