avm2: Enable stack traces for Flash Player 11.5+ and SWF18+

For Flash Player 11.5+ and SWF18+, stack traces are always enabled.
Some content uses this behavior to verify whether the user is using
Flash Player 11.5 onwards.

For Flash Player 11.4 and earlier or SWF<18, stack traces are enabled
only in the debug build.

See <https://docs.ruffle.rs/en_US/FlashPlatform/reference/actionscript/3/Error.html#getStackTrace()>

Author: kjarosh

core/src/avm2/globals/error.rs

@@ -4,6 +4,7 @@ use crate::avm2::string::AvmString;
 use crate::avm2::value::Value;
 use crate::avm2::Error;
 use crate::avm2::TObject;
+use crate::PlayerMode;
 
 pub fn call_handler<'gc>(
     activation: &mut Activation<'_, 'gc>,
@@ -24,6 +25,22 @@ pub fn get_stack_trace<'gc>(
 ) -> Result<Value<'gc>, Error<'gc>> {
     let this = this.as_object().unwrap();
 
+    // See <https://docs.ruffle.rs/en_US/FlashPlatform/reference/actionscript/3/Error.html#getStackTrace()>
+    // But note that the behavior also depends on SWF version.
+    let stack_trace_enabled = if activation.context.player_version >= 18
+        && activation.caller_movie_or_root().version() >= 18
+    {
+        // For Flash Player 11.5+ and SWF>=18, stack traces are always enabled.
+        true
+    } else {
+        // For Flash Player Player 11.4 and earlier, or for SWF<18, stack traces are enabled for debug only.
+        activation.context.player_mode == PlayerMode::Debug
+    };
+
+    if !stack_trace_enabled {
+        return Ok(Value::Null);
+    }
+
     if let Some(error) = this.as_error_object() {
         let call_stack = error.call_stack();
         if !call_stack.is_empty() {

core/src/avm2/object/error_object.rs

@@ -10,7 +10,6 @@ use crate::string::WString;
 use core::fmt;
 use gc_arena::{Collect, Gc, GcWeak};
 use std::fmt::Debug;
-use tracing::{enabled, Level};
 
 /// A class instance allocator that allocates Error objects.
 pub fn error_allocator<'gc>(
@@ -19,9 +18,8 @@ pub fn error_allocator<'gc>(
 ) -> Result<Object<'gc>, Error<'gc>> {
     let base = ScriptObjectData::new(class);
 
-    let call_stack = (enabled!(Level::INFO) || cfg!(feature = "avm_debug"))
-        .then(|| activation.avm2().call_stack().borrow().clone())
-        .unwrap_or_default();
+    // Stack trace is always collected for debugging purposes.
+    let call_stack = activation.avm2().call_stack().borrow().clone();
 
     Ok(ErrorObject(Gc::new(
         activation.gc(),