inverting speculative flag

src/librustc_typeck/astconv.rs

@@ -568,7 +568,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
         }
         tcx.check_stability(assoc_ty.def_id, Some(ref_id), binding.span);
 
-        if speculative {
+        if !speculative {
             dup_bindings.entry(assoc_ty.def_id)
                 .and_modify(|prev_span| {
                     let mut err = self.tcx().struct_span_lint_node(

src/test/ui/lint/issue-50589-multiple-associated-types.stderr

@@ -10,3 +10,14 @@ LL | fn test() ->  Box<Iterator<Item = (), Item = Unit>> {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #50589 <https://github.com/rust-lang/rust/issues/50589>
 
+warning: associated type binding `Item` specified more than once
+  --> $DIR/issue-50589-multiple-associated-types.rs:17:39
+   |
+LL | fn test() ->  Box<Iterator<Item = (), Item = Unit>> {
+   |                            ---------  ^^^^^^^^^^^ used more than once
+   |                            |
+   |                            first use of `Item`
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #50589 <https://github.com/rust-lang/rust/issues/50589>
+