Fixed support for keys that are all digits but longer than an int.

Previously such config keys would still be parsed with
`Integer#parseInt` for the sake of sorting, resulting in a `NumberFormatException`.
Now the keys consisting of digits only are parsed to a `BigInteger` and
compared as such.

This addresses the following issues:
#604
#541

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

@@ -5,6 +5,7 @@
 
 import java.io.ObjectStreamException;
 import java.io.Serializable;
+import java.math.BigInteger;
 import java.util.AbstractMap;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -426,15 +427,14 @@ private static boolean isAllDigits(String s) {
             int length = s.length();
 
             // empty string doesn't count as a number
+            // string longer than "max number of digits in a long" cannot be parsed as a long
             if (length == 0)
                 return false;
 
             for (int i = 0; i < length; ++i) {
                 char c = s.charAt(i);
 
-                if (Character.isDigit(c))
-                    continue;
-                else
+                if (!Character.isDigit(c))
                     return false;
             }
             return true;
@@ -449,7 +449,7 @@ public int compare(String a, String b) {
             boolean aDigits = isAllDigits(a);
             boolean bDigits = isAllDigits(b);
             if (aDigits && bDigits) {
-                return Integer.compare(Integer.parseInt(a), Integer.parseInt(b));
+                return new BigInteger(a).compareTo(new BigInteger(b));
             } else if (aDigits) {
                 return -1;
             } else if (bDigits) {

config/src/test/resources/test12.conf

@@ -0,0 +1,43 @@
+// this checks sorting map keys, where keys that look like numbers are treated differently
+// specifically tests very long numbers which fit neither in an Integer nor in a Long
+
+"10" = "42"
+sth = 42
+"1" = "42"
+"12" = "42"
+"123" = "42"
+"1234" = "42"
+"12345" = "42"
+"123456" = "42"
+"1234567" = "42"
+"12345678" = "42"
+"123456789" = "42"
+"1234567890" = "42"
+"12345678901" = "42"
+"123456789012" = "42"
+"1234567890123" = "42"
+"12345678901234" = "42"
+"123456789012345" = "42"
+"1234567890123456" = "42"
+"12345678901234567" = "42"
+"123456789012345678" = "42"
+"1234567890123456789" = "42"
+"12345678901234567891" = "42"
+"123456789012345678912" = "42"
+"1234567890123456789123" = "42"
+"12345678901234567891234" = "42"
+"123456789012345678912345" = "42"
+"1234567890123456789123456" = "42"
+"12345678901234567891234567" = "42"
+"123456789012345678912345678" = "42"
+"1234567890123456789123456789" = "42"
+"12345678901234567891234567890" = "42"
+"123456789012345678912345678901" = "42"
+"1234567890123456789123456789012" = "42"
+"12345678901234567891234567890123" = "42"
+"123456789012345678912345678901234" = "42"
+"1234567890123456789123456789012345" = "42"
+"12345678901234567891234567890123456" = "42"
+"123456789012345678912345678901234567" = "42"
+"1234567890123456789123456789012345678" = "42"
+"12345678901234567891234567890123456789" = "42"

config/src/test/scala/Rendering.scala

@@ -33,6 +33,7 @@ object RenderExample extends App {
     render("test01")
     render("test06")
     render("test05")
+    render("test12")
 }
 
 object RenderOptions extends App {

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

@@ -982,8 +982,8 @@ class ConfigValueTest extends TestUtils {
 
     @Test
     def renderSorting(): Unit = {
-        val config = parseConfig("""0=a,1=b,2=c,3=d,10=e,20=f,30=g""")
+        val config = parseConfig("""0=a,1=b,2=c,999999999999999999999999999999999999999999999=0,3=d,10=e,20a=f,20=g,30=h""")
         val rendered = config.root.render(ConfigRenderOptions.concise())
-        assertEquals("""{"0":"a","1":"b","2":"c","3":"d","10":"e","20":"f","30":"g"}""", rendered)
+        assertEquals("""{"0":"a","1":"b","2":"c","3":"d","10":"e","20":"g","30":"h","999999999999999999999999999999999999999999999":0,"20a":"f"}""", rendered)
     }
 }