Solution based merging for data collector

[daveMueller]

closes #1307

[daveMueller]

I guess I need some additional feedback/help here. The main problem is that I still don't fully understand how it is intended to implement IDataCollectorAttachmentProcessor. I see it beeing executed for every test project where the attachment then only is the projects test result. And also it gets executed once for the whole solution where the attachments are all the test runs results. Thus I could only check if attachments > 1 and then merge all of them together.
But from previous discussions it seems like there could be intermediate results that need to merged.
Therfore I added now a new runsettings option called MergeDirectory to store intermediate results. The idea behind that is that everytime the attachment processor triggers all attachments are merged plus the intermediate result in the MergeDirectory. The result of this merge is the new intermediate result.
Unfortunately the MergeDirectory path must be an absolute path so that this works reliable. If it is a relative path, the location changes depending on the if the processor is triggered from a project or from a solution.
cc: @MarcoRossignoli @bert2

[MarcoRossignoli]

Therfore I added now a new runsettings option called MergeDirectory to store intermediate results. The idea behind that is that everytime the attachment processor triggers all attachments are merged plus the intermediate result in the MergeDirectory. The result of this merge is the new intermediate result.

Why you need intermediate? take the directory from the first of the 2 attachments you receive and save in the same directory removing the 2 and send back. Something like a reduce. Attachments usually are inside the result directory specified in the config.

[Copilot]

Pull Request Overview

This PR implements solution based merging for the data collector by introducing a new ReportMerging option. Key changes include:

• Adding a new ReportMerging flag and parsing logic via the ReportFormatParser.
• Refactoring settings parsing and reporter creation to include JSON reports when merging is enabled.
• Implementing a new post processor (CoverletCoveragePostProcessor) for merging multiple coverage reports and updating documentation accordingly.

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/coverlet.core/Helpers/SourceRootTranslator.cs	Added an additional constructor initializing mapping dictionaries.
src/coverlet.collector/Utilities/ReportFormatParser.cs	Introduced a new helper for parsing report formats and related configuration elements.
src/coverlet.collector/Utilities/CoverletConstants.cs	Added a new constant for the ReportMerging option.
src/coverlet.collector/DataCollection/CoverletSettingsParser.cs	Refactored to use ReportFormatParser and parse the new ReportMerging flag.
src/coverlet.collector/DataCollection/CoverletSettings.cs	Added the new ReportMerging property and updated ToString output.
src/coverlet.collector/DataCollection/CoverletCoverageCollector.cs	Added a new attribute to integrate the post processor.
src/coverlet.collector/DataCollection/CoverageManager.cs	Modified reporter creation to automatically include the JSON reporter when report merging is enabled.
src/coverlet.collector/ArtifactPostProcessor/CoverletCoveragePostProcessor.cs	Added a new post processor implementing the merging logic for coverage reports.
Documentation/VSTestIntegration.md	Updated runsettings documentation to include the ReportMerging option.
Documentation/Troubleshooting.md	Added guidance for debugging the post processor.
Documentation/Changelog.md	Documented the improvements and new merging feature.

[Copilot]

Mutating settings.ReportFormats in place may introduce unintended side effects; consider assigning the updated report formats to a new local variable to preserve immutability.

Suggested change

	if (settings.ReportMerging && ! settings.ReportFormats.Contains("json"))
	settings.ReportFormats = settings.ReportFormats.Append("json").ToArray();
	return settings.ReportFormats.Select(format =>
	IReporter[] updatedReportFormats = settings.ReportFormats;
	if (settings.ReportMerging && ! updatedReportFormats.Contains("json"))
	updatedReportFormats = updatedReportFormats.Append("json").ToArray();
	return updatedReportFormats.Select(format =>

[Copilot]

Consider adding checks or logging to ensure that deleting the directory does not inadvertently remove non-report files; additional filtering criteria may improve safety.

Suggested change

	if (! string.IsNullOrEmpty(directory) && Directory.Exists(directory))
	Directory.Delete(directory, true);
	if (!string.IsNullOrEmpty(directory) && Directory.Exists(directory))
	{
	var files = Directory.GetFiles(directory);
	var reportFiles = files.Where(file => file.EndsWith(".json") || file.EndsWith(".xml")).ToList();
	if (reportFiles.Count == files.Length) // Ensure all files are report-related
	{
	Console.WriteLine($"Deleting directory: {directory}. Files: {string.Join(", ", reportFiles)}");
	Directory.Delete(directory, true);
	}
	else
	{
	Console.WriteLine($"Skipping directory: {directory}. Contains non-report files.");
	}
	}

[Copilot]

[nitpick] Since similar dictionary initializations are repeated across constructors, consider consolidating them into a common initializer to reduce duplication.

Suggested change

	_sourceRootMapping = new Dictionary<string, List<SourceRootMapping>>();
	_sourceToDeterministicPathMapping = new Dictionary<string, List<string>>();
	}
	public SourceRootTranslator(ILogger logger, IFileSystem fileSystem)
	{
	_logger = logger ?? throw new ArgumentNullException(nameof(logger));
	_fileSystem = fileSystem ?? throw new ArgumentNullException(nameof(fileSystem));
	_sourceRootMapping = new Dictionary<string, List<SourceRootMapping>>();
	_sourceToDeterministicPathMapping = new Dictionary<string, List<string>>();
	InitializeMappings();
	}
	public SourceRootTranslator(ILogger logger, IFileSystem fileSystem)
	{
	_logger = logger ?? throw new ArgumentNullException(nameof(logger));
	_fileSystem = fileSystem ?? throw new ArgumentNullException(nameof(fileSystem));
	InitializeMappings();