From 3ca291c9ae1b6de09cce76e17aa3f08e92e1a2bf Mon Sep 17 00:00:00 2001
From: Peter Zhu <peter@peterzhu.ca>
Date: Tue, 4 May 2021 13:37:02 +0000
Subject: [PATCH] Correctly update array capacity after realloc

Reallocating to a smaller size in the transient heap may result in no
change in the actual capacity but the capacity of the array is still
updated to the smaller value.

This commit changes `ary_heap_realloc` to return the new capacity which
can be used by the caller to correctly update the capacity.
---
 array.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/array.c b/array.c
index 76f11581d2..50e2418462 100644
--- a/array.c
+++ b/array.c
@@ -354,14 +354,16 @@ ary_heap_free(VALUE ary)
     }
 }
 
-static void
+static size_t
 ary_heap_realloc(VALUE ary, size_t new_capa)
 {
+    size_t alloc_capa = new_capa;
     size_t old_capa = ARY_HEAP_CAPA(ary);
 
     if (RARRAY_TRANSIENT_P(ary)) {
         if (new_capa <= old_capa) {
             /* do nothing */
+            alloc_capa = old_capa;
         }
         else {
             VALUE *new_ptr = rb_transient_heap_alloc(ary, sizeof(VALUE) * new_capa);
@@ -379,6 +381,8 @@ ary_heap_realloc(VALUE ary, size_t new_capa)
         SIZED_REALLOC_N(RARRAY(ary)->as.heap.ptr, VALUE, new_capa, old_capa);
     }
     ary_verify(ary);
+
+    return alloc_capa;
 }
 
 #if USE_TRANSIENT_HEAP
@@ -443,6 +447,7 @@ ary_resize_capa(VALUE ary, long capacity)
     assert(!ARY_SHARED_P(ary));
 
     if (capacity > RARRAY_EMBED_LEN_MAX) {
+        size_t new_capa = capacity;
         if (ARY_EMBED_P(ary)) {
             long len = ARY_EMBED_LEN(ary);
             VALUE *ptr = ary_heap_alloc(ary, capacity);
@@ -453,9 +458,9 @@ ary_resize_capa(VALUE ary, long capacity)
             ARY_SET_HEAP_LEN(ary, len);
         }
         else {
-            ary_heap_realloc(ary, capacity);
+            new_capa = ary_heap_realloc(ary, capacity);
         }
-        ARY_SET_CAPA(ary, capacity);
+        ARY_SET_CAPA(ary, new_capa);
     }
     else {
         if (!ARY_EMBED_P(ary)) {
@@ -2267,8 +2272,8 @@ rb_ary_resize(VALUE ary, long len)
     }
     else {
 	if (olen > len + ARY_DEFAULT_SIZE) {
-            ary_heap_realloc(ary, len);
-	    ARY_SET_CAPA(ary, len);
+            size_t new_capa = ary_heap_realloc(ary, len);
+            ARY_SET_CAPA(ary, new_capa);
 	}
 	ARY_SET_HEAP_LEN(ary, len);
     }