Add size assertions for Result<Value, Error> and Value

Cargo.lock

@@ -3100,9 +3100,11 @@ dependencies = [
  "ruffle_render",
  "ruffle_video",
  "ruffle_wstr",
+ "rustversion",
  "serde",
  "serde_json",
  "smallvec",
+ "static_assertions",
  "swf",
  "symphonia",
  "thiserror",
@@ -3355,6 +3357,12 @@ dependencies = [
  "transpose",
 ]
 
+[[package]]
+name = "rustversion"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "97477e48b4cf8603ad5f7aaf897467cf42ab4218a38ef76fb14c2d6773a6d6a8"
+
 [[package]]
 name = "ryu"
 version = "1.0.10"

core/Cargo.toml

@@ -43,6 +43,8 @@ lzma-rs = {version = "0.2.0", optional = true }
 dasp = { git = "https://github.com/RustAudio/dasp", rev = "f05a703", features = ["interpolate", "interpolate-linear", "signal"], optional = true }
 symphonia = { version = "0.5.1", default-features = false, features = ["mp3"], optional = true }
 enumset = "1.0.11"
+static_assertions = "1.1.0"
+rustversion = "1.0.9"
 
 [target.'cfg(not(target_family = "wasm"))'.dependencies.futures]
 version = "0.3.24"

core/src/avm2/error.rs

@@ -18,6 +18,19 @@ pub enum Error<'gc> {
     RustError(Box<dyn std::error::Error>),
 }
 
+// This type is used very frequently, so make sure it doesn't unexpectedly grow.
+// For now, we only test on Nightly, since a new niche optimization was recently
+// added (https://github.com/rust-lang/rust/pull/94075) that shrinks the size
+// relative to stable.
+
+#[rustversion::nightly]
+#[cfg(target_arch = "wasm32")]
+static_assertions::assert_eq_size!(Result<Value<'_>, Error<'_>>, [u8; 24]);
+
+#[rustversion::nightly]
+#[cfg(target_pointer_width = "64")]
+static_assertions::assert_eq_size!(Result<Value<'_>, Error<'_>>, [u8; 32]);
+
 #[inline(never)]
 #[cold]
 pub fn range_error<'gc>(

core/src/avm2/value.rs

@@ -45,6 +45,18 @@ pub enum Value<'gc> {
     Object(Object<'gc>),
 }
 
+// This type is used very frequently, so make sure it doesn't unexpectedly grow.
+// For now, we only test on Nightly, since a new niche optimization was recently
+// added (https://github.com/rust-lang/rust/pull/94075) that shrinks the size
+// relative to stable.
+
+#[cfg(target_arch = "wasm32")]
+static_assertions::assert_eq_size!(Value<'_>, [u8; 16]);
+
+#[rustversion::nightly]
+#[cfg(target_pointer_width = "64")]
+static_assertions::assert_eq_size!(Value<'_>, [u8; 24]);
+
 impl<'gc> From<AvmString<'gc>> for Value<'gc> {
     fn from(string: AvmString<'gc>) -> Self {
         Value::String(string)