diff options
20 files changed, 274 insertions, 6 deletions
diff --git a/compiler/rustc_hir_typeck/messages.ftl b/compiler/rustc_hir_typeck/messages.ftl index 6f499947d5c..3ab319a037b 100644 --- a/compiler/rustc_hir_typeck/messages.ftl +++ b/compiler/rustc_hir_typeck/messages.ftl @@ -44,6 +44,9 @@ hir_typeck_convert_using_method = try using `{$sugg}` to convert `{$found}` to ` hir_typeck_ctor_is_private = tuple struct constructor `{$def}` is private +hir_typeck_dependency_on_unit_never_type_fallback = this function depends on never type fallback being `()` + .help = specify the types explicitly + hir_typeck_deref_is_empty = this expression `Deref`s to `{$deref_ty}` which implements `is_empty` hir_typeck_expected_default_return_type = expected `()` because of default return type diff --git a/compiler/rustc_hir_typeck/src/errors.rs b/compiler/rustc_hir_typeck/src/errors.rs index 3f12f252654..6dd34024fd1 100644 --- a/compiler/rustc_hir_typeck/src/errors.rs +++ b/compiler/rustc_hir_typeck/src/errors.rs @@ -183,6 +183,11 @@ pub enum NeverTypeFallbackFlowingIntoUnsafe { Deref, } +#[derive(LintDiagnostic)] +#[help] +#[diag(hir_typeck_dependency_on_unit_never_type_fallback)] +pub struct DependencyOnUnitNeverTypeFallback {} + #[derive(Subdiagnostic)] #[multipart_suggestion( hir_typeck_add_missing_parentheses_in_range, diff --git a/compiler/rustc_hir_typeck/src/fallback.rs b/compiler/rustc_hir_typeck/src/fallback.rs index 5ba67c52ef2..06c5adae99e 100644 --- a/compiler/rustc_hir_typeck/src/fallback.rs +++ b/compiler/rustc_hir_typeck/src/fallback.rs @@ -8,12 +8,17 @@ use rustc_data_structures::{ use rustc_hir as hir; use rustc_hir::intravisit::Visitor; use rustc_hir::HirId; -use rustc_infer::infer::{DefineOpaqueTypes, InferOk}; use rustc_middle::bug; +use rustc_infer::{ + infer::{DefineOpaqueTypes, InferOk}, + traits::ObligationCause, +}; use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable}; use rustc_session::lint; use rustc_span::DUMMY_SP; use rustc_span::{def_id::LocalDefId, Span}; +use rustc_trait_selection::traits::ObligationCtxt; +use rustc_type_ir::TyVid; #[derive(Copy, Clone)] pub enum DivergingFallbackBehavior { @@ -344,6 +349,9 @@ impl<'tcx> FnCtxt<'_, 'tcx> { // `!`. let mut diverging_fallback = UnordMap::with_capacity(diverging_vids.len()); let unsafe_infer_vars = OnceCell::new(); + + self.lint_obligations_broken_by_never_type_fallback_change(behavior, &diverging_vids); + for &diverging_vid in &diverging_vids { let diverging_ty = Ty::new_var(self.tcx, diverging_vid); let root_vid = self.root_var(diverging_vid); @@ -468,6 +476,46 @@ impl<'tcx> FnCtxt<'_, 'tcx> { } } + fn lint_obligations_broken_by_never_type_fallback_change( + &self, + behavior: DivergingFallbackBehavior, + diverging_vids: &[TyVid], + ) { + let DivergingFallbackBehavior::FallbackToUnit = behavior else { return }; + + // Returns errors which happen if fallback is set to `fallback` + let try_out = |fallback| { + self.probe(|_| { + let obligations = self.fulfillment_cx.borrow().pending_obligations(); + let ocx = ObligationCtxt::new(&self.infcx); + ocx.register_obligations(obligations.iter().cloned()); + + for &diverging_vid in diverging_vids { + let diverging_ty = Ty::new_var(self.tcx, diverging_vid); + + _ = ocx.eq(&ObligationCause::dummy(), self.param_env, diverging_ty, fallback); + } + + ocx.select_where_possible() + }) + }; + + // If we have no errors with `fallback = ()`, but *do* have errors with `fallback = !`, + // then this code will be broken by the never type fallback change.qba + let unit_errors = try_out(self.tcx.types.unit); + if unit_errors.is_empty() + && let never_errors = try_out(self.tcx.types.never) + && !never_errors.is_empty() + { + self.tcx.emit_node_span_lint( + lint::builtin::DEPENDENCY_ON_UNIT_NEVER_TYPE_FALLBACK, + self.tcx.local_def_id_to_hir_id(self.body_id), + self.tcx.def_span(self.body_id), + errors::DependencyOnUnitNeverTypeFallback {}, + ) + } + } + /// Returns a graph whose nodes are (unresolved) inference variables and where /// an edge `?A -> ?B` indicates that the variable `?A` is coerced to `?B`. fn create_coercion_graph(&self) -> VecGraph<ty::TyVid, true> { diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs index 45051394ffc..e6895fbfd09 100644 --- a/compiler/rustc_lint_defs/src/builtin.rs +++ b/compiler/rustc_lint_defs/src/builtin.rs @@ -34,6 +34,7 @@ declare_lint_pass! { CONST_EVALUATABLE_UNCHECKED, CONST_ITEM_MUTATION, DEAD_CODE, + DEPENDENCY_ON_UNIT_NEVER_TYPE_FALLBACK, DEPRECATED, DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME, DEPRECATED_IN_FUTURE, @@ -4200,6 +4201,62 @@ declare_lint! { } declare_lint! { + /// The `dependency_on_unit_never_type_fallback` lint detects cases where code compiles with + /// [never type fallback] being [`()`], but will stop compiling with fallback being [`!`]. + /// + /// [never type fallback]: prim@never#never-type-fallback + /// [`()`]: prim@unit + /// [`!`]: + /// + /// ### Example + /// + /// ```rust,compile_fail + /// #![deny(dependency_on_unit_never_type_fallback)] + /// fn main() { + /// if true { + /// // return has type `!` which, is some cases, causes never type fallback + /// return + /// } else { + /// // the type produced by this call is not specified explicitly, + /// // so it will be inferred from the previous branch + /// Default::default() + /// }; + /// // depending on the fallback, this may compile (because `()` implements `Default`), + /// // or it may not (because `!` does not implement `Default`) + /// } + /// ``` + /// + /// {{produces}} + /// + /// ### Explanation + /// + /// Due to historic reasons never type fallback was `()`, meaning that `!` got spontaneously + /// coerced to `()`. There are plans to change that, but they may make the code such as above + /// not compile. Instead of depending on the fallback, you should specify the type explicitly: + /// ``` + /// if true { + /// return + /// } else { + /// // type is explicitly specified, fallback can't hurt us no more + /// <() as Default>::default() + /// }; + /// ``` + /// + /// See [Tracking Issue for making `!` fall back to `!`](https://github.com/rust-lang/rust/issues/123748). + /// + /// [`!`]: https://doc.rust-lang.org/core/primitive.never.html + /// [`()`]: https://doc.rust-lang.org/core/primitive.unit.html + pub DEPENDENCY_ON_UNIT_NEVER_TYPE_FALLBACK, + Warn, + "never type fallback affecting unsafe function calls", + @future_incompatible = FutureIncompatibleInfo { + reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps, + reference: "issue #123748 <https://github.com/rust-lang/rust/issues/123748>", + }; + report_in_external_macro +} + +declare_lint! { /// The `byte_slice_in_packed_struct_with_derive` lint detects cases where a byte slice field /// (`[u8]`) or string slice field (`str`) is used in a `packed` struct that derives one or /// more built-in traits. diff --git a/tests/ui/never_type/defaulted-never-note.fallback.stderr b/tests/ui/never_type/defaulted-never-note.fallback.stderr index 92fa9068cfd..fe9a924f64a 100644 --- a/tests/ui/never_type/defaulted-never-note.fallback.stderr +++ b/tests/ui/never_type/defaulted-never-note.fallback.stderr @@ -1,5 +1,5 @@ error[E0277]: the trait bound `!: ImplementedForUnitButNotNever` is not satisfied - --> $DIR/defaulted-never-note.rs:30:9 + --> $DIR/defaulted-never-note.rs:32:9 | LL | foo(_x); | --- ^^ the trait `ImplementedForUnitButNotNever` is not implemented for `!` diff --git a/tests/ui/never_type/defaulted-never-note.nofallback.stderr b/tests/ui/never_type/defaulted-never-note.nofallback.stderr new file mode 100644 index 00000000000..b69b8dda8f1 --- /dev/null +++ b/tests/ui/never_type/defaulted-never-note.nofallback.stderr @@ -0,0 +1,13 @@ +warning: this function depends on never type fallback being `()` + --> $DIR/defaulted-never-note.rs:28:1 + | +LL | fn smeg() { + | ^^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748> + = help: specify the types explicitly + = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default + +warning: 1 warning emitted + diff --git a/tests/ui/never_type/defaulted-never-note.rs b/tests/ui/never_type/defaulted-never-note.rs index f4e5273b33a..40861e73b39 100644 --- a/tests/ui/never_type/defaulted-never-note.rs +++ b/tests/ui/never_type/defaulted-never-note.rs @@ -26,6 +26,8 @@ fn foo<T: ImplementedForUnitButNotNever>(_t: T) {} //[fallback]~^ NOTE required by this bound in `foo` //[fallback]~| NOTE required by a bound in `foo` fn smeg() { + //[nofallback]~^ warn: this function depends on never type fallback being `()` + //[nofallback]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! let _x = return; foo(_x); //[fallback]~^ ERROR the trait bound diff --git a/tests/ui/never_type/dependency-on-fallback-to-unit.rs b/tests/ui/never_type/dependency-on-fallback-to-unit.rs new file mode 100644 index 00000000000..5448d0be2c6 --- /dev/null +++ b/tests/ui/never_type/dependency-on-fallback-to-unit.rs @@ -0,0 +1,28 @@ +//@ check-pass + +fn main() { + def(); + _ = question_mark(); +} + +fn def() { + //~^ warn: this function depends on never type fallback being `()` + //~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + match true { + false => <_>::default(), + true => return, + }; +} + +// <https://github.com/rust-lang/rust/issues/51125> +// <https://github.com/rust-lang/rust/issues/39216> +fn question_mark() -> Result<(), ()> { + //~^ warn: this function depends on never type fallback being `()` + //~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + deserialize()?; + Ok(()) +} + +fn deserialize<T: Default>() -> Result<T, ()> { + Ok(T::default()) +} diff --git a/tests/ui/never_type/dependency-on-fallback-to-unit.stderr b/tests/ui/never_type/dependency-on-fallback-to-unit.stderr new file mode 100644 index 00000000000..36c82b6d1bf --- /dev/null +++ b/tests/ui/never_type/dependency-on-fallback-to-unit.stderr @@ -0,0 +1,23 @@ +warning: this function depends on never type fallback being `()` + --> $DIR/dependency-on-fallback-to-unit.rs:8:1 + | +LL | fn def() { + | ^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748> + = help: specify the types explicitly + = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default + +warning: this function depends on never type fallback being `()` + --> $DIR/dependency-on-fallback-to-unit.rs:19:1 + | +LL | fn question_mark() -> Result<(), ()> { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748> + = help: specify the types explicitly + +warning: 2 warnings emitted + diff --git a/tests/ui/never_type/diverging-fallback-control-flow.nofallback.stderr b/tests/ui/never_type/diverging-fallback-control-flow.nofallback.stderr new file mode 100644 index 00000000000..5fbdc04ed3b --- /dev/null +++ b/tests/ui/never_type/diverging-fallback-control-flow.nofallback.stderr @@ -0,0 +1,23 @@ +warning: this function depends on never type fallback being `()` + --> $DIR/diverging-fallback-control-flow.rs:30:1 + | +LL | fn assignment() { + | ^^^^^^^^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748> + = help: specify the types explicitly + = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default + +warning: this function depends on never type fallback being `()` + --> $DIR/diverging-fallback-control-flow.rs:42:1 + | +LL | fn assignment_rev() { + | ^^^^^^^^^^^^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748> + = help: specify the types explicitly + +warning: 2 warnings emitted + diff --git a/tests/ui/never_type/diverging-fallback-control-flow.rs b/tests/ui/never_type/diverging-fallback-control-flow.rs index e209a990885..575e2e9273c 100644 --- a/tests/ui/never_type/diverging-fallback-control-flow.rs +++ b/tests/ui/never_type/diverging-fallback-control-flow.rs @@ -28,6 +28,8 @@ impl UnitDefault for () { } fn assignment() { + //[nofallback]~^ warn: this function depends on never type fallback being `()` + //[nofallback]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! let x; if true { @@ -38,6 +40,8 @@ fn assignment() { } fn assignment_rev() { + //[nofallback]~^ warn: this function depends on never type fallback being `()` + //[nofallback]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! let x; if true { diff --git a/tests/ui/never_type/diverging-fallback-no-leak.fallback.stderr b/tests/ui/never_type/diverging-fallback-no-leak.fallback.stderr index 01abf2e17f1..c5463814475 100644 --- a/tests/ui/never_type/diverging-fallback-no-leak.fallback.stderr +++ b/tests/ui/never_type/diverging-fallback-no-leak.fallback.stderr @@ -1,5 +1,5 @@ error[E0277]: the trait bound `!: Test` is not satisfied - --> $DIR/diverging-fallback-no-leak.rs:17:23 + --> $DIR/diverging-fallback-no-leak.rs:20:23 | LL | unconstrained_arg(return); | ----------------- ^^^^^^ the trait `Test` is not implemented for `!` diff --git a/tests/ui/never_type/diverging-fallback-no-leak.nofallback.stderr b/tests/ui/never_type/diverging-fallback-no-leak.nofallback.stderr new file mode 100644 index 00000000000..d11097323b3 --- /dev/null +++ b/tests/ui/never_type/diverging-fallback-no-leak.nofallback.stderr @@ -0,0 +1,13 @@ +warning: this function depends on never type fallback being `()` + --> $DIR/diverging-fallback-no-leak.rs:14:1 + | +LL | fn main() { + | ^^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748> + = help: specify the types explicitly + = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default + +warning: 1 warning emitted + diff --git a/tests/ui/never_type/diverging-fallback-no-leak.rs b/tests/ui/never_type/diverging-fallback-no-leak.rs index 425437da207..c6d59c7f273 100644 --- a/tests/ui/never_type/diverging-fallback-no-leak.rs +++ b/tests/ui/never_type/diverging-fallback-no-leak.rs @@ -12,6 +12,9 @@ impl Test for () {} fn unconstrained_arg<T: Test>(_: T) {} fn main() { + //[nofallback]~^ warn: this function depends on never type fallback being `()` + //[nofallback]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + // Here the type variable falls back to `!`, // and hence we get a type error. unconstrained_arg(return); diff --git a/tests/ui/never_type/diverging-fallback-unconstrained-return.nofallback.stderr b/tests/ui/never_type/diverging-fallback-unconstrained-return.nofallback.stderr new file mode 100644 index 00000000000..750bcfb7f89 --- /dev/null +++ b/tests/ui/never_type/diverging-fallback-unconstrained-return.nofallback.stderr @@ -0,0 +1,13 @@ +warning: this function depends on never type fallback being `()` + --> $DIR/diverging-fallback-unconstrained-return.rs:28:1 + | +LL | fn main() { + | ^^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748> + = help: specify the types explicitly + = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default + +warning: 1 warning emitted + diff --git a/tests/ui/never_type/diverging-fallback-unconstrained-return.rs b/tests/ui/never_type/diverging-fallback-unconstrained-return.rs index aeb6ee6e26e..927991db513 100644 --- a/tests/ui/never_type/diverging-fallback-unconstrained-return.rs +++ b/tests/ui/never_type/diverging-fallback-unconstrained-return.rs @@ -26,6 +26,9 @@ fn unconstrained_return<T: UnitReturn>() -> T { } fn main() { + //[nofallback]~^ warn: this function depends on never type fallback being `()` + //[nofallback]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + // In Ye Olde Days, the `T` parameter of `unconstrained_return` // winds up "entangled" with the `!` type that results from // `panic!`, and hence falls back to `()`. This is kind of unfortunate diff --git a/tests/ui/never_type/fallback-closure-ret.nofallback.stderr b/tests/ui/never_type/fallback-closure-ret.nofallback.stderr new file mode 100644 index 00000000000..9f0b9f6daea --- /dev/null +++ b/tests/ui/never_type/fallback-closure-ret.nofallback.stderr @@ -0,0 +1,13 @@ +warning: this function depends on never type fallback being `()` + --> $DIR/fallback-closure-ret.rs:21:1 + | +LL | fn main() { + | ^^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748> + = help: specify the types explicitly + = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default + +warning: 1 warning emitted + diff --git a/tests/ui/never_type/fallback-closure-ret.rs b/tests/ui/never_type/fallback-closure-ret.rs index dcf38e03a13..30f9ac54d0b 100644 --- a/tests/ui/never_type/fallback-closure-ret.rs +++ b/tests/ui/never_type/fallback-closure-ret.rs @@ -12,12 +12,14 @@ #![cfg_attr(fallback, feature(never_type_fallback))] -trait Bar { } -impl Bar for () { } -impl Bar for u32 { } +trait Bar {} +impl Bar for () {} +impl Bar for u32 {} fn foo<R: Bar>(_: impl Fn() -> R) {} fn main() { + //[nofallback]~^ warn: this function depends on never type fallback being `()` + //[nofallback]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! foo(|| panic!()); } diff --git a/tests/ui/never_type/impl_trait_fallback.rs b/tests/ui/never_type/impl_trait_fallback.rs index ce06f8f7817..fbe13dbe2ac 100644 --- a/tests/ui/never_type/impl_trait_fallback.rs +++ b/tests/ui/never_type/impl_trait_fallback.rs @@ -6,5 +6,7 @@ trait T {} impl T for () {} fn should_ret_unit() -> impl T { + //~^ warn: this function depends on never type fallback being `()` + //~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! panic!() } diff --git a/tests/ui/never_type/impl_trait_fallback.stderr b/tests/ui/never_type/impl_trait_fallback.stderr new file mode 100644 index 00000000000..87638940332 --- /dev/null +++ b/tests/ui/never_type/impl_trait_fallback.stderr @@ -0,0 +1,13 @@ +warning: this function depends on never type fallback being `()` + --> $DIR/impl_trait_fallback.rs:8:1 + | +LL | fn should_ret_unit() -> impl T { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748> + = help: specify the types explicitly + = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default + +warning: 1 warning emitted + |