Fix range error for `Array.slice`

(cherry picked from commit 7752a0d8d13e1052e6cb0f0199bd6cbb20e3abe8)

core/variant/array.cpp

@@ -454,17 +454,21 @@ Array Array::slice(int p_begin, int p_end, int p_step, bool p_deep) const {
 
 	const int s = size();
 
-	int begin = CLAMP(p_begin, -s, s);
+	if (s == 0 || (p_begin < -s && p_step < 0) || (p_begin >= s && p_step > 0)) {
+		return result;
+	}
+
+	int begin = CLAMP(p_begin, -s, s - 1);
 	if (begin < 0) {
 		begin += s;
 	}
-	int end = CLAMP(p_end, -s, s);
+	int end = CLAMP(p_end, -s - 1, s);
 	if (end < 0) {
 		end += s;
 	}
 
-	ERR_FAIL_COND_V_MSG(p_step > 0 && begin > end, result, "Slice is positive, but bounds is decreasing.");
-	ERR_FAIL_COND_V_MSG(p_step < 0 && begin < end, result, "Slice is negative, but bounds is increasing.");
+	ERR_FAIL_COND_V_MSG(p_step > 0 && begin > end, result, "Slice step is positive, but bounds are decreasing.");
+	ERR_FAIL_COND_V_MSG(p_step < 0 && begin < end, result, "Slice step is negative, but bounds are increasing.");
 
 	int result_size = (end - begin) / p_step + (((end - begin) % p_step != 0) ? 1 : 0);
 	result.resize(result_size);

doc/classes/Array.xml

@@ -584,6 +584,7 @@
 				If either [param begin] or [param end] are negative, they will be relative to the end of the array (i.e. [code]arr.slice(0, -2)[/code] is a shorthand for [code]arr.slice(0, arr.size() - 2)[/code]).
 				If specified, [param step] is the relative index between source elements. It can be negative, then [param begin] must be higher than [param end]. For example, [code][0, 1, 2, 3, 4, 5].slice(5, 1, -2)[/code] returns [code][5, 3][/code].
 				If [param deep] is true, each element will be copied by value rather than by reference.
+				[b]Note:[/b] To include the first element when [param step] is negative, use [code]arr.slice(begin, -arr.size() - 1, step)[/code] (i.e. [code][0, 1, 2].slice(1, -4, -1)[/code] returns [code][1, 0][/code]).
 			</description>
 		</method>
 		<method name="sort">

tests/core/variant/test_array.h

@@ -304,13 +304,31 @@ TEST_CASE("[Array] slice()") {
 	CHECK(slice8[1] == Variant(3));
 	CHECK(slice8[2] == Variant(1));
 
+	Array slice9 = array.slice(10, 0, -2);
+	CHECK(slice9.size() == 3);
+	CHECK(slice9[0] == Variant(5));
+	CHECK(slice9[1] == Variant(3));
+	CHECK(slice9[2] == Variant(1));
+
+	Array slice10 = array.slice(2, -10, -1);
+	CHECK(slice10.size() == 3);
+	CHECK(slice10[0] == Variant(2));
+	CHECK(slice10[1] == Variant(1));
+	CHECK(slice10[2] == Variant(0));
+
 	ERR_PRINT_OFF;
-	Array slice9 = array.slice(4, 1);
-	CHECK(slice9.size() == 0);
+	Array slice11 = array.slice(4, 1);
+	CHECK(slice11.size() == 0);
 
-	Array slice10 = array.slice(3, -4);
-	CHECK(slice10.size() == 0);
+	Array slice12 = array.slice(3, -4);
+	CHECK(slice12.size() == 0);
 	ERR_PRINT_ON;
+
+	Array slice13 = Array().slice(1);
+	CHECK(slice13.size() == 0);
+
+	Array slice14 = array.slice(6);
+	CHECK(slice14.size() == 0);
 }
 
 TEST_CASE("[Array] Duplicate array") {