InvalidCastException in GetUsageData when using nullable reference types #714

rubberduck203 · 2020-11-21T11:52:06Z

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.

commandline/src/CommandLine/Core/ReflectionExtensions.cs

Lines 39 to 48 in d443a51

    
           public static Maybe<Tuple<PropertyInfo, UsageAttribute>> GetUsageData(this Type type) 
        
           { 
        
               return 
        
                   (from pi in type.FlattenHierarchy().SelectMany(x => x.GetTypeInfo().GetProperties()) 
        
                       let attrs = pi.GetCustomAttributes(true) 
        
                       where attrs.OfType<UsageAttribute>().Any() 
        
                       select Tuple.Create(pi, (UsageAttribute)attrs.First())) 
        
                           .SingleOrDefault() 
        
                           .ToMaybe(); 
        
           }

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.

The text was updated successfully, but these errors were encountered:

See issue commandlineparser#714

rubberduck203 · 2020-11-21T13:03:36Z

Minimal reproduction can be found here: rubberduck203@90ccab8

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 · 2020-11-21T14:00:03Z

I submitted PR #715 to fix this.

There's a bug in the commandline parser library that triggers when an option class has a custom usage function and that function has more than one attribute. When a class has nullable reference type properties, it's members are all tagged with the System.Runtime.CompilerServices.NullableAttribute attribute. Disabling NRTs in just the Options.cs file fixes the bug while still allowing us to use NRTs elsewhere. A bug has been submitted upstream commandlineparser/commandline#714 As well as a pull request that fixes the issue commandlineparser/commandline#715 The compiler directive can be removed once it's accepted and released.

rubberduck203 added a commit to rubberduck203/commandline that referenced this issue Nov 21, 2020

Reproduce nullable reference type bug in GetUsageData

90ccab8

See issue commandlineparser#714

rubberduck203 added a commit to rubberduck203/commandline that referenced this issue Nov 21, 2020

Fixes commandlineparser#714: Filter out non-UsageAttributes

196763c

rubberduck203 mentioned this issue Nov 23, 2020

Fixes #27: Disable nullable reference types for options class rubberduck203/GitNStats#28

Merged

commandlineparser / commandline

InvalidCastException in GetUsageData when using nullable reference types #714

InvalidCastException in GetUsageData when using nullable reference types #714

rubberduck203 commented Nov 21, 2020

rubberduck203 commented Nov 21, 2020

rubberduck203 commented Nov 21, 2020

commandlineparser / commandline

InvalidCastException in GetUsageData when using nullable reference types #714

InvalidCastException in GetUsageData when using nullable reference types #714

Comments

rubberduck203 commented Nov 21, 2020

rubberduck203 commented Nov 21, 2020

rubberduck203 commented Nov 21, 2020