Use decltype to deduce return type of PyThread_create_key

CMakeLists.txt

@@ -81,7 +81,7 @@ if(MSVC)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4")
   endif()
 elseif ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" OR "${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wconversion")
 endif()
 
 

example/example10.cpp

@@ -13,7 +13,7 @@
 
 double my_func(int x, float y, double z) {
     std::cout << "my_func(x:int=" << x << ", y:float=" << y << ", z:float=" << z << ")" << std::endl;
-    return x*y*z;
+    return (float) x*y*z;
 }
 
 std::complex<double> my_func3(std::complex<double> c) {

example/example4.cpp

@@ -38,7 +38,7 @@ void test_function2(EMyEnumeration k) {
 
 float test_function3(int i) {
     std::cout << "test_function(" << i << ")" << std::endl;
-    return i / 2.f;
+    return (float) i / 2.f;
 }
 
 py::bytes return_bytes() {

include/pybind11/common.h

@@ -262,7 +262,7 @@ struct internals {
     std::unordered_map<const void *, void*> registered_instances;    // void * -> PyObject*
     std::unordered_set<std::pair<const PyObject *, const char *>, overload_hash> inactive_overload_cache;
 #if defined(WITH_THREAD)
-    long tstate = 0;
+    decltype(PyThread_create_key()) tstate = 0; // Usually an int but a long on Cygwin64 with Python 3.x
     PyInterpreterState *istate = nullptr;
 #endif
 };

include/pybind11/pybind11.h

@@ -1115,7 +1115,7 @@ public:
     gil_scoped_release(bool disassoc = false) : disassoc(disassoc) {
         tstate = PyEval_SaveThread();
         if (disassoc) {
-            int key = detail::get_internals().tstate;
+            auto key = detail::get_internals().tstate;
             #if PY_MAJOR_VERSION < 3
                 PyThread_delete_key_value(key);
             #else
@@ -1128,7 +1128,7 @@ public:
             return;
         PyEval_RestoreThread(tstate);
         if (disassoc) {
-            int key = detail::get_internals().tstate;
+            auto key = detail::get_internals().tstate;
             #if PY_MAJOR_VERSION < 3
                 PyThread_delete_key_value(key);
             #endif