Split pybind11 into headers and cpp files to speedup compilation

As discussed at pybind#2322, the split
is opt-in. If the PYBIND11_HEADER_ONLY is not defined, then the .cpp files
are included in the .h files.

PYBIND11_INLINE is introduced because if the header functions are marked
inline, then that makes the symbol not show in the object file, so inline
must be turned on or off depending on PYBIND11_HEADER_ONLY.

Author: cirosantilli2

CMakeLists.txt

@@ -269,3 +269,12 @@ if(NOT PYBIND11_MASTER_PROJECT)
       "${PYBIND11_INCLUDE_DIR}"
       CACHE INTERNAL "Directory where pybind11 headers are located")
 endif()
+
+find_package (Python3 COMPONENTS Development)
+include_directories(${Python3_INCLUDE_DIRS})
+add_definitions(-DPYBIND11_HEADER_ONLY=1)
+file(GLOB SOURCES ${CMAKE_SOURCE_DIR}/include/pybind11/*.cpp)
+# Produce libpybind11.a, which contains position independent object files.
+# that may be used to create a shared library.
+add_library(pybind11 STATIC ${SOURCES})
+set_property(TARGET pybind11 PROPERTY POSITION_INDEPENDENT_CODE ON)

include/pybind11/attr.h

@@ -119,7 +119,7 @@ enum op_id : int;
 enum op_type : int;
 struct undefined_t;
 template <op_id id, op_type ot, typename L = undefined_t, typename R = undefined_t> struct op_;
-inline void keep_alive_impl(size_t Nurse, size_t Patient, function_call &call, handle ret);
+void keep_alive_impl(size_t Nurse, size_t Patient, function_call &call, handle ret);
 
 /// Internal data structure which holds metadata about a keyword argument
 struct argument_record {

include/pybind11/cast.h

@@ -89,7 +89,7 @@ class loader_life_support {
 // Gets the cache entry for the given type, creating it if necessary.  The return value is the pair
 // returned by emplace, i.e. an iterator for the entry and a bool set to `true` if the entry was
 // just created.
-inline std::pair<decltype(internals::registered_types_py)::iterator, bool> all_type_info_get_cache(PyTypeObject *type);
+std::pair<decltype(internals::registered_types_py)::iterator, bool> all_type_info_get_cache(PyTypeObject *type);
 
 // Populates a just-created cache entry.
 PYBIND11_NOINLINE inline void all_type_info_populate(PyTypeObject *t, std::vector<type_info *> &bases) {
@@ -481,7 +481,7 @@ inline PyThreadState *get_thread_state_unchecked() {
 }
 
 // Forward declarations
-inline void keep_alive_impl(handle nurse, handle patient);
+void keep_alive_impl(handle nurse, handle patient);
 inline PyObject *make_new_instance(PyTypeObject *type);
 
 class type_caster_generic {

include/pybind11/detail/common.h

@@ -83,7 +83,27 @@
 #if defined(_MSC_VER)
 #  define PYBIND11_NOINLINE __declspec(noinline)
 #else
-#  define PYBIND11_NOINLINE __attribute__ ((noinline))
+#  if PYBIND11_HEADER_ONLY
+#    define PYBIND11_NOINLINE __attribute__ ((noinline))
+#  else
+// Otherwise GCC 9 would emit warnings for functions that are marked both
+// inline and noinline if we weren't enabling:
+// #pragma GCC diagnostic ignored "-Wattributes"
+// as is currently done in Pybind11. This way we remove reliance on this
+// disabled warning.
+#    define PYBIND11_NOINLINE
+#  endif
+#endif
+
+// Must be used in every .cpp function definition:
+// - on header-only mode, functions must be marked as inline
+//   to prevent multiple definitions
+// - on non-header-only mode, functions must not be marked as inline
+//   so that the symbols will be visible from other objects
+#if PYBIND11_HEADER_ONLY
+#  define PYBIND11_INLINE
+#else
+#  define PYBIND11_INLINE inline
 #endif
 
 #if defined(PYBIND11_CPP14)

include/pybind11/options.cpp

@@ -0,0 +1,23 @@
+#include "options.h"
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+PYBIND11_INLINE options::options() : previous_state(global_state()) {}
+
+PYBIND11_INLINE options::~options() {
+    global_state() = previous_state;
+}
+
+PYBIND11_INLINE options& options::disable_user_defined_docstrings() & { global_state().show_user_defined_docstrings = false; return *this; }
+
+PYBIND11_INLINE options& options::enable_user_defined_docstrings() & { global_state().show_user_defined_docstrings = true; return *this; }
+
+PYBIND11_INLINE options& options::disable_function_signatures() & { global_state().show_function_signatures = false; return *this; }
+
+PYBIND11_INLINE options& options::enable_function_signatures() & { global_state().show_function_signatures = true; return *this; }
+
+PYBIND11_INLINE bool options::show_user_defined_docstrings() { return global_state().show_user_defined_docstrings; }
+
+PYBIND11_INLINE bool options::show_function_signatures() { return global_state().show_function_signatures; }
+
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

include/pybind11/options.h

@@ -17,32 +17,30 @@ class options {
 public:
 
     // Default RAII constructor, which leaves settings as they currently are.
-    options() : previous_state(global_state()) {}
+    options();
 
     // Class is non-copyable.
     options(const options&) = delete;
     options& operator=(const options&) = delete;
 
     // Destructor, which restores settings that were in effect before.
-    ~options() {
-        global_state() = previous_state;
-    }
+    ~options();
 
     // Setter methods (affect the global state):
 
-    options& disable_user_defined_docstrings() & { global_state().show_user_defined_docstrings = false; return *this; }
+    options& disable_user_defined_docstrings() &;
 
-    options& enable_user_defined_docstrings() & { global_state().show_user_defined_docstrings = true; return *this; }
+    options& enable_user_defined_docstrings() &;
 
-    options& disable_function_signatures() & { global_state().show_function_signatures = false; return *this; }
+    options& disable_function_signatures() &;
 
-    options& enable_function_signatures() & { global_state().show_function_signatures = true; return *this; }
+    options& enable_function_signatures() &;
 
     // Getter methods (return the global state):
 
-    static bool show_user_defined_docstrings() { return global_state().show_user_defined_docstrings; }
+    static bool show_user_defined_docstrings();
 
-    static bool show_function_signatures() { return global_state().show_function_signatures; }
+    static bool show_function_signatures();
 
     // This type is not meant to be allocated on the heap.
     void* operator new(size_t) = delete;
@@ -63,3 +61,7 @@ class options {
 };
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
+
+#if !PYBIND11_HEADER_ONLY
+#include "options.cpp"
+#endif