dotnet/roslyn

Incorrect behavior when using alias refers to namespace in using alias

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#1,027 opened on Mar 4, 2015

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 (17 comments) (1 reaction) (0 assignees)C# (20,414 stars) (4,257 forks)batch import
Area-CompilersBughelp wanted

Description

extern alias Contracts1;
extern alias Contracts2;

using alias1 = Contracts1::TestContractAssembly;
using alias2 = Contracts2::TestContractAssembly;

partial class Contract : alias1.IContract, alias2.IContract
{
    int alias1.IContract.x
    {
        get
        {
            return 1;
        }
    }
    int alias2.IContract.x
    {
        get
        {
            return 1;
        }
    }
}

Both IContract types are the same - they expose an int property "x". Roslyn incorrectly reports that IContract.x has already been implemented.

This works if you inline the using aliases.

I strongly suspect that the alias points to the merged namespace symbol, rather than to the namespace symbol contained in the assembly symbol referenced by the extern alias.

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.
5
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.
needs maintainer response
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C#Roslyn compiler internalsunderstanding of extern aliases
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10
Research direction
Investigate the Roslyn source code related to namespace alias resolution. The issue suggests that alias references are incorrectly resolved to merged namespace symbols instead of assembly specific ones. Look at the SemanticModel or symbol resolution logic, likely in files like `Symbol.cs` or `NamespaceSymbol.cs`. Review comments in the issue for any suggested code paths. A fix would require ensuring that extern alias references maintain proper assembly boundaries when resolving namespaces.