WARNING: Hacks everywhere!
The logic in `main.cpp` is due a full rewrite as it's extremely hacky,
splitting argument parsing over several functions, with a mess of global state
and assumptions about what combinations of arguments or lack thereof should
mean in terms of what we want to read: game, editor, project manager, or
command line tools such as `--doctool`, `--export` or `--script`.
Until this is fully rewritten, this patch hacks things some more to ensure
that we don't fall back to the project manager in cases where it's not
warranted, and especially not *too late*, as it can mean that we haven't
properly initialized stuff like `EditorPaths` needed by the PM (which in turn
impacts what kind of path will be used for logs and the shader cache, etc...
the rabbit hole goes deep).
Fixes#41435.
Fixes#49392.
Fixes#49658.
Fixes https://github.com/godotengine/godot/issues/38202#issuecomment-773158477.
- EditorSettings: Ensure that `create()` makes a valid singleton.
Fixes#49179, fixes#49450.
- EditorPaths: Cleanup code, properly set `paths_valid`.
- EditorPaths: Move more paths validation (check, mkdir) from
EditorSettings for a better separation of concerns.
- EditorPaths: Move EditorFileSystem creation of `.godot/imported`
next to other paths.
* Shader compilation is now cached. Subsequent loads take less than a millisecond.
* Improved game, editor and project manager startup time.
* Editor uses .godot/shader_cache to store shaders.
* Game uses user://shader_cache
* Project manager uses $config_dir/shader_cache
* Options to tweak shader caching in project settings.
* Editor path configuration moved from EditorSettings to new class, EditorPaths, so it can be available early on (before shaders are compiled).
* Reworked ShaderCompilerRD to ensure deterministic shader code creation (else shader may change and cache will be invalidated).
* Added shader compression with SMOLV: https://github.com/aras-p/smol-v
