revert change removing has_infer check. Commit conservatively patches for now, but more development proceeding. Also contains a more concise test

Author: tnuha

compiler/rustc_middle/src/ty/util.rs

@@ -1368,7 +1368,6 @@ impl<'tcx> Ty<'tcx> {
     /// 2229 drop reorder migration analysis.
     #[inline]
     pub fn has_significant_drop(self, tcx: TyCtxt<'tcx>, typing_env: ty::TypingEnv<'tcx>) -> bool {
-        assert!(!self.has_non_region_infer());
         // Avoid querying in simple cases.
         match needs_drop_components(tcx, self) {
             Err(AlwaysRequiresDrop) => true,
@@ -1381,6 +1380,16 @@ impl<'tcx> Ty<'tcx> {
                     _ => self,
                 };
 
+                // FIXME
+                // We should be canonicalizing, or else moving this to a method of inference
+                // context, or *something* like that,
+                // but for now just avoid passing inference variables
+                // to queries that can't cope with them.
+                // Instead, conservatively return "true" (may change drop order).
+                if query_ty.has_infer() {
+                    return true;
+                }
+
                 // This doesn't depend on regions, so try to minimize distinct
                 // query keys used.
                 let erased = tcx.normalize_erasing_regions(typing_env, query_ty);

tests/ui/type-inference/has_sigdrop.rs

@@ -2,17 +2,7 @@
 // Inference, canonicalization, and significant drops should work nicely together.
 // Related issue: #86868
 
-#[clippy::has_significant_drop]
-struct DropGuy {}
-
-fn creator() -> DropGuy {
-    DropGuy {}
-}
-
-fn dropper() {
-    let _ = creator();
-}
-
 fn main() {
-    dropper();
+    let mut state = 0;
+    Box::new(move || state)
 }