Add enable_method_chaining to the generate macro

Author: QuantumSegfault

crates/guest-rust/macro/src/lib.rs

@@ -171,6 +171,9 @@ impl Parse for Config {
                         }
                         opts.async_ = val;
                     }
+                    Opt::EnableMethodChaining(enable) => {
+                        opts.enable_method_chaining = enable.value();
+                    }
                 }
             }
         } else {
@@ -324,6 +327,7 @@ mod kw {
     syn::custom_keyword!(disable_custom_section_link_helpers);
     syn::custom_keyword!(imports);
     syn::custom_keyword!(debug);
+    syn::custom_keyword!(enable_method_chaining);
 }
 
 #[derive(Clone)]
@@ -404,6 +408,7 @@ enum Opt {
     DisableCustomSectionLinkHelpers(syn::LitBool),
     Async(AsyncFilterSet, Span),
     Debug(syn::LitBool),
+    EnableMethodChaining(syn::LitBool),
 }
 
 impl Parse for Opt {
@@ -568,6 +573,10 @@ impl Parse for Opt {
             input.parse::<kw::debug>()?;
             input.parse::<Token![:]>()?;
             Ok(Opt::Debug(input.parse()?))
+        } else if l.peek(kw::enable_method_chaining) {
+            input.parse::<kw::enable_method_chaining>()?;
+            input.parse::<Token![:]>()?;
+            Ok(Opt::EnableMethodChaining(input.parse()?))
         } else if l.peek(Token![async]) {
             let span = input.parse::<Token![async]>()?.span;
             input.parse::<Token![:]>()?;

crates/guest-rust/src/lib.rs

@@ -860,6 +860,11 @@ extern crate std;
 ///         "-export:wasi:http/handler@0.3.0-draft#handle",
 ///         "all",
 ///     ],
+///
+///     // All resource methods with empty returns are instead generated as
+///     // returning `-> &Self`, to permit method chaining (e.g. for builder).
+///     // This expectation is also imposed on exports.
+///     enable_method_chaining: true,
 /// });
 /// ```
 ///

crates/rust/tests/codegen.rs

@@ -216,3 +216,22 @@ mod retyped_list {
         }
     });
 }
+
+#[allow(unused, reason = "testing codegen, not functionality")]
+mod method_chaining {
+    wit_bindgen::generate!({
+        inline: r#"
+        package test:method-chaining;
+        world test {
+            resource a {
+                constructor();
+                set-a: func(arg: u32);
+                set-b: func(arg: bool);
+                do: func();
+            }
+        }
+        "#,
+        generate_all,
+        enable_method_chaining: true
+    });
+}