mgca: Add ConstArg representation for const items #139558
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☔ The latest upstream changes (presumably #141343) made this pull request unmergeable. Please resolve the merge conflicts. |
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@oli-obk I've assigned you to this PR alongside me because I'd definitely want you to review it before it lands since its so CTFE involved 🤔 I don't think it needs reviewing rn though, things are so up in the air and we're not bootstrapping yet :3 |
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Some changes occurred in src/tools/rustfmt cc @rust-lang/rustfmt Some changes occurred in src/tools/clippy cc @rust-lang/clippy Some changes occurred to the CTFE machinery Some changes occurred in compiler/rustc_passes/src/check_attr.rs HIR ty lowering was modified cc @fmease Some changes occurred to constck cc @fee1-dead This PR changes a file inside |
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(rustfmt changes seem to have been accidental and have since been removed) |
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When mgca is enabled, const rhs's that are paths may have false negatives with the lints in non_copy_const.rs. But these should probably be using the trait solver anyway, and it only happens under mgca.
Also removed a test that was literally a duplicate of the one I kept.
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r=me with the oli-review commit |
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tracking issue: #132980
fixes #131046
fixes #134641
As part of implementing
min_generic_const_args, we need to distinguish const items that can be used in the type system, such as in associated const equality projections, from const items containing arbitrary const code, which must be kept out of the type system. Specifically, all "type consts" must be either concrete (no generics) or generic with a trivial expression likeNor a path to another type const item.To syntactically distinguish these cases, we require, for now at least, that users annotate all type consts with the
#[type_const]attribute. Then, we validate that the const's right-hand side is indeed eligible to be a type const and represent it differently in the HIR.We accomplish this representation using a new
ConstItemRhsenum in the HIR, and a similar but simpler enum in the AST. When#[type_const]is not applied to a const (e.g. on stable), we represent const item right-hand sides (rhs's) as HIR bodies, like before. However, when the attribute is applied, we instead lower to ahir::ConstArg. This syntactically distinguishes between trivial const args (paths) and arbitrary expressions, which are represented usingAnonConsts. Then ingenerics_of, we can take advantage of the existing machinery to bar theAnonConstrhs's from using parent generics.