[Performance] ProjectPathProvider.GetRelativePath allocates Uri objects in hot loop

[mfogliatto]

Description

ProjectPathProvider.GetRelativePath() creates two Uri objects and performs URI escaping/unescaping on every call. This method is called inside the inner loop of ProjectPathViolationDetector.GetViolationsFrom() (line 48) — once per reference × matching rule combination.

Affected Files

• src/ReferenceCop/Providers/ProjectPathProvider.cs — GetRelativePath(), lines 35-36 (new Uri() allocations)
• src/ReferenceCop/Detectors/ProjectPathViolationDetector.cs — line 48 (inner loop call site)

Impact

• Allocation pressure: Two Uri allocations + Path.GetFullPath + Uri.UnescapeDataString per inner loop iteration. For 20 rules × 50 references, that's up to 2,000 Uri objects per project build.
• Redundant computation: The repositoryRoot URI (line 35) is the same every call but recomputed each time. The projectFilePath URI for the same reference is also recomputed if multiple rules match.
• GC pressure: Uri is a relatively heavy object (parses/normalizes the URI string internally), and these short-lived allocations add GC pressure during build.

Suggested Optimization

1. Cache the repository root URI as a field computed once in the constructor:

public class ProjectPathProvider : IProjectPathProvider
{
    private readonly Uri repositoryRootUri;
    private readonly string repositoryRoot;

    public ProjectPathProvider(string repositoryRoot)
    {
        this.repositoryRoot = repositoryRoot ?? throw new ArgumentNullException(nameof(repositoryRoot));
        var normalized = Path.GetFullPath(repositoryRoot)
            .TrimEnd(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar)
            + Path.DirectorySeparatorChar;
        this.repositoryRootUri = new Uri(normalized);
    }

    public string GetRelativePath(string projectFilePath)
    {
        var fullPath = Path.GetFullPath(projectFilePath);
        var projectUri = new Uri(fullPath);
        var relativePath = Uri.UnescapeDataString(
            this.repositoryRootUri.MakeRelativeUri(projectUri).ToString());
        return relativePath.Replace(Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar);
    }
}

2. Consider using Path.GetRelativePath (available since .NET Standard 2.1 / .NET Core 2.0), which avoids Uri altogether:

public string GetRelativePath(string projectFilePath)
{
    return Path.GetRelativePath(this.repositoryRoot, projectFilePath);
}

This eliminates all Uri allocations and is the idiomatic .NET approach for relative path computation.