Rollup merge of #97743 - RalfJung:const-err-future-breakage, r=estebank

make const_err show up in future breakage reports

As tracked in #71800, const_err should become a hard error Any Day Now (TM). I'd love to move forward with that sooner rather than later; it has been deny-by-default for many years and a future incompat lint since #80394 (landed more than a year ago). Some CTFE errors are already hard errors since #86194. But before we truly make it a hard error in all cases, we now have one more intermediate step we can take -- to make it show up in future breakage reports.

Cc `````@rust-lang/wg-const-eval`````

compiler/rustc_lint_defs/src/builtin.rs

@@ -289,6 +289,7 @@ declare_lint! {
     "constant evaluation encountered erroneous expression",
     @future_incompatible = FutureIncompatibleInfo {
         reference: "issue #71800 <https://github.com/rust-lang/rust/issues/71800>",
+        reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
     };
     report_in_external_macro
 }

src/test/ui/array-slice-vec/array_const_index-0.stderr

@@ -12,3 +12,16 @@ LL | const B: i32 = (&A)[1];
 
 error: aborting due to previous error
 
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/array_const_index-0.rs:2:16
+   |
+LL | const B: i32 = (&A)[1];
+   | ---------------^^^^^^^-
+   |                |
+   |                index out of bounds: the length is 0 but the index is 1
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+

src/test/ui/array-slice-vec/array_const_index-1.stderr

@@ -12,3 +12,16 @@ LL | const B: i32 = A[1];
 
 error: aborting due to previous error
 
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/array_const_index-1.rs:2:16
+   |
+LL | const B: i32 = A[1];
+   | ---------------^^^^-
+   |                |
+   |                index out of bounds: the length is 0 but the index is 1
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+

src/test/ui/associated-consts/defaults-not-assumed-fail.stderr

@@ -29,3 +29,28 @@ LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above
 error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0080`.
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/defaults-not-assumed-fail.rs:8:19
+   |
+LL |     const B: u8 = Self::A + 1;
+   |     --------------^^^^^^^^^^^-
+   |                   |
+   |                   attempt to compute `u8::MAX + 1_u8`, which would overflow
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: erroneous constant used
+  --> $DIR/defaults-not-assumed-fail.rs:34:5
+   |
+LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+   = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+

src/test/ui/borrowck/issue-81899.stderr

@@ -27,3 +27,16 @@ LL | const _CONST: &[u8] = &f(&[], |_| {});
 error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0080`.
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/issue-81899.rs:4:23
+   |
+LL | const _CONST: &[u8] = &f(&[], |_| {});
+   | ----------------------^^^^^^^^^^^^^^^-
+   |                       |
+   |                       referenced constant has errors
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+

src/test/ui/borrowck/issue-88434-minimal-example.stderr

@@ -27,3 +27,16 @@ LL | const _CONST: &() = &f(&|_| {});
 error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0080`.
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/issue-88434-minimal-example.rs:3:21
+   |
+LL | const _CONST: &() = &f(&|_| {});
+   | --------------------^^^^^^^^^^^-
+   |                     |
+   |                     referenced constant has errors
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+

src/test/ui/borrowck/issue-88434-removal-index-should-be-less.stderr

@@ -27,3 +27,16 @@ LL | const _CONST: &[u8] = &f(&[], |_| {});
 error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0080`.
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/issue-88434-removal-index-should-be-less.rs:3:23
+   |
+LL | const _CONST: &[u8] = &f(&[], |_| {});
+   | ----------------------^^^^^^^^^^^^^^^-
+   |                       |
+   |                       referenced constant has errors
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+

src/test/ui/consts/assert-type-intrinsics.stderr

@@ -37,3 +37,45 @@ LL | |     };
 
 error: aborting due to 3 previous errors
 
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/assert-type-intrinsics.rs:14:9
+   |
+LL | /     const _BAD1: () = unsafe {
+LL | |         MaybeUninit::<!>::uninit().assume_init();
+   | |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ aborted execution: attempted to instantiate uninhabited type `!`
+LL | |     };
+   | |______-
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/assert-type-intrinsics.rs:17:9
+   |
+LL | /     const _BAD2: () = unsafe {
+LL | |         intrinsics::assert_uninit_valid::<bool>();
+   | |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ aborted execution: attempted to leave type `bool` uninitialized, which is invalid
+LL | |     };
+   | |______-
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/assert-type-intrinsics.rs:20:9
+   |
+LL | /     const _BAD3: () = unsafe {
+LL | |         intrinsics::assert_zero_valid::<&'static i32>();
+   | |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ aborted execution: attempted to zero-initialize type `&i32`, which is invalid
+LL | |     };
+   | |______-
+   |
+   = note: `#[deny(const_err)]` on by default
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+

src/test/ui/consts/assoc_const_generic_impl.stderr

@@ -22,3 +22,20 @@ LL |         let () = Self::I_AM_ZERO_SIZED;
 
 error: aborting due to previous error; 1 warning emitted
 
+Future incompatibility report: Future breakage diagnostic:
+warning: any use of this value will cause an error
+  --> $DIR/assoc_const_generic_impl.rs:11:34
+   |
+LL |     const I_AM_ZERO_SIZED: ()  = [()][std::mem::size_of::<Self>()];
+   |     -----------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
+   |                                  |
+   |                                  index out of bounds: the length is 1 but the index is 4
+   |
+note: the lint level is defined here
+  --> $DIR/assoc_const_generic_impl.rs:3:9
+   |
+LL | #![warn(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+

src/test/ui/consts/const-err-early.stderr

@@ -60,3 +60,88 @@ LL | pub const E: u8 = [5u8][1];
 
 error: aborting due to 5 previous errors
 
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/const-err-early.rs:3:19
+   |
+LL | pub const A: i8 = -i8::MIN;
+   | ------------------^^^^^^^^-
+   |                   |
+   |                   attempt to negate `i8::MIN`, which would overflow
+   |
+note: the lint level is defined here
+  --> $DIR/const-err-early.rs:1:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/const-err-early.rs:5:19
+   |
+LL | pub const B: u8 = 200u8 + 200u8;
+   | ------------------^^^^^^^^^^^^^-
+   |                   |
+   |                   attempt to compute `200_u8 + 200_u8`, which would overflow
+   |
+note: the lint level is defined here
+  --> $DIR/const-err-early.rs:1:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/const-err-early.rs:7:19
+   |
+LL | pub const C: u8 = 200u8 * 4;
+   | ------------------^^^^^^^^^-
+   |                   |
+   |                   attempt to compute `200_u8 * 4_u8`, which would overflow
+   |
+note: the lint level is defined here
+  --> $DIR/const-err-early.rs:1:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/const-err-early.rs:9:19
+   |
+LL | pub const D: u8 = 42u8 - (42u8 + 1);
+   | ------------------^^^^^^^^^^^^^^^^^-
+   |                   |
+   |                   attempt to compute `42_u8 - 43_u8`, which would overflow
+   |
+note: the lint level is defined here
+  --> $DIR/const-err-early.rs:1:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/const-err-early.rs:11:19
+   |
+LL | pub const E: u8 = [5u8][1];
+   | ------------------^^^^^^^^-
+   |                   |
+   |                   index out of bounds: the length is 1 but the index is 1
+   |
+note: the lint level is defined here
+  --> $DIR/const-err-early.rs:1:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+

src/test/ui/consts/const-err-multi.stderr

@@ -49,3 +49,71 @@ LL | pub const D: i8 = 50 - A;
 
 error: aborting due to 4 previous errors
 
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/const-err-multi.rs:3:19
+   |
+LL | pub const A: i8 = -i8::MIN;
+   | ------------------^^^^^^^^-
+   |                   |
+   |                   attempt to negate `i8::MIN`, which would overflow
+   |
+note: the lint level is defined here
+  --> $DIR/const-err-multi.rs:1:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/const-err-multi.rs:6:19
+   |
+LL | pub const B: i8 = A;
+   | ------------------^-
+   |                   |
+   |                   referenced constant has errors
+   |
+note: the lint level is defined here
+  --> $DIR/const-err-multi.rs:1:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/const-err-multi.rs:9:19
+   |
+LL | pub const C: u8 = A as u8;
+   | ------------------^-------
+   |                   |
+   |                   referenced constant has errors
+   |
+note: the lint level is defined here
+  --> $DIR/const-err-multi.rs:1:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/const-err-multi.rs:12:24
+   |
+LL | pub const D: i8 = 50 - A;
+   | -----------------------^-
+   |                        |
+   |                        referenced constant has errors
+   |
+note: the lint level is defined here
+  --> $DIR/const-err-multi.rs:1:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+

src/test/ui/consts/const-err.stderr

@@ -29,3 +29,20 @@ LL |     black_box((FOO, FOO));
 error: aborting due to 2 previous errors; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0080`.
+Future incompatibility report: Future breakage diagnostic:
+warning: any use of this value will cause an error
+  --> $DIR/const-err.rs:11:17
+   |
+LL | const FOO: u8 = [5u8][1];
+   | ----------------^^^^^^^^-
+   |                 |
+   |                 index out of bounds: the length is 1 but the index is 1
+   |
+note: the lint level is defined here
+  --> $DIR/const-err.rs:5:9
+   |
+LL | #![warn(const_err)]
+   |         ^^^^^^^^^
+   = 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 #71800 <https://github.com/rust-lang/rust/issues/71800>
+