f4f5fc3e5c
Add `Clause::ConstArgHasType` Currently the way that we check that a const arg has the correct type for the const param it is an argument for is by setting the expected type of `typeck` on the anon const of the argument to be the const param's type. In the future for a potential `min_generic_const_exprs` we will allow providing const arguments that do not have an associated anon const that can be typeck'd which will require us to actually check that the const argument has the correct type. While it would potentially be possible to just call `eq` when creating substs this would not work if we support generics of the form `const N: T, T` (the const parameters type referencing generics declared after itself). Additionally having `ConstArgHasType` will allow us to potentially make progress on removing the `ty` field of `Const` which may be desirable. Once progress has been made on this, `ConstArgHasType` will also be helpful in ensuring we do not make mistakes in trait/impl checking by declaring functions with the wrong const parameter types as the checks that the param env is compatible would catch it. (We have messed this up in the past, and with generic const parameter types these checks will get more complex) There is a [document](https://hackmd.io/wuCS6CJBQ9-fWbwaW7nQRw?view) about the types of const generics that may provide some general information on this subject --- This PR shouldn't have any impact on whether code compiles or not on stable, it primarily exists to make progress on unstable const generics features that are desirable. |
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