InvalidCastException in GetUsageData when using nullable reference types

[rubberduck203]

https://github.com/rubberduck203/GitNStats/issues/27

I recently enabled nullable reference types for my application. Since then, calling my app with the --help flag has started failing with an unhandled exception.

$ dotnet run --project src/gitnstats/gitnstats.csproj -- --help
Unhandled exception. System.InvalidCastException: Unable to cast object of type 'System.Runtime.CompilerServices.NullableAttribute' to type 'CommandLine.Text.UsageAttribute'.
   at CommandLine.Core.ReflectionExtensions.<>c.<GetUsageData>b__2_3(<>f__AnonymousType1`2 <>h__TransparentIdentifier0)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
   at CommandLine.Core.ReflectionExtensions.GetUsageData(Type type)
   at CommandLine.Text.HelpText.GetUsageFromType(Type type)
   at CommandLine.Text.HelpText.RenderUsageTextAsLines[T](ParserResult`1 parserResult, Func`2 mapperFunc)+MoveNext()
   at CSharpx.EnumerableExtensions.ToMaybe[T](IEnumerable`1 source)
   at CommandLine.Text.HelpText.AutoBuild[T](ParserResult`1 parserResult, Func`2 onError, Func`2 onExample, Boolean verbsIndex, Int32 maxDisplayWidth)
   at CommandLine.Text.HelpText.AutoBuild[T](ParserResult`1 parserResult, Func`2 onError, Int32 maxDisplayWidth)
   at CommandLine.Text.HelpText.AutoBuild[T](ParserResult`1 parserResult, Int32 maxDisplayWidth)
   at CommandLine.Parser.<>c__DisplayClass17_0`1.<DisplayHelp>b__1(IEnumerable`1 _, TextWriter writer)
   at CSharpx.MaybeExtensions.Do[T1,T2](Maybe`1 maybe, Action`2 action)
   at CommandLine.Parser.<>c__DisplayClass17_0`1.<DisplayHelp>b__0(IEnumerable`1 errors)
   at CommandLine.ParserResultExtensions.WithNotParsed[T](ParserResult`1 result, Action`1 action)
   at CommandLine.Parser.DisplayHelp[T](ParserResult`1 parserResult, TextWriter helpWriter, Int32 maxDisplayWidth)
   at CommandLine.Parser.MakeParserResult[T](ParserResult`1 parserResult, ParserSettings settings)
   at CommandLine.Parser.ParseArguments[T](IEnumerable`1 args)
   at GitNStats.Program.Main(String[] args) in /Users/rubberduck/src/GitNStats/src/gitnstats/Program.cs:line 11

The invalid cast is occurring in this block of code.

https://github.com/commandlineparser/commandline/blob/d443a51aeb3a418425e970542b3b96e9da5f62e2/src/CommandLine/Core/ReflectionExtensions.cs#L39-L48

I haven't figured out if it's occurring on line 44 or 45 yet, but GetUsageData seems to be assuming that it will only find a single attribute.

I'll do my best to update this with a minimal reproduction.

[rubberduck203]

Minimal reproduction can be found here: https://github.com/rubberduck203/commandline/commit/90ccab813e6fa5b004ffd4cf601375e32bca6093

In the test project file, enable nullable reference types This means the tests can not target net461, so we need a separate test project.

<nullable>enable</nullable>

The options class must have a nullable property, then we need to add custom usage examples in order to trigger the bug.

    public class ReflectionExtensionsTests
    {
        [Fact]
        public void GetUsageDataDoesNotExplodeWhenUsedWithNullableReferenceTypesUsingTheUsageAttribute()
        {
            typeof(NullableReferenceTypeOptions).GetUsageData();
        }
    }

    public class NullableReferenceTypeOptions
    {
        [Option(HelpText = "Define a string value here.")]
        public string? StringValue { get; set; }

        [Usage]
        public static IEnumerable<Example> Examples 
        {
            get 
            {
                yield return new Example("Run on current directory", new NullableReferenceTypeOptions());
            }
        }
    }

[rubberduck203]

I submitted PR #715 to fix this.

[cpmcgrath]

I just experienced this bug. It would be great if it could be resolved. Looking at the pull request that code change will fix the issue.

[mnivet]

I've experienced that issue too and it would be great if we can have a release of the fix !

[roa-nyx]

Still experiencing this same issue.

[rubberduck203]

The last commit to this repo was several months before I submitted the bug report & PR in 2020.

[Xitric]

@ericnewton76 any chance a fix for this could be merged, possibly the open PR? We have run into the same issue with nullable options lately, and would very much prefer not to introduce workarounds.

[JohnNilsson]

As a workaround you can wrap the offending property in a #nullable disable/#nullable restore pair