dotnet/roslyn

Wrong error message for Task.Run with invalid argument

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#10,672 opened on Apr 19, 2016

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Area-CompilersConcept-Diagnostic ClarityInvestigatinghelp wanted

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Description

Version Used: VS 2015 U2

Steps to Reproduce:

Write the following erroneous C# statement:

Task.Run(() => { }, TaskCreationOptions.LongRunning);

Expected Behavior:

A reasonable error, probably:

CS1503 Argument 2: cannot convert from 'System.Threading.Tasks.TaskCreationOptions' to 'System.Threading.CancellationToken'

Actual Behavior:

Incorrect error message:

CS1643: Not all code paths return a value in lambda expression of type 'Func'

This is possibly related to #8603.

Contributor guide

Research direction
Investigate the overload resolution logic in the compiler to understand why Task.Run is incorrectly resolved to the Func<Task> overload instead of the Action overload.
Tech stack
csharp
Domain
backend
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.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50