avm2: Error.getStackTrace should call toString

core/src/avm2/globals/error.rs

@@ -2,8 +2,8 @@ use crate::avm2::Error;
 use crate::avm2::activation::Activation;
 pub use crate::avm2::object::error_allocator;
 use crate::avm2::parameters::ParametersExt;
-use crate::avm2::string::AvmString;
 use crate::avm2::value::Value;
+use crate::string::{AvmString, WString};
 use crate::{PlayerMode, avm2_stub_method};
 
 pub fn get_error_message<'gc>(
@@ -42,10 +42,13 @@ pub fn get_stack_trace<'gc>(
     }
 
     if let Some(error) = this.as_error_object() {
-        let call_stack = error.call_stack();
-        if !call_stack.is_empty() {
-            return Ok(AvmString::new(activation.gc(), error.display_full()).into());
-        }
+        let stringified = Value::from(error).coerce_to_string(activation)?;
+
+        let mut output = WString::new();
+        output.push_str(&stringified);
+        error.call_stack().display(&mut output);
+
+        return Ok(AvmString::new(activation.gc(), output).into());
     }
     Ok(Value::Null)
 }

core/src/avm2/object/error_object.rs

@@ -112,13 +112,6 @@ impl<'gc> ErrorObject<'gc> {
         output
     }
 
-    pub fn display_full(self) -> WString {
-        let mut output = WString::new();
-        output.push_str(&self.display());
-        self.call_stack().display(&mut output);
-        output
-    }
-
     pub fn call_stack(&self) -> &CallStack<'gc> {
         &self.0.call_stack
     }

tests/tests/swfs/avm2/error_stack_trace_edge_cases/Test.as

@@ -0,0 +1,21 @@
+package {
+    import flash.display.MovieClip;
+
+    public class Test extends MovieClip {
+        public function Test() {
+            var err:Error = new Error();
+
+            Error.prototype.toString = function():String {
+                trace("toString called (1)");
+                return "from toString";
+            };
+            trace(err.getStackTrace());
+
+            Error.prototype.toString = function():String {
+                trace("toString called (2)");
+                return null;
+            };
+            trace(err.getStackTrace());
+        }
+    }
+}

tests/tests/swfs/avm2/error_stack_trace_edge_cases/output.txt

@@ -0,0 +1,6 @@
+toString called (1)
+from toString
+	at Test()
+toString called (2)
+null
+	at Test()

tests/tests/swfs/avm2/error_stack_trace_edge_cases/test.toml

@@ -0,0 +1 @@
+num_frames = 1