handle unbound vars in NTuple fields (JuliaLang#55405)

Comparing objects by `==` will happily answer nonsense for malformed
type comparisons, such as `unwrap_unionall(A) == A`. Avoid forming that
query. Additionally, need to recourse through Vararg when examining type
structure to make decisions.

Fix JuliaLang#55076
Fix JuliaLang#55189

src/builtins.c

@@ -2084,6 +2084,12 @@ static int references_name(jl_value_t *p, jl_typename_t *name, int affects_layou
         return references_name(((jl_uniontype_t*)p)->a, name, affects_layout, freevars) ||
                references_name(((jl_uniontype_t*)p)->b, name, affects_layout, freevars);
     }
+    if (jl_is_vararg(p)) {
+        jl_value_t *T = ((jl_vararg_t*)p)->T;
+        jl_value_t *N = ((jl_vararg_t*)p)->N;
+        return (T && references_name(T, name, affects_layout, freevars)) ||
+               (N && references_name(N, name, affects_layout, freevars));
+    }
     if (jl_is_typevar(p))
         return 0; // already checked by unionall, if applicable
     if (jl_is_datatype(p)) {

src/jltypes.c

@@ -1961,7 +1961,7 @@ static jl_value_t *jl_tupletype_fill(size_t n, jl_value_t *t, int check, int not
         t = normalize_unionalls(t);
         p = t;
         jl_value_t *tw = extract_wrapper(t);
-        if (tw && t != tw && jl_types_equal(t, tw))
+        if (tw && t != tw && !jl_has_free_typevars(t) && jl_types_equal(t, tw))
             t = tw;
         p = t;
         check = 0; // remember that checks are already done now
@@ -2045,7 +2045,7 @@ static jl_value_t *inst_datatype_inner(jl_datatype_t *dt, jl_svec_t *p, jl_value
             // normalize types equal to wrappers (prepare for Typeofwrapper)
             jl_value_t *tw = extract_wrapper(pi);
             if (tw && tw != pi && (tn != jl_type_typename || jl_typeof(pi) == jl_typeof(tw)) &&
-                    jl_types_equal(pi, tw)) {
+                    !jl_has_free_typevars(pi) && jl_types_equal(pi, tw)) {
                 iparams[i] = tw;
                 if (p) jl_gc_wb(p, tw);
             }
@@ -2717,7 +2717,7 @@ jl_vararg_t *jl_wrap_vararg(jl_value_t *t, jl_value_t *n, int check, int nothrow
             if (valid) {
                 t = normalize_unionalls(t);
                 jl_value_t *tw = extract_wrapper(t);
-                if (tw && t != tw && jl_types_equal(t, tw))
+                if (tw && t != tw && !jl_has_free_typevars(t) && jl_types_equal(t, tw))
                     t = tw;
             }
         }

test/core.jl

@@ -7495,6 +7495,13 @@ struct A43411{S, T}
 end
 @test isbitstype(A43411{(:a,), Tuple{Int}})
 
+# issue #55189
+struct A55189{N}
+    children::NTuple{N,A55189{N}}
+end
+@test fieldtype(A55189{2}, 1) === Tuple{A55189{2}, A55189{2}}
+@assert !isbitstype(A55189{2})
+
 # issue #44614
 struct T44614_1{T}
     m::T