dotnet/roslyn

Misleading error for await in the watch window

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#46,795 opened on Aug 13, 2020

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Area-InteractiveBughelp wanted

Description

Version Used: VS 16.7.1

Steps to Reproduce:

Attempt to use the await operator (e.g. await Task.Delay(0)) in the watch window while debugging a method.

Expected Behavior:

An error message explaining that the debugger doesn't support await, possibly suggesting to use .Result/.Wait() instead. Or even better, await works in the debugger.

Actual Behavior:

In the case of an async method, the error shown in the watch window is:

error CS4032: The 'await' operator can only be used within an async method. Consider marking this method with the 'async' modifier and changing its return type to 'Task<Task>'.

For a non-async method, the error is almost the same:

error CS4033: The 'await' operator can only be used within an async method. Consider marking this method with the 'async' modifier and changing its return type to 'Task'.

In both cases, the error is misleading: For the async method, it's already async and returns a Task, so the suggestion doesn't make sense. For the non-async method, adding async wouldn't fix the issue, so it's also wrong.

Contributor guide

Tech stack
csharp
Domain
developer experience
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
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
basic C#async/await concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Locate the source files in the Roslyn repository that emit error messages CS4032 and CS4033 (likely in the semantic analysis or error reporting modules). Modify the error message to indicate that 'await' is not supported in the watch window, rather than suggesting adding 'async'. Update any existing unit tests for these error codes. Examine how the debugger evaluates expressions to ensure the new message is appropriate.