breaking,checker: disallow initializing private struct fields outside structs module

[ttytm]

Currently, it's possible to init a struct and assign values to it's private fields. Only accessing fields directly will trigger an error.

Currently following is possible

import amod

b := amod.Bcg{ // public struct
	x: 3 // private field
}

After the changes an error will be visible on initialization (ref. to added test:struct_field_private_err.out). Eventually the change should allow for better accessibility control and improved security.

[ttytm]

Some of the remaining errors might require discussion as not all fields of them might be meant for a pub mut. Gonna make a list of the ones in question.

[ttytm]

imho the handle should eventually not be publicly mutable. But to not introduce a big breaking change for how TcpConn structs are currently created, having it pub mut is likely the only way.

[ttytm]

@spytheman you have push access to https://github.com/elliotchance/vsql? If not maybe it's okay to comment it's CI step out for now as the developer is not active for the last months.

The only left failing in the V codebase is the parser.Parser fields related to cmd/tools/measure/fmt_speed.v. I'm not sure about accessibility changes to those fields.
Update: I've set the interfering to public for now.

[spytheman]

Excellent work.

[spytheman]

@spytheman you have push access to https://github.com/elliotchance/vsql? If not maybe it's okay to comment it's CI step out for now as the developer is not active for the last months.

I do not, but @elliotchance is on Discord, so I think we can coordinate a change with a PR.

I do not want to disable the CI for it on the main repo, if we can avoid it, since it is a very substantial code base, and it has caught V bugs/regressions before.

[JalonSolov]

I have a question about this PR... how am I supposed to initialize a private field in a struct from another module, if I can't do it at instantiation time?

With this change in place, every module that has a struct with a private field will now have to supply a new or create or whatever method for that struct, in order to initialize those fields.

Either that or some sort of setter method just for those fields.

[ttytm]

Private struct fields are usually not not meant to be initialised from other modules.
For the cases where a private struct field should be initialised a factory function like it is with @[noinit] will be required.

[ttytm]

I temporary added a fork of external V apps to the CI.

The only one remaining (with more restrictive merge access) is the PR at gitly.

[spytheman]

The gitly and the ui failures are now fixed too.

I think it is good to go.