Add equals sign to list of unsafe values for plain styling (#519)

lib/js-yaml/dumper.js

@@ -23,6 +23,7 @@ var CHAR_ASTERISK             = 0x2A; /* * */
 var CHAR_COMMA                = 0x2C; /* , */
 var CHAR_MINUS                = 0x2D; /* - */
 var CHAR_COLON                = 0x3A; /* : */
+var CHAR_EQUALS               = 0x3D; /* = */
 var CHAR_GREATER_THAN         = 0x3E; /* > */
 var CHAR_QUESTION             = 0x3F; /* ? */
 var CHAR_COMMERCIAL_AT        = 0x40; /* @ */
@@ -220,12 +221,13 @@ function isPlainSafeFirst(c) {
     && c !== CHAR_RIGHT_SQUARE_BRACKET
     && c !== CHAR_LEFT_CURLY_BRACKET
     && c !== CHAR_RIGHT_CURLY_BRACKET
-    // | “#” | “&” | “*” | “!” | “|” | “>” | “'” | “"”
+    // | “#” | “&” | “*” | “!” | “|” | “=” | “>” | “'” | “"”
     && c !== CHAR_SHARP
     && c !== CHAR_AMPERSAND
     && c !== CHAR_ASTERISK
     && c !== CHAR_EXCLAMATION
     && c !== CHAR_VERTICAL_LINE
+    && c !== CHAR_EQUALS
     && c !== CHAR_GREATER_THAN
     && c !== CHAR_SINGLE_QUOTE
     && c !== CHAR_DOUBLE_QUOTE

test/issues/0519.js

@@ -0,0 +1,11 @@
+'use strict';
+
+var assert = require('assert');
+var yaml   = require('../../');
+
+test('Dumper should add quotes around equals sign', function () {
+  // pyyaml fails with unquoted `=`
+  // https://yaml-online-parser.appspot.com/?yaml=%3D%0A&type=json
+  assert.strictEqual(yaml.load(yaml.dump('=')), '=');
+  assert.strictEqual(yaml.dump('='), "'='\n");
+});