Fix cross build from macos to msvc

godot-bindings/build.rs

@@ -10,7 +10,7 @@
 // It's the only purpose of this build.rs file. If a better solution is found, this file can be removed.
 
 #[rustfmt::skip]
-fn main() {    
+fn main() {
     let mut count = 0;
     if cfg!(feature = "api-custom") { count += 1; }
     if cfg!(feature = "api-custom-json") { count += 1; }

godot-bindings/src/import.rs

@@ -63,3 +63,52 @@ pub use gdextension_api::version_4_5 as prebuilt;
 //  [line] pub use gdextension_api::version_$snakeVersion as prebuilt;
 pub use gdextension_api::version_4_5 as prebuilt;
 // ]]
+
+// Cross-compilation support:
+// Since godot-bindings is a build-dependency, it and the gdextension-api crate are compiled for the HOST platform.
+// The #[cfg] attributes in gdextension-api::load_gdextension_header_rs() evaluate for HOST, not TARGET.
+// We read CARGO_CFG_TARGET_* environment variables to select the correct platform-specific Rust bindings at runtime.
+#[cfg(not(any(feature = "api-custom", feature = "api-custom-json")))]
+pub(crate) mod prebuilt_platform {
+    use std::borrow::Cow;
+    use std::path::PathBuf;
+
+    /// Load platform-specific Rust bindings (gdextension_interface_{platform}.rs) for the TARGET platform.
+    ///
+    /// During cross-compilation, godot-bindings runs on the HOST, but needs to generate bindings for the TARGET.
+    /// This function reads CARGO_CFG_TARGET_* environment variables to determine the target platform,
+    /// then loads the appropriate gdextension_interface_{platform}.rs file from the gdextension-api crate's res/ directory.
+    pub fn load_gdextension_header_rs_for_target() -> Cow<'static, str> {
+        let target_family = std::env::var("CARGO_CFG_TARGET_FAMILY").ok();
+        let target_os = std::env::var("CARGO_CFG_TARGET_OS").ok();
+
+        let platform = match (target_family.as_deref(), target_os.as_deref()) {
+            (Some("windows"), _) => "windows",
+            (_, Some("macos" | "ios")) => "macos",
+            _ => "linux", // Linux, Android, and other Unix-like systems
+        };
+
+        load_platform_file(platform)
+    }
+
+    /// Reads gdextension_interface_{platform}.rs from the gdextension-api crate using DEP_GDEXTENSION_API_ROOT.
+    fn load_platform_file(platform: &str) -> Cow<'static, str> {
+        let dep_root = std::env::var("DEP_GDEXTENSION_API_ROOT")
+            .expect("DEP_GDEXTENSION_API_ROOT not set. This should be exported by gdextension-api's build script.");
+
+        let file_path = PathBuf::from(dep_root)
+            .join("res")
+            .join(format!("gdextension_interface_{platform}.rs"));
+
+        std::fs::read_to_string(&file_path)
+            .map(Cow::Owned)
+            .unwrap_or_else(|e| panic!(
+                "Failed to load platform-specific Rust bindings for '{platform}'.\n\
+                 Tried to read: {}\n\
+                 Error: {e}\n\
+                 \n\
+                 This is likely a cross-compilation issue or the gdextension-api version doesn't support this platform.",
+                file_path.display()
+            ))
+    }
+}

godot-bindings/src/lib.rs

@@ -129,7 +129,11 @@ mod depend_on_prebuilt {
             .unwrap_or_else(|e| panic!("failed to write gdextension_interface.h: {e}"));
         watch.record("write_header_h");
 
-        let rs_contents = prebuilt::load_gdextension_header_rs();
+        // Cross-compilation support:
+        // Since godot-bindings is a build-dependency, it and the gdextension-api crate are compiled for the HOST platform.
+        // The #[cfg] attributes in gdextension-api::load_gdextension_header_rs() evaluate for HOST, not TARGET.
+        // We read CARGO_CFG_TARGET_* environment variables to select the correct platform-specific Rust bindings at runtime.
+        let rs_contents = crate::import::prebuilt_platform::load_gdextension_header_rs_for_target();
         std::fs::write(rs_path, rs_contents.as_ref())
             .unwrap_or_else(|e| panic!("failed to write gdextension_interface.rs: {e}"));
         watch.record("write_header_rs");