Support Generic Types

[drcjt]

There is already support for generic virtual methods but no proper support for generic types e.g. List
Main motivation here is to have sufficient support of generic types for Spans to work e.g. Span as these will be beneficial in the runtime code and may open up the possibility of utf-8 string support.

Out of scope:

• Generic Interface Types
• Recursive generic types
• Anything that would require types to be determined at runtime - no intention of supporting reflection here.

Initial investigation has highlighted following issues:

• Layout algorithm does not work for open types.
• Importer is expecting IL that does not involve type parameters

Do we resolve these issues by turning open types into closed types e.g. if we have a GenericInstSig then build a fully instantiated TypeDef from the generic arguments and type def in the generic instance type, or alter the existing code to deal with GenericInstSigs?? Note the layout algorithm expects TypeDef currently.

These links might be useful

• https://github.com/SAD1992/justdecompile-plugins/blob/4b9dd241a85d65118937679164cb681ccb7441f0/De4dot.JustDecompile/De4dot/sources/de4dot.blocks/GenericArgsSubstitutor.cs#L155
• https://github.com/sathukorale/dnlib/blob/e13dbcc586b861313a409518152b633f7ef506f4/src/DotNet/GenericArgumentResolver.cs#L10

For the ILimporter do we instantiate the IL prior to the importing, effectively replacing type parameters by the known arguments for the instantiation?