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Make InferCtxt::can_eq and InferCtxt::can_sub return booleans#108010

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compiler-errors:can_eq-returns-bool
Feb 16, 2023
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Make InferCtxt::can_eq and InferCtxt::can_sub return booleans#108010
bors merged 1 commit intorust-lang:masterfrom
compiler-errors:can_eq-returns-bool

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@compiler-errors compiler-errors commented Feb 13, 2023

Nobody matches on the result, nor does the result return anything useful...

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rustbot commented Feb 13, 2023

r? @lcnr

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 13, 2023
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compiler-errors commented Feb 13, 2023 •
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After #107940 lands, this these functions should additionally use TyCtxt::check_tys_might_be_eq when the new solver is enabled, to check for deep type equality with lazy norm... but I'll leave that up to another PR.

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BoxyUwU commented Feb 13, 2023

I feel like if !self.infcx.can_eq(a, b) { is less clear than if self.infcx.can_eq(a, b).is_err(). Could we just make the return type Result<(), ()>. if we start handling nested obligations we wont be able to always return a TypeError anyway so getting rid of it would have to happen

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compiler-errors commented Feb 13, 2023

The answer to a "can" question being a boolean makes pretty good sense to me, and !self.can_do_thing() is pretty clearly "can't do thing".

We also have FnCtxt::can_coerce which has a handful of !self.can_coerce calls around the codebase already.

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lcnr commented Feb 14, 2023 •
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Ignoring for a moment that can_eq is kinda bad as a whole because it ignores nested obligations causing stuff like lazy norm to end up changing behavior I am in favor of this change.

Definitely in favor of yeeting TypeError from can_eq because I can't think of a case where you should use that TypeError to actually do anything 😅

wrt TyCtxt::check_tys_might_be_eq and lazy norm I don't yet have an opinion. I slightly prefer returning bool over result here.

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lcnr commented Feb 15, 2023

@bors r+

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bors commented Feb 15, 2023

📌 Commit eb286dd has been approved by lcnr

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 15, 2023
@matthiaskrgr matthiaskrgr mentioned this pull request Feb 15, 2023
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bors added a commit to rust-lang-ci/rust that referenced this pull request Feb 16, 2023
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Auto merge of rust-lang#108096 - matthiaskrgr:rollup-ncexzf6, r=matth…
dc7a676 
…iaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#107034 (Migrating rustc_infer to session diagnostics (part 4))
 - rust-lang#107972 (Fix unintentional UB in ui tests)
 - rust-lang#108010 (Make `InferCtxt::can_eq` and `InferCtxt::can_sub` return booleans)
 - rust-lang#108021 (make x look for x.py if shell script does not exist)
 - rust-lang#108047 (Use `target` instead of `machine` for mir interpreter integer handling.)
 - rust-lang#108049 (Don't suggest `#[doc(hidden)]` trait methods with matching return type)
 - rust-lang#108066 (Better names for illegal impl trait positions)
 - rust-lang#108076 (rustdoc: Use more let chain)
 - rust-lang#108088 (clarify correctness of `black_box`)
 - rust-lang#108094 (Demonstrate I/O in File examples)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 8f65e25 into rust-lang:master Feb 16, 2023
@rustbot rustbot added this to the 1.69.0 milestone Feb 16, 2023
@compiler-errors compiler-errors deleted the can_eq-returns-bool branch August 11, 2023 19:56
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