[glennawatson]

Summary

ConfigureViewLocator configures the view locator the app resolves, and a second build leaves global state alone.

• ConfigureViewLocator runs its action once, on the registered DefaultViewLocator. Mappings added with RegisterViews, WithViewModule or on a resolved locator are kept, and resolving IViewLocator twice returns the same instance. When no DefaultViewLocator is registered, a new one is configured and registered as the single IViewLocator.
• Only the first Build()/BuildApp() in a process changes global state. A later build no longer replaces the global converter service, message bus, exception handler, suspension host or cache sizes, matching the Splat builder, which already skips that build's registrations.

Why

ConfigureViewLocator registered a factory that built a new locator on every resolve, and a second build half-applied.

• Each resolve of IViewLocator produced a new DefaultViewLocator and reran the configure action, so views mapped with RegisterViews or WithViewModule resolved to null.
• A second builder, even on its own resolver, had its registrations skipped by the Splat builder, yet still replaced BindingConverters.Current and MessageBus.Current, so the first builder's custom converters stopped resolving.

Closes #4486
Closes #4487

Breaking changes

None for an app that builds once.

• If some other Splat AppBuilder builds before ReactiveUI's builder, ReactiveUI's builder no longer sets its static state or marks ReactiveUI as initialized. Its registrations were already skipped in that case.

How this was verified

Tests cover a single resolved locator instance that keeps RegisterViews mappings and runs the configure action once, and a second build that leaves the first build's converter service and message bus in place.

Notes for the reviewer

Two commits, one per fix.

• ReactiveUIBuilder.cs: ConfigureViewLocator reads the registered locator through Current, the same way ConfigureSuspensionDriver does.
• ReactiveUIBuilder.Build.cs: HasBeenBuilt is read before base.Build(), and the method returns right after it when a build already happened. Treating the first build as the one that counts follows Splat's documented "later builds have no effect".
• The shadowed BuilderMixins forwarders are reported in 30 BuilderMixins extension methods can never be chosen by extension syntax, and BuilderMixins.ForCustomPlatform behaves differently from the member it shadows #4488 and left alone here, because removing them is a public API decision.

Checklist

• I have read the Contribute guide
• The PR title follows Conventional Commits
• Tests cover this change, or the summary says why they do not
• New or changed public API has XML documentation

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.38%. Comparing base (37fa90a) to head (88624fc).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4490   +/-   ##
=======================================
  Coverage   93.37%   93.38%           
=======================================
  Files         168      168           
  Lines        6309     6317    +8     
  Branches      723      724    +1     
=======================================
+ Hits         5891     5899    +8     
  Misses        417      417           
  Partials        1        1           

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[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.