Add a suffix to rust functions exported to C++ side to avoid duplicate link symbols

Author: twistedfall

build.rs

@@ -177,7 +177,7 @@ fn make_modules(opencv_dir: &Path) -> Result<()> {
 	Ok(())
 }
 
-fn build_compiler(opencv: &Library) -> cc::Build {
+fn build_compiler(opencv: &Library, ffi_export_suffix: &str) -> cc::Build {
 	let mut out = cc::Build::new();
 	out.cpp(true)
 		.std("c++14") // clang says error: 'auto' return without trailing return type; deduced return types are a C++14 extension
@@ -227,6 +227,7 @@ fn build_compiler(opencv: &Library) -> cc::Build {
 	} else {
 		out.flag_if_supported("-Wa,-mbig-obj");
 	}
+	out.define("OCVRS_FFI_EXPORT_SUFFIX", ffi_export_suffix);
 	out
 }
 
@@ -247,8 +248,7 @@ fn setup_rerun() -> Result<()> {
 	Ok(())
 }
 
-fn build_wrapper(opencv: &Library) {
-	let mut cc = build_compiler(opencv);
+fn build_wrapper(mut cc: cc::Build) {
 	eprintln!("=== Compiler information: {:#?}", cc.get_compiler());
 	let modules = MODULES.get().expect("MODULES not initialized");
 	static SUPPORTED_MODULES: [&str; 67] = [
@@ -347,7 +347,8 @@ fn main() -> Result<()> {
 		return Ok(());
 	}
 
-	eprintln!("=== Crate version: {:?}", env::var_os("CARGO_PKG_VERSION"));
+	let pkg_version = env::var("CARGO_PKG_VERSION").unwrap_or_else(|_| "unknown_crate_version".to_string());
+	eprintln!("=== Crate version: {pkg_version}");
 	eprintln!("=== Environment configuration:");
 	for v in AFFECTING_ENV_VARS.into_iter().chain(DEBUG_ENV_VARS) {
 		eprintln!("===   {v} = {:?}", env::var_os(v));
@@ -421,9 +422,11 @@ fn main() -> Result<()> {
 
 	setup_rerun()?;
 
+	let ffi_export_suffix = format!("_{}", pkg_version.replace(".", "_"));
 	let binding_generator = BindingGenerator::new(build_script_path);
-	binding_generator.generate_wrapper(opencv_header_dir, &opencv)?;
-	build_wrapper(&opencv);
+	binding_generator.generate_wrapper(opencv_header_dir, &opencv, &ffi_export_suffix)?;
+	let cc = build_compiler(&opencv, &ffi_export_suffix);
+	build_wrapper(cc);
 	// -l linker args should be emitted after -l static
 	opencv.emit_cargo_metadata();
 	Ok(())

build/generator.rs

@@ -22,7 +22,7 @@ impl BindingGenerator {
 		Self { build_script_path }
 	}
 
-	pub fn generate_wrapper(&self, opencv_header_dir: &Path, opencv: &Library) -> Result<()> {
+	pub fn generate_wrapper(&self, opencv_header_dir: &Path, opencv: &Library, ffi_export_suffix: &str) -> Result<()> {
 		let target_docs_dir = env::var_os("OCVRS_DOCS_GENERATE_DIR").map(PathBuf::from);
 		let target_module_dir = OUT_DIR.join("opencv");
 		let manual_dir = SRC_DIR.join("manual");
@@ -48,8 +48,7 @@ impl BindingGenerator {
 
 		self.run(modules, opencv_header_dir, opencv)?;
 
-		let collector = Collector::new(modules, &target_module_dir, &manual_dir, &OUT_DIR);
-		collector.collect_bindings()?;
+		Collector::new(modules, &ffi_export_suffix, &target_module_dir, &manual_dir, &OUT_DIR).collect_bindings()?;
 
 		if let Some(target_docs_dir) = target_docs_dir {
 			if !target_docs_dir.exists() {

build/generator/collector.rs

@@ -9,15 +9,23 @@ use super::super::{files_with_extension, Result};
 
 pub struct Collector<'r> {
 	modules: &'r [String],
+	ffi_export_suffix: &'r str,
 	target_module_dir: &'r Path,
 	manual_dir: &'r Path,
 	out_dir: &'r Path,
 }
 
 impl<'r> Collector<'r> {
-	pub fn new(modules: &'r [String], target_module_dir: &'r Path, manual_dir: &'r Path, out_dir: &'r Path) -> Self {
+	pub fn new(
+		modules: &'r [String],
+		ffi_export_suffix: &'r str,
+		target_module_dir: &'r Path,
+		manual_dir: &'r Path,
+		out_dir: &'r Path,
+	) -> Self {
 		Self {
 			modules,
+			ffi_export_suffix,
 			target_module_dir,
 			manual_dir,
 			out_dir,
@@ -80,6 +88,7 @@ impl<'r> Collector<'r> {
 			writeln!(hub_rs, "\tpub use super::{module}::prelude::*;")?;
 		}
 		writeln!(hub_rs, "}}")?;
+		self.inject_ffi_exports(&mut hub_rs)?;
 		eprintln!("=== Total binding collection time: {:?}", start.elapsed());
 		Ok(())
 	}
@@ -172,6 +181,30 @@ impl<'r> Collector<'r> {
 		Ok(())
 	}
 
+	/// The #no_mangle function in the bindings cause duplicate export names when 2 different version of the crate are used
+	/// (https://github.com/twistedfall/opencv-rust/issues/597). This function injects the version of the exported functions with
+	/// a crate version suffix to avoid this conflict. On the C++ side it works with the help of the `OCVRS_FFI_EXPORT_SUFFIX`
+	/// macro which is passed in `build_compiler()`.
+	fn inject_ffi_exports(&self, hub_rs: &mut impl Write) -> Result<()> {
+		writeln!(hub_rs, "\nmod ffi_exports {{")?;
+		writeln!(hub_rs, "\tuse crate::mod_prelude_sys::*;")?;
+		write!(hub_rs, "\t")?;
+		writeln!(
+			hub_rs,
+			r#"#[no_mangle] unsafe extern "C" fn ocvrs_create_string{}(s: *const c_char) -> *mut String {{ crate::templ::ocvrs_create_string(s) }}"#,
+			self.ffi_export_suffix
+		)?;
+		write!(hub_rs, "\t")?;
+		writeln!(
+			hub_rs,
+			r#"#[no_mangle] unsafe extern "C" fn ocvrs_create_byte_string{}(v: *const u8, len: size_t) -> *mut Vec<u8> {{ crate::templ::ocvrs_create_byte_string(v, len) }}"#,
+			self.ffi_export_suffix
+		)?;
+		writeln!(hub_rs, "}}")?;
+
+		Ok(())
+	}
+
 	fn write_use_manual(&self, file: &mut BufWriter<File>, module: &str) -> Result<bool> {
 		if self.manual_dir.join(format!("{module}.rs")).exists() {
 			writeln!(file, "pub use crate::manual::{module}::*;")?;

src/templ.rs

@@ -112,16 +112,16 @@ macro_rules! return_receive {
 	};
 }
 
-/// The return type of this function goes into `receive_string`
-#[export_name = "ocvrs_create_string"]
-unsafe extern "C" fn ocvrs_create_string(s: *const c_char) -> *mut String {
+/// The return type of this function goes into `receive_string::<String>()`
+#[inline]
+pub unsafe fn ocvrs_create_string(s: *const c_char) -> *mut String {
 	let s = CStr::from_ptr(s).to_string_lossy().into_owned();
 	Box::into_raw(Box::new(s))
 }
 
-/// The return type of this function goes into `receive_byte_string`
-#[export_name = "ocvrs_create_byte_string"]
-unsafe extern "C" fn ocvrs_create_byte_string(v: *const u8, len: size_t) -> *mut Vec<u8> {
+/// The return type of this function goes into `receive_string::<Vec<u8>>()`
+#[inline]
+pub unsafe fn ocvrs_create_byte_string(v: *const u8, len: size_t) -> *mut Vec<u8> {
 	let byte_slice = if v.is_null() {
 		&[]
 	} else {

src_cpp/ocvrs_common.hpp

@@ -11,6 +11,8 @@
 	// strip dnn experimental ns when generating headers
 	#define CV_DNN_DONT_ADD_EXPERIMENTAL_NS
 	#define CV_DNN_DONT_ADD_INLINE_NS
+	// the FFI export suffix only matters during actual linking
+	#define OCVRS_FFI_EXPORT_SUFFIX
 #endif
 
 #include <memory>
@@ -29,9 +31,17 @@ catch (cv::Exception& e) { \
 	OCVRS_HANDLE(cv::Error::StsError, "Unspecified error, neither from OpenCV nor from std", return_name); \
 }
 
-// defined in src/templ.rs
-extern "C" void* ocvrs_create_string(const char*);
-extern "C" void* ocvrs_create_byte_string(const char*, size_t);
+// double-expansion macro trick to expand the OCVRS_FFI_EXPORT_SUFFIX macro
+#define CONCATENATE(prefix, suffix) prefix##suffix
+#define SUFFIXED_NAME(name, suffix) CONCATENATE(name, suffix)
+
+// defined in build/generator/collector.rs Collector::inject_ffi_exports, see `inject_ffi_exports()` function for explanation
+extern "C" void* SUFFIXED_NAME(ocvrs_create_string, OCVRS_FFI_EXPORT_SUFFIX)(const char*);
+extern "C" void* SUFFIXED_NAME(ocvrs_create_byte_string, OCVRS_FFI_EXPORT_SUFFIX)(const char*, size_t);
+
+// "aliases" for the above functions provided by Rust, to be used in the generated code
+inline void* ocvrs_create_string(const char* s) { return SUFFIXED_NAME(ocvrs_create_string, OCVRS_FFI_EXPORT_SUFFIX)(s); }
+inline void* ocvrs_create_byte_string(const char* s, size_t len) { return SUFFIXED_NAME(ocvrs_create_byte_string, OCVRS_FFI_EXPORT_SUFFIX)(s, len); }
 
 template<typename T> struct Result {
 	int error_code;