godot-cpp SConstruct cpp/linker visibility flags should be default 'hidden' + dynlib

[jpedrick]

Your Godot version:
N/A issue is with current tutorial

godot-cpp % git show
commit feaba551b5a5b2d13ad1c3fdd8c90e67c67ff37c (HEAD -> master, origin/master, origin/HEAD)
Merge: e9942db 517db66
Author: Rémi Verschelde <rverschelde@gmail.com>
Date:   Tue Apr 4 11:30:08 2023 +0200

    Merge pull request #1045 from zhehangd/fix_ref_crash
    
    Fix crash using Ref<T> as parameter

Issue description:

The library should have everything except the entry_symbol hidden. See Apple's guidelines: https://developer.apple.com/library/archive/documentation/DeveloperTools/Conceptual/DynamicLibraries/100-Articles/DynamicLibraryDesignGuidelines.html

This became an issue for me while working on a fix for godotengine/godot#66231 , as the library reload would immediately cause a crash. After setting the visibility, the library could load, though it seems there is still much work to be done for dynamic reloading of dynamic gdextension libraries within godot itself.

This can be fixed in a platform independent way by default in godot-cpp/SConstruct, since that is used to initialize env

On my build I view the exported symbols: nm -gm demo/bin/libgdexample.macos.editor.framework/libgdexample.macos.editor

provided SConstruct:

#!/usr/bin/env python
import os
import sys

env = SConscript("godot-cpp/SConstruct")

# For reference:
# - CCFLAGS are compilation flags shared between C and C++
# - CFLAGS are for C-specific compilation flags
# - CXXFLAGS are for C++-specific compilation flags
# - CPPFLAGS are for pre-processor flags
# - CPPDEFINES are for pre-processor defines
# - LINKFLAGS are for linking flags

# tweak this if you want to use different folders, or more folders, to store your source code in.
env.Append(CPPPATH=["src/"])
sources = Glob("src/*.cpp")

if env["platform"] == "macos":
    library = env.SharedLibrary(
        "demo/bin/libgdexample.{}.{}.framework/libgdexample.{}.{}".format(
            env["platform"], env["target"], env["platform"], env["target"]
        ),
        source=sources,
    )
else:
    library = env.SharedLibrary(
        "demo/bin/libgdexample{}{}".format(env["suffix"], env["SHLIBSUFFIX"]),
        source=sources,
    )

Default(library)

Good Sconstruct(macos+clang):

#!/usr/bin/env python
import os
import sys

env = SConscript("godot-cpp/SConstruct")

# For reference:
# - CCFLAGS are compilation flags shared between C and C++
# - CFLAGS are for C-specific compilation flags
# - CXXFLAGS are for C++-specific compilation flags
# - CPPFLAGS are for pre-processor flags
# - CPPDEFINES are for pre-processor defines
# - LINKFLAGS are for linking flags

# tweak this if you want to use different folders, or more folders, to store your source code in.
env.Append(CPPPATH=["src/"])
env.Append(CXXFLAGS=["-fvisibility=hidden"])
env.Append(LINKFLAGS=["-dynamiclib","-fvisibility=hidden"])

sources = Glob("src/*.cpp")

if env["platform"] == "macos":
    library = env.SharedLibrary(
        "demo/bin/libgdexample.{}.{}.framework/libgdexample.{}.{}".format(
            env["platform"], env["target"], env["platform"], env["target"]
        ),
        source=sources,
    )
else:
    library = env.SharedLibrary(
        "demo/bin/libgdexample{}{}".format(env["suffix"], env["SHLIBSUFFIX"]),
        source=sources,
    )

Default(library)

URL to the documentation page:

https://docs.godotengine.org/en/stable/tutorials/scripting/gdextension/gdextension_cpp_example.html