feat(rust): allow generate unused records and variants (#913)

* feat(rust): allow generate unused records and variants

* fix: empty record

* rename: allow_unused -> generate_unused_types

* test(rust): make sure unused types are exported

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

@@ -113,6 +113,9 @@ impl Parse for Config {
                     Opt::PubExportMacro(enable) => {
                         opts.pub_export_macro = enable.value();
                     }
+                    Opt::GenerateUnusedTypes(enable) => {
+                        opts.generate_unused_types = enable.value();
+                    }
                 }
             }
         } else {
@@ -231,6 +234,7 @@ mod kw {
     syn::custom_keyword!(default_bindings_module);
     syn::custom_keyword!(export_macro_name);
     syn::custom_keyword!(pub_export_macro);
+    syn::custom_keyword!(generate_unused_types);
 }
 
 #[derive(Clone)]
@@ -280,6 +284,7 @@ enum Opt {
     DefaultBindingsModule(syn::LitStr),
     ExportMacroName(syn::LitStr),
     PubExportMacro(syn::LitBool),
+    GenerateUnusedTypes(syn::LitBool),
 }
 
 impl Parse for Opt {
@@ -398,6 +403,10 @@ impl Parse for Opt {
             input.parse::<kw::pub_export_macro>()?;
             input.parse::<Token![:]>()?;
             Ok(Opt::PubExportMacro(input.parse()?))
+        } else if l.peek(kw::generate_unused_types) {
+            input.parse::<kw::generate_unused_types>()?;
+            input.parse::<Token![:]>()?;
+            Ok(Opt::GenerateUnusedTypes(input.parse()?))
         } else {
             Err(l.error())
         }

crates/guest-rust/src/lib.rs

@@ -785,6 +785,11 @@
 ///     // Disable a workaround to force wasm constructors to be run only once
 ///     // when exported functions are called.
 ///     disable_run_ctors_once_workaround: false,
+///
+///     // Whether to generate unused `record`, `enum`, `variant` types.
+///     // By default, they will not be generated unless they are used as input
+///     // or return value of a function.
+///     generate_unused_types: false,
 /// });
 /// ```
 ///

crates/rust/src/interface.rs

@@ -1329,12 +1329,13 @@ macro_rules! {macro_name} {{
 
     fn modes_of(&self, ty: TypeId) -> Vec<(String, TypeMode)> {
         let info = self.info(ty);
-        // If this type isn't actually used, no need to generate it.
-        if !info.owned && !info.borrowed {
-            return Vec::new();
-        }
         let mut result = Vec::new();
-
+        if !self.gen.opts.generate_unused_types {
+            // If this type isn't actually used, no need to generate it.
+            if !info.owned && !info.borrowed {
+                return result;
+            }
+        }
         // Generate one mode for when the type is owned and another for when
         // it's borrowed.
         let a = self.type_mode_for_id(ty, TypeOwnershipStyle::Owned, "'a");

crates/rust/src/lib.rs

@@ -182,6 +182,10 @@ pub struct Opts {
     /// candidate for being exported outside of the crate.
     #[cfg_attr(feature = "clap", arg(long))]
     pub pub_export_macro: bool,
+
+    /// Whether to generate unused structures, not generated by default (false)
+    #[cfg_attr(feature = "clap", arg(long))]
+    pub generate_unused_types: bool,
 }
 
 impl Opts {

crates/rust/tests/codegen.rs

@@ -340,6 +340,7 @@ mod custom_derives {
     use exports::my::inline::blah::Foo;
 
     struct Component;
+
     impl exports::my::inline::blah::Guest for Component {
         fn bar(cool: Foo) {
             // Check that built in derives that I've added actually work by seeing that this hashes
@@ -452,3 +453,34 @@ mod with_and_resources {
         });
     }
 }
+
+#[allow(unused)]
+mod generate_unused_types {
+    use exports::foo::bar::component::UnusedEnum;
+    use exports::foo::bar::component::UnusedRecord;
+    use exports::foo::bar::component::UnusedVariant;
+
+    wit_bindgen::generate!({
+        inline: "
+            package foo:bar;
+
+            world bindings {
+                export component;
+            }
+
+            interface component {
+                variant unused-variant {
+                    %enum(unused-enum),
+                    %record(unused-record)
+                }
+                enum unused-enum {
+                    unused
+                }
+                record unused-record {
+                    x: u32
+                }
+            }
+        ",
+        generate_unused_types: true,
+    });
+}

tests/codegen/allow-unused.wit

@@ -0,0 +1,18 @@
+package foo:bar;
+
+world bindings {
+    export component;
+}
+
+interface component {
+    variant unused-variant {
+        %enum(unused-enum),
+        %record(unused-record)
+    }
+    enum unused-enum {
+        unused
+    }
+    record unused-record {
+        x: u32
+    }
+}