#[builder(crate)] attribute and #[builder(expose_positional_fn)] replacement with #[builder(start_fn)]

Cargo.toml

@@ -147,6 +147,12 @@ missing_crate_level_docs = "warn"
 unescaped_backticks      = "warn"
 
 [workspace.lints.rust]
+# This lint is used only to warn about the changes in drop order during the
+# transition from Rust 2021 to Rust 2024. There are too many instances of this
+# lint in our code base and some of them may be false positives. So we just allow
+# this lint globally.
+tail_expr_drop_order = { level = "allow", priority = 2 }
+
 unsafe_code       = "warn"
 unstable_features = "warn"
 

benchmarks/runtime/src/args_10.rs

@@ -46,8 +46,8 @@ pub fn builder_bench() -> u32 {
         .call()
 }
 
-#[builder(expose_positional_fn = regular)]
-fn builder(
+#[builder(start_fn = builder)]
+fn regular(
     arg1: &str,
     arg2: u32,
     arg3: bool,

benchmarks/runtime/src/args_10_alloc.rs

@@ -46,8 +46,8 @@ pub fn builder_bench() -> u32 {
         .call()
 }
 
-#[builder(expose_positional_fn = regular)]
-fn builder(
+#[builder(start_fn = builder)]
+fn regular(
     arg1: String,
     arg2: u32,
     arg3: bool,

benchmarks/runtime/src/args_10_structs.rs

@@ -87,8 +87,8 @@ pub fn builder_bench() -> u32 {
         .call()
 }
 
-#[builder(expose_positional_fn = regular)]
-fn builder(
+#[builder(start_fn = builder)]
+fn regular(
     arg1: Point3D,
     arg2: u32,
     arg3: bool,

benchmarks/runtime/src/args_20.rs

@@ -121,8 +121,8 @@ pub fn builder_bench() -> u32 {
         .call()
 }
 
-#[builder(expose_positional_fn = regular)]
-fn builder(
+#[builder(start_fn = builder)]
+fn regular(
     arg1: &str,
     arg2: u32,
     arg3: bool,

benchmarks/runtime/src/args_3.rs

@@ -13,8 +13,8 @@ pub fn builder_bench() -> u32 {
     builder().arg1(arg1).arg2(arg2).maybe_arg3(arg3).call()
 }
 
-#[builder(expose_positional_fn = regular)]
-fn builder(arg1: &str, arg2: u32, arg3: Option<&str>) -> u32 {
+#[builder(start_fn = builder)]
+fn regular(arg1: &str, arg2: u32, arg3: Option<&str>) -> u32 {
     let x = arg1.parse::<u32>().unwrap() + arg2;
     let x = x + arg3.map(|x| x.parse::<u32>().unwrap()).unwrap_or(0);
     x

benchmarks/runtime/src/args_5.rs

@@ -19,8 +19,8 @@ pub fn builder_bench() -> u32 {
         .call()
 }
 
-#[builder(expose_positional_fn = regular)]
-fn builder(arg1: &str, arg2: u32, arg3: bool, arg4: Option<&str>, arg5: Option<u32>) -> u32 {
+#[builder(start_fn = builder)]
+fn regular(arg1: &str, arg2: u32, arg3: bool, arg4: Option<&str>, arg5: Option<u32>) -> u32 {
     let x = arg1.parse::<u32>().unwrap() + arg2;
     let x = x + u32::from(arg3);
     let x = x + arg4.map(|x| x.parse::<u32>().unwrap()).unwrap_or(0);

bon-macros/Cargo.toml

@@ -58,6 +58,7 @@ quote = "1"
 syn = { version = "2.0.56", features = ["full", "visit-mut", "visit"] }
 
 prettyplease = "0.2"
+rustversion  = "1.0"
 
 [features]
 default = []

bon-macros/src/bon.rs

@@ -1,39 +1,35 @@
 use crate::builder;
-use crate::normalization::{ExpandCfg, ExpansionOutput};
+use crate::normalization::{ExpandCfg, Expansion};
 use crate::util::prelude::*;
+use darling::ast::NestedMeta;
+use darling::FromMeta;
 
 pub(crate) fn generate(params: TokenStream, item: TokenStream) -> TokenStream {
-    crate::error::with_fallback(item.clone(), || try_generate(params, item))
+    crate::error::handle_errors(item.clone(), || try_generate(params, item))
         .unwrap_or_else(std::convert::identity)
 }
 
 pub(crate) fn try_generate(params: TokenStream, item: TokenStream) -> Result<TokenStream> {
     let item: syn::Item = syn::parse2(item)?;
-    let macro_path = syn::parse_quote!(::bon::bon);
 
     let ctx = ExpandCfg {
-        macro_path,
-        params,
+        current_macro: format_ident!("bon"),
+        config: params,
         item,
     };
 
-    let (params, item) = match ctx.expand_cfg()? {
-        ExpansionOutput::Expanded { params, item } => (params, item),
-        ExpansionOutput::Recurse(output) => return Ok(output),
+    let input = match ctx.expand_cfg()? {
+        Expansion::Expanded(input) => input,
+        Expansion::Recurse(output) => return Ok(output),
     };
 
-    if !params.is_empty() {
-        bail!(
-            &params,
-            "`#[bon]` attribute does not accept any parameters yet, \
-            but it will in future releases"
-        );
-    }
+    let params = NestedMeta::parse_meta_list(input.config)?;
+    let params = FromMeta::from_list(&params)?;
 
-    match item {
-        syn::Item::Impl(item_impl) => builder::item_impl::generate(item_impl),
+    match input.item {
+        syn::Item::Impl(item_impl) => builder::item_impl::generate(params, item_impl),
         _ => bail!(
-            &item,
+            &input.item,
             "`#[bon]` attribute is expected to be placed on an `impl` block \
              but it was placed on other syntax instead"
         ),

bon-macros/src/builder/builder_gen/builder_derives.rs

@@ -1,12 +1,12 @@
-use super::builder_params::{BuilderDerive, BuilderDerives};
+use super::top_level_config::{DeriveConfig, DerivesConfig};
 use super::BuilderGenCtx;
 use crate::builder::builder_gen::Member;
 use crate::util::prelude::*;
 use darling::ast::GenericParamExt;
 
 impl BuilderGenCtx {
     pub(crate) fn builder_derives(&self) -> TokenStream {
-        let BuilderDerives { clone, debug } = &self.builder_type.derives;
+        let DerivesConfig { clone, debug } = &self.builder_type.derives;
 
         let mut tokens = TokenStream::new();
 
@@ -31,7 +31,7 @@ impl BuilderGenCtx {
     fn where_clause_for_derive(
         &self,
         target_trait_bounds: &TokenStream,
-        derive: &BuilderDerive,
+        derive: &DeriveConfig,
     ) -> TokenStream {
         let derive_specific_predicates = derive
             .bounds
@@ -64,7 +64,8 @@ impl BuilderGenCtx {
         }
     }
 
-    fn derive_clone(&self, derive: &BuilderDerive) -> TokenStream {
+    fn derive_clone(&self, derive: &DeriveConfig) -> TokenStream {
+        let bon = &self.bon;
         let generics_decl = &self.generics.decl_without_defaults;
         let generic_args = &self.generics.args;
         let builder_ident = &self.builder_type.ident;
@@ -113,7 +114,7 @@ impl BuilderGenCtx {
             let ty = member.underlying_norm_ty();
 
             quote! {
-                ::bon::private::derives::clone_member::<#ty>(
+                #bon::__private::derives::clone_member::<#ty>(
                     &self.#named_members_field.#member_index
                 )
             }
@@ -153,10 +154,11 @@ impl BuilderGenCtx {
         }
     }
 
-    fn derive_debug(&self, derive: &BuilderDerive) -> TokenStream {
+    fn derive_debug(&self, derive: &DeriveConfig) -> TokenStream {
         let receiver_field = &self.ident_pool.receiver;
         let start_fn_args_field = &self.ident_pool.start_fn_args;
         let named_members_field = &self.ident_pool.named_members;
+        let bon = &self.bon;
 
         let format_members = self.members.iter().filter_map(|member| {
             match member {
@@ -168,7 +170,7 @@ impl BuilderGenCtx {
                         if let Some(value) = &self.#named_members_field.#member_index {
                             output.field(
                                 #member_ident_str,
-                                ::bon::private::derives::as_dyn_debug::<#member_ty>(value)
+                                #bon::__private::derives::as_dyn_debug::<#member_ty>(value)
                             );
                         }
                     })
@@ -180,7 +182,7 @@ impl BuilderGenCtx {
                     Some(quote! {
                         output.field(
                             #member_ident_str,
-                            ::bon::private::derives::as_dyn_debug::<#member_ty>(
+                            #bon::__private::derives::as_dyn_debug::<#member_ty>(
                                 &self.#start_fn_args_field.#member_index
                             )
                         );
@@ -199,7 +201,7 @@ impl BuilderGenCtx {
             quote! {
                 output.field(
                     "self",
-                    ::bon::private::derives::as_dyn_debug::<#ty>(
+                    #bon::__private::derives::as_dyn_debug::<#ty>(
                         &self.#receiver_field
                     )
                 );

bon-macros/src/builder/builder_gen/finish_fn.rs

@@ -31,16 +31,15 @@ impl super::BuilderGenCtx {
             self.#named_members_field.#index
         };
 
-        let param_default = member
-            .params
+        let default = member
+            .config
             .default
             .as_ref()
             .map(|default| default.value.as_ref());
 
-        match param_default {
+        match default {
             Some(Some(default)) => {
-                let has_into = member.params.into.is_present();
-                let default = if has_into {
+                let default = if member.config.into.is_present() {
                     quote! { Into::into((|| #default)()) }
                 } else {
                     quote! { #default }