avm1: Add allow_empty param to Activation:resolve_target_display_object

In some cases, the empty string path "" should resolve to the
starting clip. In other cases, it should be considered invalid.

Add a parameter to control this behavior, and set this to false
for MovieClip::hit_test to prevent `clip.hitTest("")` from
returning true.

core/src/avm1/activation.rs

@@ -681,7 +681,7 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
         let target = self.context.avm1.pop();
         let source = self.context.avm1.pop();
         let start_clip = self.target_clip_or_root();
-        let source_clip = self.resolve_target_display_object(start_clip, source)?;
+        let source_clip = self.resolve_target_display_object(start_clip, source, true)?;
 
         if let Some(movie_clip) = source_clip.and_then(|o| o.as_movie_clip()) {
             let _ = globals::movie_clip::duplicate_movie_clip_with_bias(
@@ -1159,7 +1159,7 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
         let prop_index = self.context.avm1.pop().into_number_v1() as usize;
         let path = self.context.avm1.pop();
         let ret = if let Some(target) = self.target_clip() {
-            if let Some(clip) = self.resolve_target_display_object(target, path)? {
+            if let Some(clip) = self.resolve_target_display_object(target, path, true)? {
                 let display_properties = self.context.avm1.display_properties;
                 let props = display_properties.write(self.context.gc_context);
                 if let Some(property) = props.get_by_index(prop_index) {
@@ -1264,7 +1264,7 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
                 target.as_display_object()
             } else {
                 let start = self.target_clip_or_root();
-                self.resolve_target_display_object(start, target.clone())?
+                self.resolve_target_display_object(start, target.clone(), true)?
             }
         } else {
             Some(self.target_clip_or_root())
@@ -1794,7 +1794,7 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
     fn action_remove_sprite(&mut self) -> Result<FrameControl<'gc>, Error<'gc>> {
         let target = self.context.avm1.pop();
         let start_clip = self.target_clip_or_root();
-        let target_clip = self.resolve_target_display_object(start_clip, target)?;
+        let target_clip = self.resolve_target_display_object(start_clip, target, true)?;
 
         if let Some(target_clip) = target_clip.and_then(|o| o.as_movie_clip()) {
             let _ = globals::movie_clip::remove_movie_clip(target_clip, self, &[]);
@@ -1826,7 +1826,7 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
         let prop_index = self.context.avm1.pop().coerce_to_u32(self)? as usize;
         let path = self.context.avm1.pop();
         if let Some(target) = self.target_clip() {
-            if let Some(clip) = self.resolve_target_display_object(target, path)? {
+            if let Some(clip) = self.resolve_target_display_object(target, path, true)? {
                 let display_properties = self.context.avm1.display_properties;
                 let props = display_properties.read();
                 if let Some(property) = props.get_by_index(prop_index) {
@@ -1957,7 +1957,7 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
     fn action_start_drag(&mut self) -> Result<FrameControl<'gc>, Error<'gc>> {
         let target = self.context.avm1.pop();
         let start_clip = self.target_clip_or_root();
-        let display_object = self.resolve_target_display_object(start_clip, target)?;
+        let display_object = self.resolve_target_display_object(start_clip, target, true)?;
         if let Some(display_object) = display_object {
             let lock_center = self.context.avm1.pop();
             let constrain = self.context.avm1.pop().as_bool(self.current_swf_version());
@@ -2406,10 +2406,13 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
     ///
     /// A target path always resolves via the display list. It can look
     /// at the prototype chain, but not the scope chain.
+    ///
+    /// `allow_empty` will allow the empty string to resolve to the start movie clip.
     pub fn resolve_target_display_object(
         &mut self,
         start: DisplayObject<'gc>,
         target: Value<'gc>,
+        allow_empty: bool,
     ) -> Result<Option<DisplayObject<'gc>>, Error<'gc>> {
         // If the value you got was a display object, we can just toss it straight back.
         if let Value::Object(o) = target {
@@ -2422,6 +2425,11 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
         // This means that values like `undefined` will resolve to clips with an instance name of
         // `"undefined"`, for example.
         let path = target.coerce_to_string(self)?;
+
+        if !allow_empty && path.is_empty() {
+            return Ok(None);
+        }
+
         let root = start.root();
         let start = start.object().coerce_to_object(self);
         Ok(self

core/src/avm1/globals/color.rs

@@ -82,9 +82,9 @@ fn target<'gc>(
     // depending on which timeline its called from!
     let target = this.get("target", activation)?;
     // Undefined or empty target is no-op.
-    if target != Value::Undefined && !matches!(&target, &Value::String(ref s) if s.is_empty()) {
+    if target != Value::Undefined {
         let start_clip = activation.target_clip_or_root();
-        activation.resolve_target_display_object(start_clip, target)
+        activation.resolve_target_display_object(start_clip, target, false)
     } else {
         Ok(None)
     }

core/src/avm1/globals/movie_clip.rs

@@ -138,8 +138,11 @@ pub fn hit_test<'gc>(
             return Ok(ret.into());
         }
     } else if args.len() == 1 {
-        let other = activation
+        let other = activation.resolve_target_display_object(
-            .resolve_target_display_object(movie_clip.into(), args.get(0).unwrap().clone())?;
+            movie_clip.into(),
+            args.get(0).unwrap().clone(),
+            false,
+        )?;
         if let Some(other) = other {
             return Ok(other
                 .world_bounds()
@@ -921,7 +924,9 @@ fn swap_depths<'gc>(
     let mut depth = None;
     if let Value::Number(n) = arg {
         depth = Some(crate::ecma_conversions::f64_to_wrapping_i32(n).wrapping_add(AVM_DEPTH_BIAS));
-    } else if let Some(target) = activation.resolve_target_display_object(movie_clip.into(), arg)? {
+    } else if let Some(target) =
+        activation.resolve_target_display_object(movie_clip.into(), arg, false)?
+    {
         if let Some(target_parent) = target.parent() {
             if DisplayObject::ptr_eq(target_parent, parent.into()) {
                 depth = Some(target.depth())
@@ -996,6 +1001,7 @@ fn get_bounds<'gc>(
             activation.resolve_target_display_object(
                 movie_clip.into(),
                 AvmString::new(activation.context.gc_context, path.to_string()).into(),
+                false,
             )?
         }
         None => Some(movie_clip.into()),

core/tests/swfs/avm1/movieclip_hittest/output.txt

@@ -78,3 +78,7 @@ true
 // circle.hitTest('/')
 true
 
+// String path, ''
+// circle.hitTest('')
+false
+