Preserve fn and {} for start_fn so that rustdoc generates correct links

bon-macros/src/builder/builder_gen/input_fn/mod.rs

@@ -12,6 +12,7 @@ use crate::util::prelude::*;
 use std::borrow::Cow;
 use std::rc::Rc;
 use syn::punctuated::Punctuated;
+use syn::spanned::Spanned;
 use syn::visit_mut::VisitMut;
 
 pub(crate) struct FnInputCtx<'a> {
@@ -97,6 +98,11 @@ impl<'a> FnInputCtx<'a> {
                     .collect(),
                 params.fn_item.norm.sig.generics.where_clause.clone(),
             )),
+            // We don't use params.fn_item.orig.span() here because that span
+            // only contains the annotations before the function and the
+            // function name. Block contains function name + implementation
+            // which is what rustdoc normally links to.
+            span: Some(params.fn_item.orig.block.span()),
         };
 
         let self_ty_prefix = params.impl_ctx.as_deref().and_then(|impl_ctx| {

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

@@ -187,6 +187,7 @@ impl StructInputCtx {
             vis: start_fn_vis.map(SpannedKey::into_value),
             docs: start_fn_docs,
             generics: None,
+            span: None,
         };
 
         let assoc_method_ctx = Some(AssocMethodCtxParams {

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

@@ -85,6 +85,9 @@ pub(super) struct StartFn {
 
     /// Overrides the default generics
     pub(super) generics: Option<Generics>,
+
+    /// Preserve a span the documentation for `start_fn` should link to.
+    pub(super) span: Span,
 }
 
 pub(super) struct StartFnParams {
@@ -97,6 +100,9 @@ pub(super) struct StartFnParams {
 
     /// Overrides the default generics
     pub(super) generics: Option<Generics>,
+    /// Preserve a span the documentation for `start_fn` should link to.
+    /// Defaults to macro callsite if not supplied.
+    pub(super) span: Option<Span>,
 }
 
 pub(super) struct BuilderType {
@@ -309,6 +315,7 @@ impl BuilderGenCtx {
             vis: start_fn.vis.unwrap_or_else(|| builder_type.vis.clone()),
             docs: start_fn.docs,
             generics: start_fn.generics,
+            span: start_fn.span.unwrap_or_else(Span::call_site),
         };
 
         let finish_fn = FinishFn {

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

@@ -96,8 +96,23 @@ impl super::BuilderGenCtx {
             };
 
         let const_ = &self.const_;
-
-        syn::parse_quote! {
+        // add the `clippy::needless_lifetimes` lint if before rust version 1.87
+        // Rust version 1.87 includes a clippy change where `needless_lifetimes`
+        // was split with the more complex part of the lint going to
+        // `elidable_lifetime_names`. For versions since 1.87 we want to block
+        // `elidable_lifetime_names` (See
+        // https://github.com/elastio/bon/pull/341#discussion_r2398893516 for
+        // an explanation).
+        let needless_lifetime_lint = if rustversion::cfg!(before(1.87)) {
+            format_ident!("needless_lifetimes")
+        } else {
+            format_ident!("elidable_lifetime_names")
+        };
+
+        // Construct using a span which links to our original implementation.
+        // This ensures rustdoc doesn't just link every method to the macro
+        // callsite.
+        syn::parse_quote_spanned! {self.start_fn.span=>
             #(#docs)*
             #[inline(always)]
             #[allow(
@@ -108,6 +123,7 @@ impl super::BuilderGenCtx {
                 // Let's keep it as non-const for now to avoid restricting ourselfves to only
                 // const operations.
                 clippy::missing_const_for_fn,
+                clippy::#needless_lifetime_lint
             )]
             #vis #const_ fn #start_fn_ident< #(#generics_decl),* >(
                 #receiver

bon/src/lib.rs

@@ -14,7 +14,7 @@
 // Rexport all macros from the proc-macro crate.
 pub use bon_macros::{bon, builder, map, set, Builder};
 
-/// Small utility declarative macros for creating colletions with [`Into`] conversions.
+/// Small utility declarative macros for creating collections with [`Into`] conversions.
 mod collections;
 
 #[doc(hidden)]

bon/tests/integration/builder/attr_bon.rs

@@ -102,6 +102,7 @@ fn receiver_variations() {
         }
 
         #[builder]
+        #[allow(dead_code)]
         fn mut_self_as_pin_mut_self(mut self: Pin<&mut Self>) {
             #[allow(clippy::self_assignment, unused_assignments)]
             {

bon/tests/integration/builder/attr_const.rs

@@ -205,6 +205,7 @@ mod msrv_1_61 {
         #[test]
         const fn test_function() {
             #[builder(const)]
+            #[allow(unreachable_pub)]
             pub const fn sut(#[builder(getter)] _x: u32) {}
 
             sut().x(1).call();
@@ -217,6 +218,7 @@ mod msrv_1_61 {
             #[bon]
             impl Sut {
                 #[builder(const)]
+                #[allow(unreachable_pub)]
                 pub const fn sut(#[builder(getter)] _x: u32) {}
             }
 

bon/tests/integration/builder/attr_top_level_start_fn.rs

@@ -52,6 +52,7 @@ fn test_method() {
 fn test_function() {
     {
         #[builder(start_fn(name = sut_builder))]
+        #[allow(dead_code)]
         fn sut(arg1: bool, arg2: u32) -> impl fmt::Debug {
             (arg1, arg2)
         }
@@ -61,6 +62,7 @@ fn test_function() {
 
     {
         #[builder(start_fn = sut_builder)]
+        #[allow(dead_code)]
         fn sut(arg1: u32) -> u32 {
             arg1
         }
@@ -70,6 +72,7 @@ fn test_function() {
 
     {
         #[builder(start_fn(name = sut_builder, vis = ""))]
+        #[allow(dead_code)]
         fn sut(arg1: u32) -> u32 {
             arg1
         }