Ensure longer option is parsed when aliases are prefixed (#1177)

* Ensure longer option is parsed when aliases are prefixed

* PR feedback

Author: sfoslund

src/System.CommandLine.Tests/OptionTests.cs

@@ -371,6 +371,15 @@ public void When_Name_is_set_to_its_current_value_then_it_is_not_removed_from_al
             option.Aliases.Should().Contain("name");
         }
 
+        [Fact]
+        public void When_aliases_overlap_the_longer_alias_is_chosen()
+        {
+            var option = new Option<string>(new[] { "-o", "-option" });
+
+            var parseResult = option.Parse("-option value");
+            parseResult.ValueForOption(option).Should().Be("value");
+        }
+
         protected override Symbol CreateSymbol(string name) => new Option(name);
     }
 }

src/System.CommandLine/Parsing/StringExtensions.cs

@@ -204,6 +204,12 @@ bool CanBeUnbundled(string arg, out IReadOnlyList<string>? replacement)
                     return false;
                 }
 
+                // don't unbundle if this is a known option
+                if (knownTokens.ContainsKey(arg))
+                {
+                    return false;
+                }
+
                 var (prefix, alias) = arg.SplitPrefix();
 
                 return prefix == "-" &&