c# - Reflection with generic syntax fails on a return parameter of an overridden method -

to avoid old-fashioned non-generic syntax when searching attributes of known type, 1 uses extension methods in system.reflection.customattributeextensions class (since .net 4.5).

however appears fail if search attribute on return parameter of overridden method (or accessor of overridden property/indexer).

i experiencing .net 4.6.1.

simple reproduction (complete):

using system; using system.reflection;  namespace reflectiontrouble {   class b   {     //[return: mymark("in base class")] // uncommenting not     public virtual int m() => 0;   }    class c : b   {     [return: mymark("in inheriting class")] // commenting away attribute not     public override int m() => -1;   }    [attributeusage(attributetargets.returnvalue, allowmultiple = false, inherited = false)] // commenting away attributeusage not   sealed class mymarkattribute : attribute   {     public string descr { get; }      public mymarkattribute(string descr)     {       descr = descr;     }      public override string tostring() => $"mymark({descr})";   }    static class program   {     static void main()     {       var derivedreturnval = typeof(c).getmethod("m").returnparameter;        // usual new generic syntax (extension method in system.refelction namespace):       var attr = derivedreturnval.getcustomattribute<mymarkattribute>(); // blows here, system.indexoutofrangeexception: index outside bounds of array.       console.writeline(attr);        // old non-generic syntax without extension method works:       var attr2 = ((mymarkattribute[])(derivedreturnval.getcustomattributes(typeof(mymarkattribute), false)))[0]; // ok       console.writeline(attr2);     }   } } 

the code may "too long read", overridden method attribute on return parameter , obvious attempt retrieve attribute instance.

stack trace:

unhandled exception: system.indexoutofrangeexception: index outside bounds of array.    @ system.attribute.getparentdefinition(parameterinfo param)    @ system.attribute.internalparamgetcustomattributes(parameterinfo param, type type, boolean inherit)    @ system.attribute.getcustomattributes(parameterinfo element, type attributetype, boolean inherit)    @ system.attribute.getcustomattribute(parameterinfo element, type attributetype, boolean inherit)    @ system.reflection.customattributeextensions.getcustomattribute[t](parameterinfo element)    @ reflectiontrouble.program.main() in c:\mypath\program.cs:line 38

am doing wrong?

is bug, , if yes, well-known, , old bug?

this indeed looks bug. problem seems inheritance. work:

returnparameter.getcustomattribute<mymark>(inherit: false) 

retrieving attributes have 2 code paths work bit differently: memberinfo.getcustomattribute (older) , attribute.getcustomattribute (newer , recommended). there generic extension methods, use latter, newer approach. difference between these indeed way handle inheritance. .net 1.0 ignored inherit parameter properties, events , parameters. in order not break things, static methods on attribute introduced in .net 2.0 (together bug).

seems neglected special-case return value parameter when going inheritance tree (see here). can open issue in github repo or connect bug.