generate a module trait and call it

crates/generate/src/module_trait.rs

@@ -0,0 +1,33 @@
+use proc_macro2::TokenStream;
+use quote::quote;
+
+use crate::names::Names;
+use witx::Module;
+
+pub fn define_module_trait(names: &Names, m: &Module) -> TokenStream {
+    let traitname = names.trait_name(&m.name);
+    let traitmethods = m.funcs().map(|f| {
+        let funcname = names.func(&f.name);
+        let args = f.params.iter().map(|arg| {
+            let arg_name = names.func_param(&arg.name);
+            let arg_type = names.type_ref(&arg.tref);
+            quote!(#arg_name: #arg_type)
+        });
+        let rets = f
+            .results
+            .iter()
+            .skip(1)
+            .map(|ret| names.type_ref(&ret.tref));
+        let err = f
+            .results
+            .get(0)
+            .map(|err_result| names.type_ref(&err_result.tref))
+            .unwrap_or(quote!(()));
+        quote!(fn #funcname(&mut self, #(#args),*) -> Result<(#(#rets),*), #err>;)
+    });
+    quote! {
+        pub trait #traitname {
+            #(#traitmethods)*
+        }
+    }
+}