feat(rust): Adds the ability to specify custom derive attributes

crates/rust-lib/src/lib.rs

@@ -1,4 +1,5 @@
 use heck::*;
+use std::collections::BTreeSet;
 use std::fmt;
 use std::str::FromStr;
 use wit_bindgen_core::abi::{Bitcast, LiftLower, WasmType};
@@ -91,6 +92,9 @@ pub trait RustGenerator<'a> {
 
     fn is_exported_resource(&self, ty: TypeId) -> bool;
 
+    /// Return any additional derive attributes to add to the generated types
+    fn additional_derives(&self) -> &[String];
+
     fn mark_resource_owned(&mut self, resource: TypeId);
 
     fn push_str(&mut self, s: &str);
@@ -159,7 +163,7 @@ pub trait RustGenerator<'a> {
         param_mode: TypeMode,
         sig: &FnSig,
     ) -> Vec<String> {
-        let params = self.print_docs_and_params(func, param_mode, &sig);
+        let params = self.print_docs_and_params(func, param_mode, sig);
         if let FunctionKind::Constructor(_) = &func.kind {
             self.push_str(" -> Self")
         } else {
@@ -198,7 +202,7 @@ pub trait RustGenerator<'a> {
         } else {
             &func.name
         };
-        self.push_str(&to_rust_ident(&func_name));
+        self.push_str(&to_rust_ident(func_name));
         if let Some(generics) = &sig.generics {
             self.push_str(generics);
         }
@@ -563,7 +567,7 @@ pub trait RustGenerator<'a> {
         if self.uses_two_names(&info) {
             result.push((self.param_name(ty), TypeMode::AllBorrowed("'a")));
         }
-        return result;
+        result
     }
 
     fn print_typedef_record(
@@ -574,6 +578,9 @@ pub trait RustGenerator<'a> {
         derive_component: bool,
     ) {
         let info = self.info(id);
+        // We use a BTree set to make sure we don't have any duplicates and we have a stable order
+        let additional_derives: BTreeSet<String> =
+            self.additional_derives().iter().cloned().collect();
         for (name, mode) in self.modes_of(id) {
             let lt = self.lifetime_for(&info, mode);
             self.rustdoc(docs);
@@ -586,12 +593,17 @@ pub trait RustGenerator<'a> {
                 self.push_str("#[derive(wasmtime::component::Lower)]\n");
                 self.push_str("#[component(record)]\n");
             }
-
+            let mut derives = additional_derives.clone();
             if info.is_copy() {
                 self.push_str("#[repr(C)]\n");
-                self.push_str("#[derive(Copy, Clone)]\n");
+                derives.extend(["Copy", "Clone"].into_iter().map(|s| s.to_string()));
             } else if info.is_clone() {
-                self.push_str("#[derive(Clone)]\n");
+                derives.insert("Clone".to_string());
+            }
+            if !derives.is_empty() {
+                self.push_str("#[derive(");
+                self.push_str(&derives.into_iter().collect::<Vec<_>>().join(", "));
+                self.push_str(")]\n")
             }
             self.push_str(&format!("pub struct {}", name));
             self.print_generics(lt);
@@ -707,7 +719,9 @@ pub trait RustGenerator<'a> {
         Self: Sized,
     {
         let info = self.info(id);
-
+        // We use a BTree set to make sure we don't have any duplicates and have a stable order
+        let additional_derives: BTreeSet<String> =
+            self.additional_derives().iter().cloned().collect();
         for (name, mode) in self.modes_of(id) {
             self.rustdoc(docs);
             let lt = self.lifetime_for(&info, mode);
@@ -719,10 +733,16 @@ pub trait RustGenerator<'a> {
                 self.push_str("#[derive(wasmtime::component::Lower)]\n");
                 self.push_str(&format!("#[component({})]\n", derive_component));
             }
+            let mut derives = additional_derives.clone();
             if info.is_copy() {
-                self.push_str("#[derive(Copy, Clone)]\n");
+                derives.extend(["Copy", "Clone"].into_iter().map(|s| s.to_string()));
             } else if info.is_clone() {
-                self.push_str("#[derive(Clone)]\n");
+                derives.insert("Clone".to_string());
+            }
+            if !derives.is_empty() {
+                self.push_str("#[derive(");
+                self.push_str(&derives.into_iter().collect::<Vec<_>>().join(", "));
+                self.push_str(")]\n")
             }
             self.push_str(&format!("pub enum {name}"));
             self.print_generics(lt);
@@ -873,7 +893,17 @@ pub trait RustGenerator<'a> {
         }
         self.push_str("#[repr(");
         self.int_repr(enum_.tag());
-        self.push_str(")]\n#[derive(Clone, Copy, PartialEq, Eq)]\n");
+        self.push_str(")]\n");
+        // We use a BTree set to make sure we don't have any duplicates and a stable order
+        let mut derives: BTreeSet<String> = self.additional_derives().iter().cloned().collect();
+        derives.extend(
+            ["Clone", "Copy", "PartialEq", "Eq"]
+                .into_iter()
+                .map(|s| s.to_string()),
+        );
+        self.push_str("#[derive(");
+        self.push_str(&derives.into_iter().collect::<Vec<_>>().join(", "));
+        self.push_str(")]\n");
         self.push_str(&format!("pub enum {name} {{\n"));
         for case in enum_.cases.iter() {
             self.rustdoc(&case.docs);
@@ -1167,10 +1197,10 @@ pub trait RustFunctionGenerator {
         for (field, val) in ty.fields.iter().zip(operands) {
             result.push_str(&to_rust_ident(&field.name));
             result.push_str(": ");
-            result.push_str(&val);
+            result.push_str(val);
             result.push_str(",\n");
         }
-        result.push_str("}");
+        result.push('}');
         results.push(result);
     }
 

crates/rust-macro/Cargo.toml

@@ -17,7 +17,8 @@ test = false
 
 [dependencies]
 proc-macro2 = "1.0"
-syn = "2.0"
+syn = { version = "2.0", features = ["printing"] }
+quote = "1"
 wit-bindgen-core = { workspace = true }
 wit-bindgen-rust = { workspace = true }
 wit-bindgen-rust-lib = { workspace = true }

crates/rust-macro/src/lib.rs

@@ -1,4 +1,5 @@
 use proc_macro2::{Span, TokenStream};
+use quote::ToTokens;
 use std::path::{Path, PathBuf};
 use syn::parse::{Error, Parse, ParseStream, Result};
 use syn::punctuated::Punctuated;
@@ -73,6 +74,12 @@ impl Parse for Config {
                         opts.stubs = true;
                     }
                     Opt::ExportPrefix(prefix) => opts.export_prefix = Some(prefix.value()),
+                    Opt::AdditionalDerives(paths) => {
+                        opts.additional_derive_attributes = paths
+                            .into_iter()
+                            .map(|p| p.into_token_stream().to_string())
+                            .collect()
+                    }
                 }
             }
         } else {
@@ -101,7 +108,7 @@ fn parse_source(source: &Option<Source>) -> anyhow::Result<(Resolve, PackageId,
     let root = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap());
     let mut parse = |path: &Path| -> anyhow::Result<_> {
         if path.is_dir() {
-            let (pkg, sources) = resolve.push_dir(&path)?;
+            let (pkg, sources) = resolve.push_dir(path)?;
             files = sources;
             Ok(pkg)
         } else {
@@ -112,9 +119,9 @@ fn parse_source(source: &Option<Source>) -> anyhow::Result<(Resolve, PackageId,
     };
     let pkg = match source {
         Some(Source::Inline(s)) => {
-            resolve.push(UnresolvedPackage::parse("macro-input".as_ref(), &s)?)?
+            resolve.push(UnresolvedPackage::parse("macro-input".as_ref(), s)?)?
         }
-        Some(Source::Path(s)) => parse(&root.join(&s))?,
+        Some(Source::Path(s)) => parse(&root.join(s))?,
         None => parse(&root.join("wit"))?,
     };
 
@@ -159,6 +166,7 @@ mod kw {
     syn::custom_keyword!(exports);
     syn::custom_keyword!(stubs);
     syn::custom_keyword!(export_prefix);
+    syn::custom_keyword!(additional_derives);
 }
 
 #[derive(Clone)]
@@ -216,6 +224,8 @@ enum Opt {
     Exports(Vec<Export>),
     Stubs,
     ExportPrefix(syn::LitStr),
+    // Parse as paths so we can take the concrete types/macro names rather than raw strings
+    AdditionalDerives(Vec<syn::Path>),
 }
 
 impl Parse for Opt {
@@ -306,6 +316,13 @@ impl Parse for Opt {
             input.parse::<kw::export_prefix>()?;
             input.parse::<Token![:]>()?;
             Ok(Opt::ExportPrefix(input.parse()?))
+        } else if l.peek(kw::additional_derives) {
+            input.parse::<kw::additional_derives>()?;
+            input.parse::<Token![:]>()?;
+            let contents;
+            syn::bracketed!(contents in input);
+            let list = Punctuated::<_, Token![,]>::parse_terminated(&contents)?;
+            Ok(Opt::AdditionalDerives(list.iter().cloned().collect()))
         } else {
             Err(l.error())
         }

crates/rust/Cargo.toml

@@ -27,3 +27,6 @@ clap = { workspace = true, optional = true }
 [dev-dependencies]
 wit-bindgen = { path = '../guest-rust' }
 test-helpers = { path = '../test-helpers' }
+# For use with the custom attributes test
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1"

crates/rust/src/lib.rs

@@ -142,6 +142,13 @@ pub struct Opts {
     /// This defaults to `wit_bindgen::bitflags`.
     #[cfg_attr(feature = "clap", arg(long))]
     pub bitflags_path: Option<String>,
+
+    /// Additional derive attributes to add to generated types. If using in a CLI, this flag can be
+    /// specified multiple times to add multiple attributes.
+    ///
+    /// These derive attributes will be added to any generated structs or enums
+    #[cfg_attr(feature = "clap", arg(long = "additional_derive_attribute", short = 'd', default_values_t = Vec::<String>::new()))]
+    pub additional_derive_attributes: Vec<String>,
 }
 
 impl Opts {
@@ -543,9 +550,11 @@ impl InterfaceGenerator<'_> {
                     .entry(export_key)
                     .or_insert((trait_name, local_impl_name, Vec::new()));
             let prev = mem::take(&mut self.src);
-            let mut sig = FnSig::default();
-            sig.use_item_name = true;
-            sig.private = true;
+            let mut sig = FnSig {
+                use_item_name: true,
+                private: true,
+                ..Default::default()
+            };
             if let FunctionKind::Method(_) = &func.kind {
                 sig.self_arg = Some("&self".into());
                 sig.self_is_first_param = true;
@@ -915,9 +924,11 @@ impl InterfaceGenerator<'_> {
             if self.gen.skip.contains(&func.name) {
                 continue;
             }
-            let mut sig = FnSig::default();
-            sig.use_item_name = true;
-            sig.private = true;
+            let mut sig = FnSig {
+                use_item_name: true,
+                private: true,
+                ..Default::default()
+            };
             if let FunctionKind::Method(_) = &func.kind {
                 sig.self_arg = Some("&self".into());
                 sig.self_is_first_param = true;
@@ -939,6 +950,10 @@ impl<'a> RustGenerator<'a> for InterfaceGenerator<'a> {
         self.gen.opts.ownership
     }
 
+    fn additional_derives(&self) -> &[String] {
+        &self.gen.opts.additional_derive_attributes
+    }
+
     fn path_to_interface(&self, interface: InterfaceId) -> Option<String> {
         let mut path = String::new();
         if let Identifier::Interface(cur, name) = self.identifier {
@@ -958,7 +973,7 @@ impl<'a> RustGenerator<'a> for InterfaceGenerator<'a> {
             }
         }
         let name = &self.gen.interface_names[&interface];
-        path.push_str(&name);
+        path.push_str(name);
         Some(path)
     }
 
@@ -1340,7 +1355,7 @@ impl<'a, 'b> FunctionBindgen<'a, 'b> {
             sig.push_str(wasm_type(*param));
             sig.push_str(", ");
         }
-        sig.push_str(")");
+        sig.push(')');
         assert!(results.len() < 2);
         for result in results.iter() {
             sig.push_str(" -> ");
@@ -1398,7 +1413,7 @@ impl Bindgen for FunctionBindgen<'_, '_> {
     }
 
     fn finish_block(&mut self, operands: &mut Vec<String>) {
-        if self.cleanup.len() > 0 {
+        if !self.cleanup.is_empty() {
             self.needs_cleanup_list = true;
             self.push_str("cleanup_list.extend_from_slice(&[");
             for (ptr, layout) in mem::take(&mut self.cleanup) {
@@ -1677,7 +1692,7 @@ impl Bindgen for FunctionBindgen<'_, '_> {
                         self.push_str(&format!(" => {{\n{block}\n}}\n"));
                     }
                 }
-                if results.len() == 0 {
+                if results.is_empty() {
                     self.push_str("}\n");
                 } else {
                     self.push_str("};\n");
@@ -1901,7 +1916,7 @@ impl Bindgen for FunctionBindgen<'_, '_> {
                 self.push_str(&format!(
                     "if ptr.is_null()\n{{\nalloc::handle_alloc_error({layout});\n}}\nptr\n}}",
                 ));
-                self.push_str(&format!("else {{\n::core::ptr::null_mut()\n}};\n",));
+                self.push_str("else {{\n::core::ptr::null_mut()\n}};\n");
                 self.push_str(&format!("for (i, e) in {vec}.into_iter().enumerate() {{\n",));
                 self.push_str(&format!(
                     "let base = {result} as i32 + (i as i32) * {size};\n",
@@ -1964,7 +1979,7 @@ impl Bindgen for FunctionBindgen<'_, '_> {
                 );
 
                 // ... then call the function with all our operands
-                if sig.results.len() > 0 {
+                if !sig.results.is_empty() {
                     self.push_str("let ret = ");
                     results.push("ret".to_string());
                 }

crates/rust/tests/codegen.rs

@@ -300,3 +300,49 @@ mod package_with_versions {
         }
     }
 }
+
+mod custom_derives {
+    use std::collections::{hash_map::RandomState, HashSet};
+
+    wit_bindgen::generate!({
+        inline: "
+            package my:inline
+
+            interface blah {
+                record foo {
+                    field1: string,
+                    field2: list<u32>
+                }
+
+                bar: func(cool: foo)
+            }
+
+            world baz {
+                export blah
+            }
+        ",
+        exports: {
+            "my:inline/blah": Component
+        },
+        // Clone is included by default almost everywhere, so include it here to make sure it
+        // doesn't conflict
+        additional_derives: [serde::Serialize, serde::Deserialize, Hash, Clone, PartialEq, Eq],
+    });
+
+    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
+            let _blah: HashSet<Foo, RandomState> = HashSet::from_iter([Foo {
+                field1: "hello".to_string(),
+                field2: vec![1, 2, 3],
+            }]);
+
+            // Check that the attributes from an external crate actually work. If they don't work,
+            // compilation will fail here
+            let _ = serde_json::to_string(&cool);
+        }
+    }
+}