sparse-checkout: require starting '/' in cone mode patterns

Add check for missing initial '/' when verifying cone patterns in
`add_pattern_to_hashsets(...)`, disabling cone patterns if not found. Update
tests in `t1091-sparse-checkout-builtin.sh` to ensure the starting '/' is
present unless the test verifies behavior when it is missing.

The implicit assumption of a starting '/' in cone mode patterns exists
throughout the code paths of `git sparse-checkout`, including in the
construction of the sparse pattern hashmaps. However, without enforcement of
that assumption, the presence of a directory pattern missing the starting
'/' would cause any subsequent cone mode `git sparse-checkout add` to enter
an infinite recursive loop in `insert_recursive_pattern(...)`
(`sparse-checkout.c`). By adding the starting '/' requirement to
`add_pattern_to_hashsets(...)` (`dir.c`), cone mode is disabled on the
pattern list, forcing `git sparse-checkout add` to exit early.

Signed-off-by: Victoria Dye <[email protected]>

Author: vdye

dir.c

@@ -715,6 +715,11 @@ static void add_pattern_to_hashsets(struct pattern_list *pl, struct path_pattern
 	if (!pl->use_cone_patterns)
 		return;
 
+	if (*given->pattern != '/') {
+		warning(_("unrecognized pattern: '%s'"), given->pattern);
+		goto clear_hashmaps;
+	}
+
 	if (given->flags & PATTERN_FLAG_NEGATIVE &&
 	    given->flags & PATTERN_FLAG_MUSTBEDIR &&
 	    !strcmp(given->pattern, "/*")) {

t/t1091-sparse-checkout-builtin.sh

@@ -216,7 +216,7 @@ 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
 '
@@ -608,7 +608,7 @@ test_expect_success 'pattern-checks: starting "*"' '
 	cat >repo/.git/info/sparse-checkout <<-\EOF &&
 	/*
 	!/*/
-	*eep/
+	/*eep/
 	EOF
 	check_read_tree_errors repo "a deep" "disabling cone pattern matching"
 '
@@ -619,12 +619,21 @@ test_expect_success 'pattern-checks: contained glob characters' '
 		cat >repo/.git/info/sparse-checkout <<-EOF &&
 		/*
 		!/*/
-		something$c-else/
+		/something$c-else/
 		EOF
 		check_read_tree_errors repo "a" "disabling cone pattern matching" || return 1
 	done
 '
 
+test_expect_success 'pattern-checks: starting "/"' '
+	cat >repo/.git/info/sparse-checkout <<-\EOF &&
+	/*
+	!/*/
+	deep/
+	EOF
+	check_read_tree_errors repo "a deep" "disabling cone pattern matching"
+'
+
 test_expect_success BSLASHPSPEC 'pattern-checks: escaped characters' '
 	git clone repo escaped &&
 	TREEOID=$(git -C escaped rev-parse HEAD:folder1) &&
@@ -777,4 +786,34 @@ test_expect_success 'init with cone mode verifies existing cone patterns' '
 	test_must_fail git -C repo config core.sparsecheckoutcone
 '
 
+# NEEDSWORK: in the case of directory patterns like `deep/`, it might be worth trying
+# to "correct" the patterns to match a cone mode style. However, that may be more difficult
+# for nested directories (like `deep/deeper1/`) in which multiple individual patterns
+# would be mapped from the original (`/deep/`, `!/deep/*/`, `/deep/deeper1/`).
+test_expect_success 'add cone pattern disallowed with existing non-cone directory pattern' '
+	rm -f repo/.git/info/sparse-checkout &&
+
+	git -C repo sparse-checkout init --cone &&
+
+	# Manually set the sparse checkout pattern to a directory pattern
+	# without preceding slash
+	cat >repo/.git/info/sparse-checkout <<-\EOF &&
+	deep/
+	EOF
+
+	# `add` fails because `deep/` is not a valid cone pattern.
+	test_must_fail git -C repo sparse-checkout add folder1/ 2>err &&
+	test_i18ngrep "existing sparse-checkout patterns do not use cone mode" err &&
+
+	# `set` succeeds with same patterns set properly for cone mode.
+	git -C repo sparse-checkout set deep/ folder1/ &&
+	cat >expect <<-\EOF &&
+	/*
+	!/*/
+	/deep/
+	/folder1/
+	EOF
+	test_cmp expect repo/.git/info/sparse-checkout
+'
+
 test_done