Rollup merge of #102568 - compiler-errors:lint-unsatisfied-opaques, r=oli-obk

Lint against nested opaque types that don't satisfy associated type bounds

See the test failures for examples of places where this lint would fire.

r? `@oli-obk`

compiler/rustc_middle/src/lint.rs

@@ -446,7 +446,9 @@ pub fn in_external_macro(sess: &Session, span: Span) -> bool {
     match expn_data.kind {
         ExpnKind::Inlined
         | ExpnKind::Root
-        | ExpnKind::Desugaring(DesugaringKind::ForLoop | DesugaringKind::WhileLoop) => false,
+        | ExpnKind::Desugaring(
+            DesugaringKind::ForLoop | DesugaringKind::WhileLoop | DesugaringKind::OpaqueTy,
+        ) => false,
         ExpnKind::AstPass(_) | ExpnKind::Desugaring(_) => true, // well, it's "external"
         ExpnKind::Macro(MacroKind::Bang, _) => {
             // Dummy span for the `def_site` means it's an external macro.