From 6b76ac3d18764415eb7c7646b9cc32c1c2b1a782 Mon Sep 17 00:00:00 2001
From: Calvin Rose <calsrose@gmail.com>
Date: Sun, 10 Nov 2019 14:50:21 -0600
Subject: [PATCH] Fix bug when appending buffer to self.

janet_to_string_b had a bug when printing buffers.
---
 CHANGELOG.md      |  3 +++
 src/core/pp.c     | 10 ++++++----
 test/suite7.janet |  7 +++++++
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7b6afd67..97cf0fa5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,9 @@
 # Changelog
 All notable changes to this project will be documented in this file.
 
+### Unreleased
+- Fix bug when printing buffer to self in some cases.
+
 ## 1.5.0 - 2019-11-10
 - `os/date` now defaults to UTC.
 - Add `--test` flag to jpm to test libraries on installation.
diff --git a/src/core/pp.c b/src/core/pp.c
index 9a8e27b0..2e39a04f 100644
--- a/src/core/pp.c
+++ b/src/core/pp.c
@@ -253,11 +253,13 @@ void janet_to_string_b(JanetBuffer *buffer, Janet x) {
         default:
             janet_description_b(buffer, x);
             break;
-        case JANET_BUFFER:
-            janet_buffer_push_bytes(buffer,
-                                    janet_unwrap_buffer(x)->data,
-                                    janet_unwrap_buffer(x)->count);
+        case JANET_BUFFER: {
+            JanetBuffer *to = janet_unwrap_buffer(x);
+            /* Prevent resizing buffer while appending */
+            if (buffer == to) janet_buffer_extra(buffer, to->count);
+            janet_buffer_push_bytes(buffer, to->data, to->count);
             break;
+        }
         case JANET_STRING:
         case JANET_SYMBOL:
         case JANET_KEYWORD:
diff --git a/test/suite7.janet b/test/suite7.janet
index ebb24c0a..500d8d91 100644
--- a/test/suite7.janet
+++ b/test/suite7.janet
@@ -221,4 +221,11 @@
                 :week-day 3}
                (os/date 1388608200)) "os/date")
 
+# Appending buffer to self
+
+(with-dyns [:out @""]
+  (prin "abcd")
+  (prin (dyn :out))
+  (assert (deep= (dyn :out) @"abcdabcd") "print buffer to self"))
+
 (end-suite)