Detect uninhabited types early in const eval.

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -335,8 +335,8 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
     }
 
     #[inline(always)]
-    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>, _layout: TyAndLayout<'tcx>) -> bool {
-        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks
+    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool {
+        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks || layout.abi.is_uninhabited()
     }
 
     fn alignment_check_failed(

tests/ui/consts/const-eval/ub-uninhabit.rs

@@ -14,12 +14,12 @@ union MaybeUninit<T: Copy> {
 }
 
 const BAD_BAD_BAD: Bar = unsafe { MaybeUninit { uninit: () }.init };
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
 
 const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
 //~^ ERROR it is undefined behavior to use this value
 
 const BAD_BAD_ARRAY: [Bar; 1] = unsafe { MaybeUninit { uninit: () }.init };
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
 
 fn main() {}

tests/ui/consts/const-eval/ub-uninhabit.stderr

@@ -1,11 +1,8 @@
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-uninhabit.rs:16:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-uninhabit.rs:16:35
    |
 LL | const BAD_BAD_BAD: Bar = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a value of uninhabited type Bar
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: $SIZE, align: $ALIGN) {}
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a value of uninhabited type Bar
 
 error[E0080]: it is undefined behavior to use this value
   --> $DIR/ub-uninhabit.rs:19:1
@@ -18,14 +15,11 @@ LL | const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
                HEX_DUMP
            }
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-uninhabit.rs:22:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ub-uninhabit.rs:22:42
    |
 LL | const BAD_BAD_ARRAY: [Bar; 1] = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered a value of uninhabited type Bar
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: $SIZE, align: $ALIGN) {}
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered a value of uninhabited type Bar
 
 error: aborting due to 3 previous errors
 

tests/ui/consts/const-eval/validate_uninhabited_zsts.32bit.stderr

@@ -24,14 +24,11 @@ note: inside `FOO`
 LL | const FOO: [empty::Empty; 3] = [foo(); 3];
    |                                 ^^^^^
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/validate_uninhabited_zsts.rs:21:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/validate_uninhabited_zsts.rs:21:42
    |
 LL | const BAR: [empty::Empty; 3] = [unsafe { std::mem::transmute(()) }; 3];
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0].0: encountered a value of uninhabited type empty::Void
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 0, align: 1) {}
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered a value of uninhabited type empty::Void
 
 warning: the type `empty::Empty` does not permit zero-initialization
   --> $DIR/validate_uninhabited_zsts.rs:21:42

tests/ui/consts/const-eval/validate_uninhabited_zsts.64bit.stderr

@@ -24,14 +24,11 @@ note: inside `FOO`
 LL | const FOO: [empty::Empty; 3] = [foo(); 3];
    |                                 ^^^^^
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/validate_uninhabited_zsts.rs:21:1
+error[E0080]: evaluation of constant value failed
+  --> $DIR/validate_uninhabited_zsts.rs:21:42
    |
 LL | const BAR: [empty::Empty; 3] = [unsafe { std::mem::transmute(()) }; 3];
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0].0: encountered a value of uninhabited type empty::Void
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 0, align: 1) {}
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered a value of uninhabited type empty::Void
 
 warning: the type `empty::Empty` does not permit zero-initialization
   --> $DIR/validate_uninhabited_zsts.rs:21:42

tests/ui/consts/const-eval/validate_uninhabited_zsts.rs

@@ -19,7 +19,7 @@ pub mod empty {
 const FOO: [empty::Empty; 3] = [foo(); 3];
 
 const BAR: [empty::Empty; 3] = [unsafe { std::mem::transmute(()) }; 3];
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
 //~| WARN the type `empty::Empty` does not permit zero-initialization
 
 fn main() {

tests/ui/consts/issue-64506.rs

@@ -1,4 +1,4 @@
-// check-pass
+// check-fail
 
 #[derive(Copy, Clone)]
 pub struct ChildStdin {
@@ -14,6 +14,7 @@ const FOO: () = {
         b: (),
     }
     let x = unsafe { Foo { b: () }.a };
+    //~^ ERROR: evaluation of constant value failed
     let x = &x.inner;
 };
 

tests/ui/consts/issue-64506.stderr

@@ -0,0 +1,9 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/issue-64506.rs:16:22
+   |
+LL |     let x = unsafe { Foo { b: () }.a };
+   |                      ^^^^^^^^^^^^^^^ constructing invalid value at .inner: encountered a value of uninhabited type AnonPipe
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.