Fix handling of u32 between Rust and JS

All numbers in WebAssembly are signed and then each operation on them
may optionally have an unsigned version. This means that when we pass
large signed numbers to JS they actually show up as large negative
numbers even though JS numbers can faithfully represent the type.

This is fixed by adding `>>>0` in a few locations in the generated
bindings to coerce the JS value into an unsigned value.

Closes #1388

crates/cli-support/src/descriptor.rs

@@ -99,6 +99,10 @@ pub enum VectorKind {
     Anyref,
 }
 
+pub struct Number {
+    u32: bool,
+}
+
 impl Descriptor {
     pub fn decode(mut data: &[u32]) -> Descriptor {
         let descriptor = Descriptor::_decode(&mut data);
@@ -149,18 +153,21 @@ impl Descriptor {
         }
     }
 
-    pub fn is_number(&self) -> bool {
+    /// Returns `Some` if this type is a number, and the boolean returned
+    /// represents whether it's `u32` and needs the sign reset when it goes
+    /// into JS because JS is otherwise receiving a `i32`
+    pub fn number(&self) -> Option<Number> {
         match *self {
             Descriptor::I8
             | Descriptor::U8
             | Descriptor::I16
             | Descriptor::U16
             | Descriptor::I32
-            | Descriptor::U32
             | Descriptor::F32
             | Descriptor::F64
-            | Descriptor::Enum { .. } => true,
-            _ => return false,
+            | Descriptor::Enum { .. } => Some(Number { u32: false }),
+            Descriptor::U32 => Some(Number { u32: true }),
+            _ => None,
         }
     }
 
@@ -360,3 +367,9 @@ impl VectorKind {
         }
     }
 }
+
+impl Number {
+    pub fn is_u32(&self) -> bool {
+        self.u32
+    }
+}

crates/cli-support/src/js/js2rust.rs

@@ -384,7 +384,7 @@ impl<'a, 'b> Js2Rust<'a, 'b> {
             return Ok(self);
         }
 
-        if arg.is_number() {
+        if arg.number().is_some() {
             self.js_arguments.push((name.clone(), "number".to_string()));
 
             if self.cx.config.debug {
@@ -681,9 +681,13 @@ impl<'a, 'b> Js2Rust<'a, 'b> {
             return Ok(self);
         }
 
-        if ty.is_number() {
+        if let Some(num) = ty.number() {
             self.ret_ty = "number".to_string();
-            self.ret_expr = format!("return RET;");
+            if num.is_u32() {
+                self.ret_expr = format!("return RET >>> 0;");
+            } else {
+                self.ret_expr = format!("return RET;");
+            }
             return Ok(self);
         }
 

crates/cli-support/src/js/rust2js.rs

@@ -309,8 +309,16 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
             return Ok(());
         }
 
+        if let Some(num) = arg.number() {
+            if num.is_u32() {
+                self.js_arguments.push(format!("{} >>> 0", abi));
+            } else {
+                self.js_arguments.push(abi);
+            }
+            return Ok(());
+        }
+
         let invoc_arg = match *arg {
-            ref d if d.is_number() => abi,
             Descriptor::Boolean => format!("{} !== 0", abi),
             Descriptor::Char => format!("String.fromCodePoint({})", abi),
             _ => bail!(
@@ -504,7 +512,7 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
 
             return Ok(());
         }
-        if ty.is_number() {
+        if ty.number().is_some() {
             self.ret_expr = "return JS;".to_string();
             return Ok(());
         }

tests/wasm/math.js

@@ -1,5 +1,37 @@
 const wasm = require('wasm-bindgen-test.js');
+const assert = require('assert');
 
 exports.js_auto_bind_math = () => {
     wasm.math(1.0, 2.0);
 };
+
+exports.roundtrip = x => x;
+
+exports.test_js_roundtrip = () => {
+  assert.strictEqual(wasm.rust_roundtrip_i8(0), 0);
+  assert.strictEqual(wasm.rust_roundtrip_i8(0x80), -128);
+  assert.strictEqual(wasm.rust_roundtrip_i8(0x7f), 127);
+
+  assert.strictEqual(wasm.rust_roundtrip_i16(0), 0);
+  assert.strictEqual(wasm.rust_roundtrip_i16(0x8000), -32768);
+  assert.strictEqual(wasm.rust_roundtrip_i16(0x7fff), 32767);
+
+  assert.strictEqual(wasm.rust_roundtrip_i32(0), 0);
+  assert.strictEqual(wasm.rust_roundtrip_i32(0x80000000), -2147483648);
+  assert.strictEqual(wasm.rust_roundtrip_i32(0x7fffffff), 2147483647);
+
+  assert.strictEqual(wasm.rust_roundtrip_u8(0), 0);
+  assert.strictEqual(wasm.rust_roundtrip_u8(0x80), 128);
+  assert.strictEqual(wasm.rust_roundtrip_u8(0x7f), 127);
+  assert.strictEqual(wasm.rust_roundtrip_u8(0xff), 255);
+
+  assert.strictEqual(wasm.rust_roundtrip_u16(0), 0);
+  assert.strictEqual(wasm.rust_roundtrip_u16(0x8000), 32768);
+  assert.strictEqual(wasm.rust_roundtrip_u16(0x7fff), 32767);
+  assert.strictEqual(wasm.rust_roundtrip_u16(0xffff), 65535);
+
+  assert.strictEqual(wasm.rust_roundtrip_u32(0), 0);
+  assert.strictEqual(wasm.rust_roundtrip_u32(0x80000000), 2147483648);
+  assert.strictEqual(wasm.rust_roundtrip_u32(0x7fffffff), 2147483647);
+  assert.strictEqual(wasm.rust_roundtrip_u32(0xffffffff), 4294967295);
+};

tests/wasm/math.rs

@@ -4,6 +4,26 @@ use wasm_bindgen_test::*;
 #[wasm_bindgen(module = "tests/wasm/math.js")]
 extern "C" {
     fn js_auto_bind_math();
+
+    // There's an identity function called `roundtrip` in the module and we bind
+    // that one function with multiple different signatures here. Note that the
+    // return value is always `f64` to faithfully capture what was sent to JS
+    // (what we're interested in) because all JS numbers fit in `f64` anyway.
+    // This is testing what happens when we pass numbers to JS and what it sees.
+    #[wasm_bindgen(js_name = roundtrip)]
+    fn roundtrip_i8(a: i8) -> f64;
+    #[wasm_bindgen(js_name = roundtrip)]
+    fn roundtrip_i16(a: i16) -> f64;
+    #[wasm_bindgen(js_name = roundtrip)]
+    fn roundtrip_i32(a: i32) -> f64;
+    #[wasm_bindgen(js_name = roundtrip)]
+    fn roundtrip_u8(a: u8) -> f64;
+    #[wasm_bindgen(js_name = roundtrip)]
+    fn roundtrip_u16(a: u16) -> f64;
+    #[wasm_bindgen(js_name = roundtrip)]
+    fn roundtrip_u32(a: u32) -> f64;
+
+    fn test_js_roundtrip();
 }
 
 #[wasm_bindgen]
@@ -65,3 +85,44 @@ pub fn math(a: f32, b: f64) -> f64 {
 fn auto_bind_math() {
     js_auto_bind_math();
 }
+
+macro_rules! t_roundtrip {
+    ($f:ident($e:expr)) => (assert_eq!($f($e), $e as f64))
+}
+
+#[wasm_bindgen_test]
+fn limits_correct() {
+    t_roundtrip!(roundtrip_i8(i8::min_value()));
+    t_roundtrip!(roundtrip_i8(0));
+    t_roundtrip!(roundtrip_i8(i8::max_value()));
+    t_roundtrip!(roundtrip_i16(i16::min_value()));
+    t_roundtrip!(roundtrip_i16(0));
+    t_roundtrip!(roundtrip_i16(i16::max_value()));
+    t_roundtrip!(roundtrip_i32(i32::min_value()));
+    t_roundtrip!(roundtrip_i32(0));
+    t_roundtrip!(roundtrip_i32(i32::max_value()));
+    t_roundtrip!(roundtrip_u8(u8::min_value()));
+    t_roundtrip!(roundtrip_u8(0));
+    t_roundtrip!(roundtrip_u8(u8::max_value()));
+    t_roundtrip!(roundtrip_u16(u16::min_value()));
+    t_roundtrip!(roundtrip_u16(0));
+    t_roundtrip!(roundtrip_u16(u16::max_value()));
+    t_roundtrip!(roundtrip_u32(u32::min_value()));
+    t_roundtrip!(roundtrip_u32(0));
+    t_roundtrip!(roundtrip_u32(u32::max_value()));
+
+    test_js_roundtrip();
+
+    #[wasm_bindgen]
+    pub fn rust_roundtrip_i8(a: i8) -> i8 { a }
+    #[wasm_bindgen]
+    pub fn rust_roundtrip_i16(a: i16) -> i16 { a }
+    #[wasm_bindgen]
+    pub fn rust_roundtrip_i32(a: i32) -> i32 { a }
+    #[wasm_bindgen]
+    pub fn rust_roundtrip_u8(a: u8) -> u8 { a }
+    #[wasm_bindgen]
+    pub fn rust_roundtrip_u16(a: u16) -> u16 { a }
+    #[wasm_bindgen]
+    pub fn rust_roundtrip_u32(a: u32) -> u32 { a }
+}