Fix: emit extern "C" fn for functions declared in extern "C" blocks

crates/libs/rdl/src/clang/cx.rs

@@ -289,6 +289,10 @@ impl Cursor {
     pub fn result_type(&self) -> Type {
         Type(unsafe { clang_getCursorResultType(self.0) })
     }
+
+    pub fn language(&self) -> CXLanguageKind {
+        unsafe { clang_getCursorLanguage(self.0) }
+    }
 }
 
 pub struct Type(CXType);

crates/libs/rdl/src/clang/fn.rs

@@ -7,10 +7,16 @@ pub struct Fn {
     pub library: String,
     pub params: Vec<Param>,
     pub return_type: metadata::Type,
+    pub extern_c: bool,
 }
 
 impl Fn {
-    pub fn parse(cursor: Cursor, namespace: &str, library: &str) -> Result<Self, Error> {
+    pub fn parse(
+        cursor: Cursor,
+        namespace: &str,
+        library: &str,
+        extern_c: bool,
+    ) -> Result<Self, Error> {
         let name = cursor.name();
         let return_type = cursor.result_type().to_type(namespace);
 
@@ -32,6 +38,7 @@ impl Fn {
             library: library.to_string(),
             params,
             return_type,
+            extern_c,
         })
     }
 
@@ -53,9 +60,15 @@ impl Fn {
             }
         };
 
+        let abi = if self.extern_c {
+            quote! { "C" }
+        } else {
+            quote! {}
+        };
+
         Ok(quote! {
             #[library(#library)]
-            extern fn #name(#(#params),*) #return_type;
+            extern #abi fn #name(#(#params),*) #return_type;
         })
     }
 }

crates/libs/rdl/src/clang/mod.rs

@@ -203,7 +203,32 @@ impl Clang {
                     }
                 }
                 CXCursor_FunctionDecl if !child.is_definition() => {
-                    collector.insert(Item::Fn(Fn::parse(child, &self.namespace, &self.library)?));
+                    collector.insert(Item::Fn(Fn::parse(
+                        child,
+                        &self.namespace,
+                        &self.library,
+                        false,
+                    )?));
+                }
+                // Recurse into `extern "C" { }` or `extern "C++" { }` blocks so
+                // that function declarations inside them are collected with the
+                // correct ABI annotation.
+                CXCursor_LinkageSpec => {
+                    for inner in child.children() {
+                        if !inner.is_from_main_file() {
+                            continue;
+                        }
+                        if inner.kind() == CXCursor_FunctionDecl && !inner.is_definition() {
+                            // A function inside `extern "C" { }` has C language linkage.
+                            let extern_c = inner.language() == CXLanguage_C;
+                            collector.insert(Item::Fn(Fn::parse(
+                                inner,
+                                &self.namespace,
+                                &self.library,
+                                extern_c,
+                            )?));
+                        }
+                    }
                 }
                 CXCursor_MacroDefinition => {
                     if let Some(c) = Const::parse(child, &self.namespace, tu)? {

crates/tests/libs/clang/roundtrip/fn_extern_c.h

@@ -0,0 +1,5 @@
+extern "C"
+{
+    unsigned int GetTickCount();
+    void SetLastErrorEx(unsigned a, signed b);
+}

crates/tests/libs/clang/roundtrip/fn_extern_c.rdl

@@ -0,0 +1,7 @@
+#[win32]
+mod Test {
+    #[library("test.dll")]
+    extern "C" fn GetTickCount() -> u32;
+    #[library("test.dll")]
+    extern "C" fn SetLastErrorEx(a: u32, b: i32);
+}