Fix accidental early evaluation of imported using binding

In `using A.B`, we need to evaluate `A.B` to add the module to the
using list. However, in `using A: B`, we do not care about the value
of `A.B`, we only operate at the binding level. These two operations
share a code path and the evaluation of `A.B` happens early and is
unused on the `using A: B` path. I believe this was an unintentional
oversight when the latter syntax was added. Fixes #54954.

src/toplevel.c

@@ -821,14 +821,14 @@ JL_DLLEXPORT jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_val
             if (jl_is_expr(a) && ((jl_expr_t*)a)->head == jl_dot_sym) {
                 name = NULL;
                 jl_module_t *import = eval_import_path(m, from, ((jl_expr_t*)a)->args, &name, "using");
-                jl_module_t *u = import;
-                if (name != NULL)
-                    u = (jl_module_t*)jl_eval_global_var(import, name);
                 if (from) {
                     // `using A: B` and `using A: B.c` syntax
                     jl_module_use(m, import, name);
                 }
                 else {
+                    jl_module_t *u = import;
+                    if (name != NULL)
+                        u = (jl_module_t*)jl_eval_global_var(import, name);
                     if (!jl_is_module(u))
                         jl_eval_errorf(m, *toplevel_filename, *toplevel_lineno,
                             "invalid using path: \"%s\" does not name a module",

test/syntax.jl

@@ -3858,3 +3858,10 @@ end
         @test isa(expr.args[1], Union{GlobalRef, Symbol})
     end
 end
+
+# Test that globals can be `using`'d even if they are not yet defined
+module UndefGlobal54954
+    global theglobal54954::Int
+end
+using .UndefGlobal54954: theglobal54954
+@test Core.get_binding_type(@__MODULE__, :theglobal54954) === Int