Fix bug when appending buffer to self.

janet_to_string_b had a bug when printing buffers.

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.

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:

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)