avm1: Fix scope of function calls in SWFv5 vs. SWFv6+

Fix various scope behavior when executing a function:

 * For function calls in SWFv6+, functions are proper closures and
   close over the SWF version, base clip, and scope of their
   defining function.
 * Function calls in SWFv5 are not closures, and use the version,
   base clip, and scope of `this` when the function is called.

Fixes #5502.

core/src/avm1/function.rs

@@ -224,9 +224,57 @@ impl<'gc> Executable<'gc> {
                 nf(activation, this, args)
             }
             Executable::Action(af) => {
+                let this_obj = match this {
+                    Value::Object(obj) => Some(obj),
+                    _ => None,
+                };
+
+                let target = activation.target_clip_or_root();
+                let (swf_version, base_clip, parent_scope) = if activation.swf_version() >= 6 {
+                    // Function calls in a v6+ SWF are proper closures, and "close" over the scope that defined the function:
+                    // * Use the SWF version from the SWF that defined the function.
+                    // * Use the base clip from when the function was defined.
+                    // * Close over the scope from when the function was defined.
+                    let base_clip = if !af.base_clip.removed() {
+                        af.base_clip
+                    } else {
+                        this_obj
+                            .and_then(|this| this.as_display_object())
+                            .unwrap_or(target)
+                    };
+                    (af.swf_version(), base_clip, af.scope())
+                } else {
+                    // Function calls in a v5 SWF are *not* closures, and will use the settings of
+                    // `this`, regardless of the function's origin:
+                    // * Use the SWF version of `this`.
+                    // * Use the base clip of `this`.
+                    // * Allocate a new scope using the given base clip. No previous scope is closed over.
+                    let base_clip = this_obj
+                        .and_then(|this| this.as_display_object())
+                        .unwrap_or(target);
+                    let swf_version = base_clip.swf_version();
+                    let base_clip_obj = match base_clip.object() {
+                        Value::Object(o) => o,
+                        _ => unreachable!(),
+                    };
+                    // TODO: It would be nice to avoid these extra Scope allocs.
+                    let scope = GcCell::allocate(
+                        activation.context.gc_context,
+                        Scope::new(
+                            GcCell::allocate(
+                                activation.context.gc_context,
+                                Scope::from_global_object(activation.context.avm1.globals),
+                            ),
+                            super::scope::ScopeClass::Target,
+                            base_clip_obj,
+                        ),
+                    );
+                    (swf_version, base_clip, scope)
+                };
+
                 let child_scope = GcCell::allocate(
                     activation.context.gc_context,
-                    Scope::new_local_scope(af.scope(), activation.context.gc_context),
+                    Scope::new_local_scope(parent_scope, activation.context.gc_context),
                 );
 
                 let arguments = if af.flags.contains(FunctionFlags::SUPPRESS_ARGUMENTS) {
@@ -252,11 +300,6 @@ impl<'gc> Executable<'gc> {
                     Attribute::DONT_ENUM,
                 );
 
-                let this_obj = match this {
-                    Value::Object(obj) => Some(obj),
-                    _ => None,
-                };
-
                 // TODO: `super` should only be defined if this was a method call (depth > 0?)
                 // `f[""]()` emits a CallMethod op, causing `this` to be undefined, but `super` is a function; what is it?
                 let super_object: Option<Object<'gc>> = this_obj.and_then(|this| {
@@ -267,19 +310,6 @@ impl<'gc> Executable<'gc> {
                     }
                 });
 
-                let effective_version = if activation.swf_version() > 5 {
-                    if !af.base_clip.removed() {
-                        af.base_clip.swf_version()
-                    } else {
-                        af.swf_version()
-                    }
-                } else {
-                    this_obj
-                        .and_then(|this| this.as_display_object())
-                        .map(|dn| dn.swf_version())
-                        .unwrap_or(activation.context.player_version)
-                };
-
                 let name = if cfg!(feature = "avm_debug") {
                     let mut result = match af.name.map(ExecutionName::Dynamic).unwrap_or(name) {
                         ExecutionName::Static(n) => n.to_owned(),
@@ -301,17 +331,10 @@ impl<'gc> Executable<'gc> {
                 };
 
                 let max_recursion_depth = activation.context.avm1.max_recursion_depth();
-                let base_clip = if effective_version > 5 && !af.base_clip.removed() {
-                    af.base_clip
-                } else {
-                    this_obj
-                        .and_then(|this| this.as_display_object())
-                        .unwrap_or_else(|| activation.base_clip())
-                };
                 let mut frame = Activation::from_action(
                     activation.context.reborrow(),
                     activation.id.function(name, reason, max_recursion_depth)?,
-                    effective_version,
+                    swf_version,
                     child_scope,
                     af.constant_pool,
                     base_clip,