Add multiplier format support to RunSettings

src/xunit.runner.visualstudio/Utility/RunSettings.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Globalization;
 using System.Text.RegularExpressions;
 
 namespace Xunit.Runner.VisualStudio;
@@ -94,8 +95,28 @@ public static RunSettings Parse(string? settingsXml)
 							result.LongRunningTestSeconds = longRunningTestSeconds;
 
 						var maxParallelThreadsString = xunitElement.Element(Constants.Xunit.MaxParallelThreads)?.Value;
-						if (int.TryParse(maxParallelThreadsString, out var maxParallelThreads) && maxParallelThreads >= -1)
-							result.MaxParallelThreads = maxParallelThreads;
+						if (maxParallelThreadsString is not null)
+							switch (maxParallelThreadsString)
+							{
+								case "default":
+									result.MaxParallelThreads = 0;
+									break;
+
+								case "unlimited":
+									result.MaxParallelThreads = -1;
+									break;
+
+								default:
+									var match = ConfigUtility.MultiplierStyleMaxParallelThreadsRegex.Match(maxParallelThreadsString);
+									// Use invariant format and convert ',' to '.' so we can always support both formats, regardless of locale
+									// If we stick to locale-only parsing, we could break people when moving from one locale to another (for example,
+									// from people running tests on their desktop in a comma locale vs. running them in CI with a decimal locale).
+									if (match.Success && decimal.TryParse(match.Groups[1].Value.Replace(',', '.'), NumberStyles.AllowDecimalPoint, CultureInfo.InvariantCulture, out var maxThreadMultiplier))
+										result.MaxParallelThreads = (int)(maxThreadMultiplier * Environment.ProcessorCount);
+									else if (int.TryParse(maxParallelThreadsString, out var threadValue) && threadValue >= -1)
+										result.MaxParallelThreads = threadValue;
+									break;
+							}
 
 						var methodDisplayString = xunitElement.Element(Constants.Xunit.MethodDisplay)?.Value;
 						if (Enum.TryParse<TestMethodDisplay>(methodDisplayString, ignoreCase: true, out var methodDisplay))

test/test.xunit.runner.visualstudio/RunSettingsTests.cs

@@ -1,3 +1,4 @@
+using System;
 using Xunit;
 using Xunit.Runner.VisualStudio;
 
@@ -16,6 +17,7 @@ void AssertDefaultValues(RunSettings runSettings)
 		Assert.Null(runSettings.MethodDisplay);
 		Assert.Null(runSettings.MethodDisplayOptions);
 		Assert.Null(runSettings.NoAutoReporters);
+		Assert.Null(runSettings.ParallelAlgorithm);
 		Assert.Null(runSettings.ParallelizeAssembly);
 		Assert.Null(runSettings.ParallelizeTestCollections);
 		Assert.Null(runSettings.PreEnumerateTheories);
@@ -182,11 +184,21 @@ public void LongRunningTestSeconds(int value, int? expected)
 		Assert.Equal(expected, runSettings.LongRunningTestSeconds);
 	}
 
+	public static readonly TheoryData<string, int?> MaxParallelThreadData = new()
+	{
+		{ "blarch", null },
+		{ "-2", null },
+		{ "-1", -1 },
+		{ "0", 0 },
+		{ "42", 42 },
+		{ "unlimited", -1 },
+		{ "default", 0 },
+		{ "2.0x", Environment.ProcessorCount * 2 },
+	};
+
 	[Theory]
-	[InlineData(-2, null)]
-	[InlineData(-1, -1)]
-	[InlineData(42, 42)]
-	public void MaxParallelThreads(int value, int? expected)
+	[MemberData(nameof(MaxParallelThreadData))]
+	public void MaxParallelThreads(string value, int? expected)
 	{
 		string settingsXml =
 $@"<?xml version=""1.0"" encoding=""utf-8""?>