From ca6c67be682f6616ab989c10e5bcada2d260946a Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Fri, 15 Jul 2016 06:21:55 -0600
Subject: [PATCH] fix `unsafe-immutable-hash-...` on hash table from `read`

When `read` parses a literal hash table, it inserts an placeholder
just in case it's needed for cycles. The `unsafe-immutable-hash-...`
operations in some cases did not detect and remove the placeholder.

Closes #1376

Merge to v6.6
---
 pkgs/racket-test-core/tests/racket/unsafe.rktl | 14 ++++++++++++++
 racket/src/racket/src/hash.c                   |  4 ++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/pkgs/racket-test-core/tests/racket/unsafe.rktl b/pkgs/racket-test-core/tests/racket/unsafe.rktl
index 4238692bbc..1b4d33601d 100644
--- a/pkgs/racket-test-core/tests/racket/unsafe.rktl
+++ b/pkgs/racket-test-core/tests/racket/unsafe.rktl
@@ -679,4 +679,18 @@
     (err/rt-test
         (unsafe-weak-hash-iterate-next ht i) exn:fail:contract? err-msg)))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; Check that `unsafe-immutable-hash-...` proplerly handles an
+;; indirection created by `read`:
+
+(test '((a . 1) (b . 2))
+      sort
+      (for/list (((k v) (in-immutable-hash (read (open-input-string "#hash((a . 1) (b . 2))")))))
+        (cons k v))
+      <
+      #:key cdr)
+
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
 (report-errs)
diff --git a/racket/src/racket/src/hash.c b/racket/src/racket/src/hash.c
index 74171890c6..36bff1e04b 100644
--- a/racket/src/racket/src/hash.c
+++ b/racket/src/racket/src/hash.c
@@ -2885,6 +2885,7 @@ XFORM_NONGCING void scheme_unsafe_hash_tree_subtree(Scheme_Object *obj, Scheme_O
       subtree = (Scheme_Hash_Tree *)SCHEME_CHAPERONE_VAL(obj);
     else
       subtree = (Scheme_Hash_Tree *)obj;
+    subtree = resolve_placeholder(subtree);
     i = SCHEME_INT_VAL(args);
     while (i >= (1<<(2*mzHAMT_LOG_WORD_SIZE))) {
       subtree = (Scheme_Hash_Tree *)subtree->els[i & ((1<<mzHAMT_LOG_WORD_SIZE)-1)];
@@ -2916,6 +2917,7 @@ Scheme_Object *scheme_unsafe_hash_tree_next(Scheme_Hash_Tree *ht, Scheme_Object
     stack = SCHEME_CDDR(args);
     level = -1; /* -1 = too big */
   } else {
+    ht = resolve_placeholder(ht);
     i = SCHEME_INT_VAL(args);
     level = 0;
     while (i >= (1<<(2*mzHAMT_LOG_WORD_SIZE))) {
@@ -2928,8 +2930,6 @@ Scheme_Object *scheme_unsafe_hash_tree_next(Scheme_Hash_Tree *ht, Scheme_Object
     i = i & ((1<<mzHAMT_LOG_WORD_SIZE)-1);
   }
 
-  /* ht = resolve_placeholder(ht); /\* only check this in iterate-first *\/ */
-
   while (1) {
     if (!i) { /* pop up the tree */
       if (level == -1) {