[ruby/psych] Ensure strings with only underscores are not processed as Integer

A string similar to "0x____" should be treated as a string.
Currently it is processed as an Integer.

This alters the regex specified by http://yaml.org/type/int.html
to ensure at least one numerical symbol is present in the string
before converting to Integer.

https://github.com/ruby/psych/commit/81479b203e

ext/psych/lib/psych/scalar_scanner.rb

@@ -13,18 +13,18 @@ module Psych
     # Base 60, [-+]inf and NaN are handled separately
     FLOAT = /^(?:[-+]?([0-9][0-9_,]*)?\.[0-9]*([eE][-+][0-9]+)?(?# base 10))$/x
 
-    # Taken from http://yaml.org/type/int.html
-    INTEGER_STRICT = /^(?:[-+]?0b[0-1_]+                  (?# base 2)
-                         |[-+]?0[0-7_]+                   (?# base 8)
-                         |[-+]?(0|[1-9][0-9_]*)           (?# base 10)
-                         |[-+]?0x[0-9a-fA-F_]+            (?# base 16))$/x
+    # Taken from http://yaml.org/type/int.html and modified to ensure at least one numerical symbol exists
+    INTEGER_STRICT = /^(?:[-+]?0b[_]*[0-1][0-1_]*             (?# base 2)
+                         |[-+]?0[_]*[0-7][0-7_]*              (?# base 8)
+                         |[-+]?(0|[1-9][0-9_]*)               (?# base 10)
+                         |[-+]?0x[_]*[0-9a-fA-F][0-9a-fA-F_]* (?# base 16))$/x
 
     # Same as above, but allows commas.
     # Not to YML spec, but kept for backwards compatibility
-    INTEGER_LEGACY = /^(?:[-+]?0b[0-1_,]+                        (?# base 2)
-                         |[-+]?0[0-7_,]+                         (?# base 8)
+    INTEGER_LEGACY = /^(?:[-+]?0b[_,]*[0-1][0-1_,]*                (?# base 2)
+                         |[-+]?0[_,]*[0-7][0-7_,]*                 (?# base 8)
                          |[-+]?(?:0|[1-9](?:[0-9]|,[0-9]|_[0-9])*) (?# base 10)
-                         |[-+]?0x[0-9a-fA-F_,]+                  (?# base 16))$/x
+                         |[-+]?0x[_,]*[0-9a-fA-F][0-9a-fA-F_,]*    (?# base 16))$/x
 
     attr_reader :class_loader
 

test/psych/test_scalar_scanner.rb

@@ -126,6 +126,19 @@ module Psych
       assert_equal '100_', ss.tokenize('100_')
     end
 
+    def test_scan_strings_with_legacy_int_delimiters
+      assert_equal '0x_,_', ss.tokenize('0x_,_')
+      assert_equal '+0__,,', ss.tokenize('+0__,,')
+      assert_equal '-0b,_,', ss.tokenize('-0b,_,')
+    end
+
+    def test_scan_strings_with_strict_int_delimiters
+      scanner = Psych::ScalarScanner.new ClassLoader.new, strict_integer: true
+      assert_equal '0x___', scanner.tokenize('0x___')
+      assert_equal '+0____', scanner.tokenize('+0____')
+      assert_equal '-0b___', scanner.tokenize('-0b___')
+    end
+
     def test_scan_int_commas_and_underscores
       # NB: This test is to ensure backward compatibility with prior Psych versions,
       # not to test against any actual YAML specification.