fix: use consistent u32 type for enum constants on Windows (#4)

bindgen generates enum constants as i32 on Windows MSVC (C standard:
enum underlying type is int) but u32 on GCC/Clang when all values are
non-negative. This causes type mismatch errors when using the constants.

Add .default_enum_style(bindgen::EnumVariation::Consts) combined with
.translate_enum_integer_types(true) to force consistent unsigned types
across all platforms.

Co-authored-by: kaju <kajukitli@users.noreply.github.com>

Author: kajukitli

build.rs

@@ -266,6 +266,11 @@ fn generate_bindings(out_dir: &Path, include_dir: &Path) {
     .allowlist_function("nghttp2_.*")
     .allowlist_type("nghttp2_.*")
     .allowlist_var("NGHTTP2_.*")
+    // Generate enum constants with consistent types across platforms.
+    // Without this, C enums become i32 on MSVC (C standard: enum is int)
+    // but u32 on GCC/Clang (where the underlying type matches the values).
+    .default_enum_style(bindgen::EnumVariation::Consts)
+    .translate_enum_integer_types(true)
     // Opaque types that should not derive Copy
     .opaque_type("nghttp2_session")
     .opaque_type("nghttp2_rcbuf")