Allow single dash as a value (#669)

Author: moh-hassan

Diff for: src/CommandLine/Core/Tokenizer.cs

@@ -135,6 +135,12 @@ private static IEnumerable<Token> TokenizeShortName(
             string value,
             Func<string, NameLookupResult> nameLookup)
         {
+            //Allow single dash as a value
+            if (value.Length == 1 && value[0] == '-')
+            {
+                yield return Token.Value(value);
+                yield break;
+            }
             if (value.Length > 1 && value[0] == '-' && value[1] != '-')
             {
                 var text = value.Substring(1);

Diff for: tests/CommandLine.Tests/Unit/Core/TokenizerTests.cs

@@ -123,6 +123,26 @@ public void Should_return_error_if_option_format_with_equals_is_not_correct()
             Assert.Equal(ErrorType.BadFormatTokenError, tokens.First().Tag);
             Assert.Equal(ErrorType.BadFormatTokenError, tokens.Last().Tag);
         }
+
+
+        [Theory]
+        [InlineData(new[] { "-a", "-" }, 2,"a","-")]
+        [InlineData(new[] { "--file", "-" }, 2,"file","-")]
+        [InlineData(new[] { "-f-" }, 2,"f", "-")]
+        [InlineData(new[] { "--file=-" }, 2, "file", "-")]
+        [InlineData(new[] { "-a", "--" }, 1, "a", "a")]
+        public void single_dash_as_a_value(string[] args, int countExcepted,string first,string last)
+        {
+            //Arrange
+            //Act
+            var result = Tokenizer.Tokenize(args, name => NameLookupResult.OtherOptionFound, token => token);
+            var tokens = result.SucceededWith().ToList();
+            //Assert
+            tokens.Should().NotBeNull();
+            tokens.Count.Should().Be(countExcepted);
+            tokens.First().Text.Should().Be(first);
+            tokens.Last().Text.Should().Be(last);
+        }
     }
 
 }