dotnet/runtime

C# compiler should not report CS0649 when the fields in question are marked with [DataMember] attribute

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#45,207 opened on Nov 25, 2020

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area-Serializationhelp wanted

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Description

Version Used:

Visual studio 2019 16.8.2

Steps to Reproduce:

Compile code like this:

[DataContract]
sealed class TimeSeriesPoint
{
	[DataMember]
	public float compliance, volume;
}

Expected Behavior:

Maybe no warnings at all.

Maybe a different message, like "...will always have its default value 0, unless set by deserializing".

Actual Behavior:

Warning CS0649: Field 'TimeSeriesPoint.volume' is never assigned to, and will always have its default value 0.

This is incorrect because despite these fields are never assigned to, they won't always have a default value, due to serialization.

Contributor guide

Research direction
Investigate the Roslyn compiler's logic for emitting CS0649 and determine why fields with [DataMember] are not excluded from the warning. Trace the flow from attribute detection to warning emission.
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.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
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
GitC#
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50