Add #[must_use] to functions annotated with __attribute__((warn_unused_result))

Author: flowbish

src/codegen/helpers.rs

@@ -36,6 +36,12 @@ pub mod attributes {
         }
     }
 
+    pub fn must_use() -> quote::Tokens {
+        quote! {
+            #[must_use]
+        }
+    }
+
     pub fn doc(comment: String) -> quote::Tokens {
         // Doc comments are already preprocessed into nice `///` formats by the
         // time they get here. Just make sure that we have newlines around it so

src/codegen/mod.rs

@@ -2154,9 +2154,13 @@ impl MethodCodegen for Method {
         let mut attrs = vec![];
         attrs.push(attributes::inline());
 
+        if signature.must_use() && ctx.options().rust_features().must_use_function {
+            attrs.push(attributes::must_use());
+        }
+
         let name = ctx.rust_ident(&name);
         methods.push(quote! {
-            #[inline]
+            #(#attrs)*
             pub unsafe fn #name ( #( #args ),* ) #ret {
                 #block
             }
@@ -3374,6 +3378,10 @@ impl CodeGenerator for Function {
 
         let mut attributes = vec![];
 
+        if signature.must_use() && ctx.options().rust_features().must_use_function {
+            attributes.push(attributes::must_use());
+        }
+
         if let Some(comment) = item.comment(ctx) {
             attributes.push(attributes::doc(comment));
         }

src/features.rs

@@ -98,6 +98,8 @@ macro_rules! rust_target_base {
             => Stable_1_25 => 1.25;
             /// Rust stable 1.26
             => Stable_1_26 => 1.26;
+            /// Rust stable 1.27
+            => Stable_1_27 => 1.27;
             /// Nightly rust
             => Nightly => nightly;
         );
@@ -178,6 +180,10 @@ rust_feature_def!(
         /// [i128 / u128 support](https://doc.rust-lang.org/std/primitive.i128.html)
         => i128_and_u128;
     }
+    Stable_1_27 {
+        /// `must_use` attribute on functions ([PR](https://github.com/rust-lang/rust/pull/48925))
+        => must_use_function;
+    }
     Nightly {
         /// `thiscall` calling convention ([Tracking issue](https://github.com/rust-lang/rust/issues/42202))
         => thiscall_abi;

src/ir/function.rs

@@ -221,6 +221,9 @@ pub struct FunctionSig {
     /// Whether this function is variadic.
     is_variadic: bool,
 
+    /// Whether this function's return value must be used.
+    must_use: bool,
+
     /// The ABI of this function.
     abi: Abi,
 }
@@ -310,12 +313,14 @@ impl FunctionSig {
         return_type: TypeId,
         arguments: Vec<(Option<String>, TypeId)>,
         is_variadic: bool,
+        must_use: bool,
         abi: Abi,
     ) -> Self {
         FunctionSig {
             return_type: return_type,
             argument_types: arguments,
             is_variadic: is_variadic,
+            must_use: must_use,
             abi: abi,
         }
     }
@@ -387,6 +392,24 @@ impl FunctionSig {
             }
         };
 
+        let mut must_use = false;
+        cursor.visit(|cur| {
+            if cur.kind() == CXCursor_UnexposedAttr {
+                let attr_warn_unused_result = cur.tokens().map(|tokens| {
+                    tokens.iter().any(|t| {
+                        t.kind == CXToken_Identifier && t.spelling == "warn_unused_result"
+                    })
+                }).unwrap_or(false);
+
+                if attr_warn_unused_result {
+                    must_use = true;
+                    return CXChildVisit_Break;
+                }
+            }
+
+            CXChildVisit_Continue
+        });
+
         let is_method = cursor.kind() == CXCursor_CXXMethod;
         let is_constructor = cursor.kind() == CXCursor_Constructor;
         let is_destructor = cursor.kind() == CXCursor_Destructor;
@@ -458,7 +481,7 @@ impl FunctionSig {
             warn!("Unknown calling convention: {:?}", call_conv);
         }
 
-        Ok(Self::new(ret.into(), args, ty.is_variadic(), abi))
+        Ok(Self::new(ret.into(), args, ty.is_variadic(), must_use, abi))
     }
 
     /// Get this function signature's return type.
@@ -484,6 +507,11 @@ impl FunctionSig {
         self.is_variadic && !self.argument_types.is_empty()
     }
 
+    /// Must this function's return value be used?
+    pub fn must_use(&self) -> bool {
+        self.must_use
+    }
+
     /// Are function pointers with this signature able to derive Rust traits?
     /// Rust only supports deriving traits for function pointers with a limited
     /// number of parameters and a couple ABIs.

tests/expectations/tests/attribute_warn_unused_result.rs

@@ -0,0 +1,44 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+#[repr(C)]
+#[derive(Debug, Default, Copy, Clone)]
+pub struct Foo {
+    pub _address: u8,
+}
+#[test]
+fn bindgen_test_layout_Foo() {
+    assert_eq!(
+        ::std::mem::size_of::<Foo>(),
+        1usize,
+        concat!("Size of: ", stringify!(Foo))
+    );
+    assert_eq!(
+        ::std::mem::align_of::<Foo>(),
+        1usize,
+        concat!("Alignment of ", stringify!(Foo))
+    );
+}
+extern "C" {
+    #[must_use]
+    #[link_name = "\u{1}_ZN3Foo3fooEi"]
+    pub fn Foo_foo(this: *mut Foo, arg1: ::std::os::raw::c_int) -> ::std::os::raw::c_int;
+}
+impl Foo {
+    #[inline]
+    #[must_use]
+    pub unsafe fn foo(&mut self, arg1: ::std::os::raw::c_int) -> ::std::os::raw::c_int {
+        Foo_foo(self, arg1)
+    }
+}
+extern "C" {
+    #[must_use]
+    #[link_name = "\u{1}_Z3fooi"]
+    pub fn foo(arg1: ::std::os::raw::c_int) -> ::std::os::raw::c_int;
+}

tests/expectations/tests/attribute_warn_unused_result_pre_1_27.rs

@@ -0,0 +1,41 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+#[repr(C)]
+#[derive(Debug, Default, Copy, Clone)]
+pub struct Foo {
+    pub _address: u8,
+}
+#[test]
+fn bindgen_test_layout_Foo() {
+    assert_eq!(
+        ::std::mem::size_of::<Foo>(),
+        1usize,
+        concat!("Size of: ", stringify!(Foo))
+    );
+    assert_eq!(
+        ::std::mem::align_of::<Foo>(),
+        1usize,
+        concat!("Alignment of ", stringify!(Foo))
+    );
+}
+extern "C" {
+    #[link_name = "\u{1}_ZN3Foo3fooEi"]
+    pub fn Foo_foo(this: *mut Foo, arg1: ::std::os::raw::c_int) -> ::std::os::raw::c_int;
+}
+impl Foo {
+    #[inline]
+    pub unsafe fn foo(&mut self, arg1: ::std::os::raw::c_int) -> ::std::os::raw::c_int {
+        Foo_foo(self, arg1)
+    }
+}
+extern "C" {
+    #[link_name = "\u{1}_Z3fooi"]
+    pub fn foo(arg1: ::std::os::raw::c_int) -> ::std::os::raw::c_int;
+}

tests/headers/attribute_warn_unused_result.hpp

@@ -0,0 +1,10 @@
+// bindgen-flags: --rust-target 1.27
+
+class Foo {
+public:
+    __attribute__((warn_unused_result))
+    int foo(int);
+};
+
+__attribute__((warn_unused_result))
+int foo(int);

tests/headers/attribute_warn_unused_result_pre_1_27.hpp

@@ -0,0 +1,8 @@
+class Foo {
+public:
+    __attribute__((warn_unused_result))
+    int foo(int);
+};
+
+__attribute__((warn_unused_result))
+int foo(int);