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

+ Make them into lints which are reported in deps.

Author: WaffleLapkin

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::EditionAndFutureReleaseError(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

@@ -366,8 +366,9 @@ pub enum FutureIncompatibilityReason {
     /// This will be an error in a future release, and
     /// Cargo should create a report even for dependencies
     ///
-    /// This is the *only* reason that will make future incompatibility warnings show up in cargo's
-    /// reports. All other future incompatibility warnings are not visible when they occur in a
+    /// This and [`FutureReleaseError`] are the *only* reasons that will make
+    /// future incompatibility warnings show up in cargo's reports. All other
+    /// future incompatibility warnings are not visible when they occur in a
     /// dependency.
     ///
     /// Choose this variant after the lint has been sitting in the
@@ -419,6 +420,17 @@ 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 [`FutureReleaseErrorReportInDeps`]
+    /// 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
+    /// [`FutureReleaseErrorReportInDeps`]: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps
+    EditionAndFutureReleaseError(Edition),
     /// A custom reason.
     ///
     /// Choose this variant if the built-in text of the diagnostic of the
@@ -431,9 +443,14 @@ 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) => Some(e),
+
+            FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps
+            | FutureIncompatibilityReason::FutureReleaseErrorReportInDeps
+            | FutureIncompatibilityReason::FutureReleaseSemanticsChange
+            | FutureIncompatibilityReason::Custom(_) => None,
         }
     }
 }

compiler/rustc_middle/src/lint.rs

@@ -294,6 +294,7 @@ pub fn lint_level(
                 matches!(
                     incompat.reason,
                     FutureIncompatibilityReason::FutureReleaseErrorReportInDeps
+                        | FutureIncompatibilityReason::EditionAndFutureReleaseError(_)
                 )
             },
         );
@@ -382,6 +383,12 @@ 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::Custom(reason) => reason.to_owned(),
             };
 

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
@@ -58,3 +58,66 @@ LL |     help::<(), _>(1)?;
 
 warning: 3 warnings emitted
 
+Future incompatibility report: Future breakage diagnostic:
+warning: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:17:1
+   |
+LL | fn m() {
+   | ^^^^^^
+   |
+   = 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
+  --> $DIR/never-type-fallback-breaking.rs:21:17
+   |
+LL |         true => Default::default(),
+   |                 ^^^^^^^^^^^^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` 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:29:1
+   |
+LL | fn q() -> Option<()> {
+   | ^^^^^^^^^^^^^^^^^^^^
+   |
+   = 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
+  --> $DIR/never-type-fallback-breaking.rs:36:5
+   |
+LL |     deserialize()?;
+   |     ^^^^^^^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` 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:46:1
+   |
+LL | fn meow() -> Result<(), ()> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = 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
+  --> $DIR/never-type-fallback-breaking.rs:49:5
+   |
+LL |     help(1)?;
+   |     ^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     help::<(), _>(1)?;
+   |         +++++++++
+

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
@@ -20,3 +20,24 @@ LL |     let _x: () = return;
 
 warning: 1 warning emitted
 
+Future incompatibility report: Future breakage diagnostic:
+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 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
+  --> $DIR/defaulted-never-note.rs:32:9
+   |
+LL |     foo(_x);
+   |         ^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     let _x: () = return;
+   |           ++++
+

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
@@ -39,3 +39,45 @@ LL |     deserialize::<()>()?;
 
 warning: 2 warnings emitted
 
+Future incompatibility report: Future breakage diagnostic:
+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 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
+  --> $DIR/dependency-on-fallback-to-unit.rs:12:19
+   |
+LL |         false => <_>::default(),
+   |                   ^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |         false => <()>::default(),
+   |                   ~~
+
+Future breakage diagnostic:
+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 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
+  --> $DIR/dependency-on-fallback-to-unit.rs:22:5
+   |
+LL |     deserialize()?;
+   |     ^^^^^^^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     deserialize::<()>()?;
+   |                ++++++
+