Add C ABI for wasm-bindgen compat

Author: tlively

src/librustc_target/abi/call/mod.rs

@@ -21,6 +21,7 @@ mod x86;
 mod x86_64;
 mod x86_win64;
 mod wasm32;
+mod wasm32_bindgen_compat;
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 pub enum PassMode {
@@ -564,6 +565,8 @@ impl<'a, Ty> FnType<'a, Ty> {
             "hexagon" => hexagon::compute_abi_info(self),
             "riscv32" => riscv::compute_abi_info(self, 32),
             "riscv64" => riscv::compute_abi_info(self, 64),
+            "wasm32" if cx.target_spec().target_os != "emscripten"
+                => wasm32_bindgen_compat::compute_abi_info(self),
             "wasm32" | "asmjs" => wasm32::compute_abi_info(cx, self),
             a => return Err(format!("unrecognized arch \"{}\" in target specification", a))
         }

src/librustc_target/abi/call/wasm32_bindgen_compat.rs

@@ -0,0 +1,27 @@
+// This is not and has never been a correct C ABI for WebAssembly, but
+// for a long time this was the C ABI that Rust used. wasm-bindgen
+// depends on ABI details for this ABI and is incompatible with the
+// correct C ABI, so this ABI is being kept around until wasm-bindgen
+// can be fixed to work with the correct ABI. See #63649 for further
+// discussion.
+
+use crate::abi::call::{FnType, ArgType};
+
+fn classify_ret_ty<Ty>(ret: &mut ArgType<'_, Ty>) {
+    ret.extend_integer_width_to(32);
+}
+
+fn classify_arg_ty<Ty>(arg: &mut ArgType<'_, Ty>) {
+    arg.extend_integer_width_to(32);
+}
+
+pub fn compute_abi_info<Ty>(fty: &mut FnType<'_, Ty>) {
+    if !fty.ret.is_ignore() {
+        classify_ret_ty(&mut fty.ret);
+    }
+
+    for arg in &mut fty.args {
+        if arg.is_ignore() { continue; }
+        classify_arg_ty(arg);
+    }
+}