Read CppInterOp location from CPPINTEROP_BIN_DIR env var

CMakeLists.txt

@@ -64,7 +64,7 @@ else()
 endif()
 
 target_compile_definitions(cppyy-backend PRIVATE
-  CPPINTEROP_DIR="${_interop_install_dir}"
+  CPPINTEROP_BIN_DIR="${_interop_install_dir}"
   CMAKE_SHARED_LIBRARY_SUFFIX="${CMAKE_SHARED_LIBRARY_SUFFIX}"
 )
 

clingwrapper/src/clingwrapper.cxx

@@ -109,15 +109,50 @@ bool is_integral(std::string& s)
         s.end(), [](unsigned char c) { return !std::isdigit(c); }) == s.end();
 }
 
+// CppInterOp artifacts prefix (the directory containing lib/ and include/):
+// the CPPINTEROP_BIN_DIR environment variable overrides the compile-time
+// default.
+static inline
+std::string cppinterop_dir()
+{
+    if (const char* env = getenv("CPPINTEROP_BIN_DIR"))
+        return env;
+#ifdef CPPINTEROP_BIN_DIR
+    return CPPINTEROP_BIN_DIR;
+#else
+    return "";
+#endif
+}
+
+static inline
+std::string cppinterop_lib_path()
+{
+    std::string dir = cppinterop_dir();
+    if (dir.empty())
+        return "";
+#ifdef CMAKE_SHARED_LIBRARY_SUFFIX
+    // CMake sets the correct per-platform suffix (.so/.dylib/.dll).
+    return dir + "/lib/libclangCppInterOp" CMAKE_SHARED_LIBRARY_SUFFIX;
+#else
+    // Non-CMake builds (no suffix defined): default to .so.
+    return dir + "/lib/libclangCppInterOp.so";
+#endif
+}
+
 class ApplicationStarter {
   Cppyy::TInterp_t Interp;
 public:
     ApplicationStarter() {
         std::lock_guard<std::recursive_mutex> Lock(InterOpMutex);
-        if (!Cpp::LoadDispatchAPI(
-                CPPINTEROP_DIR
-                "/lib/libclangCppInterOp" CMAKE_SHARED_LIBRARY_SUFFIX)) {
-            std::cerr << "[cppyy-backend] Failed to load CppInterOp" << std::endl;
+        const std::string lib_path = cppinterop_lib_path();
+        if (lib_path.empty()) {
+            std::cerr << "[cppyy-backend] CppInterOp location unknown: set the"
+                " CPPINTEROP_BIN_DIR environment variable" << std::endl;
+            return;
+        }
+        if (!Cpp::LoadDispatchAPI(lib_path.c_str())) {
+            std::cerr << "[cppyy-backend] Failed to load CppInterOp from "
+                << lib_path << std::endl;
             return;
         }
         // Check if somebody already loaded CppInterOp and created an
@@ -185,7 +220,7 @@ class ApplicationStarter {
         Cpp::AddIncludePath((ClingSrc + "/tools/cling/include").c_str());
         Cpp::AddIncludePath((ClingSrc + "/include").c_str());
         Cpp::AddIncludePath((ClingBuildDir + "/include").c_str());
-        Cpp::AddIncludePath((std::string(CPPINTEROP_DIR) + "/include").c_str());
+        Cpp::AddIncludePath((cppinterop_dir() + "/include").c_str());
         Cpp::LoadLibrary("libstdc++", /* lookup= */ true);
 
         // load frequently used headers