Generate #[must_use]

This is the Rust equivalent of the `warn_unused_result` attribute.

Co-authored-by: Jan Walther <[email protected]>

crates/header-translator/src/method.rs

@@ -53,6 +53,7 @@ pub(crate) struct MethodModifiers {
     non_isolated: bool,
     sendable: Option<bool>,
     pub(crate) mainthreadonly: bool,
+    must_use: bool,
 }
 
 impl MethodModifiers {
@@ -108,7 +109,7 @@ impl MethodModifiers {
                 // <https://clang.llvm.org/docs/AttributeReference.html#objc-requires-super>
             }
             EntityKind::WarnUnusedResultAttr => {
-                // TODO: Emit `#[must_use]` on this
+                this.must_use = true;
             }
             EntityKind::ObjCClassRef
             | EntityKind::ObjCProtocolRef
@@ -261,6 +262,7 @@ pub struct Method {
     non_isolated: bool,
     mainthreadonly: bool,
     weak_property: bool,
+    must_use: bool,
 }
 
 #[derive(Debug)]
@@ -509,6 +511,7 @@ impl Method {
                 non_isolated: modifiers.non_isolated,
                 mainthreadonly,
                 weak_property: false,
+                must_use: modifiers.must_use,
             },
         ))
     }
@@ -583,6 +586,7 @@ impl Method {
                 mainthreadonly,
                 // Don't show `weak`-ness on getters
                 weak_property: false,
+                must_use: modifiers.must_use,
             })
         } else {
             None
@@ -626,6 +630,7 @@ impl Method {
                     non_isolated: modifiers.non_isolated,
                     mainthreadonly,
                     weak_property: attributes.map(|a| a.weak).unwrap_or(false),
+                    must_use: modifiers.must_use,
                 })
             } else {
                 None
@@ -686,6 +691,10 @@ impl fmt::Display for Method {
 
         write!(f, "{}", self.availability)?;
 
+        if self.must_use {
+            writeln!(f, "        #[must_use]")?;
+        }
+
         if self.is_optional {
             writeln!(f, "        #[optional]")?;
         }

crates/header-translator/src/stmt.rs

@@ -525,6 +525,7 @@ pub enum Stmt {
         // Some -> inline function.
         body: Option<()>,
         safe: bool,
+        must_use: bool,
     },
     /// typedef Type TypedefName;
     AliasDecl {
@@ -1357,6 +1358,7 @@ impl Stmt {
                 let result_type = entity.get_result_type().expect("function result type");
                 let result_type = Ty::parse_function_return(result_type, context);
                 let mut arguments = Vec::new();
+                let mut must_use = false;
 
                 if entity.is_static_method() {
                     warn!("unexpected static method");
@@ -1390,7 +1392,7 @@ impl Stmt {
                         arguments.push((name, ty))
                     }
                     EntityKind::WarnUnusedResultAttr => {
-                        // TODO: Emit `#[must_use]` on this
+                        must_use = true;
                     }
                     EntityKind::PureAttr => {
                         // Ignore, we currently have no way of marking
@@ -1415,6 +1417,7 @@ impl Stmt {
                     result_type,
                     body,
                     safe: !data.unsafe_,
+                    must_use,
                 }]
             }
             EntityKind::UnionDecl => {
@@ -2338,6 +2341,7 @@ impl Stmt {
                     result_type,
                     body: Some(_),
                     safe: _,
+                    must_use: _,
                 } => {
                     write!(f, "// TODO: ")?;
                     write!(f, "pub fn {}(", id.name)?;
@@ -2354,13 +2358,17 @@ impl Stmt {
                     result_type,
                     body: None,
                     safe: false,
+                    must_use,
                 } => {
                     // Functions are always C-unwind, since we don't know
                     // anything about them.
                     writeln!(f, "extern \"C-unwind\" {{")?;
 
                     write!(f, "    {}", self.cfg_gate_ln(config))?;
                     write!(f, "    {availability}")?;
+                    if *must_use {
+                        writeln!(f, "    #[must_use]")?;
+                    }
                     write!(f, "    pub fn {}(", id.name)?;
                     for (param, arg_ty) in arguments {
                         let param = handle_reserved(&crate::to_snake_case(param));
@@ -2378,9 +2386,13 @@ impl Stmt {
                     result_type,
                     body: None,
                     safe: true,
+                    must_use,
                 } => {
                     write!(f, "{}", self.cfg_gate_ln(config))?;
                     write!(f, "{availability}")?;
+                    if *must_use {
+                        writeln!(f, "#[must_use]")?;
+                    }
                     writeln!(f, "#[inline]")?;
                     write!(f, "pub extern \"C-unwind\" fn {}(", id.name)?;
                     for (param, arg_ty) in arguments {

crates/objc2/src/topics/about_generated/CHANGELOG.md

@@ -28,6 +28,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   - `EventKitUI` / `objc2-event-kit-ui`.
   - `IOSurface` / `objc2-io-surface`.
   - `ScreenSaver` / `objc2-screen-saver`.
+* Added `#[must_use]` attributes where the C headers have them.
 
 ### Changed
 * Allow using `MainThreadBound` without the `NSThread` feature flag.