Emit ForbiddenBound fatally if meeting complex bounds

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -1,5 +1,5 @@
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
-use rustc_ast::{self as ast, AttrVec, NodeId, PatKind, attr, token};
+use rustc_ast::{self as ast, AttrVec, GenericBound, NodeId, PatKind, attr, token};
 use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP, BuiltinAttribute, Features};
 use rustc_session::Session;
 use rustc_session::parse::{feature_err, feature_warn};
@@ -152,7 +152,14 @@ impl<'a> PostExpansionVisitor<'a> {
         for param in params {
             if !param.bounds.is_empty() {
                 let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
-                self.sess.dcx().emit_err(errors::ForbiddenBound { spans });
+                if param.bounds.iter().any(|bound| matches!(bound, GenericBound::Trait(_))) {
+                    // Issue #149695
+                    // Abort immediately otherwise items defined in complex bounds will be lowered into HIR,
+                    // which will cause ICEs when errors of the items visit unlowered parents.
+                    self.sess.dcx().emit_fatal(errors::ForbiddenBound { spans });
+                } else {
+                    self.sess.dcx().emit_err(errors::ForbiddenBound { spans });
+                }
             }
         }
     }

tests/ui/closures/binder/bounds-on-closure-type-binders.rs

@@ -10,5 +10,4 @@ fn main() {
     // Regression test for issue #119067
     let _ = for<T: Trait> || -> () {};
     //~^ ERROR bounds cannot be used in this context
-    //~| ERROR late-bound type parameter not allowed on closures
 }

tests/ui/closures/binder/bounds-on-closure-type-binders.stderr

@@ -4,11 +4,5 @@ error: bounds cannot be used in this context
 LL |     let _ = for<T: Trait> || -> () {};
    |                    ^^^^^
 
-error: late-bound type parameter not allowed on closures
-  --> $DIR/bounds-on-closure-type-binders.rs:11:17
-   |
-LL |     let _ = for<T: Trait> || -> () {};
-   |                 ^
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 

tests/ui/traits/non_lifetime_binders/bad-bounds.rs

@@ -0,0 +1,11 @@
+//@ edition 2024
+
+#![feature(non_lifetime_binders)]
+fn produce() -> for<A: A<{ //~ ERROR expected trait, found type parameter `A`
+    //~^ ERROR bounds cannot be used in this context
+    #[derive(Hash)]
+    enum A {}
+    struct A<A>; //~ ERROR the name `A` is defined multiple times
+}>> Trait {} //~ ERROR cannot find trait `Trait` in this scope
+
+fn main() {}

tests/ui/traits/non_lifetime_binders/bad-bounds.stderr

@@ -0,0 +1,46 @@
+error[E0428]: the name `A` is defined multiple times
+  --> $DIR/bad-bounds.rs:8:5
+   |
+LL |     enum A {}
+   |     ------ previous definition of the type `A` here
+LL |     struct A<A>;
+   |     ^^^^^^^^^^^^ `A` redefined here
+   |
+   = note: `A` must be defined only once in the type namespace of this block
+
+error[E0404]: expected trait, found type parameter `A`
+  --> $DIR/bad-bounds.rs:4:24
+   |
+LL |   fn produce() -> for<A: A<{
+   |  _____________________-__^
+   | |                     |
+   | |                     found this type parameter
+LL | |
+LL | |     #[derive(Hash)]
+LL | |     enum A {}
+LL | |     struct A<A>;
+LL | | }>> Trait {}
+   | |__^ not a trait
+
+error[E0405]: cannot find trait `Trait` in this scope
+  --> $DIR/bad-bounds.rs:9:5
+   |
+LL | }>> Trait {}
+   |     ^^^^^ not found in this scope
+
+error: bounds cannot be used in this context
+  --> $DIR/bad-bounds.rs:4:24
+   |
+LL |   fn produce() -> for<A: A<{
+   |  ________________________^
+LL | |
+LL | |     #[derive(Hash)]
+LL | |     enum A {}
+LL | |     struct A<A>;
+LL | | }>> Trait {}
+   | |__^
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0404, E0405, E0428.
+For more information about an error, try `rustc --explain E0404`.