dotnet/roslyn

VBC emitting extra console output on warning with " error:"

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#5,724 opened on Oct 6, 2015

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 (14 comments) (3 reactions) (0 assignees)C# (4,257 forks)batch import
Area-CompilersBughelp wanted

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Description

Couldn't find an existing issue for this one (but could've missed it).

Compile the following piece of VB code in VS2015 with the "Implicit Type; Object Assumed" option set to "Warning":

Module Module1

    Sub Main()

        ' Causes build to fail
        Dim sEvent = String.Concat(" Error:", "Whatever")
        ' Won't cause build to fail
        Dim sEvent2 = String.Concat(" Another: ", "Whatever")
    End Sub

End Module

Both variable declarations will trigger a BC42020 warning. However, when the compiler encounters the sEvent declaration, it will include the line in the compiler output right after the warning, because it has the text " Error:" (leading space makes a difference).

This causes MSBuild/VS2015 to think the build failed and generate an strange error entry in the Errors window, even though only warnings were emitted during the build.

Contributor guide

Research direction
Trace the VBC warning emission in Roslyn's VB compiler to find where the string 'Error:' is output. Investigate why MSBuild interprets it as an error and adjust the output to avoid false positives.
Tech stack
csharp
Domain
compilers
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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
Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65