Report never type lints in dependencies

compiler/rustc_lint_defs/src/builtin.rs

@@ -4131,6 +4131,7 @@ declare_lint! {
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::EditionAndFutureReleaseSemanticsChange(Edition::Edition2024),
         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>",
+        report_in_deps: true,
     };
     @edition Edition2024 => Deny;
     report_in_external_macro
@@ -4185,6 +4186,7 @@ declare_lint! {
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::EditionAndFutureReleaseError(Edition::Edition2024),
         reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>",
+        report_in_deps: true,
     };
     report_in_external_macro
 }

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

@@ -96,3 +96,108 @@ LL |     takes_apit2(mk::<()>()?);
 
 warning: 5 warnings emitted
 
+Future incompatibility report: Future breakage diagnostic:
+warning: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:18:1
+   |
+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 <https://doc.rust-lang.org/nightly/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
+   |
+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:30:1
+   |
+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 <https://doc.rust-lang.org/nightly/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
+   |
+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:47:1
+   |
+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 <https://doc.rust-lang.org/nightly/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
+   |
+LL |     help(1)?;
+   |     ^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` 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
+   |
+LL | pub fn fallback_return() -> 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 <https://doc.rust-lang.org/nightly/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
+   |
+LL |     takes_apit(|| Default::default())?;
+   |                   ^^^^^^^^^^^^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` 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
+   |
+LL | fn fully_apit() -> 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 <https://doc.rust-lang.org/nightly/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
+   |
+LL |     takes_apit2(mk()?);
+   |                 ^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     takes_apit2(mk::<()>()?);
+   |                   ++++++
+

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

@@ -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 <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = 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/dependency-on-fallback-to-unit.stderr

@@ -40,3 +40,46 @@ 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 <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = 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(),
+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 <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = 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::<()>()?;
+   |                ++++++
+

tests/ui/never_type/diverging-fallback-control-flow.nofallback.stderr

@@ -39,3 +39,45 @@ LL |     let x: ();
 
 warning: 2 warnings emitted
 
+Future incompatibility report: Future breakage diagnostic:
+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 Rust 2024 and in a future release in all editions!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `!: UnitDefault` will fail
+  --> $DIR/diverging-fallback-control-flow.rs:36:13
+   |
+LL |         x = UnitDefault::default();
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     let x: ();
+   |          ++++
+
+Future breakage diagnostic:
+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 Rust 2024 and in a future release in all editions!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `!: UnitDefault` will fail
+  --> $DIR/diverging-fallback-control-flow.rs:50:13
+   |
+LL |         x = UnitDefault::default();
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     let x: ();
+   |          ++++
+

tests/ui/never_type/diverging-fallback-no-leak.nofallback.stderr

@@ -20,3 +20,24 @@ LL |     unconstrained_arg::<()>(return);
 
 warning: 1 warning emitted
 
+Future incompatibility report: Future breakage diagnostic:
+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 Rust 2024 and in a future release in all editions!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `!: Test` will fail
+  --> $DIR/diverging-fallback-no-leak.rs:20:23
+   |
+LL |     unconstrained_arg(return);
+   |                       ^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     unconstrained_arg::<()>(return);
+   |                      ++++++
+

tests/ui/never_type/diverging-fallback-unconstrained-return.nofallback.stderr

@@ -20,3 +20,24 @@ LL |     let _: () = if true { unconstrained_return() } else { panic!() };
 
 warning: 1 warning emitted
 
+Future incompatibility report: Future breakage diagnostic:
+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 Rust 2024 and in a future release in all editions!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `!: UnitReturn` will fail
+  --> $DIR/diverging-fallback-unconstrained-return.rs:39:23
+   |
+LL |     let _ = if true { unconstrained_return() } else { panic!() };
+   |                       ^^^^^^^^^^^^^^^^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     let _: () = if true { unconstrained_return() } else { panic!() };
+   |          ++++
+

tests/ui/never_type/dont-suggest-turbofish-from-expansion.stderr

@@ -24,3 +24,28 @@ LL |         let created: () = create_ok_default()?;
 
 error: aborting due to 1 previous error
 
+Future incompatibility report: Future breakage diagnostic:
+error: this function depends on never type fallback being `()`
+  --> $DIR/dont-suggest-turbofish-from-expansion.rs:10:1
+   |
+LL | fn main() -> 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 <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `!: Default` will fail
+  --> $DIR/dont-suggest-turbofish-from-expansion.rs:14:23
+   |
+LL |         let created = create_ok_default()?;
+   |                       ^^^^^^^^^^^^^^^^^^^
+note: the lint level is defined here
+  --> $DIR/dont-suggest-turbofish-from-expansion.rs:1:9
+   |
+LL | #![deny(dependency_on_unit_never_type_fallback)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: use `()` annotations to avoid fallback changes
+   |
+LL |         let created: () = create_ok_default()?;
+   |                    ++++
+

tests/ui/never_type/fallback-closure-ret.nofallback.stderr

@@ -20,3 +20,24 @@ LL |     foo::<()>(|| panic!());
 
 warning: 1 warning emitted
 
+Future incompatibility report: Future breakage diagnostic:
+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 Rust 2024 and in a future release in all editions!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `!: Bar` will fail
+  --> $DIR/fallback-closure-ret.rs:24:5
+   |
+LL |     foo(|| panic!());
+   |     ^^^^^^^^^^^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     foo::<()>(|| panic!());
+   |        ++++++
+

tests/ui/never_type/impl_trait_fallback.stderr

@@ -16,3 +16,20 @@ LL | fn should_ret_unit() -> impl T {
 
 warning: 1 warning emitted
 
+Future incompatibility report: Future breakage diagnostic:
+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 Rust 2024 and in a future release in all editions!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `!: T` will fail
+  --> $DIR/impl_trait_fallback.rs:8:25
+   |
+LL | fn should_ret_unit() -> impl T {
+   |                         ^^^^^^
+   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
+

tests/ui/never_type/lint-breaking-2024-assign-underscore.stderr

@@ -24,3 +24,28 @@ LL |     _ = foo::<()>()?;
 
 error: aborting due to 1 previous error
 
+Future incompatibility report: Future breakage diagnostic:
+error: this function depends on never type fallback being `()`
+  --> $DIR/lint-breaking-2024-assign-underscore.rs:10:1
+   |
+LL | fn test() -> 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 <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `!: Default` will fail
+  --> $DIR/lint-breaking-2024-assign-underscore.rs:13:9
+   |
+LL |     _ = foo()?;
+   |         ^^^^^
+note: the lint level is defined here
+  --> $DIR/lint-breaking-2024-assign-underscore.rs:4:9
+   |
+LL | #![deny(dependency_on_unit_never_type_fallback)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     _ = foo::<()>()?;
+   |            ++++++
+