Support #[wasm_bindgen(setter, js_name = ...)]

Previously we'd require the explicit `js_name` to *also* start with
`set_`, but when explicitly specified it shouldn't be mangled at all!

Closes #584

crates/backend/src/ast.rs

@@ -168,6 +168,7 @@ pub struct ImportEnum {
 pub struct Function {
     pub name: String,
     pub name_span: Span,
+    pub renamed_via_js_name: bool,
     pub arguments: Vec<syn::ArgCaptured>,
     pub ret: Option<syn::Type>,
     pub rust_attrs: Vec<syn::Attribute>,
@@ -393,6 +394,14 @@ impl ImportFunction {
     /// for a setter in javascript (in this case `xxx`, so you can write `obj.xxx = val`)
     fn infer_setter_property(&self) -> Result<String, Diagnostic> {
         let name = self.function.name.to_string();
+
+        // if `#[wasm_bindgen(js_name = "...")]` is used then that explicitly
+        // because it was hand-written anyway.
+        if self.function.renamed_via_js_name {
+            return Ok(name)
+        }
+
+        // Otherwise we infer names based on the Rust function name.
         if !name.starts_with("set_") {
             bail_span!(
                 syn::token::Pub(self.function.name_span),

crates/macro-support/src/parser.rs

@@ -689,6 +689,7 @@ fn function_from_decl(
         ast::Function {
             name: js_name.map(|s| s.0.to_string()).unwrap_or(decl_name.to_string()),
             name_span: js_name.map(|s| s.1).unwrap_or(decl_name.span()),
+            renamed_via_js_name: js_name.is_some(),
             arguments,
             ret,
             rust_vis: vis,

crates/macro/ui-tests/invalid-setter.stderr

@@ -4,11 +4,5 @@ error: setters must start with `set_`, found: a
 10 |     fn a(this: &A, b: i32);
    |        ^
 
-error: setters must start with `set_`, found: x
-  --> $DIR/invalid-setter.rs:15:46
-   |
-15 |     #[wasm_bindgen(setter, method, js_name = x)]
-   |                                              ^
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 

crates/webidl/src/util.rs

@@ -4,7 +4,7 @@ use std::ptr;
 use backend;
 use backend::util::{ident_ty, leading_colon_path_ty, raw_ident, rust_ident};
 use heck::{CamelCase, ShoutySnakeCase, SnakeCase};
-use proc_macro2::Ident;
+use proc_macro2::{Ident, Span};
 use syn;
 use weedle;
 use weedle::attribute::{ExtendedAttributeList, ExtendedAttribute};
@@ -304,6 +304,8 @@ impl<'src> FirstPassRecord<'src> {
         Some(backend::ast::ImportFunction {
             function: backend::ast::Function {
                 name: js_name.to_string(),
+                name_span: Span::call_site(),
+                renamed_via_js_name: false,
                 arguments,
                 ret: ret.clone(),
                 rust_attrs: vec![],