GDScript: add an optional message parameter to assert()

Before this patch, assert() only took the condition to assert on:

    assert(item_data)

Now, it can optionally take a string that will be printed upon failure:

    assert(item_data, item_name + " has no item data in ItemDatabase")

This makes it easier to immediately see what the issue is by being
able to write informative failure messages.

Thanks to @wiped1 for sharing their patch, upon which this is based.

Closes #17082

1 files changed, 9 insertions, 4 deletions

diff --git a/modules/gdscript/gdscript_function.cpp b/modules/gdscript/gdscript_function.cpp
index 68f2a9473e..bdeea9cef3 100644
--- a/modules/gdscript/gdscript_function.cpp
+++ b/modules/gdscript/gdscript_function.cpp
@@ -1475,20 +1475,25 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 			DISPATCH_OPCODE;
 
 			OPCODE(OPCODE_ASSERT) {
-				CHECK_SPACE(2);
+				CHECK_SPACE(3);
 
 #ifdef DEBUG_ENABLED
 				GET_VARIANT_PTR(test, 1);
+				GET_VARIANT_PTR(message, 2);
 				bool result = test->booleanize();
 
 				if (!result) {
-
-					err_text = "Assertion failed.";
+					const String &message_str = *message;
+					if (message_str.empty()) {
+						err_text = "Assertion failed.";
+					} else {
+						err_text = "Assertion failed: " + message_str;
+					}
 					OPCODE_BREAK;
 				}
 
 #endif
-				ip += 2;
+				ip += 3;
 			}
 			DISPATCH_OPCODE;