add comment and bless some tests

Author: vn-ki

compiler/rustc_mir/src/const_eval/machine.rs

@@ -38,7 +38,11 @@ impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
         if instance.def.requires_caller_location(self.tcx()) {
             return Ok(false);
         }
-        // only memoize instrinsics
+        // Only memoize instrinsics. This was added in #79594 while adding the `const_allocate` intrinsic.
+        // We only memoize intrinsics because it would be unsound to memoize functions
+        // which might interact with the heap.
+        // Additionally, const_allocate intrinsic is impure and thus should not be memoized;
+        // it will not be memoized because it has non-ZST args
         if !matches!(instance.def, InstanceDef::Intrinsic(_)) {
             return Ok(false);
         }

src/test/ui/const-generics/const-argument-if-length.full.stderr

@@ -11,12 +11,6 @@ LL |     if std::mem::size_of::<T>() == 0 {
 LL | pub const fn size_of<T>() -> usize {
    |                      - required by this bound in `std::mem::size_of`
 
-error[E0080]: evaluation of constant value failed
-  --> $DIR/const-argument-if-length.rs:19:15
-   |
-LL |     pad: [u8; is_zst::<T>()],
-   |               ^^^^^^^^^^^^^ referenced constant has errors
-
 error[E0277]: the size for values of type `T` cannot be known at compilation time
   --> $DIR/const-argument-if-length.rs:17:12
    |
@@ -36,7 +30,6 @@ help: the `Box` type always has a statically known size and allocates its conten
 LL |     value: Box<T>,
    |            ^^^^ ^
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0080, E0277.
-For more information about an error, try `rustc --explain E0080`.
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/const-generics/const-argument-if-length.rs

@@ -18,7 +18,6 @@ pub struct AtLeastByte<T: ?Sized> {
     //~^ ERROR the size for values of type `T` cannot be known at compilation time
     pad: [u8; is_zst::<T>()],
     //[min]~^ ERROR generic parameters may not be used in const operations
-    //[full]~^^ ERROR evaluation of constant value failed
 }
 
 fn main() {}

src/test/ui/consts/const-eval/erroneous-const.stderr

@@ -24,18 +24,18 @@ note: the lint level is defined here
 LL | #![warn(const_err, unconditional_panic)]
    |         ^^^^^^^^^
 
-error[E0080]: evaluation of constant value failed
+error[E0080]: could not evaluate static initializer
   --> $DIR/erroneous-const.rs:12:17
    |
 LL |         let _ = PrintName::<T>::VOID;
-   |                 ^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
-
-error[E0080]: could not evaluate static initializer
-  --> $DIR/erroneous-const.rs:16:22
-   |
+   |                 ^^^^^^^^^^^^^^^^^^^^
+   |                 |
+   |                 referenced constant has errors
+   |                 inside `no_codegen::<i32>` at $DIR/erroneous-const.rs:12:17
+...
 LL | pub static FOO: () = no_codegen::<i32>();
-   |                      ^^^^^^^^^^^^^^^^^^^ referenced constant has errors
+   |                      ------------------- inside `FOO` at $DIR/erroneous-const.rs:16:22
 
-error: aborting due to 2 previous errors; 2 warnings emitted
+error: aborting due to previous error; 2 warnings emitted
 
 For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/const-eval/unwind-abort.rs

@@ -2,10 +2,10 @@
 
 #[unwind(aborts)]
 const fn foo() {
-    panic!() //~ evaluation of constant value failed
+    panic!() //~ 5:13: any use of this value will cause an error [const_err]
 }
 
-const _: () = foo(); //~ any use of this value will cause an error
+const _: () = foo();
 // Ensure that the CTFE engine handles calls to `#[unwind(aborts)]` gracefully
 
 fn main() {

src/test/ui/consts/const-eval/unwind-abort.stderr

@@ -1,21 +1,18 @@
-error[E0080]: evaluation of constant value failed
+error: any use of this value will cause an error
   --> $DIR/unwind-abort.rs:5:5
    |
 LL |     panic!()
-   |     ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/unwind-abort.rs:5:5
-   |
-   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: any use of this value will cause an error
-  --> $DIR/unwind-abort.rs:8:15
-   |
+   |     ^^^^^^^^
+   |     |
+   |     the evaluated program panicked at 'explicit panic', $DIR/unwind-abort.rs:5:5
+   |     inside `foo` at $SRC_DIR/std/src/macros.rs:LL:COL
+   |     inside `_` at $DIR/unwind-abort.rs:8:15
+...
 LL | const _: () = foo();
-   | --------------^^^^^-
-   |               |
-   |               referenced constant has errors
+   | --------------------
    |
    = note: `#[deny(const_err)]` on by default
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/const-size_of-cycle.stderr

@@ -14,11 +14,6 @@ note: ...which requires const-evaluating + checking `Foo::bytes::{constant#0}`..
    |
 LL |     bytes: [u8; std::mem::size_of::<Foo>()]
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires const-evaluating + checking `std::mem::size_of`...
-  --> $SRC_DIR/core/src/mem/mod.rs:LL:COL
-   |
-LL | pub const fn size_of<T>() -> usize {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: ...which requires computing layout of `Foo`...
    = note: ...which requires normalizing `[u8; _]`...
    = note: ...which again requires simplifying constant for the type system `Foo::bytes::{constant#0}`, completing the cycle

src/test/ui/consts/uninhabited-const-issue-61744.rs

@@ -1,15 +1,15 @@
 // build-fail
 
 pub const unsafe fn fake_type<T>() -> T {
-    hint_unreachable()
+    hint_unreachable() //~ 4:23: any use of this value will cause an error [const_err]
 }
 
 pub const unsafe fn hint_unreachable() -> ! {
-    fake_type() //~ ERROR evaluation of constant value failed
+    fake_type()
 }
 
 trait Const {
-    const CONSTANT: i32 = unsafe { fake_type() }; //~ ERROR any use of this value will cause an err
+    const CONSTANT: i32 = unsafe { fake_type() };
 }
 
 impl<T> Const for T {}