Fix Windows path too long.

Author: timcassell

src/BenchmarkDotNet/Running/BuildPartition.cs

@@ -4,6 +4,7 @@
 using System.Threading;
 using BenchmarkDotNet.Characteristics;
 using BenchmarkDotNet.Configs;
+using BenchmarkDotNet.Detectors;
 using BenchmarkDotNet.Environments;
 using BenchmarkDotNet.Helpers;
 using BenchmarkDotNet.Jobs;
@@ -33,6 +34,21 @@ public BuildPartition(BenchmarkBuildInfo[] benchmarks, IResolver resolver)
             string folderInfo = RepresentativeBenchmarkCase.Job.FolderInfo;
             int id = Interlocked.Increment(ref s_partitionCounter);
             ProgramName = $"{benchmarkAssemblyName}-{folderInfo}-{id}";
+            // Very long program name can cause the path to exceed Window's 260 character limit,
+            // for example BenchmarkDotNet.IntegrationTests.ManualRunning.MultipleFrameworks.
+            // 36 is an arbitrary limit, but it's the length of Guid strings which is what was used previously.
+            if (OsDetector.IsWindows() && ProgramName.Length > 36)
+            {
+                ProgramName = $"{benchmarkAssemblyName}-{id}";
+                if (ProgramName.Length > 36)
+                {
+                    ProgramName = $"{folderInfo}-{id}";
+                    if (ProgramName.Length > 36)
+                    {
+                        ProgramName = id.ToString();
+                    }
+                }
+            }
             LogBuildOutput = benchmarks[0].Config.Options.IsSet(ConfigOptions.LogBuildOutput);
             GenerateMSBuildBinLog = benchmarks[0].Config.Options.IsSet(ConfigOptions.GenerateMSBuildBinLog);
         }