remove feature(never_type_fallback)

Author: WaffleLapkin

compiler/rustc_feature/src/removed.rs

@@ -189,6 +189,8 @@ declare_features! (
      Some("subsumed by `#![feature(allocator_internals)]`")),
     /// Allows use of unary negate on unsigned integers, e.g., -e for e: u8
     (removed, negate_unsigned, "1.0.0", Some(29645), None),
+    /// Allows diverging expressions to fall back to `!` rather than `()`.
+    (removed, never_type_fallback, "CURRENT_RUSTC_VERSION", Some(65992), Some("removed in favor of unconditional fallback"), 148871),
     /// Allows `#[no_coverage]` on functions.
     /// The feature was renamed to `coverage_attribute` and the attribute to `#[coverage(on|off)]`
     (removed, no_coverage, "1.74.0", Some(84605), Some("renamed to `coverage_attribute`"), 114656),

compiler/rustc_feature/src/unstable.rs

@@ -596,8 +596,6 @@ declare_features! (
     (incomplete, never_patterns, "1.76.0", Some(118155)),
     /// Allows the `!` type. Does not imply 'exhaustive_patterns' (below) any more.
     (unstable, never_type, "1.13.0", Some(35121)),
-    /// Allows diverging expressions to fall back to `!` rather than `()`.
-    (unstable, never_type_fallback, "1.41.0", Some(65992)),
     /// Switch `..` syntax to use the new (`Copy + IntoIterator`) range types.
     (unstable, new_range, "1.86.0", Some(123741)),
     /// Allows `#![no_core]`.

compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs

@@ -265,7 +265,7 @@ pub(super) fn find_opaque_ty_constraints_for_rpit<'tcx>(
                 // so we can just make the hidden type be `!`.
                 // For backwards compatibility reasons, we fall back to
                 // `()` until we the diverging default is changed.
-                EarlyBinder::bind(Ty::new_diverging_default(tcx))
+                EarlyBinder::bind(tcx.types.unit)
             }
         }
         DefiningScopeKind::MirBorrowck => match tcx.mir_borrowck(owner_def_id) {

compiler/rustc_middle/src/ty/sty.rs

@@ -878,11 +878,6 @@ impl<'tcx> Ty<'tcx> {
         Ty::new_imm_ref(tcx, tcx.lifetimes.re_static, tcx.types.str_)
     }
 
-    #[inline]
-    pub fn new_diverging_default(tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
-        if tcx.features().never_type_fallback() { tcx.types.never } else { tcx.types.unit }
-    }
-
     // lang and diagnostic tys
 
     fn new_generic_adt(tcx: TyCtxt<'tcx>, wrapper_def_id: DefId, ty_param: Ty<'tcx>) -> Ty<'tcx> {

tests/ui/binding/empty-types-in-patterns.rs

@@ -1,6 +1,7 @@
 //@ run-pass
+//@ edition: 2024
 
-#![feature(never_type, never_type_fallback)]
+#![feature(never_type)]
 #![feature(exhaustive_patterns)]
 
 #![allow(unreachable_patterns)]

tests/ui/coercion/coerce-issue-49593-box-never.nofallback.stderr

@@ -1,13 +1,13 @@
 error[E0277]: the trait bound `(): std::error::Error` is not satisfied
-  --> $DIR/coerce-issue-49593-box-never.rs:18:5
+  --> $DIR/coerce-issue-49593-box-never.rs:17:5
    |
 LL |     Box::<_ /* ! */>::new(x)
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
    |
    = note: required for the cast from `Box<()>` to `Box<(dyn std::error::Error + 'static)>`
 
 error[E0277]: the trait bound `(): std::error::Error` is not satisfied
-  --> $DIR/coerce-issue-49593-box-never.rs:24:5
+  --> $DIR/coerce-issue-49593-box-never.rs:23:5
    |
 LL |     raw_ptr_box::<_ /* ! */>(x)
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`

tests/ui/coercion/coerce-issue-49593-box-never.rs

@@ -1,9 +1,8 @@
 //@ revisions: nofallback fallback
+//@[fallback] edition: 2024
 //@[fallback] check-pass
 
 #![feature(never_type)]
-#![cfg_attr(fallback, feature(never_type_fallback))]
-#![allow(unreachable_code)]
 
 use std::error::Error;
 use std::mem;

tests/ui/never_type/defaulted-never-note.fallback.stderr

@@ -1,20 +1,20 @@
 error[E0277]: the trait bound `!: ImplementedForUnitButNotNever` is not satisfied
-  --> $DIR/defaulted-never-note.rs:31:9
+  --> $DIR/defaulted-never-note.rs:27:9
    |
 LL |     foo(_x);
    |     --- ^^ the trait `ImplementedForUnitButNotNever` is not implemented for `!`
    |     |
    |     required by a bound introduced by this call
    |
 help: the trait `ImplementedForUnitButNotNever` is implemented for `()`
-  --> $DIR/defaulted-never-note.rs:24:1
+  --> $DIR/defaulted-never-note.rs:20:1
    |
 LL | impl ImplementedForUnitButNotNever for () {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error might have been caused by changes to Rust's type-inference algorithm (see issue #48950 <https://github.com/rust-lang/rust/issues/48950> for more information)
    = help: you might have intended to use the type `()` here instead
 note: required by a bound in `foo`
-  --> $DIR/defaulted-never-note.rs:26:11
+  --> $DIR/defaulted-never-note.rs:22:11
    |
 LL | fn foo<T: ImplementedForUnitButNotNever>(_t: T) {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `foo`

tests/ui/never_type/defaulted-never-note.nofallback.stderr

@@ -1,13 +1,13 @@
 Future incompatibility report: Future breakage diagnostic:
 warning: this function depends on never type fallback being `()`
-  --> $DIR/defaulted-never-note.rs:29:1
+  --> $DIR/defaulted-never-note.rs:25:1
    |
 LL | fn smeg() {
    | ^^^^^^^^^
    |
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: ImplementedForUnitButNotNever` will fail
-  --> $DIR/defaulted-never-note.rs:31:9
+  --> $DIR/defaulted-never-note.rs:27:9
    |
 LL |     foo(_x);
    |         ^^

tests/ui/never_type/defaulted-never-note.rs

@@ -1,13 +1,9 @@
 //@ revisions: nofallback fallback
+//@[fallback] edition: 2024
 //@[nofallback] run-pass
 //@[fallback] check-fail
 
-// We need to opt into the `never_type_fallback` feature
-// to trigger the requirement that this is testing.
-#![cfg_attr(fallback, feature(never_type, never_type_fallback))]
-
-#![allow(unused)]
-#![expect(dependency_on_unit_never_type_fallback)]
+#![expect(dependency_on_unit_never_type_fallback, unused)]
 
 trait Deserialize: Sized {
     fn deserialize() -> Result<Self, String>;