Rollup merge of rust-lang#132978 - WaffleLapkin:very-semantic-change-…

…kind, r=compiler-errors

Mention both release *and* edition breakage for never type lints

This PR makes ~~two changes~~ a change to the never type lints (`dependency_on_unit_never_type_fallback` and `never_type_fallback_flowing_into_unsafe`):
1.  Change the wording of the note to mention that the breaking change will be made in an edition _and_ in a future release
2. ~~Make these warnings be reported in deps (hopefully the lints are matured enough)~~

r? `@compiler-errors`
cc `@ehuss`
closes rust-lang#132930

compiler/rustc_lint_defs/src/builtin.rs

@@ -4185,7 +4185,7 @@ declare_lint! {
     Warn,
     "never type fallback affecting unsafe function calls",
     @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
+        reason: FutureIncompatibilityReason::EditionAndFutureReleaseSemanticsChange(Edition::Edition2024),
         reference: "issue #123748 <https://github.com/rust-lang/rust/issues/123748>",
     };
     @edition Edition2024 => Deny;
@@ -4239,7 +4239,7 @@ declare_lint! {
     Warn,
     "never type fallback affecting unsafe function calls",
     @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
+        reason: FutureIncompatibilityReason::EditionAndFutureReleaseError(Edition::Edition2024),
         reference: "issue #123748 <https://github.com/rust-lang/rust/issues/123748>",
     };
     report_in_external_macro

compiler/rustc_lint_defs/src/lib.rs

@@ -381,6 +381,8 @@ pub enum FutureIncompatibilityReason {
     /// hard errors (and the lint removed). Preferably when there is some
     /// confidence that the number of impacted projects is very small (few
     /// should have a broken dependency in their dependency tree).
+    ///
+    /// [`EditionAndFutureReleaseError`]: FutureIncompatibilityReason::EditionAndFutureReleaseError
     FutureReleaseErrorReportInDeps,
     /// Code that changes meaning in some way in a
     /// future release.
@@ -419,6 +421,28 @@ pub enum FutureIncompatibilityReason {
     /// slightly changes the text of the diagnostic, but is otherwise the
     /// same.
     EditionSemanticsChange(Edition),
+    /// This will be an error in the provided edition *and* in a future
+    /// release.
+    ///
+    /// This variant a combination of [`FutureReleaseErrorDontReportInDeps`]
+    /// and [`EditionError`]. This is useful in rare cases when we
+    /// want to have "preview" of a breaking change in an edition, but do a
+    /// breaking change later on all editions anyway.
+    ///
+    /// [`EditionError`]: FutureIncompatibilityReason::EditionError
+    /// [`FutureReleaseErrorDontReportInDeps`]: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps
+    EditionAndFutureReleaseError(Edition),
+    /// This will change meaning in the provided edition *and* in a future
+    /// release.
+    ///
+    /// This variant a combination of [`FutureReleaseSemanticsChange`]
+    /// and [`EditionSemanticsChange`]. This is useful in rare cases when we
+    /// want to have "preview" of a breaking change in an edition, but do a
+    /// breaking change later on all editions anyway.
+    ///
+    /// [`EditionSemanticsChange`]: FutureIncompatibilityReason::EditionSemanticsChange
+    /// [`FutureReleaseSemanticsChange`]: FutureIncompatibilityReason::FutureReleaseSemanticsChange
+    EditionAndFutureReleaseSemanticsChange(Edition),
     /// A custom reason.
     ///
     /// Choose this variant if the built-in text of the diagnostic of the
@@ -431,9 +455,15 @@ pub enum FutureIncompatibilityReason {
 impl FutureIncompatibilityReason {
     pub fn edition(self) -> Option<Edition> {
         match self {
-            Self::EditionError(e) => Some(e),
-            Self::EditionSemanticsChange(e) => Some(e),
-            _ => None,
+            Self::EditionError(e)
+            | Self::EditionSemanticsChange(e)
+            | Self::EditionAndFutureReleaseError(e)
+            | Self::EditionAndFutureReleaseSemanticsChange(e) => Some(e),
+
+            FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps
+            | FutureIncompatibilityReason::FutureReleaseErrorReportInDeps
+            | FutureIncompatibilityReason::FutureReleaseSemanticsChange
+            | FutureIncompatibilityReason::Custom(_) => None,
         }
     }
 }

compiler/rustc_middle/src/lint.rs

@@ -382,6 +382,17 @@ pub fn lint_level(
                 FutureIncompatibilityReason::EditionSemanticsChange(edition) => {
                     format!("this changes meaning in Rust {edition}")
                 }
+                FutureIncompatibilityReason::EditionAndFutureReleaseError(edition) => {
+                    format!(
+                        "this was previously accepted by the compiler but is being phased out; \
+                         it will become a hard error in Rust {edition} and in a future release in all editions!"
+                    )
+                }
+                FutureIncompatibilityReason::EditionAndFutureReleaseSemanticsChange(edition) => {
+                    format!(
+                        "this changes meaning in Rust {edition} and in a future release in all editions!"
+                    )
+                }
                 FutureIncompatibilityReason::Custom(reason) => reason.to_owned(),
             };
 

tests/ui/delegation/unsupported.rs

@@ -10,15 +10,11 @@ mod opaque {
     mod to_reuse {
         use super::Trait;
 
-        pub fn opaque_ret() -> impl Trait { unimplemented!() }
-        //~^ 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!
+        pub fn opaque_ret() -> impl Trait { () }
     }
 
     trait ToReuse {
-        fn opaque_ret() -> impl Trait { unimplemented!() }
-        //~^ 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!
+        fn opaque_ret() -> impl Trait { () }
     }
 
     // FIXME: Inherited `impl Trait`s create query cycles when used inside trait impls.

tests/ui/delegation/unsupported.stderr

@@ -1,74 +1,43 @@
-error[E0391]: cycle detected when computing type of `opaque::<impl at $DIR/unsupported.rs:25:5: 25:24>::{synthetic#0}`
-  --> $DIR/unsupported.rs:26:25
+error[E0391]: cycle detected when computing type of `opaque::<impl at $DIR/unsupported.rs:21:5: 21:24>::{synthetic#0}`
+  --> $DIR/unsupported.rs:22:25
    |
 LL |         reuse to_reuse::opaque_ret;
    |                         ^^^^^^^^^^
    |
 note: ...which requires comparing an impl and trait method signature, inferring any hidden `impl Trait` types in the process...
-  --> $DIR/unsupported.rs:26:25
+  --> $DIR/unsupported.rs:22:25
    |
 LL |         reuse to_reuse::opaque_ret;
    |                         ^^^^^^^^^^
-   = note: ...which again requires computing type of `opaque::<impl at $DIR/unsupported.rs:25:5: 25:24>::{synthetic#0}`, completing the cycle
-note: cycle used when checking that `opaque::<impl at $DIR/unsupported.rs:25:5: 25:24>` is well-formed
-  --> $DIR/unsupported.rs:25:5
+   = note: ...which again requires computing type of `opaque::<impl at $DIR/unsupported.rs:21:5: 21:24>::{synthetic#0}`, completing the cycle
+note: cycle used when checking that `opaque::<impl at $DIR/unsupported.rs:21:5: 21:24>` is well-formed
+  --> $DIR/unsupported.rs:21:5
    |
 LL |     impl ToReuse for u8 {
    |     ^^^^^^^^^^^^^^^^^^^
    = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
 
-warning: this function depends on never type fallback being `()`
-  --> $DIR/unsupported.rs:13:9
-   |
-LL |         pub fn opaque_ret() -> impl Trait { unimplemented!() }
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = 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: in edition 2024, the requirement `!: opaque::Trait` will fail
-  --> $DIR/unsupported.rs:13:32
-   |
-LL |         pub fn opaque_ret() -> impl Trait { unimplemented!() }
-   |                                ^^^^^^^^^^
-   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
-
-warning: this function depends on never type fallback being `()`
-  --> $DIR/unsupported.rs:19:9
-   |
-LL |         fn opaque_ret() -> impl Trait { unimplemented!() }
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = 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: in edition 2024, the requirement `!: opaque::Trait` will fail
-  --> $DIR/unsupported.rs:19:28
-   |
-LL |         fn opaque_ret() -> impl Trait { unimplemented!() }
-   |                            ^^^^^^^^^^
-
-error[E0391]: cycle detected when computing type of `opaque::<impl at $DIR/unsupported.rs:28:5: 28:25>::{synthetic#0}`
-  --> $DIR/unsupported.rs:29:24
+error[E0391]: cycle detected when computing type of `opaque::<impl at $DIR/unsupported.rs:24:5: 24:25>::{synthetic#0}`
+  --> $DIR/unsupported.rs:25:24
    |
 LL |         reuse ToReuse::opaque_ret;
    |                        ^^^^^^^^^^
    |
 note: ...which requires comparing an impl and trait method signature, inferring any hidden `impl Trait` types in the process...
-  --> $DIR/unsupported.rs:29:24
+  --> $DIR/unsupported.rs:25:24
    |
 LL |         reuse ToReuse::opaque_ret;
    |                        ^^^^^^^^^^
-   = note: ...which again requires computing type of `opaque::<impl at $DIR/unsupported.rs:28:5: 28:25>::{synthetic#0}`, completing the cycle
-note: cycle used when checking that `opaque::<impl at $DIR/unsupported.rs:28:5: 28:25>` is well-formed
-  --> $DIR/unsupported.rs:28:5
+   = note: ...which again requires computing type of `opaque::<impl at $DIR/unsupported.rs:24:5: 24:25>::{synthetic#0}`, completing the cycle
+note: cycle used when checking that `opaque::<impl at $DIR/unsupported.rs:24:5: 24:25>` is well-formed
+  --> $DIR/unsupported.rs:24:5
    |
 LL |     impl ToReuse for u16 {
    |     ^^^^^^^^^^^^^^^^^^^^
    = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
 
 error: recursive delegation is not supported yet
-  --> $DIR/unsupported.rs:42:22
+  --> $DIR/unsupported.rs:38:22
    |
 LL |         pub reuse to_reuse2::foo;
    |                              --- callee defined here
@@ -77,14 +46,14 @@ LL |     reuse to_reuse1::foo;
    |                      ^^^
 
 error[E0283]: type annotations needed
-  --> $DIR/unsupported.rs:52:18
+  --> $DIR/unsupported.rs:48:18
    |
 LL |     reuse Trait::foo;
    |                  ^^^ cannot infer type
    |
    = note: cannot satisfy `_: effects::Trait`
 
-error: aborting due to 4 previous errors; 2 warnings emitted
+error: aborting due to 4 previous errors
 
 Some errors have detailed explanations: E0283, E0391.
 For more information about an error, try `rustc --explain E0283`.

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

@@ -16,7 +16,7 @@ fn main() {
 
 fn m() {
     //[e2021]~^ this function depends on never type fallback being `()`
-    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    //[e2021]~| 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
@@ -28,7 +28,7 @@ fn m() {
 
 fn q() -> Option<()> {
     //[e2021]~^ this function depends on never type fallback being `()`
-    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    //[e2021]~| 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())
     }
@@ -45,7 +45,7 @@ fn help<'a: 'a, T: Into<()>, U>(_: U) -> Result<T, ()> {
 }
 fn meow() -> Result<(), ()> {
     //[e2021]~^ this function depends on never type fallback being `()`
-    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    //[e2021]~| 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(())

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

@@ -4,7 +4,7 @@ warning: this function depends on never type fallback being `()`
 LL | fn m() {
    | ^^^^^^
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: 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!
    = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
@@ -24,7 +24,7 @@ warning: this function depends on never type fallback being `()`
 LL | fn q() -> Option<()> {
    | ^^^^^^^^^^^^^^^^^^^^
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: 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!
    = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
@@ -43,7 +43,7 @@ warning: this function depends on never type fallback being `()`
 LL | fn meow() -> Result<(), ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: 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!
    = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `(): From<!>` will fail

tests/ui/editions/never-type-fallback-breaking.rs

@@ -16,7 +16,7 @@ fn main() {
 
 fn m() {
     //[e2021]~^ this function depends on never type fallback being `()`
-    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    //[e2021]~| 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
@@ -28,7 +28,7 @@ fn m() {
 
 fn q() -> Option<()> {
     //[e2021]~^ this function depends on never type fallback being `()`
-    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    //[e2021]~| 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())
     }
@@ -45,7 +45,7 @@ fn help<'a: 'a, T: Into<()>, U>(_: U) -> Result<T, ()> {
 }
 fn meow() -> Result<(), ()> {
     //[e2021]~^ this function depends on never type fallback being `()`
-    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    //[e2021]~| 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(())

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

@@ -4,7 +4,7 @@ warning: this function depends on never type fallback being `()`
 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!
+   = warning: 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!
    = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: ImplementedForUnitButNotNever` will fail

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

@@ -27,7 +27,7 @@ fn foo<T: ImplementedForUnitButNotNever>(_t: T) {}
 //[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!
+    //[nofallback]~| 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 = return;
     foo(_x);
     //[fallback]~^ ERROR the trait bound

tests/ui/never_type/dependency-on-fallback-to-unit.rs

@@ -7,7 +7,7 @@ fn main() {
 
 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!
+    //~| 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!
     match true {
         false => <_>::default(),
         true => return,
@@ -18,7 +18,7 @@ fn def() {
 // <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!
+    //~| 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!
     deserialize()?;
     Ok(())
 }

tests/ui/never_type/dependency-on-fallback-to-unit.stderr

@@ -4,7 +4,7 @@ warning: this function depends on never type fallback being `()`
 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!
+   = warning: 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!
    = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
@@ -24,7 +24,7 @@ warning: this function depends on never type fallback being `()`
 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!
+   = warning: 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!
    = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail