What's new

It's been a while since our last beta release because as we approach the 2.0 milestone, we're making more breaking changes, and we're trying to group them into fewer releases in order to minimize churn.

System.CommandLine

• Added an Argument.LegalFileNamesOnly extension method to improve file validations. (Thanks, @AronParker !)

• Made significant improvements to HelpBuilder to enable more fine-grained customization of help output. (Thanks, @Keboo!)

• Added an optional description parameter to an Argument<T> constructor to match Option<T>. (Thanks, @database64128!)

• CommandHandler.Create can now specify abstract methods, which can vary by the derived class at invocation time. (Thanks, @ycrumeyrolle!)

• Improved support for POSIX bundled arguments when no delimiter is used. (Thanks, @sfoslund)

• Ahora se puede localizar la ayuda (pero todavia se necesita marcar -h para pedirla 🤔). (Thanks, @Keboo!)

• Added XML documentation for a number of types. (Thanks, @pieter-venter!)

• Added a ParseResult parameter to Symbol.GetSuggestions and to the signature for SuggestDelegate. The GetSuggestions change is not a source-breaking change because we've also added an extension method supporting the older signature. (Thanks, @thoemmi!)

• Fixed a bug where trailing spaces would break response file parsing. (Thanks, @hackf5!)

• Introduced IIdentifierSymbol, which Option and Command implement, but Argument does not.

• Enabled customization of exit codes on error by passing an exitErrorCode argument to various CommandLineBuilder methods: UseExceptionHandler, UseParseDirective, UseParseErrorReporting, and UseVersionOption. (Thanks, @Keboo!)

• Custom argument parsers using ParseArgument<T> can now partially consume tokens using ArgumentResult.OnlyTake(int), allowing other symbols to consume the remaining tokens.

• CommandHandler.Create now provides overloads for up to 16 parameters. We used to go to 11, but it wasn't enough.

• The debug directive now requires opt-in from the user, in order to prevent it from being used maliciously to block a process. (Thanks, @Keboo!)

• Numerous performance improvements, benefitting speed and memory footprint. (Thanks, @paulomorgado!) Here's a sample:

  BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19042
  Intel Core i7-6700 CPU 3.40GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
  .NET Core SDK=5.0.300-preview.21180.15
  [Host]    : .NET Core 5.0.5 (CoreCLR 5.0.521.16609, CoreFX 5.0.521.16609), X64 RyuJIT
  MediumRun : .NET Core 5.0.5 (CoreCLR 5.0.521.16609, CoreFX 5.0.521.16609), X64 RyuJIT
  
  Job=MediumRun  Force=True  IterationCount=15  
  LaunchCount=2  RunStrategy=ColdStart  WarmupCount=10  
  

  Method	NuGetReferences	Mean	Error	StdDev	Median	Ratio	RatioSD	Gen 0	Gen 1	Gen 2	Allocated
  SimpleParseAndInvoke	System.CommandLine 2.0.0-beta1.20371.2	21.89 ms	59.16 ms	88.54 ms	1.0039 ms	1.00	0.00	-	-	-	52.84 KB
  SimpleParseAndInvoke	System.CommandLine 2.0.0-beta1.21214.1	17.16 ms	49.76 ms	74.48 ms	0.7997 ms	0.83	0.18	-	-	-	45.48 KB

• Various bug fixes.

System.CommandLine.Hosting

• Added IHostBuilder.GetInvocationContext extension methods for accessing InvocationContext in order to do invocation-specific dependency injection and more. (Thanks, @fredrikhr!)

Breaking changes

• Option.Argument has been removed from the public API. Option/Option<T> constructors have been adjusted so that functionality for option arguments (such as setting default values and custom argument parsers) is available via Option and Option<T>.

• Model binding no longer passes null for unspecified argument and option values of IEnumerable or string types. Instead, it passes an empty array or list of the appropriate type, or string.Empty, respectively.

• SuggestDelegate now takes a ParseResult parameter in addition to the existing string textToMatch parameter.

• InvocationContext.ResultCode has been renamed to InvocationContext.ExitCode.

• The following string-based lookup APIs have been removed because they can be ambiguous when more than one symbol matches:

  • ParseResult[string]
  • CommandResult.OptionResult(string)
  • CommandResult[string]

• System.CommandLine.Invocation.Process has been removed from the public API.