bug: Go 1.22 alternates naming of anonymous functions

[ivokub]

Description

For tracking which hints to be used we construct function name and hash it to get a short identifier for the function. However, for anonymous functions var func = func( ...) the naming convention changed from github.com/consensys/gnark/std/...pkg..glob.func1 to github.com/consensys/gnark/std/...pkg.init.func1. As the hint IDs are also embedded inside the compiled circuits then this means that the solver may not resolve the hint implementation.

This issue tracks the process and to let the users know of the potential bugs.

We already have implemented PR #1043 to not use anonymous function as hints. But I guess for more safer approach we could add a rewrite in gnark to rewrite .init.funcN to ..glob.funcN.

[gbotrel]

@ivokub can you do a quick PR with

.init.funcN to ..glob.funcN

? And a non regression test; don't want to hit the same issue in another deployment.
--> I'm not sure #1043 isn't dangerous; it means circuits compiled before #1043 are not compatible with a process compiled post #1043 right ?

[ivokub]

@ivokub can you do a quick PR with

.init.funcN to ..glob.funcN

? And a non regression test; don't want to hit the same issue in another deployment. --> I'm not sure #1043 isn't dangerous; it means circuits compiled before #1043 are not compatible with a process compiled post #1043 right ?

Indeed #1043 breaks compatibility between pre- and post 1043 circuits. So if we have a circuit compiled pre-1043, then solver/prover post-1043 fails as the hints are not found.

But still, I think 1043 is better for long-term as ensures more consistency. Instead of reverting I think it would better to add explicit hint overrides (for both Go <1.22 and =1.22 naming convention) to keep the backwards compatibility. I'd be happy to do it if makes sense.

[gbotrel]

Mmhhh no for the hint overhide, I think it's dirty ^^.
For Linea we can just recompile the circuits -- if that's the only change and the actual constraints are unchanged it's not a big issue.

[ivokub]

Yup, didn't change the constraints. Only changed hints defined as

var Hint = func(mod *big.Int, inputs []*big.Int, outputs []*big.Int) error {
//
}

to

func Hint(mod *big.Int, inputs []*big.Int, outputs []*big.Int) error {
//
}

in std/algebra packages.

[ivokub]

So to summarize - I'll only add the rewrite from "new-style anonymous functions" to old-style and a regression test which ensures that GetHintName is static for both anonymous and explicit function.