fix expand + compile + write + read + module->namespace

... + prefix-in + relative-path module. All of those ingredients
(or some similar alternatives) are necessary to trigger a slow
way of saving module context for interaction evaluation where
a module-path index shift was getting lost.

pkgs/racket-test-core/tests/racket/module.rktl

@@ -1827,6 +1827,33 @@ case of module-leve bindings; it doesn't cover local bindings.
 
 (dynamic-require ''rexports-values-from-kernel 'f)
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Check that shifts associated with re-expansion are
+;; properly tracked for `module->namespace`
+
+(parameterize ([current-load-relative-directory
+                (let-values ([(b n dir?)
+                              (split-path
+                               (collection-file-path "promise.rkt" "racket"))])
+                  b)])
+  (let* ([e (expand (namespace-syntax-introduce
+                     (datum->syntax #f '(module m racket/base
+                                         ;; A prefixed import forces saving of the
+                                         ;; context as a syntax object in marshaled
+                                         ;; form:
+                                         (require (prefix-in p: "promise.rkt"))))))]
+         [c (compile e)]
+         [o (open-output-bytes)]
+         [_ (write c o)]
+         [r (parameterize ([read-accept-compiled #t])
+              (read (open-input-bytes (get-output-bytes o))))])
+    (parameterize ([current-namespace (make-base-namespace)])
+      (eval r)
+      (dynamic-require ''m #f)
+      (parameterize ([current-namespace (module->namespace ''m)])
+        (and (memq 'p:force (namespace-mapped-symbols))
+             #t)))))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/racket/src/module.c

@@ -7601,6 +7601,12 @@ static Scheme_Object *do_module(Scheme_Object *form, Scheme_Comp_Env *env,
   /* phase shift to replace self_modidx of previous expansion: */
   fm = scheme_stx_shift(fm, NULL, this_empty_self_modidx, self_modidx, NULL,
                         m->insp, m->insp);
+  if (m->ii_src) {
+    /* shift the initial import to record the chain for rn_stx */
+    ii = scheme_stx_shift(m->ii_src, NULL, this_empty_self_modidx, self_modidx, NULL,
+                          m->insp, m->insp);
+    m->ii_src = ii;
+  }
 
   fm = scheme_stx_add_module_frame_context(fm, rn_set);