Fix "Replace with method" refactoring for partial properties

[Copilot]

Fix: "Replace with method" refactoring for partial properties

Problem

When using "Replace property with method" refactoring on a partial property:

• The partial modifier was not preserved on generated methods
• Both declaration and implementation parts were generated with bodies, causing compilation errors (CS0161 and CS0111)

Solution

This PR fixes the issue by:

1. Updating DeclarationModifiers.From to correctly detect partial methods, properties, and events
2. Modifying the method generation logic to create declaration-only methods for partial definitions
3. Adding comprehensive test coverage

Changes Made

1. DeclarationModifiers.From (src/Workspaces/Core/Portable/Editing/DeclarationModifiers.cs)

// A method, property, or event is partial if it's a partial definition, has a partial definition part, or has a partial implementation part
var isPartial = (method?.IsPartialDefinition == true || method?.PartialDefinitionPart != null || method?.PartialImplementationPart != null) ||
               (property?.IsPartialDefinition == true || property?.PartialDefinitionPart != null || property?.PartialImplementationPart != null) ||
               (@event?.IsPartialDefinition == true || @event?.PartialDefinitionPart != null || @event?.PartialImplementationPart != null);

• Detects partial symbols by checking IsPartialDefinition, PartialDefinitionPart, and PartialImplementationPart
• Now includes support for partial events in addition to methods and properties
• Ensures the partial modifier is added to both declaration and implementation methods

2. CSharpReplacePropertyWithMethodsService (src/Features/CSharp/Portable/ReplacePropertyWithMethods/CSharpReplacePropertyWithMethodsService.cs)

• Added early return in GetGetMethodWorker when getMethod.IsPartialDefinition is true
• Added early return in GetSetMethodWorker when setMethod.IsPartialDefinition is true
• These early returns prevent body generation for partial definition methods

3. Test Coverage (src/Features/CSharpTest/ReplacePropertyWithMethods/ReplacePropertyWithMethodsTests.cs)

• TestPartialPropertyWithImplementation - Verifies getter-only partial property transformation
• TestPartialPropertyWithBody - Verifies partial property with getter and setter transformation

Example Transformation

Before:

partial class C
{
    public partial int P { get; }
}

partial class C
{
    public partial int P => 0;
}

After (Expected):

partial class C
{
    public partial int GetP();  // ✅ partial modifier, no body
}

partial class C
{
    public partial int GetP()  // ✅ partial modifier, with body
    {
        return 0;
    }
}

Testing

• Built successfully without errors
• Added unit tests for partial property scenarios
• Addressed code review feedback to include events and all partial checks

Fixes #81068

Original prompt

---

This section details on the original issue you should resolve

<issue_title>"Replace with method" on partial property generates two implementation parts and does not add partial modifier</issue_title>
<issue_description>Version Used: VS 18.0.0 Insiders

Steps to Reproduce:
On the first P symbol, open the lightbulb menu and select "Replace 'P' with method".

partial class C
{
    public partial int P { get; }
}

partial class C
{
    public partial int P => 0;
}

Expected Behavior:

partial class C
{
    public partial int GetP(); // <-- partial modifier; declaration part without body
}

partial class C
{
    public partial int GetP() // <-- partial modifier
    {
        return 0;
    }
}

Actual Behavior:

partial class C
{
    public int GetP() // CS0161: 'C.GetP()': not all code paths return a value
    {
    }
}

partial class C
{
    public int GetP() // CS0111: Type 'C' already defines a member called 'GetP' with the same parameter types
    {
        return 0;
    }
}

</issue_description>

<agent_instructions>@copilot Update 'replace with method' to preserve 'partial' from teh property to the method. If we had a partial-definition property (no actual body) we should get the same sort of partial-def method. And similarly if we started with the partial-impl. The information should be available on the symbols to do the right thing.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes "Replace with method" on partial property generates two implementation parts and does not add partial modifier #81068

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[CyrusNajmabadi]

@copilot check for events as well. Also, i think you need to check for any of PartialDefinitionPart, PartialImplementationPart or IsPartialDefinition

[Copilot]

Done. Added event support and now checking IsPartialDefinition, PartialDefinitionPart, and PartialImplementationPart for all three symbol types (methods, properties, and events). See commit f266974.

[CyrusNajmabadi]

Superceded by #81067