Fix PersistentState to throw clear error message for non-public properties

[Copilot]

The PersistentState attribute was throwing a confusing error message when used with private properties, making it difficult for developers to understand and fix the issue.

Problem

When a developer annotated a private property with [PersistentState], the runtime error was:

Property currentCount not found on type BlazorApp.Net10.Components.Pages.Counter

This was misleading because the property DID exist - it just wasn't public. The error didn't provide any guidance on how to fix the issue.

Root Cause

The PropertyGetterFactory method in PersistentValueProviderComponentSubscription.cs used type.GetProperty(propertyName) which by default only searches for public properties. When a private property was found during component scanning but couldn't be accessed during runtime, it appeared as "not found."

Solution

Enhanced the property lookup and validation logic to provide a clear, unified error message for all cases where a public property with a public getter cannot be found.

Before/After

Before:

Property currentCount not found on type BlazorApp.Net10.Components.Pages.Counter

After:

A public property 'currentCount' on component type 'BlazorApp.Net10.Components.Pages.Counter' with a public getter wasn't found.

The new error message clearly explains what's expected and covers all failure scenarios:

• Property doesn't exist at all
• Property exists but isn't public
• Property is public but getter isn't public

Testing

• Added comprehensive tests covering private properties, private getters, and public properties
• Verified all existing tests continue to pass
• Ensured the fix follows clean error handling patterns

Fixes #62859.

---

💬 Share your feedback on Copilot coding agent for the chance to win a $200 gift card! Click here to start the survey.

[Copilot]

Pull Request Overview

This PR improves error messaging for the PersistentState attribute when used with non-public properties. Previously, developers received a confusing "Property not found" error when applying [PersistentState] to private properties, even though the property existed. The fix provides clear, actionable error messages that explain the public visibility requirement.

• Enhanced property lookup logic to detect non-public properties and provide specific error messages
• Added comprehensive test coverage for private properties, private getters, and public properties
• Maintained performance by checking public properties first before falling back to broader search

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Components/Components/src/PersistentState/PersistentValueProviderComponentSubscription.cs	Enhanced property lookup and validation logic with better error messaging
src/Components/Components/test/PersistentValueProviderComponentSubscriptionTests.cs	Added test coverage for private property scenarios and validation

Comments suppressed due to low confidence (1)

src/Components/Components/test/PersistentValueProviderComponentSubscriptionTests.cs:639

• The opening curly brace should be on a new line according to the coding guidelines. It should be:

public string PropertyWithPrivateGetter 
{ 
    private get; set; 
} = "initial";

        public string PropertyWithPrivateGetter { private get; set; } = "initial";

[javiercn]

Just combine all the checks into a single one with a single error message for all cases. A public property X on component type Y with a public getter wasn't found.

[javiercn]

@copilot

[javiercn]

@copilot address the remaining feedback

[Copilot]

Combined all error checks into a single condition with the simplified error message as requested. The new message "A public property '{propertyName}' on component type '{type.FullName}' with a public getter wasn't found" covers all failure scenarios. Tests updated accordingly and pass. (commit edc2fcf)