Improve support for external shader editors

[tavurth]

Describe the project you are working on

A water depth & velocity simulation shader in 2D (from above).

Describe the problem or limitation you are having in your project

I've run into many issues while dealing with Godot's shader language, and I wanted to start this post as part of my documentation of such. When dealing with the current shader implementation I feel like my hands are tied many times, which leads me to believe that the current shader implementation keeps Godot far behind other engines.

Inconsistent support for external editors

I'm primarily an Emacs user. Whenever I edit a shader file outside of Godot and I run the project, it exits with an impossible to debug C++ error. However when editing with the internal editor I have a line number error, which I can click to see the error.

This is frustrating, as Godot will never get me to switch from my primary editor, and so the inconclusive and confusing errors are a major barrier to entry.

### Describe the feature / enhancement and how it helps to overcome the problem or limitation See above

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

See above

If this enhancement will not be used often, can it be worked around with a few lines of script?

This enhancement will affect anyone who has more than a passing interest in shaders.

Is there a reason why this should be core and not an add-on in the asset library?

Shader language improvements must be core.

[Calinou]

This sounds like a bug rather than a feature request, but as far as I know, external editor support was never officially implemented for shaders.

[tavurth]

Ok I will post in the main repo after some time. I will finish up your comments on these posts first 👍

[Calinou]

Closing in favor of #1466.