Rollup of 2 pull requests

compiler/rustc_lint/src/unused.rs

@@ -273,13 +273,13 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
             expr: &hir::Expr<'_>,
             span: Span,
         ) -> Option<MustUsePath> {
-            if ty.is_unit()
-                || !ty.is_inhabited_from(
-                    cx.tcx,
-                    cx.tcx.parent_module(expr.hir_id).to_def_id(),
-                    cx.typing_env(),
-                )
-            {
+            if ty.is_unit() {
+                return Some(MustUsePath::Suppressed);
+            }
+            let parent_mod_did = cx.tcx.parent_module(expr.hir_id).to_def_id();
+            let is_uninhabited =
+                |t: Ty<'tcx>| !t.is_inhabited_from(cx.tcx, parent_mod_did, cx.typing_env());
+            if is_uninhabited(ty) {
                 return Some(MustUsePath::Suppressed);
             }
 
@@ -293,6 +293,22 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                     is_ty_must_use(cx, pinned_ty, expr, span)
                         .map(|inner| MustUsePath::Pinned(Box::new(inner)))
                 }
+                // Suppress warnings on `Result<(), Uninhabited>` (e.g. `Result<(), !>`).
+                ty::Adt(def, args)
+                    if cx.tcx.is_diagnostic_item(sym::Result, def.did())
+                        && args.type_at(0).is_unit()
+                        && is_uninhabited(args.type_at(1)) =>
+                {
+                    Some(MustUsePath::Suppressed)
+                }
+                // Suppress warnings on `ControlFlow<Uninhabited, ()>` (e.g. `ControlFlow<!, ()>`).
+                ty::Adt(def, args)
+                    if cx.tcx.is_diagnostic_item(sym::ControlFlow, def.did())
+                        && args.type_at(1).is_unit()
+                        && is_uninhabited(args.type_at(0)) =>
+                {
+                    Some(MustUsePath::Suppressed)
+                }
                 ty::Adt(def, _) => is_def_must_use(cx, def.did(), span),
                 ty::Alias(ty::Opaque | ty::Projection, ty::AliasTy { def_id: def, .. }) => {
                     elaborate(cx.tcx, cx.tcx.explicit_item_self_bounds(def).iter_identity_copied())

compiler/rustc_lint_defs/src/builtin.rs

@@ -4065,7 +4065,6 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust,compile_fail
-    /// #![deny(never_type_fallback_flowing_into_unsafe)]
     /// fn main() {
     ///     if true {
     ///         // return has type `!` which, is some cases, causes never type fallback
@@ -4100,7 +4099,7 @@ declare_lint! {
     /// [`!`]: https://doc.rust-lang.org/core/primitive.never.html
     /// [`()`]: https://doc.rust-lang.org/core/primitive.unit.html
     pub NEVER_TYPE_FALLBACK_FLOWING_INTO_UNSAFE,
-    Warn,
+    Deny,
     "never type fallback affecting unsafe function calls",
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::EditionAndFutureReleaseSemanticsChange(Edition::Edition2024),
@@ -4122,7 +4121,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust,compile_fail,edition2021
-    /// #![deny(dependency_on_unit_never_type_fallback)]
+    /// # #![deny(dependency_on_unit_never_type_fallback)]
     /// fn main() {
     ///     if true {
     ///         // return has type `!` which, is some cases, causes never type fallback
@@ -4155,7 +4154,7 @@ declare_lint! {
     ///
     /// See [Tracking Issue for making `!` fall back to `!`](https://github.com/rust-lang/rust/issues/123748).
     pub DEPENDENCY_ON_UNIT_NEVER_TYPE_FALLBACK,
-    Warn,
+    Deny,
     "never type fallback affecting unsafe function calls",
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::EditionAndFutureReleaseError(Edition::Edition2024),

tests/ui/editions/never-type-fallback-breaking.e2021.fixed

@@ -3,9 +3,7 @@
 //@[e2021] edition: 2021
 //@[e2024] edition: 2024
 //
-//@[e2021] run-pass
 //@[e2021] run-rustfix
-//@[e2024] check-fail
 
 fn main() {
     m();
@@ -16,8 +14,8 @@ fn main() {
 }
 
 fn m() {
-    //[e2021]~^ WARN this function depends on never type fallback being `()`
-    //[e2021]~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
+    //[e2021]~^ error: this function depends on never type fallback being `()`
+    //[e2021]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
     let x: () = match true {
         true => Default::default(),
         //[e2024]~^ error: the trait bound `!: Default` is not satisfied
@@ -28,8 +26,8 @@ fn m() {
 }
 
 fn q() -> Option<()> {
-    //[e2021]~^ WARN this function depends on never type fallback being `()`
-    //[e2021]~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
+    //[e2021]~^ error: this function depends on never type fallback being `()`
+    //[e2021]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
     fn deserialize<T: Default>() -> Option<T> {
         Some(T::default())
     }
@@ -45,8 +43,8 @@ fn help<'a: 'a, T: Into<()>, U>(_: U) -> Result<T, ()> {
     Err(())
 }
 fn meow() -> Result<(), ()> {
-    //[e2021]~^ WARN this function depends on never type fallback being `()`
-    //[e2021]~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
+    //[e2021]~^ error: this function depends on never type fallback being `()`
+    //[e2021]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
     help::<(), _>(1)?;
     //[e2024]~^ error: the trait bound `(): From<!>` is not satisfied
     Ok(())
@@ -57,8 +55,8 @@ pub fn takes_apit<T>(_y: impl Fn() -> T) -> Result<T, ()> {
 }
 
 pub fn fallback_return() -> Result<(), ()> {
-    //[e2021]~^ WARN this function depends on never type fallback being `()`
-    //[e2021]~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
+    //[e2021]~^ error: this function depends on never type fallback being `()`
+    //[e2021]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
     takes_apit::<()>(|| Default::default())?;
     //[e2024]~^ error: the trait bound `!: Default` is not satisfied
     Ok(())
@@ -71,8 +69,8 @@ fn mk<T>() -> Result<T, ()> {
 fn takes_apit2(_x: impl Default) {}
 
 fn fully_apit() -> Result<(), ()> {
-    //[e2021]~^ WARN this function depends on never type fallback being `()`
-    //[e2021]~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
+    //[e2021]~^ error: this function depends on never type fallback being `()`
+    //[e2021]~| warn: this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
     takes_apit2(mk::<()>()?);
     //[e2024]~^ error: the trait bound `!: Default` is not satisfied
     Ok(())

tests/ui/editions/never-type-fallback-breaking.e2021.stderr

@@ -1,5 +1,5 @@
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:18:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:16:1
    |
 LL | fn m() {
    | ^^^^^^
@@ -8,18 +8,18 @@ LL | fn m() {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:22:17
+  --> $DIR/never-type-fallback-breaking.rs:20:17
    |
 LL |         true => Default::default(),
    |                 ^^^^^^^^^^^^^^^^^^
-   = note: `#[warn(dependency_on_unit_never_type_fallback)]` (part of `#[warn(rust_2024_compatibility)]`) on by default
+   = note: `#[deny(dependency_on_unit_never_type_fallback)]` (part of `#[deny(rust_2024_compatibility)]`) on by default
 help: use `()` annotations to avoid fallback changes
    |
 LL |     let x: () = match true {
    |          ++++
 
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:30:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:28:1
    |
 LL | fn q() -> Option<()> {
    | ^^^^^^^^^^^^^^^^^^^^
@@ -28,7 +28,7 @@ LL | fn q() -> Option<()> {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:37:5
+  --> $DIR/never-type-fallback-breaking.rs:35:5
    |
 LL |     deserialize()?;
    |     ^^^^^^^^^^^^^
@@ -37,8 +37,8 @@ help: use `()` annotations to avoid fallback changes
 LL |     deserialize::<()>()?;
    |                ++++++
 
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:47:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:45:1
    |
 LL | fn meow() -> Result<(), ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -47,7 +47,7 @@ LL | fn meow() -> Result<(), ()> {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `(): From<!>` will fail
-  --> $DIR/never-type-fallback-breaking.rs:50:5
+  --> $DIR/never-type-fallback-breaking.rs:48:5
    |
 LL |     help(1)?;
    |     ^^^^^^^
@@ -56,8 +56,8 @@ help: use `()` annotations to avoid fallback changes
 LL |     help::<(), _>(1)?;
    |         +++++++++
 
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:59:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:57:1
    |
 LL | pub fn fallback_return() -> Result<(), ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -66,7 +66,7 @@ LL | pub fn fallback_return() -> Result<(), ()> {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:62:19
+  --> $DIR/never-type-fallback-breaking.rs:60:19
    |
 LL |     takes_apit(|| Default::default())?;
    |                   ^^^^^^^^^^^^^^^^^^
@@ -75,8 +75,8 @@ help: use `()` annotations to avoid fallback changes
 LL |     takes_apit::<()>(|| Default::default())?;
    |               ++++++
 
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:73:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:71:1
    |
 LL | fn fully_apit() -> Result<(), ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -85,7 +85,7 @@ LL | fn fully_apit() -> Result<(), ()> {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:76:17
+  --> $DIR/never-type-fallback-breaking.rs:74:17
    |
 LL |     takes_apit2(mk()?);
    |                 ^^^^^
@@ -94,11 +94,11 @@ help: use `()` annotations to avoid fallback changes
 LL |     takes_apit2(mk::<()>()?);
    |                   ++++++
 
-warning: 5 warnings emitted
+error: aborting due to 5 previous errors
 
 Future incompatibility report: Future breakage diagnostic:
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:18:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:16:1
    |
 LL | fn m() {
    | ^^^^^^
@@ -107,19 +107,19 @@ LL | fn m() {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:22:17
+  --> $DIR/never-type-fallback-breaking.rs:20:17
    |
 LL |         true => Default::default(),
    |                 ^^^^^^^^^^^^^^^^^^
-   = note: `#[warn(dependency_on_unit_never_type_fallback)]` (part of `#[warn(rust_2024_compatibility)]`) on by default
+   = note: `#[deny(dependency_on_unit_never_type_fallback)]` (part of `#[deny(rust_2024_compatibility)]`) on by default
 help: use `()` annotations to avoid fallback changes
    |
 LL |     let x: () = match true {
    |          ++++
 
 Future breakage diagnostic:
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:30:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:28:1
    |
 LL | fn q() -> Option<()> {
    | ^^^^^^^^^^^^^^^^^^^^
@@ -128,19 +128,19 @@ LL | fn q() -> Option<()> {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:37:5
+  --> $DIR/never-type-fallback-breaking.rs:35:5
    |
 LL |     deserialize()?;
    |     ^^^^^^^^^^^^^
-   = note: `#[warn(dependency_on_unit_never_type_fallback)]` (part of `#[warn(rust_2024_compatibility)]`) on by default
+   = note: `#[deny(dependency_on_unit_never_type_fallback)]` (part of `#[deny(rust_2024_compatibility)]`) on by default
 help: use `()` annotations to avoid fallback changes
    |
 LL |     deserialize::<()>()?;
    |                ++++++
 
 Future breakage diagnostic:
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:47:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:45:1
    |
 LL | fn meow() -> Result<(), ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -149,19 +149,19 @@ LL | fn meow() -> Result<(), ()> {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `(): From<!>` will fail
-  --> $DIR/never-type-fallback-breaking.rs:50:5
+  --> $DIR/never-type-fallback-breaking.rs:48:5
    |
 LL |     help(1)?;
    |     ^^^^^^^
-   = note: `#[warn(dependency_on_unit_never_type_fallback)]` (part of `#[warn(rust_2024_compatibility)]`) on by default
+   = note: `#[deny(dependency_on_unit_never_type_fallback)]` (part of `#[deny(rust_2024_compatibility)]`) on by default
 help: use `()` annotations to avoid fallback changes
    |
 LL |     help::<(), _>(1)?;
    |         +++++++++
 
 Future breakage diagnostic:
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:59:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:57:1
    |
 LL | pub fn fallback_return() -> Result<(), ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -170,19 +170,19 @@ LL | pub fn fallback_return() -> Result<(), ()> {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:62:19
+  --> $DIR/never-type-fallback-breaking.rs:60:19
    |
 LL |     takes_apit(|| Default::default())?;
    |                   ^^^^^^^^^^^^^^^^^^
-   = note: `#[warn(dependency_on_unit_never_type_fallback)]` (part of `#[warn(rust_2024_compatibility)]`) on by default
+   = note: `#[deny(dependency_on_unit_never_type_fallback)]` (part of `#[deny(rust_2024_compatibility)]`) on by default
 help: use `()` annotations to avoid fallback changes
    |
 LL |     takes_apit::<()>(|| Default::default())?;
    |               ++++++
 
 Future breakage diagnostic:
-warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:73:1
+error: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:71:1
    |
 LL | fn fully_apit() -> Result<(), ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -191,11 +191,11 @@ LL | fn fully_apit() -> Result<(), ()> {
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:76:17
+  --> $DIR/never-type-fallback-breaking.rs:74:17
    |
 LL |     takes_apit2(mk()?);
    |                 ^^^^^
-   = note: `#[warn(dependency_on_unit_never_type_fallback)]` (part of `#[warn(rust_2024_compatibility)]`) on by default
+   = note: `#[deny(dependency_on_unit_never_type_fallback)]` (part of `#[deny(rust_2024_compatibility)]`) on by default
 help: use `()` annotations to avoid fallback changes
    |
 LL |     takes_apit2(mk::<()>()?);