Treat BOM as whitespace, fixes #75

HOCON.md

@@ -116,13 +116,14 @@ defined as follows:
  - any Unicode space separator (Zs category), line separator (Zl
    category), or paragraph separator (Zp category), including
    nonbreaking spaces (such as 0x00A0, 0x2007, and 0x202F).
+   The BOM (0xFEFF) must also be treated as whitespace.
  - tab (`\t` 0x0009), newline ('\n' 0x000A), vertical tab ('\v'
    0x000B)`, form feed (`\f' 0x000C), carriage return ('\r'
    0x000D), file separator (0x001C), group separator (0x001D),
    record separator (0x001E), unit separator (0x001F).
 
 In Java, the `isWhitespace()` method covers these characters with
-the exception of nonbreaking spaces.
+the exception of nonbreaking spaces and the BOM.
 
 While all Unicode separators should be treated as whitespace, in
 this spec "newline" refers only and specifically to ASCII newline

config/src/main/java/com/typesafe/config/impl/ConfigImplUtil.java

@@ -105,6 +105,10 @@ final public class ConfigImplUtil {
         case '\u00A0':
         case '\u2007':
         case '\u202F':
+            // this one is the BOM, see
+            // http://www.unicode.org/faq/utf_bom.html#BOM
+            // we just accept it as a zero-width nonbreaking space.
+        case '\uFEFF':
             return true;
         default:
             return Character.isWhitespace(codepoint);

config/src/test/resources/bom.conf

@@ -0,0 +1,2 @@
+#
+foo = bar

config/src/test/scala/com/typesafe/config/impl/ConfParserTest.scala

@@ -614,4 +614,32 @@ class ConfParserTest extends TestUtils {
 
         assertTrue("including basename URL doesn't load anything", conf.isEmpty())
     }
+
+    @Test
+    def acceptBOMStartingFile() {
+        // BOM at start of file should be ignored
+        val conf = ConfigFactory.parseResources("bom.conf")
+        assertEquals("bar", conf.getString("foo"))
+    }
+
+    @Test
+    def acceptBOMStartOfStringConfig() {
+        // BOM at start of file is just whitespace, so ignored
+        val conf = ConfigFactory.parseString("\uFEFFfoo=bar")
+        assertEquals("bar", conf.getString("foo"))
+    }
+
+    @Test
+    def acceptBOMInStringValue() {
+        // BOM inside quotes should be preserved, just as other whitespace would be
+        val conf = ConfigFactory.parseString("foo=\"\uFEFF\uFEFF\"")
+        assertEquals("\uFEFF\uFEFF", conf.getString("foo"))
+    }
+
+    @Test
+    def acceptBOMWhitespace() {
+        // BOM here should be treated like other whitespace (ignored, since no quotes)
+        val conf = ConfigFactory.parseString("foo= \uFEFFbar\uFEFF")
+        assertEquals("bar", conf.getString("foo"))
+    }
 }