Allow redefinitions in compiled code as in `(define round round)'.

* module/ice-9/psyntax-pp.scm: Regenerate.

* module/ice-9/psyntax.scm (chi-top)[define-form]: If a same-named
  imported variable exists, take its value instead of `#f'.

* test-suite/tests/compiler.test ("psyntax")["redefinition"]: New tests.

module/ice-9/psyntax.scm

@@ -1198,7 +1198,13 @@
                 ;; affect compile-time environment (once we have booted)
                 (if (and (not (module-local-variable (current-module) n))
                          (current-module))
-                    (module-define! (current-module) n #f))
+                    (let ((old (module-variable (current-module) n)))
+                      ;; use value of the same-named imported variable, if
+                      ;; any
+                      (module-define! (current-module) n
+                                      (if (variable? old)
+                                          (variable-ref old)
+                                          #f))))
                 (eval-if-c&e m
                   (build-global-definition s n (chi e r w mod))
                   mod))

test-suite/tests/compiler.test

@@ -25,3 +25,13 @@
 
   (pass-if "compile to value"
     (equal? (compile 1) 1)))
+
+
+(with-test-prefix "psyntax"
+
+  (pass-if "redefinition"
+    ;; In this case the locally-bound `round' must have the same value as the
+    ;; imported `round'.  See the same test in `syntax.test' for details.
+    (let ((o1 (compile '(define round round)))
+          (o2 (compile '(eq? round (@@ (guile) round)))))
+      o2)))