Allow const eval failures if the cause is a type layout issue

Author: oli-obk

compiler/rustc_const_eval/src/const_eval/error.rs

@@ -2,7 +2,7 @@ use std::mem;
 
 use rustc_errors::{DiagArgName, DiagArgValue, DiagMessage, Diagnostic, IntoDiagArg};
 use rustc_hir::CRATE_HIR_ID;
-use rustc_middle::mir::interpret::Provenance;
+use rustc_middle::mir::interpret::{Provenance, ReportedErrorInfo};
 use rustc_middle::mir::AssertKind;
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::TyCtxt;
@@ -139,9 +139,10 @@ where
             ErrorHandled::TooGeneric(span)
         }
         err_inval!(AlreadyReported(guar)) => ErrorHandled::Reported(guar, span),
-        err_inval!(Layout(LayoutError::ReferencesError(guar))) => {
-            ErrorHandled::Reported(guar.into(), span)
-        }
+        err_inval!(Layout(LayoutError::ReferencesError(guar))) => ErrorHandled::Reported(
+            ReportedErrorInfo::tainted_by_errors(guar),
+            span,
+        ),
         // Report remaining errors.
         _ => {
             let (our_span, frames) = get_span_and_frames();

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -1181,9 +1181,20 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
         M::eval_mir_constant(self, *val, span, layout, |ecx, val, span, layout| {
             let const_val = val.eval(*ecx.tcx, ecx.param_env, span).map_err(|err| {
-                if M::ALL_CONSTS_ARE_PRECHECKED && !matches!(err, ErrorHandled::TooGeneric(..)) {
-                    // Looks like the const is not captued by `required_consts`, that's bad.
-                    bug!("interpret const eval failure of {val:?} which is not in required_consts");
+                if M::ALL_CONSTS_ARE_PRECHECKED {
+                    match err {
+                        ErrorHandled::TooGeneric(..) => {},
+                        ErrorHandled::Reported(reported, span) => {
+                            if reported.is_tainted_by_errors() {
+                                // const-eval will return "tainted" errors if e.g. the layout cannot
+                                // be computed as the type references non-existing names.
+                                // See <https://github.com/rust-lang/rust/issues/124348>.
+                            } else {
+                                // Looks like the const is not captued by `required_consts`, that's bad.
+                                span_bug!(span, "interpret const eval failure of {val:?} which is not in required_consts");
+                            }
+                        }
+                    }
                 }
                 err.emit_note(*ecx.tcx);
                 err

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -66,6 +66,9 @@ impl ReportedErrorInfo {
     pub fn tainted_by_errors(error: ErrorGuaranteed) -> ReportedErrorInfo {
         ReportedErrorInfo { is_tainted_by_errors: true, error }
     }
+    pub fn is_tainted_by_errors(&self) -> bool {
+        self.is_tainted_by_errors
+    }
 }
 
 impl From<ErrorGuaranteed> for ReportedErrorInfo {

tests/crashes/124348.rs

@@ -0,0 +1,12 @@
+//! ICE test #124348
+//! We should not be running const eval if the layout has errors.
+
+enum Eek {
+    TheConst,
+    UnusedByTheConst(Sum),
+    //~^ ERROR cannot find type `Sum` in this scope
+}
+
+const EEK_ZERO: &[Eek] = &[];
+
+fn main() {}

tests/ui/consts/erroneous_type_in_const_return_value.rs

@@ -0,0 +1,14 @@
+error[E0412]: cannot find type `Sum` in this scope
+  --> $DIR/erroneous_type_in_const_return_value.rs:6:22
+   |
+LL |     UnusedByTheConst(Sum),
+   |                      ^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+LL + use std::iter::Sum;
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0412`.

tests/ui/consts/erroneous_type_in_const_return_value.stderr

@@ -9,20 +9,6 @@ help: consider importing this trait
 LL + use std::iter::Sum;
    |
 
-note: erroneous constant encountered
-  --> $DIR/erroneous_type_in_promoted.rs:11:29
-   |
-LL |     let x: &'static [Eek] = &[];
-   |                             ^^^
-
-note: erroneous constant encountered
-  --> $DIR/erroneous_type_in_promoted.rs:11:29
-   |
-LL |     let x: &'static [Eek] = &[];
-   |                             ^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
 error: aborting due to 1 previous error
 
 For more information about this error, try `rustc --explain E0412`.