From 045cf69ba4b26a17bd20b1c2f5677fa099851594 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Fri, 12 Apr 2013 14:58:01 -0600
Subject: [PATCH] racket/enter: fix exception handling & propagation for
 `enter!'

Merge to v5.3.4
(cherry picked from commit 9a52894b8bed6193b44b217cae3a5532ae2eb7bc)
---
 collects/racket/enter.rkt       | 31 ++++++++++++++++++++++---------
 collects/tests/racket/enter.rkt |  9 +++++++++
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/collects/racket/enter.rkt b/collects/racket/enter.rkt
index 630bbc9ed6..12d333a5e1 100644
--- a/collects/racket/enter.rkt
+++ b/collects/racket/enter.rkt
@@ -35,15 +35,28 @@
 (define (do-enter! mod flags)
   (let ([flags (check-flags flags)])
     (if mod
-      (let* ([none "none"]
-             [exn (with-handlers ([void (lambda (exn)
-                                          (log-enter!-error "~a" (exn-message exn)))])
-                    (enter-require mod flags)
-                    none)]
-             [ns (module->namespace mod)])
-        (current-namespace ns)
-        (unless (memq '#:dont-re-require-enter flags)
-          (namespace-require 'racket/enter))
+      (let* ([none (gensym)]
+             [exn (with-handlers ([void (lambda (exn) exn)])
+                    (if (module-path? mod)
+                        (enter-require mod flags)
+                        (raise-argument-error 'enter! "module-path?" mod))
+                    none)])
+        ;; Try to switch to the module namespace,
+        ;; even if there was an exception, because the
+        ;; idea is to allow debugging from inside the
+        ;; module. If any excepiton happens in trying to
+        ;; switch to the declared module, log that as
+        ;; an internal exception.
+        (with-handlers ([void (lambda (exn)
+                                (if (exn? exn)
+                                    (log-enter!-error (exn-message exn))
+                                    (log-enter!-error "~s" exn)))])
+          (when (and (module-path? mod)
+                     (module-declared? mod #f))
+            (let ([ns (module->namespace mod)])
+              (current-namespace ns)
+              (unless (memq '#:dont-re-require-enter flags)
+                (namespace-require 'racket/enter)))))
         (unless (eq? none exn) (raise exn)))
       (current-namespace orig-namespace))))
 
diff --git a/collects/tests/racket/enter.rkt b/collects/tests/racket/enter.rkt
index eff20c87f2..6561df64e5 100644
--- a/collects/tests/racket/enter.rkt
+++ b/collects/tests/racket/enter.rkt
@@ -1,4 +1,13 @@
 #lang racket
 (require racket/enter)
 
+;; Make sure that when a module has a syntax error, we still
+;; switch into the module's namespace:
+(parameterize ([current-namespace (make-base-namespace)])
+  (eval '(module f racket/base (define f 'yes) (raise-user-error 'oops "broken")))
+  (with-handlers ([exn:fail:user? void]) (enter! 'f))
+  (unless (eq? 'yes (eval 'f))
+    (error "not in f?")))
+
+;; Make sure that `enter!' can work on lots of modules:
 (enter! slideshow/pict)