dotnet/roslyn

Code fix for CS1612 when assigning to a nested struct field or property

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#51,512 opened on Feb 26, 2021

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 (3 comments) (1 reaction) (0 assignees)C# (4,257 forks)batch import
Area-IDEIDE-CodeStylehelp wanted

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Description

It's not uncommon to write this code, then back up and realize you have to rewrite the entire assignment into three lines.

class C
{
    public S StructProperty { get; set; }

    void M()
    {
        /* ❌ CS1612 Cannot modify the return value of 'C.StructProperty' because it is not a variable
        ↓↓↓↓↓↓↓↓↓↓↓↓↓↓ */
        StructProperty.InnerProperty = 42;
    }
}

struct S
{
    public int InnerProperty { get; set; }
}

It would save me time if there was a light bulb fix 💡 Copy and set updated 'StructProperty' value:

        var structProperty = StructProperty;
        structProperty.InnerProperty = 42;
        StructProperty = structProperty;

I don't mind if it bails at a certain level of nesting because I rarely see such code, but there could be value in handling at least two struct properties at the end of the chain. (x.StructProperty.NestedStructProperty.Y = 42;)

This issue could be linked from the big table in https://github.com/dotnet/roslyn/issues/23326.

Contributor guide

Research direction
Investigate the Roslyn code base to understand how code fixes are implemented for CS1612. Look at existing similar code fixes (e.g., for CS0200) as a reference. Implement a code fix that copies the struct to a local variable, modifies the property, and assigns back. Consider handling nested structs.
Tech stack
csharp
Domain
backenddevtools
Issue type
Feature
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.
Stale
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