Also bail out if predicates contain errors.

compiler/rustc_mir_transform/src/impossible_predicates.rs

@@ -41,7 +41,7 @@ impl<'tcx> MirPass<'tcx> for ImpossiblePredicates {
         tracing::trace!(def_id = ?body.source.def_id());
         let predicates = tcx.predicates_of(body.source.def_id()).instantiate_identity(tcx);
         tracing::trace!(?predicates);
-        let predicates = predicates
+        let predicates: Vec<_> = predicates
             .predicates
             .into_iter()
             .filter(|p| {
@@ -54,7 +54,7 @@ impl<'tcx> MirPass<'tcx> for ImpossiblePredicates {
             })
             .collect();
         tracing::trace!(?predicates);
-        if traits::impossible_predicates(tcx, predicates) {
+        if predicates.references_error() || traits::impossible_predicates(tcx, predicates) {
             trace!("found unsatisfiable predicates");
             // Clear the body to only contain a single `unreachable` statement.
             let bbs = body.basic_blocks.as_mut();

tests/crashes/140100.rs

@@ -1,7 +0,0 @@
-//@ known-bug: #140100
-fn a()
-where
-    b: Sized,
-{
-    println!()
-}

tests/crashes/140365.rs

@@ -1,8 +0,0 @@
-//@ known-bug: #140365
-//@compile-flags: -C opt-level=1 -Zvalidate-mir
-fn f() -> &'static str
-where
-    Self: Sized,
-{
-    ""
-}

tests/ui/mir/meaningless-bound.rs

@@ -0,0 +1,20 @@
+//! Regression test for #140100 and #140365
+//@compile-flags: -C opt-level=1 -Zvalidate-mir
+
+fn a()
+where
+    b: Sized,
+    //~^ ERROR cannot find type `b` in this scope
+{
+    println!()
+}
+
+fn f() -> &'static str
+where
+    Self: Sized,
+    //~^ ERROR cannot find type `Self` in this scope
+{
+    ""
+}
+
+fn main() {}

tests/ui/mir/meaningless-bound.stderr

@@ -0,0 +1,19 @@
+error[E0412]: cannot find type `b` in this scope
+  --> $DIR/meaningless-bound.rs:6:5
+   |
+LL |     b: Sized,
+   |     ^ not found in this scope
+
+error[E0411]: cannot find type `Self` in this scope
+  --> $DIR/meaningless-bound.rs:14:5
+   |
+LL | fn f() -> &'static str
+   |    - `Self` not allowed in a function
+LL | where
+LL |     Self: Sized,
+   |     ^^^^ `Self` is only available in impls, traits, and type definitions
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0411, E0412.
+For more information about an error, try `rustc --explain E0411`.