Fix Windows path too long

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;
@@ -28,11 +29,7 @@ public BuildPartition(BenchmarkBuildInfo[] benchmarks, IResolver resolver)
             Resolver = resolver;
             RepresentativeBenchmarkCase = benchmarks[0].BenchmarkCase;
             Benchmarks = benchmarks;
-            // Combine the benchmark's assembly name, folder info, and build partition id.
-            string benchmarkAssemblyName = RepresentativeBenchmarkCase.Descriptor.Type.Assembly.GetName().Name;
-            string folderInfo = RepresentativeBenchmarkCase.Job.FolderInfo;
-            int id = Interlocked.Increment(ref s_partitionCounter);
-            ProgramName = $"{benchmarkAssemblyName}-{folderInfo}-{id}";
+            ProgramName = GetProgramName(RepresentativeBenchmarkCase, Interlocked.Increment(ref s_partitionCounter));
             LogBuildOutput = benchmarks[0].Config.Options.IsSet(ConfigOptions.LogBuildOutput);
             GenerateMSBuildBinLog = benchmarks[0].Config.Options.IsSet(ConfigOptions.GenerateMSBuildBinLog);
         }
@@ -85,6 +82,32 @@ private static string GetResolvedAssemblyLocation(Assembly assembly) =>
             // manually construct the path.
             assembly.Location.Length == 0 ? Path.Combine(AppContext.BaseDirectory, assembly.GetName().Name) : assembly.Location;
 
+        internal static string GetProgramName(BenchmarkCase representativeBenchmarkCase, int id)
+        {
+            // Combine the benchmark's assembly name, folder info, and build partition id.
+            string benchmarkAssemblyName = representativeBenchmarkCase.Descriptor.Type.Assembly.GetName().Name;
+            string folderInfo = representativeBenchmarkCase.Job.FolderInfo;
+            var programName = $"{benchmarkAssemblyName}-{folderInfo}-{id}";
+            // Very long program name can cause the path to exceed Windows' 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)
+            {
+                return programName;
+            }
+            programName = $"{benchmarkAssemblyName}-{id}";
+            if (programName.Length <= 36)
+            {
+                return programName;
+            }
+            programName = $"{folderInfo}-{id}";
+            if (programName.Length <= 36)
+            {
+                return programName;
+            }
+            return id.ToString();
+        }
+
         internal bool ForcedNoDependenciesForIntegrationTests
         {
             get

tests/BenchmarkDotNet.IntegrationTests/InProcessEmitTest.cs

@@ -70,12 +70,11 @@ private void DiffEmit(Summary summary)
                 return;
 
             var benchmarkCase = summary.BenchmarksCases.First();
-            var caseName = $"{benchmarkCase.Descriptor.Type.Assembly.GetName().Name}-{benchmarkCase.Job.FolderInfo}";
             // The benchmark config built jobs with 2 toolchains, 1 InProcessEmit and 1 Roslyn,
             // so we need to subtract 1 from the partition counter to obtain the emit output.
             NaiveRunnableEmitDiff.RunDiff(
-                $@"{caseName}-{BuildPartition.s_partitionCounter}.exe",
-                $@"{caseName}-{BuildPartition.s_partitionCounter - 1}Emitted.dll",
+                $@"{BuildPartition.GetProgramName(benchmarkCase, BuildPartition.s_partitionCounter)}.exe",
+                $@"{BuildPartition.GetProgramName(benchmarkCase, BuildPartition.s_partitionCounter - 1)}Emitted.dll",
                 ConsoleLogger.Default);
         }