From 1a09f450c874d57883f56a7a0c298be5db183569 Mon Sep 17 00:00:00 2001
From: Christian Poveda Ruiz <31802960+pvdrz@users.noreply.github.com>
Date: Mon, 11 Sep 2023 16:48:04 -0500
Subject: [PATCH] Use void in parameterless functions (#2633)

* Use void for parameterless function arguments

* Update tests

* Update CHANGELOG.md
---
 CHANGELOG.md                                  |  2 ++
 .../tests/generated/wrap_static_fns.c         |  1 +
 .../expectations/tests/wrap-static-fns.rs     |  6 ++++
 bindgen-tests/tests/headers/wrap-static-fns.h |  4 +++
 bindgen/codegen/serialize.rs                  | 35 +++++++++++--------
 5 files changed, 33 insertions(+), 15 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index fa5af68580..9b536800fe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -179,6 +179,8 @@
 
 ## Added
 ## Changed
+- The `--wrap-static-fns` feature was updated so function types that has no
+  argument use `void` as its sole argument.
 ## Removed
 ## Fixed
 ## Security
diff --git a/bindgen-tests/tests/expectations/tests/generated/wrap_static_fns.c b/bindgen-tests/tests/expectations/tests/generated/wrap_static_fns.c
index cf1106ec76..a8fd5045d2 100644
--- a/bindgen-tests/tests/expectations/tests/generated/wrap_static_fns.c
+++ b/bindgen-tests/tests/expectations/tests/generated/wrap_static_fns.c
@@ -11,6 +11,7 @@ int takes_alias__extern(func f) { return takes_alias(f); }
 int takes_qualified__extern(const int *const *arg) { return takes_qualified(arg); }
 enum foo takes_enum__extern(const enum foo f) { return takes_enum(f); }
 void nevermore__extern(void) { nevermore(); }
+int takes_fn_with_no_args__extern(int (f) (void)) { return takes_fn_with_no_args(f); }
 void no_extra_argument__extern(__builtin_va_list va) { no_extra_argument(va); }
 int many_va_list__extern(int i, __builtin_va_list va1, __builtin_va_list va2) { return many_va_list(i, va1, va2); }
 int wrap_as_variadic_fn1__extern(int i, ...) {
diff --git a/bindgen-tests/tests/expectations/tests/wrap-static-fns.rs b/bindgen-tests/tests/expectations/tests/wrap-static-fns.rs
index 03f3907ed2..46b369b2f4 100644
--- a/bindgen-tests/tests/expectations/tests/wrap-static-fns.rs
+++ b/bindgen-tests/tests/expectations/tests/wrap-static-fns.rs
@@ -50,6 +50,12 @@ extern "C" {
     #[link_name = "nevermore__extern"]
     pub fn nevermore();
 }
+extern "C" {
+    #[link_name = "takes_fn_with_no_args__extern"]
+    pub fn takes_fn_with_no_args(
+        f: ::std::option::Option<unsafe extern "C" fn() -> ::std::os::raw::c_int>,
+    ) -> ::std::os::raw::c_int;
+}
 extern "C" {
     #[link_name = "no_extra_argument__extern"]
     pub fn no_extra_argument(va: *mut __va_list_tag);
diff --git a/bindgen-tests/tests/headers/wrap-static-fns.h b/bindgen-tests/tests/headers/wrap-static-fns.h
index 8dcabe7b30..131b7ab15f 100644
--- a/bindgen-tests/tests/headers/wrap-static-fns.h
+++ b/bindgen-tests/tests/headers/wrap-static-fns.h
@@ -52,6 +52,10 @@ static inline void nevermore() {
     while (1) { }
 }
 
+static inline int takes_fn_with_no_args(int(f)(void)) {
+    return f();
+}
+
 static inline int variadic(int x, ...) {
     return x;
 }
diff --git a/bindgen/codegen/serialize.rs b/bindgen/codegen/serialize.rs
index 58e0882faf..02c4680263 100644
--- a/bindgen/codegen/serialize.rs
+++ b/bindgen/codegen/serialize.rs
@@ -322,21 +322,26 @@ impl<'a> CSerialize<'a> for Type {
                 }
                 write!(writer, ")")?;
 
-                write!(writer, " (")?;
-                serialize_sep(
-                    ", ",
-                    signature.argument_types().iter(),
-                    ctx,
-                    writer,
-                    |(name, type_id), ctx, buf| {
-                        let mut stack = vec![];
-                        if let Some(name) = name {
-                            stack.push(name.clone());
-                        }
-                        type_id.serialize(ctx, (), &mut stack, buf)
-                    },
-                )?;
-                write!(writer, ")")?
+                let args = signature.argument_types();
+                if args.is_empty() {
+                    write!(writer, " (void)")?;
+                } else {
+                    write!(writer, " (")?;
+                    serialize_sep(
+                        ", ",
+                        args.iter(),
+                        ctx,
+                        writer,
+                        |(name, type_id), ctx, buf| {
+                            let mut stack = vec![];
+                            if let Some(name) = name {
+                                stack.push(name.clone());
+                            }
+                            type_id.serialize(ctx, (), &mut stack, buf)
+                        },
+                    )?;
+                    write!(writer, ")")?
+                }
             }
             TypeKind::ResolvedTypeRef(type_id) => {
                 if self.is_const() {