update internal terminology: Substs -> GenericArgs

[lcnr]

change substitutions to the more familiar name of generic arguments in the compiler.

this work was started in #113591 but there are still some uses of the old terminology left.

How to work on this

grep for remaining uses of subst, substitution and substitute and figure out how to replace them with the new terminology: instantiate and generic argument

cc #110254 @oli-obk

[lcnr]

This does require some familiarity with the compiler as I assume it to be very annoying to rebase in case there are issues with the implementation.

[ghost]

@lcnr can i work on this?

[ghost]

@rustbot claim

[mdibaiee]

@AnakinSkywalkeer are you still working on this? If not I would like to work on this.

[ghost]

@AnakinSkywalkeer are you still working on this? If not I would like to work on this.

sure

[mdibaiee]

@rustbot claim

[lcnr]

there are still quite a few uses of subst, substitution and substitute left, so I am keeping this open for now

[DavidCoy77]

there are still quite a few uses of subst, substitution and substitute left, so I am keeping this open for now

I'm interested in contributing, but I'm new to Rust and GitHub. I've noticed this issue is marked "E-mentor", so if you'd be willing to offer guidance I'd love to help!

Thanks,
David

[ShoyuVanilla]

@rustbot claim

[RalfJung]

I realize it's too late to ask for this now, but... was there ever an MCP for this?
I personally find "substitute" a lot more clear than "instantiate". "instantiate" works when a generic function is instantiated, but once we are inside a generic function, we have a whole bunch of terms and types that reference generic parameters. I seems strange to say that we "instantiate" these terms, I never encountered this use of the term "instantiate" before -- what we do is we substitute the generic parameters for their concrete values.

Not all jargon is bad. Subtle technical concepts need precise terms to describe them.

[lcnr]

I realize it's too late to ask for this now, but... was there ever an MCP for this?

yes-ish

rust-lang/compiler-team#451 which was discussed in https://rust-lang.zulipchat.com/#narrow/stream/233931-xxx/topic/Rename.20various.20internal.20things.20compiler-team.23451

after quite a while @oli-obk then opened #110254 which was discussed in https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/naming.20bikeshedding

I think the situation is unfortunate and looking back it would have likely been better to open separate MCPs for each individual change. Because the original second was a "I agree with most of these changes, idc about the others" and then we never really got official confirmation for any of them, so any actual name changes have been somewhat vibe based :/

[RalfJung]

That MCP suggested subst → replace_generics, which sounds better to me than "instantiate". I guess it was avoided because it was too long?

[lcnr]

https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/naming.20bikeshedding/near/349032402

[RalfJung]

🤷 maybe I'm in the minority here. I teach substitution in class so I'm obviously biased towards finding this a completely natural term to begin with, so I have a fairly high bar for what I consider a good replacement.

[ShoyuVanilla]

Hmm, would it be better to change it into other suitable name? Maybe I just opened PR without sufficient considerations.
TBH I myself prefer more academic terms in codes like substitutions or skolemizations(unrelated here but IIRC it is also renamed in rustc some time ago).
The reason I worked on this is, while reading rust compiler dev guide book to learn about rustc, I saw some naming mismatches between the book and rustc, and thought that this would be a good first issue to work on 😅

[RalfJung]

I'm happy the skolemization term is gone as I was never convinced that this was actually skolemization in the sense it is used in e.g. logic. ;)

[ShoyuVanilla]

I'm happy the skolemization term is gone as I was never convinced that this was actually skolemization in the sense it is used in e.g. logic. ;)

Didn't know that cause I was not using rust that day 😄

[camsteffen]

As a compiler amateur, I also find "substitute" to be more intuitive than "instantiate". My understanding is (correct me if I'm wrong): you take a type representation with generic values and you substitute those generic values with concrete types to produce another type representation. I think the word was helpful for me to build that mental model when digging into rustc.

[RalfJung]

Yes that understanding sounds right.

Also worth mentioning, we have a type called Instance in rustc that shows up quite a bit. However, the new usage of "instantiate" is unrelated to that -- we're now instantiating types and MIR statements and whatnot, without there being an Instance in these cases. "Instance" refers to the specific case of instantiating a generic function, not an arbitrary generic thing.