Propagate #[target_feature] attributes on #[builder]-generated finishing functions (#284)

Author: lilyyy411

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

@@ -157,9 +157,23 @@ impl super::BuilderGenCtx {
         let state_var = &self.state_var;
         let const_ = &self.const_;
 
+        // `#[target_feature]` is not compatible with `#[inline(always)]`,
+        // so we need to downgrade it to `#[inline]
+        let inline_attr = self
+            .finish_fn
+            .special_attrs
+            .iter()
+            .find_map(|attr| {
+                attr.meta
+                    .path()
+                    .is_ident("target_feature")
+                    .then(|| quote! { #[inline] })
+            })
+            .unwrap_or_else(|| quote! { #[inline(always)] });
+
         quote! {
             #(#attrs)*
-            #[inline(always)]
+            #inline_attr
             #[allow(
                 // This is intentional. We want the builder syntax to compile away
                 clippy::inline_always,

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

@@ -485,7 +485,7 @@ fn merge_generic_params(
         .collect()
 }
 
-const PROPAGATED_ATTRIBUTES: &[&str] = &["must_use", "track_caller"];
+const PROPAGATED_ATTRIBUTES: &[&str] = &["must_use", "track_caller", "target_feature"];
 
 fn get_propagated_attrs(attrs: &[syn::Attribute]) -> Result<Vec<syn::Attribute>> {
     PROPAGATED_ATTRIBUTES

bon/tests/integration/builder/mod.rs

@@ -25,6 +25,7 @@ mod orig_fn_naming;
 mod positional_members;
 mod raw_idents;
 mod smoke;
+mod target_feature;
 mod track_caller;
 
 use crate::prelude::*;

bon/tests/integration/builder/target_feature.rs

@@ -0,0 +1,41 @@
+#[cfg(target_arch = "x86_64")]
+#[rustversion::since(1.86.0)]
+mod msrv_1_86 {
+    #![allow(dead_code)]
+    use crate::prelude::*;
+
+    #[test]
+    fn target_feature_function() {
+        #[builder]
+        #[target_feature(enable = "avx2")]
+        fn building_but_wider(_x: [u8; 32], _y: [u32; 8]) {}
+
+        #[target_feature(enable = "avx2")]
+        #[allow(unsafe_code)]
+        unsafe fn wider() {
+            building_but_wider().x([0; 32]).y([1; 8]).call();
+        }
+    }
+
+    #[test]
+    fn target_feature_method() {
+        #[repr(C, align(32))]
+        struct Brick([u8; 32]);
+        struct Senti;
+
+        #[bon]
+        impl Senti {
+            #[builder(finish_fn = yatta_but_wide)]
+            #[target_feature(enable = "avx2")]
+            fn new(brick: Brick) -> Self {
+                let Brick(_) = brick;
+                Self
+            }
+            #[target_feature(enable = "avx2")]
+            #[allow(unsafe_code)]
+            unsafe fn briiick() {
+                Self::builder().brick(Brick([0; 32])).yatta_but_wide();
+            }
+        }
+    }
+}

bon/tests/integration/builder/track_caller.rs

@@ -18,7 +18,7 @@ impl From<&'_ Location<'_>> for LineCol {
 }
 
 #[test]
-fn track_caller_fn() {
+fn track_caller_function() {
     #[builder]
     #[track_caller]
     fn dont_brick(_x: u32) -> LineCol {
@@ -39,7 +39,7 @@ fn track_caller_fn() {
 }
 
 #[test]
-fn track_caller_impl_block() {
+fn track_caller_method() {
     struct Brick;
     struct Senti;
     #[bon]

bon/tests/integration/ui/compile_fail/attr_builder.rs

@@ -72,3 +72,7 @@ fn destructuring2((_, _): (u32, u32)) {}
 #[track_caller]
 #[track_caller]
 fn double_track_caller() {}
+#[builder]
+#[target_feature(enable = "")]
+#[target_feature(enable = "")]
+fn double_invalid_target_feature() {}

bon/tests/integration/ui/compile_fail/attr_builder.stderr

@@ -89,3 +89,21 @@ error: found multiple #[track_caller], but bon only works with exactly one or ze
    |
 73 | #[track_caller]
    | ^
+
+error: found multiple #[target_feature], but bon only works with exactly one or zero.
+  --> tests/integration/ui/compile_fail/attr_builder.rs:77:1
+   |
+77 | #[target_feature(enable = "")]
+   | ^
+
+error: the feature named `` is not valid for this target
+  --> tests/integration/ui/compile_fail/attr_builder.rs:76:18
+   |
+76 | #[target_feature(enable = "")]
+   |                  ^^^^^^^^^^^ `` is not valid for this target
+
+error: the feature named `` is not valid for this target
+  --> tests/integration/ui/compile_fail/attr_builder.rs:77:18
+   |
+77 | #[target_feature(enable = "")]
+   |                  ^^^^^^^^^^^ `` is not valid for this target