[Performance] XmlSerializer instantiation on every compilation analysis

[mfogliatto]

Problem

XmlConfigurationLoader creates a new XmlSerializer(typeof(ReferenceCopConfig)) instance on every call to ParseConfigFrom(). In .NET, XmlSerializer constructors that take a single Type argument generate and compile a dynamic assembly at runtime. While the framework caches these for new XmlSerializer(type), this still incurs reflection overhead on each instantiation.

More critically, since this runs inside a Roslyn analyzer (ReferenceCopAnalyzer.Initialize → RegisterCompilationAction), it executes on every compilation during IDE editing. This creates unnecessary GC pressure and CPU work in a hot path.

Affected File

src/ReferenceCop/Configuration/XmlConfigurationLoader.cs — ParseConfigFrom() method (line ~50)

Impact

• Medium — Adds latency to every compilation action in the IDE (Roslyn analyzers should be as fast as possible)
• Repeated object allocation and reflection on a hot path
• Multiplied across all projects in a solution that reference ReferenceCop

Suggested Optimization

Cache the XmlSerializer instance as a static field:

private static readonly XmlSerializer Serializer = new XmlSerializer(typeof(ReferenceCopConfig));

private static ReferenceCopConfig ParseConfigFrom(Stream stream)
{
    return (ReferenceCopConfig)Serializer.Deserialize(stream);
}

XmlSerializer is thread-safe for deserialization, so a shared static instance is safe here.