Fixed support for keys that look like numbers longer than an int.

Previously such config keys would still be parsed with
`Integer#parseInt`, resulting in a `NumberFormatException`.
Now the number-like keys are parsed to a Long (no measures made but
performance expected hit expected to be negligible) if their numbers of
digits is shorter than the number of digits in `Long.MAX_VALUE`.

One could have also tried to parse numbers exactly up to `Long.MAX_VALUE`,
but added usability doesn't seem to match the required complexity - in
fact, one could also argue that the current loop-based checking if a key
looks like a number is a bit of an overkill, but I didn't want to dig into
the original reason for why a regexp was not used, instead focusing on
fixing an apparent bug in the most straightforward way.

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

@@ -421,20 +421,20 @@ public AbstractConfigValue modifyChild(String key, AbstractConfigValue v) {
     // this is only Serializable to chill out a findbugs warning
     static final private class RenderComparator implements java.util.Comparator<String>, Serializable {
         private static final long serialVersionUID = 1L;
+        private static final int MAX_DIGITS_IN_LONG = Long.toString(Long.MAX_VALUE).length();
 
-        private static boolean isAllDigits(String s) {
+        private static boolean safeToParseAsLong(String s) {
             int length = s.length();
 
             // empty string doesn't count as a number
-            if (length == 0)
+            // string longer than "max number of digits in a long" cannot be parsed as a long
+            if (length == 0 || length >= MAX_DIGITS_IN_LONG)
                 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;
@@ -446,13 +446,13 @@ private static boolean isAllDigits(String s) {
         // (numeric indices) appear in order.
         @Override
         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));
-            } else if (aDigits) {
+            boolean aParsable = safeToParseAsLong(a);
+            boolean bParsable = safeToParseAsLong(b);
+            if (aParsable && bParsable) {
+                return Long.compare(Long.parseLong(a), Long.parseLong(b));
+            } else if (aParsable) {
                 return -1;
-            } else if (bDigits) {
+            } else if (bParsable) {
                 return 1;
             } else {
                 return a.compareTo(b);

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 {