Auto merge of #71049 - eddyb:const-err, r=oli-obk

Add `ConstKind::Error` and convert `ErrorHandled::Reported` to it.

By replicating the `ty::Error` approach to encoding "an error has occurred", all of the mechanisms that skip redundant/downstream errors are engaged and help out (see the reduction in test output).

This PR also adds `ErrorHandled::Linted` for the lint case because using `ErrorHandled::Reported` *without* having emitted an error that is *guaranteed* to stop compilation, is incorrect now.

r? @oli-obk cc @rust-lang/wg-const-eval @varkor @yodaldevoid

Author: bors

src/librustc_codegen_ssa/mir/operand.rs

@@ -6,6 +6,7 @@ use crate::glue;
 use crate::traits::*;
 use crate::MemFlags;
 
+use rustc_errors::ErrorReported;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::{ConstValue, ErrorHandled, Pointer, Scalar};
 use rustc_middle::ty::layout::TyAndLayout;
@@ -447,8 +448,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 self.eval_mir_constant_to_operand(bx, constant).unwrap_or_else(|err| {
                     match err {
                         // errored or at least linted
-                        ErrorHandled::Reported => {}
-                        ErrorHandled::TooGeneric => bug!("codgen encountered polymorphic constant"),
+                        ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted => {}
+                        ErrorHandled::TooGeneric => {
+                            bug!("codegen encountered polymorphic constant")
+                        }
                     }
                     // Allow RalfJ to sleep soundly knowing that even refactorings that remove
                     // the above error (or silence it under some conditions) will not cause UB.

src/librustc_infer/infer/error_reporting/mod.rs

@@ -304,8 +304,8 @@ pub fn unexpected_hidden_region_diagnostic(
         // down this path which gives a decent human readable
         // explanation.
         //
-        // (*) if not, the `tainted_by_errors` flag would be set to
-        // true in any case, so we wouldn't be here at all.
+        // (*) if not, the `tainted_by_errors` field would be set to
+        // `Some(ErrorReported)` in any case, so we wouldn't be here at all.
         note_and_explain_free_region(
             tcx,
             &mut err,