fix #40742, unset has_concrete_subtype for types like Tuple{:x}

Author: JeffBezanson

src/jltypes.c

@@ -1099,6 +1099,12 @@ void jl_precompute_memoized_dt(jl_datatype_t *dt, int cacheable)
                 ((!jl_is_kind(p) && ((jl_datatype_t*)p)->isconcretetype) ||
                  (((jl_datatype_t*)p)->name == jl_type_typename && !((jl_datatype_t*)p)->hasfreetypevars));
         }
+        if (istuple && dt->has_concrete_subtype) {
+            if (jl_is_vararg(p))
+                p = ((jl_vararg_t*)p)->T;
+            if (p && !jl_is_type(p) && !jl_is_typevar(p))
+                dt->has_concrete_subtype = 0;
+        }
     }
     if (dt->name == jl_type_typename)
         cacheable = 0; // the cache for Type ignores parameter normalization, so it can't be used as a regular hash

test/compiler/inference.jl

@@ -3270,3 +3270,6 @@ end == [Union{Some{Float64}, Some{Int}, Some{UInt8}}]
         true
     end
 end
+
+# issue #40742
+@test code_typed(string, (Vector{Tuple{:x}},))[1][2] === String