From f3dba3eb6bf44685cb2290d48204e81a84fc09a6 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Wed, 3 Dec 2014 06:59:08 -0700
Subject: [PATCH] fix over-eager shortcut in the implementaiton of continuation
 jumps

Don't jump past a prompt when jumping to a continuation that is
a prefix of the current one.

Reported by Max New
---
 .../racket-test/tests/racket/prompt-tests.rktl    | 13 +++++++++++++
 racket/src/racket/src/eval.c                      | 15 +++++++++++++--
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/pkgs/racket-pkgs/racket-test/tests/racket/prompt-tests.rktl b/pkgs/racket-pkgs/racket-test/tests/racket/prompt-tests.rktl
index f90d533eed..888706338e 100644
--- a/pkgs/racket-pkgs/racket-test/tests/racket/prompt-tests.rktl
+++ b/pkgs/racket-pkgs/racket-test/tests/racket/prompt-tests.rktl
@@ -322,6 +322,19 @@
 
 (test-breaks-ok)
 
+;; Make sure a jump to an enclosing continuation doesn't
+;; skip over a prompt:
+(test 25 values (+ 5
+                   (call-with-continuation-prompt
+                    (lambda ()
+                      (+ 1
+                         (call/cc
+                          (lambda (k)
+                            (+ 17
+                               (call-with-continuation-prompt
+                                (lambda ()
+                                  (k 1)))))))))))
+
 ;; ----------------------------------------
 ;; Overlapping continuations
 
diff --git a/racket/src/racket/src/eval.c b/racket/src/racket/src/eval.c
index de0b3bc891..f3d5786c66 100644
--- a/racket/src/racket/src/eval.c
+++ b/racket/src/racket/src/eval.c
@@ -1478,6 +1478,10 @@ static Scheme_Prompt *lookup_cont_prompt(Scheme_Cont *c,
   Scheme_Prompt *prompt;
   Scheme_Object *pt;
 
+  if (!c->runstack_copied)
+    /* This continuation is the same as another... */
+    c = c->buf_ptr->buf.cont;
+
   pt = c->prompt_tag;
   if (SCHEME_NP_CHAPERONEP(pt))
     pt = SCHEME_CHAPERONE_VAL(pt);
@@ -1615,10 +1619,17 @@ Scheme_Object *scheme_jump_to_continuation(Scheme_Object *obj, int num_rands, Sc
 
   c = (Scheme_Cont *)obj;
   
+  /* Shortcut: if the target continuation is an extension of the current
+     continuation, and if no prompt is in the way, then escape directly. */
   if (can_ec
       && c->escape_cont
-      && scheme_escape_continuation_ok(c->escape_cont))
-    scheme_escape_to_continuation(c->escape_cont, num_rands, rands, (Scheme_Object *)c);
+      && scheme_escape_continuation_ok(c->escape_cont)) {
+    prompt = lookup_cont_prompt(c, &prompt_mc, &prompt_pos, LOOKUP_NO_PROMPT);
+    if (!prompt || (prompt->id
+                    && (prompt->id == c->prompt_id)
+                    && !prompt_mc))
+      scheme_escape_to_continuation(c->escape_cont, num_rands, rands, (Scheme_Object *)c);
+  }
       
   if (num_rands != 1) {
     GC_CAN_IGNORE Scheme_Object **vals;