Stabilize inline `const {}` expressions.

• New section: Const Blocks

Prevent opaque types being instantiated twice with different regions within the same function.

• No change: already described in 4.12.2:51

Stabilize WebAssembly target features that are in phase 4 and 5.

• No change: cfg and cfg_attr configuration predicates are not part of the FLS

Add the `redundant_lifetimes` lint to detect lifetimes which are semantically redundant.

• No change: lints are not part of the FLS

Stabilize the `unnameable_types` lint for public types that can’t be named.

• No change: lints are not part of the FLS

Enable debuginfo in macros, and stabilize `-C collapse-macro-debuginfo` and `#[collapse_debuginfo]`.

• New section: Attribute collapse_debuginfo

Propagate temporary lifetime extension into `if` and `match` expressions.

• New paragraphs: 15.8.1:9, 15.8.1:10, 15.8.1:11

Restrict promotion of `const fn` calls.

• No change: already described in 7.4.1:6

Warn against refining impls of crate-private traits with `refining_impl_trait` lint.

• No change: lints are not part of the FLS

Stabilize associated type bounds (RFC 2289).

• New paragraph: 12.3:5

Stabilize importing `main` from other modules or crates.

• No change: this lifted restriction was not previously described in the FLS

• While updating the FLS to account for this feature, we realized that the way the FLS described crate types was incorrect. We rectified this:

  • New section: Program Entry Point

  • New glossary entry: crate type

  • New paragraphs: 18.3:2, 18.3:3, 18.3:4, 18.3:6

  • Updated glossary entries: binary crate, library crate, proc-macro crate

  • Updated paragraphs: 18.3:5, 18.3:9, 18.3:8

  • Moved paragraph: 18.7:2

Check return types of function types for well-formedness

• No change: the exact trait resolution implementation is not part of the FLS

Rework `impl Trait` lifetime inference

• New paragraphs: 4.8.1:3, 4.8.1:4, 4.8.1:5

Change inductive trait solver cycles to be ambiguous

• No change: the exact trait solver is not part of the FLS

Stabilize `#[cfg(target_abi = …)]`

• No change: cfg and cfg_attr configuration predicates are not part of the FLS

Stabilize the `#[diagnostic]` namespace and `#[diagnostic::on_unimplemented]` attribute

• No change: tool attributes are not part of the FLS

Make async-fn-in-trait implementable with concrete signatures

• No change: no paragraph in the FLS forbids this prior incompatability

Make matching on NaN a hard error, and remove the rest of `illegal_floating_point_literal_pattern`

• New paragraph: 5.1.2:3

static mut: allow mutable reference to arbitrary types, not just slices and arrays

• No change: this lifted restriction was not previously described in the FLS

Extend `invalid_reference_casting` to include references casting to bigger memory layout

• No change: lints are not part of the FLS

Add `non_contiguous_range_endpoints` lint for singleton gaps after exclusive ranges

• No change: lints are not part of the FLS

Add `wasm_c_abi` lint for use of older wasm-bindgen versions

• No change: lints are not part of the FLS

Update `indirect_structural_match` and `pointer_structural_match` lints to match RFC

• No change: lints are not part of the FLS

Make non-`PartialEq`-typed consts as patterns a hard error

• No change: already described in 5.1.4:4

Split `refining_impl_trait` lint into `_reachable`, `_internal` variants

• No change: lints are not part of the FLS

Remove unnecessary type inference when using associated types inside of higher ranked `where`-bounds

• No change: the FLS does not specify type inference to such a degree

Weaken eager detection of cyclic types during type inference

• No change: the FLS does not specify type inference to such a degree

`trait Trait: Auto {}`: allow upcasting from `dyn Trait` to `dyn Trait + Auto`

• New paragraph: 4.12.3:29

Reveal opaque types within the defining body for exhaustiveness checking.

• No change: the FLS does not specify introspection of the concrete type of the match expression scrutinee to such a degree

Stabilize C-string literals.

• New section: C String Literals

Stabilize THIR unsafeck.

• No change: not a language change

Add lint `static_mut_refs` to warn on references to mutable statics.

• No change: lints are not part of the FLS

Support async recursive calls (as long as they have indirection).

• No change: this lifted restriction was not previously described in the FLS

Undeprecate lint `unstable_features` and make use of it in the compiler.

• No change: lints are not part of the FLS

Make inductive cycles in coherence ambiguous always.

• No change: the FLS does not describe the trait solver to such a degree

Get rid of type-driven traversal in const-eval interning, only as a future compatibility lint for now.

• No change: this lifted restriction was not previously described in the FLS

Deny braced macro invocations in let-else.

• New paragraph: 8.1:4