types: fix array unshift operations and add test coverage

 - Fix `ucv_array_unshift()` improperly rejecting operation on empty arrays
 - Fix `uc_unshift()` improperly reversing maintaining argument order
 - Add missing test coverage for `push()`, `pop()`, `unshift()` and
   `shift()` array operations.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

6 files changed, 182 insertions, 4 deletions

diff --git a/lib.c b/lib.c
index 0366a13..a0a1b9b 100644
--- a/lib.c
+++ b/lib.c
@@ -464,18 +464,18 @@ static uc_value_t *
 uc_unshift(uc_vm_t *vm, size_t nargs)
 {
 	uc_value_t *arr = uc_fn_arg(0);
-	uc_value_t *item = NULL;
+	uc_value_t *item;
 	size_t i;
 
 	if (!assert_mutable_array(vm, arr))
 		return NULL;
 
 	for (i = 1; i < nargs; i++) {
-		item = uc_fn_arg(i);
+		item = uc_fn_arg(nargs - i);
 		ucv_array_unshift(arr, ucv_get(item));
 	}
 
-	return ucv_get(item);
+	return (nargs > 1) ? ucv_get(uc_fn_arg(nargs - 1)) : NULL;
 }
 
 static uc_value_t *
diff --git a/tests/custom/03_stdlib/65_push b/tests/custom/03_stdlib/65_push
new file mode 100644
index 0000000..c6707dd
--- /dev/null
+++ b/tests/custom/03_stdlib/65_push
@@ -0,0 +1,52 @@
+The `push()` function appends the given argument(s) to the end of the given array
+while maintaining their order.
+
+Returns the last pushed value.
+
+Returns `null` if the given destination argment is not an array.
+
+Throws a type exception if the given array is immuatable.
+
+-- Testcase --
+{%
+	let arr = [];
+
+	printf("%.J\n", [
+		// push one element
+		push(arr, 123),
+
+		// push multiple elements
+		push(arr, 1, 2, 3),
+
+		// push null values
+		push(arr, null, null, 4),
+
+		// push no-op
+		push(arr),
+
+		// push with invalid destination
+		push({}, 1, 2, 3)
+	]);
+
+	printf("%.J\n", arr);
+%}
+-- End --
+
+-- Expect stdout --
+[
+	123,
+	3,
+	4,
+	null,
+	null
+]
+[
+	123,
+	1,
+	2,
+	3,
+	null,
+	null,
+	4
+]
+-- End --
diff --git a/tests/custom/03_stdlib/66_unshift b/tests/custom/03_stdlib/66_unshift
new file mode 100644
index 0000000..9771661
--- /dev/null
+++ b/tests/custom/03_stdlib/66_unshift
@@ -0,0 +1,52 @@
+The `unshift()` function places the given argument(s) at the begin of the
+given array while maintaining their order.
+
+Returns the last added value.
+
+Returns `null` if the given destination argment is not an array.
+
+Throws a type exception if the given array is immuatable.
+
+-- Testcase --
+{%
+	let arr = [];
+
+	printf("%.J\n", [
+		// add one element
+		unshift(arr, 123),
+
+		// add multiple elements
+		unshift(arr, 1, 2, 3),
+
+		// add null values
+		unshift(arr, null, null, 4),
+
+		// no-op
+		unshift(arr),
+
+		// invalid destination
+		unshift({}, 1, 2, 3)
+	]);
+
+	printf("%.J\n", arr);
+%}
+-- End --
+
+-- Expect stdout --
+[
+	123,
+	3,
+	4,
+	null,
+	null
+]
+[
+	null,
+	null,
+	4,
+	1,
+	2,
+	3,
+	123
+]
+-- End --
diff --git a/tests/custom/03_stdlib/67_pop b/tests/custom/03_stdlib/67_pop
new file mode 100644
index 0000000..1af11fa
--- /dev/null
+++ b/tests/custom/03_stdlib/67_pop
@@ -0,0 +1,37 @@
+The `pop()` function removes the last element of the given source array.
+
+Returns the removed value.
+
+Returns `null` if the given source argment is not an array.
+
+Throws a type exception if the given array is immuatable.
+
+-- Testcase --
+{%
+	let arr = [ 1, null, 3 ];
+
+	printf("%.J\n", [
+		// remove one element
+		pop(arr),
+
+		// remove a null element
+		pop(arr),
+
+		// invalid source
+		pop({ test: true })
+	]);
+
+	printf("%.J\n", arr);
+%}
+-- End --
+
+-- Expect stdout --
+[
+	3,
+	null,
+	null
+]
+[
+	1
+]
+-- End --
diff --git a/tests/custom/03_stdlib/68_shift b/tests/custom/03_stdlib/68_shift
new file mode 100644
index 0000000..7b0df89
--- /dev/null
+++ b/tests/custom/03_stdlib/68_shift
@@ -0,0 +1,37 @@
+The `shift()` function removes the first element of the given source array.
+
+Returns the removed value.
+
+Returns `null` if the given source argment is not an array.
+
+Throws a type exception if the given array is immuatable.
+
+-- Testcase --
+{%
+	let arr = [ 1, null, 3 ];
+
+	printf("%.J\n", [
+		// remove one element
+		shift(arr),
+
+		// remove a null element
+		shift(arr),
+
+		// invalid source
+		shift({ test: true })
+	]);
+
+	printf("%.J\n", arr);
+%}
+-- End --
+
+-- Expect stdout --
+[
+	1,
+	null,
+	null
+]
+[
+	3
+]
+-- End --
diff --git a/types.c b/types.c
index cde2221..321392e 100644
--- a/types.c
+++ b/types.c
@@ -772,7 +772,7 @@ ucv_array_unshift(uc_value_t *uv, uc_value_t *item)
 	uc_array_t *array = (uc_array_t *)uv;
 	size_t i;
 
-	if (ucv_type(uv) != UC_ARRAY || array->count == 0)
+	if (ucv_type(uv) != UC_ARRAY)
 		return NULL;
 
 	array->count++;