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Represent type-level consts with new-and-improved `hir::ConstArg` ### Summary This is a step toward `min_generic_const_exprs`. We now represent all const generic arguments using an enum that differentiates between const *paths* (temporarily just bare const params) and arbitrary anon consts that may perform computations. This will enable us to cleanly implement the `min_generic_const_args` plan of allowing the use of generics in paths used as const args, while disallowing their use in arbitrary anon consts. Here is a summary of the salient aspects of this change: - Add `current_def_id_parent` to `LoweringContext` This is needed to track anon const parents properly once we implement `ConstArgKind::Path` (which requires moving anon const def-creation outside of `DefCollector`). - Create `hir::ConstArgKind` enum with `Path` and `Anon` variants. Use it in the existing `hir::ConstArg` struct, replacing the previous `hir::AnonConst` field. - Use `ConstArg` for all instances of const args. Specifically, use it instead of `AnonConst` for assoc item constraints, array lengths, and const param defaults. - Some `ast::AnonConst`s now have their `DefId`s created in rustc_ast_lowering rather than `DefCollector`. This is because in some cases they will end up becoming a `ConstArgKind::Path` instead, which has no `DefId`. We have to solve this in a hacky way where we guess whether the `AnonConst` could end up as a path const since we can't know for sure until after name resolution (`N` could refer to a free const or a nullary struct). If it has no chance as being a const param, then we create a `DefId` in `DefCollector` -- otherwise we decide during ast_lowering. This will have to be updated once all path consts use `ConstArgKind::Path`. - We explicitly use `ConstArgHasType` for array lengths, rather than implicitly relying on anon const type feeding -- this is due to the addition of `ConstArgKind::Path`. - Some tests have their outputs changed, but the changes are for the most part minor (including removing duplicate or almost-duplicate errors). One test now ICEs, but it is for an incomplete, unstable feature and is now tracked at https://github.com/rust-lang/rust/issues/127009. ### Followup items post-merge - Use `ConstArgKind::Path` for all const paths, not just const params. - Fix (no github dont close this issue) #127009 - If a path in generic args doesn't resolve as a type, try to resolve as a const instead (do this in rustc_resolve). Then remove the special-casing from `rustc_ast_lowering`, so that all params will automatically be lowered as `ConstArgKind::Path`. - (?) Consider making `const_evaluatable_unchecked` a hard error, or at least trying it in crater r? `@BoxyUwU` |
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| impl-trait | ||
| rfc-0000-never_patterns | ||
| rfc-0107-bind-by-move-pattern-guards | ||
| rfc-1014-stdout-existential-crisis | ||
| rfc-1445-restrict-constants-in-patterns | ||
| rfc-1623-static | ||
| rfc-1717-dllimport | ||
| rfc-1789-as-cell | ||
| rfc-1857-stabilize-drop-order | ||
| rfc-1937-termination-trait | ||
| rfc-2005-default-binding-mode | ||
| rfc-2008-non-exhaustive | ||
| rfc-2027-object-safe-for-dispatch | ||
| rfc-2091-track-caller | ||
| rfc-2093-infer-outlives | ||
| rfc-2126-crate-paths | ||
| rfc-2126-extern-absolute-paths | ||
| rfc-2151-raw-identifiers | ||
| rfc-2175-or-if-while-let | ||
| rfc-2294-if-let-guard | ||
| rfc-2302-self-struct-ctor | ||
| rfc-2306-convert-id | ||
| rfc-2361-dbg-macro | ||
| rfc-2396-target_feature-11 | ||
| rfc-2421-unreserve-pure-offsetof-sizeof-alignof | ||
| rfc-2457-non-ascii-idents | ||
| rfc-2497-if-let-chains | ||
| rfc-2528-type-changing-struct-update | ||
| rfc-2565-param-attrs | ||
| rfc-2627-raw-dylib | ||
| rfc-2632-const-trait-impl | ||
| rfc-3348-c-string-literals | ||
| type-alias-impl-trait | ||