dotnet/roslyn

VB SemanticModel fails to bind type argument inside cref even though compiler produces no error

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#2,197 opened on Apr 23, 2015

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Area-CompilersBugConcept-APIhelp wanted

Description

The C# compiler (SemanticModel) correctly returns a TypeParameter symbol for the U in <see cref="C{U}"/> in the below example. I can validate this in the syntax visualizer (see below screenshot) and this also works via API (for example if I get symbol for C{U} and inspect its symbol.TypeArguments. capture

For the corresponding case in VB, U does not bind (see below screenshot). If I get symbol for C(Of U) and inspect its symbol.TypeArguments, I get back a ErrorTypeSymbol. capture2

Shouldn't the VB compiler be able to return a valid symbol in the above case (considering that the code didn't produce any errors)? Why do the two compilers behave differently here.

Contributor guide

Tech stack
csharp
Domain
tooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C# and VB basicsRoslyn SemanticModelCompiler binding concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15
Research direction
Investigate the VB compiler's implementation of cref binding in documentation comments. Compare with the C# compiler's handling in the same area. Look at the SemanticModel methods for resolving type arguments in crefs. Check if the VB compiler has a similar code path for C(Of U) as C# does for C<U>. The issue's screenshots show the difference in the syntax visualizer, so start by examining the VB syntax tree for the cref and see where binding fails. Also search for any existing tests related to cref binding in VB.