Make pre-bindgened output more portable and support no_std (still requires a libc, though)

imgui-sys/Cargo.toml

@@ -13,6 +13,9 @@ links = "imgui"
 # exclude json, lua, and the imgui subdirs (imgui/examples, imgui/docs, etc)
 exclude = ["third-party/*.json", "third-party/*.lua", "third-party/imgui/*/"]
 
+[dependencies]
+cty = "0.2"
+
 [build-dependencies]
 cc = "1.0"
 

imgui-sys/src/lib.rs

@@ -1,3 +1,4 @@
+#![no_std]
 #[cfg(feature = "wasm")]
 mod wasm_bindings;
 
@@ -95,7 +96,7 @@ impl Into<(f32, f32, f32, f32)> for ImVec4 {
 
 #[test]
 fn test_imvec2_memory_layout() {
-    use std::mem;
+    use core::mem;
     assert_eq!(mem::size_of::<ImVec2>(), mem::size_of::<[f32; 2]>());
     assert_eq!(mem::align_of::<ImVec2>(), mem::align_of::<[f32; 2]>());
     let test = ImVec2::new(1.0, 2.0);
@@ -107,7 +108,7 @@ fn test_imvec2_memory_layout() {
 
 #[test]
 fn test_imvec4_memory_layout() {
-    use std::mem;
+    use core::mem;
     assert_eq!(mem::size_of::<ImVec4>(), mem::size_of::<[f32; 4]>());
     assert_eq!(mem::align_of::<ImVec4>(), mem::align_of::<[f32; 4]>());
     let test = ImVec4::new(1.0, 2.0, 3.0, 4.0);

xtask/src/bindgen.rs

@@ -107,16 +107,22 @@ fn generate_binding_file(
         "--size_t-is-usize",
         "--no-prepend-enum-name",
         "--no-doc-comments",
+        // Layout tests aren't portable (they hardcode type sizes), and for
+        // our case they just serve to sanity check rustc's implementation of
+        // `#[repr(C)]`. If we bind directly to C++ ever, we should reconsider this.
+        "--no-layout-tests",
         "--with-derive-default",
         "--with-derive-partialeq",
         "--with-derive-eq",
         "--with-derive-hash",
         "--impl-debug",
+        "--use-core",
     ];
     cmd.args(a);
     cmd.args(&["--blacklist-type", "__darwin_size_t"]);
     cmd.args(&["--raw-line", "#![allow(nonstandard_style, clippy::all)]"]);
     cmd.arg("--output").arg(output);
+    cmd.args(&["--ctypes-prefix", "cty"]);
 
     if let Some(name) = wasm_import_mod {
         cmd.args(&["--wasm-import-module-name", &name]);