Fix Components: prevent collection modification during nested component navigation with SupplyParameterFromQuery

[claudiogodoy99]

fix(Components): prevent collection modification during nested component

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Summary of the changes (Less than 80 chars)

Description

Problem

When NavigateTo causes a parent component with
[SupplyParameterFromQuery] to conditionally render a child component
(also with [SupplyParameterFromQuery]), the child's subscription
modifies the _subscribers HashSet during enumeration in
OnLocationChanged, causing an InvalidOperationException.

Solution

Added _isProcessingLocationChange flag to route new subscribers to
_pendingSubscribers during location change processing. This ensures
that the _subscribers collection is not modified while being
enumerated.

Changes

• SupplyParameterFromQueryValueProvider.cs:

  • Added _isProcessingLocationChange boolean field
  • Updated Subscribe method to check this flag and route to pending
    subscribers when processing
  • Wrapped OnLocationChanged logic in try-finally block to set/reset
    the flag
  • Ensures subscribers are added to _pendingSubscribers during
    location change processing

• SupplyParameterFromQueryValueProviderTest.cs (new file):

  • Added comprehensive unit test that reproduces the collection
    modification scenario
  • Tests navigation causing nested component rendering with query
    parameters
  • Verifies no exception is thrown during the enumeration-modification
    scenario

Fixes #64929

Testing

• Added unit test
  NavigationWithNestedComponentsDoesNotThrowCollectionModifiedException
  that specifically reproduces and validates the fix for the concurrent
  modification issue
• Test creates a parent component that conditionally renders a child
  based on query parameters
• Verifies that navigation triggering child component subscription
  doesn't throw exceptions

[Copilot]

Pull request overview

This PR fixes a collection modification exception that occurs when navigation causes nested components with [SupplyParameterFromQuery] to be conditionally rendered during location change processing.

Key changes:

• Introduces a flag-based mechanism to defer subscriber registration during location change processing
• Adds comprehensive test coverage for the nested component navigation scenario

Reviewed changes

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

File	Description
src/Components/Components/src/Routing/SupplyParameterFromQueryValueProvider.cs	Adds _isProcessingLocationChange flag and logic to route new subscribers to a pending collection during location change processing, preventing collection modification exceptions
src/Components/Components/test/Rendering/SupplyParameterFromQueryValueProviderTest.cs	Adds new test file with comprehensive test that reproduces the collection modification scenario with nested components using query parameters

[claudiogodoy99]

Tests aspnetcore-ci (Build Tests: Helix x64 Subset 1) are failing, but it does not seem to be related with the modification.

[claudiogodoy99]

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[ilonatommy]

@claudiogodoy99, thank you for your contribution.

This approach looks good. It helps us keep the _subscribers of O(1) access type and avoids copying the collection to an array.

Because the update is connected with Routing, it makes sense to move the test file to src\Components\Components\test\Routing, not Rendering. The namespace for test should be Microsoft.AspNetCore.Components.Routing; (without Test).