This PR completes [RFC 213](https://github.com/rust-lang/rfcs/blob/master/text/0213-defaulted-type-params.md) by allowing default type parameters to influence inference. This is almost certainly a breaking change due to interactions between default type parameters and the old fallback algorithm used for integral and floating point literals.
The error messages still require polish but I wanted to get early review and feedback from others on the the changes, error messages, and test cases. I also imagine we will want to run anywhere from 1-3 versions of this on crater and evaluate the impact, and it would be best to get that ball rolling.
The only outstanding issue I'm aware of is that type alias defaults don't work. It seems this may require significant restructuring, since during inference type aliases have already been expanded. @nikomatsakis might be able to provide some clarity here.
r? @nikomatsakis
cc @eddyb @Gankro @aturon @brson
The algorithm was not correctly detecting conflicts after moving
defaults into TypeVariableValue. The updated algorithm
correctly detects and reports conflicts with information about
where the conflict occured and which items the defaults were
introduced by. The span's for said items are not being correctly
attached and still need to be patched.
This patch allows type parameter defaults to influence type inference. This is a possible breaking change since it effects the way type inference works and will have different behavior when mixing defaults and literal fallback.
Correct regression in type-inference caused by failing to reconfirm that
the object trait matches the required trait during trait selection. The
existing code was checking that the object trait WOULD match (in a
probe), but never executing the match outside of a probe.
This corrects various regressions observed in the wild, including
issue #26952. Fixes#26952.
r? @eddyb
cc @frankmcsherry
***Edit: Fixed now.*** I'm pretty sure the way I'm using LLVMReplaceAllUsesWith here is
unsafe... but before I figure out how to fix that, I'd like a
reality-check: is this actually useful?
This introduces a test for #23389 and improves the error behaviour to treat the malformed LHS as an error, not a compiler bug.
The parse phase that precedes the call to `check_lhs_nt_follows` could possibly be enhanced to police the format itself (which the old code suggests was the original intention), but I'm not sure that's any nicer than just parsing the matcher as generic rust code and then policing the specific requirements for being a macro matcher afterwards (as this does).
Fixes#23389
The borrow checker doesn't allow constructing such a type at runtime
using safe code, but there isn't any reason to ban them in the type checker.
Included in this commit is an example of a neat static doubly-linked list.
Feature-gated under the static_recursion gate to be on the safe side, but
there are unlikely to be any reasons this shouldn't be turned on by
default.
I'll be adding more commits to this PR as the weekend progresses. Was hoping to make this a mega-PR, but getting some eyes on this early would be nice too.
r? @steveklabnik
r? @eddyb on the object safety bits
cc @michaelsproul
Part of #24407
Hi all.
This is my first contribution to Rust and fixes an issue causing an invalid error message to be presented to the user when using unit struct as length of a repeat expression, issue #27008. The solution is based on suggestions by @oli-obk, but as I'm a complete newbie to this, I have no clue if I got them right :)
The biggest concern I have is that if the `NodeId` I'm returning is the correct one or not (it's not meaningful in this case but I think it would be nice to get it right).
As title!
I should probably be bunching these up a bit more, but I'm not sure when my time is going to disappear on me. Once my schedule stabilises I'll try to start batching them into larger PRs.
Part of #24407.
r? @Manishearth
Was browsing somebody else's code and came across a snippet using labels. Looking around, it seems like there was an example for this in [rustbyexample](http://rustbyexample.com/flow_control/loop/nested.html) but none in trpl.
Refactors the "desugaring" of closures to expose the types of the upvars. This is necessary to be faithful with how actual structs work. The reasoning of the particular desugaring that I chose is explained in a fairly detailed comment.
As a side-effect, recursive closure types are prohibited unless a trait object intermediary is used. This fixes#25954 and also eliminates concerns about unrepresentable closure types that have infinite size, I believe. I don't believe this can cause regressions because of #25954.
(As for motivation, besides #25954 etc, this work is also intended as refactoring in support of incremental compilation, since closures are one of the thornier cases encountered when attempting to split node-ids into item-ids and within-item-ids. The goal is to eliminate the "internal def-id" distinction in astdecoding. However, I have to do more work on trans to really make progress there.)
r? @nrc
