Add --sys-fn-ptrs to generate function pointer types (#3782)

Co-authored-by: Kenny Kerr <[email protected]>

Author: uint-nate

.github/workflows/clippy.yml

@@ -302,6 +302,8 @@ jobs:
         run:  cargo clippy -p test_structs --tests
       - name: Check test_sys
         run:  cargo clippy -p test_sys --tests
+      - name: Check test_sys_fn_ptrs
+        run:  cargo clippy -p test_sys_fn_ptrs --tests
       - name: Check test_targets
         run:  cargo clippy -p test_targets --tests
       - name: Check test_threading

.github/workflows/test.yml

@@ -331,6 +331,8 @@ jobs:
         run:  cargo test -p test_structs --target ${{ matrix.target }}
       - name: Test test_sys
         run:  cargo test -p test_sys --target ${{ matrix.target }}
+      - name: Test test_sys_fn_ptrs
+        run:  cargo test -p test_sys_fn_ptrs --target ${{ matrix.target }}
       - name: Test test_targets
         run:  cargo test -p test_targets --target ${{ matrix.target }}
       - name: Test test_threading
@@ -359,10 +361,10 @@ jobs:
         run:  cargo test -p tool_bindgen --target ${{ matrix.target }}
       - name: Test tool_bindings
         run:  cargo test -p tool_bindings --target ${{ matrix.target }}
-      - name: Test tool_gnu
-        run:  cargo test -p tool_gnu --target ${{ matrix.target }}
       - name: Clean
         run:  cargo clean
+      - name: Test tool_gnu
+        run:  cargo test -p tool_gnu --target ${{ matrix.target }}
       - name: Test tool_license
         run:  cargo test -p tool_license --target ${{ matrix.target }}
       - name: Test tool_merge

crates/libs/bindgen/src/config/mod.rs

@@ -20,6 +20,7 @@ pub struct Config<'a> {
     pub package: bool,
     pub rustfmt: &'a str,
     pub sys: bool,
+    pub sys_fn_ptrs: bool,
     pub implement: bool,
     pub specific_deps: bool,
     pub derive: &'a Derive,

crates/libs/bindgen/src/lib.rs

@@ -81,6 +81,7 @@ use method_names::*;
 /// | `--no-comment` | Avoids generating the code generation comment. |
 /// | `--no-deps` | Avoids dependencies on the various `windows-*` crates. |
 /// | `--sys` | Generates raw or sys-style Rust bindings. |
+/// | `--sys-fn-ptrs` | Additionally generates function pointers for sys-style Rust bindings. |
 /// | `--implement` | Includes implementation traits for WinRT interfaces. |
 /// | `--link` | Overrides the default `windows-link` implementation for system calls. |
 ///
@@ -278,6 +279,7 @@ where
     let mut rustfmt = String::new();
     let mut output = String::new();
     let mut sys = false;
+    let mut sys_fn_ptrs = false;
     let mut link = String::new();
     let mut index = false;
 
@@ -301,6 +303,7 @@ where
                 "--no-toml" => no_toml = true,
                 "--package" => package = true,
                 "--sys" => sys = true,
+                "--sys-fn-ptrs" => sys_fn_ptrs = true,
                 "--implement" => implement = true,
                 "--specific-deps" => specific_deps = true,
                 "--link" => kind = ArgKind::Link,
@@ -435,6 +438,7 @@ where
         rustfmt: &rustfmt,
         output: &output,
         sys,
+        sys_fn_ptrs,
         implement,
         specific_deps,
         link: &link,

crates/libs/bindgen/src/types/cpp_fn.rs

@@ -27,6 +27,35 @@ impl CppFn {
         self.type_name().write(config, &[])
     }
 
+    pub fn write_fn_ptr(&self, config: &Config<'_>, underlying_types: bool) -> TokenStream {
+        let ptr_name = self.method.name().to_string();
+        let name = to_ident(&ptr_name);
+        let abi = self.method.calling_convention();
+        let signature = self.method.signature(self.namespace, &[]);
+
+        let params = signature.params.iter().map(|param| {
+            let name = param.write_ident();
+            let ty = if underlying_types {
+                param.underlying_type().write_abi(config)
+            } else {
+                param.write_abi(config)
+            };
+            quote! { #name: #ty }
+        });
+
+        let return_sig = config.write_return_sig(self.method, &signature, underlying_types);
+
+        let vararg = if config.sys && signature.call_flags.contains(MethodCallAttributes::VARARG) {
+            quote! { , ... }
+        } else {
+            quote! {}
+        };
+
+        quote! {
+            pub type #name = unsafe extern #abi fn(#(#params),* #vararg) #return_sig;
+        }
+    }
+
     pub fn write_link(&self, config: &Config, underlying_types: bool) -> TokenStream {
         let library = self.method.module_name();
         let symbol = self.method.import_name();
@@ -71,18 +100,30 @@ impl CppFn {
         let name = to_ident(self.method.name());
         let signature = self.method.signature(self.namespace, &[]);
 
+        let fn_ptr = self.write_fn_ptr(config, false);
         let link = self.write_link(config, false);
         let arches = write_arches(self.method);
         let cfg = self.write_cfg(config);
         let cfg = quote! { #arches #cfg };
         let window_long = self.write_window_long();
 
         if config.sys {
-            return quote! {
-                #cfg
-                #link
-                #window_long
-            };
+            if config.sys_fn_ptrs {
+                return quote! {
+                    #cfg
+                    #fn_ptr
+                    #window_long
+                    #cfg
+                    #link
+                    #window_long
+                };
+            } else {
+                return quote! {
+                    #cfg
+                    #link
+                    #window_long
+                };
+            }
         }
 
         let method = CppMethod::new(self.method, self.namespace);

crates/tests/misc/sys_fn_ptrs/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "test_sys_fn_ptrs"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[lib]
+doc = false
+doctest = false
+
+[dependencies.windows-result]
+workspace = true
+
+[dependencies.windows-strings]
+workspace = true
+
+[dependencies.windows-link]
+workspace = true
+
+[build-dependencies.windows-bindgen]
+workspace = true
+
+[lints]
+workspace = true

crates/tests/misc/sys_fn_ptrs/build.rs

@@ -0,0 +1,18 @@
+fn main() {
+    windows_bindgen::bindgen([
+        "--out",
+        "src/bindings.rs",
+        "--filter",
+        "WebAuthNAuthenticatorMakeCredential",
+        "WebAuthNAuthenticatorGetAssertion",
+        "LoadLibraryExA",
+        "GetProcAddress",
+        "FreeLibrary",
+        "LOAD_LIBRARY_SEARCH_DEFAULT_DIRS",
+        "--sys",
+        "--sys-fn-ptrs",
+        "--no-comment",
+        "--no-deps",
+    ])
+    .unwrap();
+}