[WIP] Versioning, back-porting, version-detection & forward/backward compatibility

[follower]

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TL;DW:

It would be useful/nice to have:

• A godot-cpp-specific version #define or similar that could be used to conditionally include different code when building with different branches, especially in situations like Ref<> where workarounds that were required in earlier versions cause crashes in later versions. (See: [WIP] Summarise current feature state (especially Ref) vs app/branch versions #417)

• Significant godot-cpp fixes (like the Ref<> one above) back-ported from 3.2 to 3.1 so that in many cases one code-base can support both Godot 3.1 & 3.2. (Or, prioritize 3.1 and forward-port to 3.2.)

Update: It seems like the Ref<> issue is compatible with earlier versions also.

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• Versioning, back-porting, version-detection & forward/backward compatibility

• Back-porting to branches of godot-cpp specific fixes/improvements.

• Compile-time version detection

• Run-time version detection

Maybe in:

• https://github.com/godotengine/godot-cpp/blob/master/include/core/Godot.hpp
• https://github.com/godotengine/godot-cpp/blob/master/include/core/GodotGlobal.hpp
• https://github.com/godotengine/godot-cpp/blob/master/include/core/Defs.hpp

Related:

• Tag specific commits for each Godot stable version godot-headers#53
• Provide tag for 3.2 and 3.2.1 godot-headers#70
• [GDNative] Rethink the backward compatibily for Godot classes & ptrcall godot#35464
• Before loading any of the API structs, look for version "1.3" and abort if found godot-rust/gdnative#396
• GDNative: merge API structs, bump version of merged structs. godot#39183
• GDNative: Add bindings for the Packed*Array ptr() and ptrw() functions. godot#39064
• Bringing the 3.2 branch in line with Godot 3.2 godot-headers#74
• godotengine/godot-headers@f212219
• The size of godot_variant seems wrong on 32bit builds godot-headers#72

[WIP]

[Calinou]

See also godotengine/godot-docs#5744. We are discussing what to do for the 3.x branch and whether it's worth trying to support multiple minor versions with a single compiled add-on, but it doesn't seem to be feasible or worth it.