webrpc-gen fails to load templates with unknown template function(s)

[VojtechVitek]

failed to load templates from ../webrpc/gen-golang: template: struct.go.tmpl:23: function "trimPrefix" not defined

I thought we'd be able to require specific Template Functions API from within the templates & that's why we have introduced minVersion .WebrpcGenVersion "v0.7.0" function. However, it looks like Go templates look up all the functions up-front and fail early before even executing the template (no matter if the missing function would be executed or not).

We'll need to support this in some other way, so we have better & user-friendly errors.

[VojtechVitek]

I think we could experiment with multiple template entrypoints:

• "main" for the code-generation
• "help" for printing help
• "version" for printing minimal required webrpc-gen version
• "schema" for printing required webrpc schema (v1 / v2 /...)

Instead of getting this generic error template: struct.go.tmpl:23: function "trimPrefix" not defined, I'd expect webrpc-gen to print something like

• -target=golang@v0.8.0 requires v2 schema; please update your schema file
• or -target=golang@v0.8.0 requires at least webrpc-gen v0.8.0+, please update webprc-gen

[pkieltyka]

Yes makes sense