Give a message with a span on validation error

Author: scottmcm

compiler/rustc_mir_transform/src/validate.rs

@@ -119,14 +119,16 @@ impl<'a, 'tcx> CfgChecker<'a, 'tcx> {
     #[track_caller]
     fn fail(&self, location: Location, msg: impl AsRef<str>) {
         // We might see broken MIR when other errors have already occurred.
-        assert!(
-            self.tcx.dcx().has_errors().is_some(),
-            "broken MIR in {:?} ({}) at {:?}:\n{}",
-            self.body.source.instance,
-            self.when,
-            location,
-            msg.as_ref(),
-        );
+        if self.tcx.dcx().has_errors().is_none() {
+            span_bug!(
+                self.body.span,
+                "broken MIR in {:?} ({}) at {:?}:\n{}",
+                self.body.source.instance,
+                self.when,
+                location,
+                msg.as_ref(),
+            );
+        }
     }
 
     fn check_edge(&mut self, location: Location, bb: BasicBlock, edge_kind: EdgeKind) {

tests/ui/mir/validate/critical-edge.rs

@@ -12,6 +12,8 @@ use core::intrinsics::mir::*;
 #[custom_mir(dialect = "runtime", phase = "optimized")]
 #[inline(always)]
 pub fn f(a: u32) -> u32 {
+//~^ ERROR broken MIR in Item
+//~| ERROR encountered critical edge in `Call` terminator
     mir! {
         {
             match a {
@@ -29,5 +31,3 @@ pub fn f(a: u32) -> u32 {
         }
     }
 }
-
-//~? RAW encountered critical edge in `Call` terminator