Rollup merge of #80394 - RalfJung:const-err-future, r=oli-obk

make const_err a future incompat lint This is the first step for #71800: make const_err a future-incompat lint. I also rewrote the const_err lint description as the old one seemed wrong. This has the unfortunate side-effect of making const-eval error even more verbose by making the const_err message longer without fixing the redundancy caused by additionally emitting an error on each use site of the constant. We cannot fix that redundancy until const_err is a *hard* error (at that point the error-on-use-site can be turned into a `delay_span_bug!` for uses of monomorphic consts, and into a nicely rendered error for [lazily / post-monomorhization evaluated] associated consts). ~~The one annoying effect of this PR is that `let _x = &(1/(1-1));` now also shows the future-incompat warning, even though of course we will *not* make this a hard error. We'll instead (hopefully) stop promoting it -- see rust-lang/rfcs#3027. The only way I see to avoid the future-incompat warning is to use a different lint for "failure to evaluate promoted".~~ Cc `@rust-lang/wg-const-eval`
rust-lang · Feb 3, 2021 · 00dabfb · 00dabfb
2 parents 6ad11e2 + 8477d35
commit 00dabfb
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diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
@@ -255,6 +255,10 @@ declare_lint! {
     pub CONST_ERR,
     Deny,
     "constant evaluation encountered erroneous expression",
+    @future_incompatible = FutureIncompatibleInfo {
+        reference: "issue #71800 <https://github.com/rust-lang/rust/issues/71800>",
+        edition: None,
+    };
     report_in_external_macro
 }
 

diff --git a/src/test/ui/array-slice-vec/array_const_index-0.rs b/src/test/ui/array-slice-vec/array_const_index-0.rs
@@ -2,6 +2,7 @@ const A: &'static [i32] = &[];
 const B: i32 = (&A)[1];
 //~^ index out of bounds: the length is 0 but the index is 1
 //~| ERROR any use of this value will cause an error
+//~| WARN this was previously accepted by the compiler but is being phased out
 
 fn main() {
     let _ = B;

diff --git a/src/test/ui/array-slice-vec/array_const_index-0.stderr b/src/test/ui/array-slice-vec/array_const_index-0.stderr
@@ -7,6 +7,8 @@ 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>
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/array-slice-vec/array_const_index-1.rs b/src/test/ui/array-slice-vec/array_const_index-1.rs
@@ -2,6 +2,7 @@ const A: [i32; 0] = [];
 const B: i32 = A[1];
 //~^ index out of bounds: the length is 0 but the index is 1
 //~| ERROR any use of this value will cause an error
+//~| WARN this was previously accepted by the compiler but is being phased out
 
 fn main() {
     let _ = B;

diff --git a/src/test/ui/array-slice-vec/array_const_index-1.stderr b/src/test/ui/array-slice-vec/array_const_index-1.stderr
@@ -7,6 +7,8 @@ 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>
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/associated-consts/defaults-not-assumed-fail.rs b/src/test/ui/associated-consts/defaults-not-assumed-fail.rs
@@ -7,6 +7,7 @@ trait Tr {
     // `Self::A` must not be assumed to hold inside the trait.
     const B: u8 = Self::A + 1;
     //~^ ERROR any use of this value will cause an error
+    //~| WARN this was previously accepted by the compiler but is being phased out
 }
 
 // An impl that doesn't override any constant will NOT cause a const eval error
@@ -33,6 +34,7 @@ fn main() {
     assert_eq!(<() as Tr>::B, 0);    // causes the error above
     //~^ ERROR evaluation of constant value failed
     //~| ERROR erroneous constant used
+    //~| WARN this was previously accepted by the compiler but is being phased out
 
     assert_eq!(<u8 as Tr>::A, 254);
     assert_eq!(<u8 as Tr>::B, 255);

diff --git a/src/test/ui/associated-consts/defaults-not-assumed-fail.stderr b/src/test/ui/associated-consts/defaults-not-assumed-fail.stderr
@@ -7,19 +7,23 @@ 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>
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/defaults-not-assumed-fail.rs:33:16
+  --> $DIR/defaults-not-assumed-fail.rs:34:16
    |
 LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above
    |                ^^^^^^^^^^^^^ referenced constant has errors
 
 error: erroneous constant used
-  --> $DIR/defaults-not-assumed-fail.rs:33:5
+  --> $DIR/defaults-not-assumed-fail.rs:34:5
    |
 LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
    |
+   = 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 a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 3 previous errors

diff --git a/src/test/ui/const-ptr/out_of_bounds_read.stderr b/src/test/ui/const-ptr/out_of_bounds_read.stderr
@@ -15,6 +15,8 @@ LL |     const _READ: u32 = unsafe { ptr::read(PAST_END_PTR) };
    |     ------------------------------------------------------
    |
    = 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>
 
 error: any use of this value will cause an error
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
@@ -32,6 +34,9 @@ LL |     unsafe { copy_nonoverlapping(src, dst, count) }
    |
 LL |     const _CONST_READ: u32 = unsafe { PAST_END_PTR.read() };
    |     --------------------------------------------------------
+   |
+   = 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>
 
 error: any use of this value will cause an error
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
@@ -49,6 +54,9 @@ LL |     unsafe { copy_nonoverlapping(src, dst, count) }
    |
 LL |     const _MUT_READ: u32 = unsafe { (PAST_END_PTR as *mut u32).read() };
    |     --------------------------------------------------------------------
+   |
+   = 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>
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/consts/assoc_const_generic_impl.rs b/src/test/ui/consts/assoc_const_generic_impl.rs
@@ -9,6 +9,7 @@ trait ZeroSized: Sized {
 
 impl<T: Sized> ZeroSized for T {
     const I_AM_ZERO_SIZED: ()  = [()][std::mem::size_of::<Self>()]; //~ WARN any use of this value
+    //~| WARN this was previously accepted by the compiler but is being phased out
     fn requires_zero_size(self) {
         let () = Self::I_AM_ZERO_SIZED; //~ ERROR erroneous constant encountered
         println!("requires_zero_size called");

diff --git a/src/test/ui/consts/assoc_const_generic_impl.stderr b/src/test/ui/consts/assoc_const_generic_impl.stderr
@@ -11,9 +11,11 @@ note: the lint level is defined here
    |
 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>
 
 error: erroneous constant encountered
-  --> $DIR/assoc_const_generic_impl.rs:13:18
+  --> $DIR/assoc_const_generic_impl.rs:14:18
    |
 LL |         let () = Self::I_AM_ZERO_SIZED;
    |                  ^^^^^^^^^^^^^^^^^^^^^

diff --git a/src/test/ui/consts/assume-type-intrinsics.stderr b/src/test/ui/consts/assume-type-intrinsics.stderr
@@ -16,6 +16,8 @@ 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>
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/consts/const-err-early.rs b/src/test/ui/consts/const-err-early.rs
@@ -1,10 +1,15 @@
 #![deny(const_err)]
 
 pub const A: i8 = -i8::MIN; //~ ERROR const_err
+//~| WARN this was previously accepted by the compiler but is being phased out
 pub const B: u8 = 200u8 + 200u8; //~ ERROR const_err
+//~| WARN this was previously accepted by the compiler but is being phased out
 pub const C: u8 = 200u8 * 4; //~ ERROR const_err
+//~| WARN this was previously accepted by the compiler but is being phased out
 pub const D: u8 = 42u8 - (42u8 + 1); //~ ERROR const_err
+//~| WARN this was previously accepted by the compiler but is being phased out
 pub const E: u8 = [5u8][1]; //~ ERROR const_err
+//~| WARN this was previously accepted by the compiler but is being phased out
 
 fn main() {
     let _a = A;

diff --git a/src/test/ui/consts/const-err-early.stderr b/src/test/ui/consts/const-err-early.stderr
@@ -11,38 +11,52 @@ note: the lint level is defined here
    |
 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>
 
 error: any use of this value will cause an error
-  --> $DIR/const-err-early.rs:4:19
+  --> $DIR/const-err-early.rs:5:19
    |
 LL | pub const B: u8 = 200u8 + 200u8;
    | ------------------^^^^^^^^^^^^^-
    |                   |
    |                   attempt to compute `200_u8 + 200_u8`, which would overflow
+   |
+   = 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>
 
 error: any use of this value will cause an error
-  --> $DIR/const-err-early.rs:5:19
+  --> $DIR/const-err-early.rs:7:19
    |
 LL | pub const C: u8 = 200u8 * 4;
    | ------------------^^^^^^^^^-
    |                   |
    |                   attempt to compute `200_u8 * 4_u8`, which would overflow
+   |
+   = 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>
 
 error: any use of this value will cause an error
-  --> $DIR/const-err-early.rs:6:19
+  --> $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
+   |
+   = 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>
 
 error: any use of this value will cause an error
-  --> $DIR/const-err-early.rs:7:19
+  --> $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
+   |
+   = 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>
 
 error: aborting due to 5 previous errors
 
diff --git a/src/test/ui/consts/const-err-multi.rs b/src/test/ui/consts/const-err-multi.rs
@@ -2,12 +2,16 @@
 
 pub const A: i8 = -i8::MIN;
 //~^ ERROR const_err
+//~| WARN this was previously accepted by the compiler but is being phased out
 pub const B: i8 = A;
 //~^ ERROR const_err
+//~| WARN this was previously accepted by the compiler but is being phased out
 pub const C: u8 = A as u8;
 //~^ ERROR const_err
+//~| WARN this was previously accepted by the compiler but is being phased out
 pub const D: i8 = 50 - A;
 //~^ ERROR const_err
+//~| WARN this was previously accepted by the compiler but is being phased out
 
 fn main() {
     let _ = (A, B, C, D);

diff --git a/src/test/ui/consts/const-err-multi.stderr b/src/test/ui/consts/const-err-multi.stderr
@@ -11,30 +11,41 @@ note: the lint level is defined here
    |
 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>
 
 error: any use of this value will cause an error
-  --> $DIR/const-err-multi.rs:5:19
+  --> $DIR/const-err-multi.rs:6:19
    |
 LL | pub const B: i8 = A;
    | ------------------^-
    |                   |
    |                   referenced constant has errors
+   |
+   = 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>
 
 error: any use of this value will cause an error
-  --> $DIR/const-err-multi.rs:7:19
+  --> $DIR/const-err-multi.rs:9:19
    |
 LL | pub const C: u8 = A as u8;
    | ------------------^-------
    |                   |
    |                   referenced constant has errors
+   |
+   = 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>
 
 error: any use of this value will cause an error
-  --> $DIR/const-err-multi.rs:9:24
+  --> $DIR/const-err-multi.rs:12:24
    |
 LL | pub const D: i8 = 50 - A;
    | -----------------------^-
    |                        |
    |                        referenced constant has errors
+   |
+   = 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>
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/consts/const-err.rs b/src/test/ui/consts/const-err.rs
@@ -10,6 +10,7 @@ fn black_box<T>(_: T) {
 
 const FOO: u8 = [5u8][1];
 //~^ WARN any use of this value will cause an error
+//~| WARN this was previously accepted by the compiler but is being phased out
 
 fn main() {
     black_box((FOO, FOO));

diff --git a/src/test/ui/consts/const-err.stderr b/src/test/ui/consts/const-err.stderr
@@ -11,15 +11,17 @@ note: the lint level is defined here
    |
 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>
 
 error[E0080]: erroneous constant used
-  --> $DIR/const-err.rs:15:16
+  --> $DIR/const-err.rs:16:16
    |
 LL |     black_box((FOO, FOO));
    |                ^^^ referenced constant has errors
 
 error[E0080]: erroneous constant used
-  --> $DIR/const-err.rs:15:21
+  --> $DIR/const-err.rs:16:21
    |
 LL |     black_box((FOO, FOO));
    |                     ^^^ referenced constant has errors

diff --git a/src/test/ui/consts/const-eval/conditional_array_execution.rs b/src/test/ui/consts/const-eval/conditional_array_execution.rs
@@ -6,9 +6,11 @@ const X: u32 = 5;
 const Y: u32 = 6;
 const FOO: u32 = [X - Y, Y - X][(X < Y) as usize];
 //~^ WARN any use of this value will cause an error
+//~| WARN this was previously accepted by the compiler but is being phased out
 
 fn main() {
     println!("{}", FOO);
     //~^ ERROR
     //~| WARN erroneous constant used [const_err]
+    //~| WARN this was previously accepted by the compiler but is being phased out
 }
diff --git a/src/test/ui/consts/const-eval/conditional_array_execution.stderr b/src/test/ui/consts/const-eval/conditional_array_execution.stderr
@@ -11,18 +11,23 @@ note: the lint level is defined here
    |
 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>
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/conditional_array_execution.rs:11:20
+  --> $DIR/conditional_array_execution.rs:12:20
    |
 LL |     println!("{}", FOO);
    |                    ^^^ referenced constant has errors
 
 warning: erroneous constant used
-  --> $DIR/conditional_array_execution.rs:11:20
+  --> $DIR/conditional_array_execution.rs:12:20
    |
 LL |     println!("{}", FOO);
    |                    ^^^ referenced constant has errors
+   |
+   = 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>
 
 error: aborting due to previous error; 2 warnings emitted