…on (#13440)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Jan Provazník <janprovaznik@microsoft.com>

…tInMetadata performance (#13386)

I recommend reviewing this pull request commit-by-commit.

# Summary of Changes

- Introduce new MSBuild.Benchmarks project for tackling performance
investigations.
- Add a few benchmarks for various methods on `ItemSpecModifiers`.
- Make several performance fixes related to `ItemSpecModifiers` and
`BuildInMetadata`.
- General clean up.

Across the board, most benchmarks are **3×–35× faster** with
**allocations eliminated or reduced by 93–100%**. The largest wins are
in repeated-access and multi-item scenarios, which are the most
representative of real build workloads. The full details are below but
here are the highlights.

## Highlights

### 🚀 Speed Improvements (.NET 10.0)

| Benchmark | Before | After | Speedup |
|---|---|---|---|
| `IsItemSpecModifier_AllModifiers` | 151.4 ns | 38.5 ns | **3.9×** |
| `GetItemSpecModifier_DefiningProjectDirectory` | 812.2 ns | 72.4 ns |
**11.2×** |
| `TaskItem_AllDerivableModifiers_Once` | 434.5 ns | 87.4 ns | **5.0×**
|
| `TaskItem_FilenameAndExtension_Repeated` | 908.5 ns | 173.7 ns |
**5.2×** |
| `TaskItem_Filename_ManyItems` | 9,651 ns | 1,857 ns | **5.2×** |
| `TaskItem_FullPathDerivedModifiers_Repeated` | 2,128 ns | 321.6 ns |
**6.6×** |
| `TaskItem_DefiningProjectDirectory_Repeated` | 9,121 ns | 970.8 ns |
**9.4×** |
| `PI_DefiningProjectDirectory_Repeated` | 9,092 ns | 1,021 ns |
**8.9×** |
| `PI_DefiningProjectFullPath_AllItems_Multi` | 35,245 ns | 9,947 ns |
**3.5×** |
| `PI_DefiningProjectDir_AllItems_Multi_Repeated` | 878,931 ns | 103,961
ns | **8.5×** |
| `PI_FilenameExtension_AllItems` | 22,698 ns | 5,343 ns | **4.2×** |
| `PI_FilenameExtension_AllItems_Repeated` | 181,612 ns | 67,028 ns |
**2.7×** |

### 🧹 Allocation Reductions (.NET 10.0)

| Benchmark | Before | After | Reduction |
|---|---|---|---|
| `TaskItem_AllDerivableModifiers_Once` | 1,232 B | **0 B** | 100% |
| `TaskItem_FilenameAndExtension_Repeated` | 640 B | **0 B** | 100% |
| `TaskItem_Filename_ManyItems` | 7,920 B | **0 B** | 100% |
| `TaskItem_FullPathDerivedModifiers_Repeated` | 7,120 B | **0 B** |
100% |
| `TaskItem_DefiningProjectDirectory_Repeated` | 8,240 B | **0 B** |
100% |
| `TaskItem_AllDefiningProjectModifiers_Once` | 912 B | **0 B** | 100% |
| `TaskItem_DefiningProjectNameExtension_AllItems` | 8,800 B | **0 B** |
100% |
| `GetItemSpecModifier_DefiningProjectDirectory` | 536 B | **0 B** |
100% |
| `PI_FilenameExtension_AllItems_Repeated` | 143,840 B | **640 B** |
99.6% |
| `PI_DefiningProjectDir_AllItems_Multi_Repeated` | 824,640 B | **640
B** | 99.9% |
| `PI_FilenameExtension_AllItems` | 14,384 B | **64 B** | 99.6% |
| `PI_DefiningProjectDirectory_Repeated` | 8,304 B | **64 B** | 99.2% |
| `PI_AllDerivableModifiers_Once` | 1,296 B | **64 B** | 95.1% |
| `PI_AllDefiningProjectModifiers_Once` | 976 B | **64 B** | 93.4% |

### 📊 .NET Framework 4.8.1

| Benchmark | Before | After | Speedup |
|---|---|---|---|
| `GetItemSpecModifier_DefiningProjectDirectory` | 5,467 ns | 156.8 ns |
**34.9×** |
| `TaskItem_DefiningProjectDirectory_Repeated` | 58,025 ns | 2,539 ns |
**22.9×** |
| `PI_DefiningProjectDir_AllItems_Multi_Repeated` | 6,399 μs | 282.3 μs
| **22.7×** |
| `TaskItem_Filename_ManyItems` | 110,078 ns | 6,916 ns | **15.9×** |
| `TaskItem_FullPathDerivedModifiers_Repeated` | 26,619 ns | 2,262 ns |
**11.8×** |
| `PI_FilenameExtension_AllItems_Repeated` | 2,162 μs | 202.6 μs |
**10.7×** |
| `TaskItem_AllDerivableModifiers_Once` | 5,322 ns | 507.2 ns |
**10.5×** |
| `PI_FilenameExtension_AllItems` | 216,406 ns | 20,366 ns | **10.6×** |
| `TaskItem_FilenameAndExtension_Repeated` | 10,238 ns | 664.7 ns |
**15.4×** |
| `PI_AllDerivableModifiers_Once` | 5,525 ns | 688.6 ns | **8.0×** |
| `PI_DefiningProjectDirectory_Repeated` | 64,204 ns | 2,796 ns |
**23.0×** |
| `PI_AllDefiningProjectModifiers_Once` | 9,808 ns | 1,154 ns | **8.5×**
|
| `TaskItem_AllDefiningProjectModifiers_Once` | 8,636 ns | 965.3 ns |
**8.9×** |

## 'Quick-and-Dirty' Telemetry

I had Copilot write some "quick-and-dirty" telemetry to track
information in `ItemSpecModifiers` and dump it to a file. I built
MSBuild with that extra telemetry and then built Roslyn (starting from
`Microsoft.VisualStudio.LanguageServices.CSharp.csproj`) using that
MSBuild. This gave me a dump with loads of interesting details. For
example, `IsItemSpecModifier` was called 901,057 times.

<details>
  <summary><b>Full Quick-and-Dirty Telemetry Dump</b></summary>

```
=== ItemSpecModifiers Telemetry (2026-03-12T09:38:41.0365991-07:00) ===

--- Top-level method calls ---
  IsItemSpecModifier:            901,057
  IsDerivableItemSpecModifier:   144,857
  GetItemSpecModifier:           180,890

--- Compute helper calls ---
  ComputeFullPath:     75,443
  ComputeRootDir:      84
  ComputeFilename:     57,426
  ComputeExtension:    32,071
  ComputeRelativeDir:  22
  ComputeDirectory:    84
  ComputeModifiedTime: 0
  ComputeCreatedTime:  0
  ComputeAccessedTime: 0

--- Per-modifier breakdown (inside GetItemSpecModifier) ---
  FullPath:                    44,783
  RootDir:                     41
  Filename:                    57,426
  Extension:                   6,462
  RelativeDir:                 22
  Directory:                   41
  RecursiveDir:                0
  Identity:                    15,814
  ModifiedTime:                0
  CreatedTime:                 0
  AccessedTime:                0
  DefiningProjectFullPath:     30,535
  DefiningProjectDirectory:    43
  DefiningProjectName:         0
  DefiningProjectExtension:    25,609

==========================================================
  Per-ItemSpec Modifier Hit Matrix
==========================================================

  Unique item specs seen:       13,809
  Item specs hit > 1 time:      13,005
  Grand total modifier lookups: 180,890

--- Top 50 hottest item specs (by total modifier calls) ---

  #1 (1,502 calls): System.Runtime.CompilerServices.InternalsVisibleTo
      Identity                              751
      DefiningProjectFullPath               751

  #2 (380 calls): D:\Projects\roslyn\artifacts\bin\Microsoft.CodeAnalysis\Debug\netstandard2.0\Microsoft.CodeAnalysis.dll
      FullPath                               17
      Filename                              280
      Extension                              40
      Identity                               21
      DefiningProjectFullPath                22

  #3 (270 calls): D:\Projects\roslyn\artifacts\bin\Microsoft.CodeAnalysis.Scripting\Debug\netstandard2.0\Microsoft.CodeAnalysis.Scripting.dll
      FullPath                               12
      Filename                              195
      Extension                              30
      Identity                               16
      DefiningProjectFullPath                17

  #4 (270 calls): D:\Projects\roslyn\artifacts\bin\Microsoft.CodeAnalysis.Workspaces\Debug\netstandard2.0\Microsoft.CodeAnalysis.Workspaces.dll
      FullPath                               12
      Filename                              195
      Extension                              30
      Identity                               16
      DefiningProjectFullPath                17

  #5 (247 calls): D:\.nuget\packages\system.threading.tasks.extensions\4.6.3\lib\netstandard2.0\System.Threading.Tasks.Extensions.dll
      FullPath                               13
      Filename                              221
      Identity                               13

  #6 (247 calls): D:\.nuget\packages\system.memory\4.6.3\lib\netstandard2.0\System.Memory.dll
      FullPath                               13
      Filename                              221
      Identity                               13

  #7 (247 calls): D:\.nuget\packages\system.buffers\4.6.1\lib\netstandard2.0\System.Buffers.dll
      FullPath                               13
      Filename                              221
      Identity                               13

  #8 (247 calls): D:\.nuget\packages\system.numerics.vectors\4.6.1\lib\netstandard2.0\System.Numerics.Vectors.dll
      FullPath                               13
      Filename                              221
      Identity                               13

  #9 (247 calls): D:\.nuget\packages\system.text.encoding.codepages\8.0.0\lib\netstandard2.0\System.Text.Encoding.CodePages.dll
      FullPath                               13
      Filename                              221
      Identity                               13

  #10 (247 calls): D:\.nuget\packages\system.runtime.compilerservices.unsafe\6.1.2\lib\netstandard2.0\System.Runtime.CompilerServices.Unsafe.dll
      FullPath                               13
      Filename                              221
      Identity                               13

  #11 (245 calls): D:\.nuget\packages\microsoft.dotnet.arcade.sdk\10.0.0-beta.26160.1\tools\Assets\DotNetPackageIcon.png
      FullPath                               48
      Filename                               40
      Extension                              70
      Identity                                2
      DefiningProjectFullPath                37
      DefiningProjectDirectory                8
      DefiningProjectExtension               40

  #12 (245 calls): D:\Projects\roslyn\eng\targets\..\..\src\NuGet\ThirdPartyNotices.rtf
      FullPath                               48
      Filename                               40
      Extension                              70
      Identity                                2
      DefiningProjectFullPath                37
      DefiningProjectDirectory                8
      DefiningProjectExtension               40

  #13 (240 calls): D:\.nuget\packages\system.collections.immutable\10.0.1\lib\netstandard2.0\System.Collections.Immutable.dll
      FullPath                               12
      Filename                              216
      Identity                               12

  #14 (240 calls): D:\.nuget\packages\system.reflection.metadata\10.0.1\lib\netstandard2.0\System.Reflection.Metadata.dll
      FullPath                               12
      Filename                              216
      Identity                               12

  #15 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Web.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #16 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Threading.ThreadPool.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #17 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.IO.FileSystem.Watcher.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #18 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Resources.ResourceManager.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #19 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.IO.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #20 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.IO.Pipes.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #21 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.IO.MemoryMappedFiles.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #22 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.ValueTuple.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #23 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Console.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #24 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Linq.Parallel.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #25 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Security.Claims.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #26 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.IO.UnmanagedMemoryStream.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #27 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Threading.Overlapped.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #28 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Drawing.Primitives.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #29 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Net.WebSockets.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #30 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Security.Cryptography.Algorithms.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #31 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.IO.FileSystem.DriveInfo.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #32 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Diagnostics.Tracing.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #33 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Linq.Expressions.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #34 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Security.Principal.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #35 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Globalization.Calendars.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #36 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Security.Cryptography.Primitives.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #37 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.ObjectModel.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #38 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Xml.XDocument.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #39 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Collections.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #40 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.ComponentModel.TypeConverter.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #41 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Runtime.InteropServices.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #42 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Collections.Concurrent.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #43 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Collections.Specialized.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #44 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Dynamic.Runtime.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #45 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Net.Requests.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #46 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Security.Cryptography.X509Certificates.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #47 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Net.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #48 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.IO.Compression.ZipFile.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #49 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Xml.XmlSerializer.dll
      FullPath                               13
      Filename                              208
      Identity                               13

  #50 (234 calls): D:\.nuget\packages\netstandard.library\2.0.3\build\netstandard2.0\ref\System.Runtime.CompilerServices.VisualC.dll
      FullPath                               13
      Filename                              208
      Identity                               13

--- Repetition histogram (total modifier calls per item spec → count of item specs) ---

     1,502 calls  →         1 item specs
       380 calls  →         1 item specs
       270 calls  →         2 item specs
       247 calls  →         6 item specs
       245 calls  →         2 item specs
       240 calls  →         2 item specs
       234 calls  →       112 item specs
       226 calls  →         1 item specs
       224 calls  →         2 item specs
       204 calls  →         4 item specs
       196 calls  →         1 item specs
       164 calls  →        13 item specs
       160 calls  →         2 item specs
       151 calls  →         3 item specs
       144 calls  →        53 item specs
       140 calls  →         6 item specs
       138 calls  →         4 item specs
       134 calls  →         1 item specs
       132 calls  →         7 item specs
       122 calls  →         2 item specs
       117 calls  →        14 item specs
       113 calls  →       124 item specs
       111 calls  →         1 item specs
       110 calls  →         2 item specs
       109 calls  →         1 item specs
       101 calls  →         3 item specs
       100 calls  →         2 item specs
        99 calls  →         1 item specs
        98 calls  →         1 item specs
        91 calls  →         5 item specs
        89 calls  →        59 item specs
        86 calls  →         2 item specs
        84 calls  →         1 item specs
        82 calls  →         2 item specs
        80 calls  →         7 item specs
        78 calls  →         1 item specs
        76 calls  →         2 item specs
        75 calls  →         1 item specs
        74 calls  →         5 item specs
        73 calls  →         3 item specs
        72 calls  →         2 item specs
        70 calls  →         1 item specs
        66 calls  →         5 item specs
        65 calls  →         5 item specs
        60 calls  →        10 item specs
        58 calls  →         8 item specs
        57 calls  →         1 item specs
        56 calls  →         1 item specs
        54 calls  →         6 item specs
        52 calls  →         3 item specs
        51 calls  →         8 item specs
        50 calls  →         1 item specs
        49 calls  →         2 item specs
        48 calls  →         3 item specs
        47 calls  →         1 item specs
        46 calls  →         1 item specs
        45 calls  →        13 item specs
        44 calls  →        20 item specs
        41 calls  →         2 item specs
        40 calls  →         8 item specs
        39 calls  →         1 item specs
        37 calls  →         4 item specs
        36 calls  →        51 item specs
        35 calls  →         5 item specs
        34 calls  →         1 item specs
        33 calls  →         1 item specs
        32 calls  →         2 item specs
        30 calls  →         4 item specs
        29 calls  →        11 item specs
        28 calls  →        20 item specs
        27 calls  →        11 item specs
        26 calls  →        16 item specs
        24 calls  →        30 item specs
        23 calls  →         3 item specs
        22 calls  →       153 item specs
        21 calls  →         1 item specs
        20 calls  →        26 item specs
        19 calls  →         1 item specs
        18 calls  →       109 item specs
        16 calls  →        30 item specs
        15 calls  →        35 item specs
        14 calls  →       383 item specs
        13 calls  →       166 item specs
        12 calls  →     1,051 item specs
        11 calls  →         1 item specs
        10 calls  →        70 item specs
         9 calls  →        43 item specs
         8 calls  →     7,012 item specs
         7 calls  →        50 item specs
         6 calls  →       910 item specs
         5 calls  →     1,420 item specs
         4 calls  →       449 item specs
         3 calls  →        32 item specs
         2 calls  →       340 item specs
         1 calls  →       804 item specs
```
</details>

## Initial Benchmark Results

### .NET 10.0

| Method | Mean | Error | StdDev | Gen0 | Allocated |
|---------------------------------------------
|--------------:|------------:|------------:|-------:|----------:|
| IsItemSpecModifier_AllModifiers | 151.425 ns | 0.1309 ns | 0.1161 ns |
- | - |
| IsDerivableItemSpecModifier_RecursiveDir | 2.522 ns | 0.0028 ns |
0.0025 ns | - | - |
| GetItemSpecModifier_FullPath | 267.552 ns | 0.3441 ns | 0.3050 ns | -
| - |
| GetItemSpecModifier_Directory | 359.023 ns | 0.7603 ns | 0.6740 ns |
0.0224 | 376 B |
| GetItemSpecModifier_ModifiedTime | 28,544.061 ns | 237.0185 ns |
221.7073 ns | - | 176 B |
| GetItemSpecModifier_DefiningProjectDirectory | 812.229 ns | 3.3636 ns
| 2.9817 ns | 0.0315 | 536 B |
| TaskItem_AllDerivableModifiers_Once | 434.5 ns | 4.36 ns | 4.08 ns |
0.0734 | 1232 B |
| TaskItem_FilenameAndExtension_Repeated | 908.5 ns | 1.13 ns | 1.00 ns
| 0.0381 | 640 B |
| TaskItem_Filename_ManyItems | 9,651.3 ns | 29.02 ns | 25.72 ns |
0.4730 | 7920 B |
| TaskItem_FullPathDerivedModifiers_Repeated | 2,127.6 ns | 7.45 ns |
6.60 ns | 0.4234 | 7120 B |
| ProjectItemInstance_AllDerivableModifiers_Once | 513.4 ns | 2.93 ns |
2.74 ns | 0.0772 | 1296 B |
| ProjectItemInstance_FilenameExtension_AllItems | 22,697.6 ns | 68.62
ns | 64.19 ns | 0.8545 | 14384 B |
| ProjectItemInstance_FilenameExtension_AllItems_Repeated | 181,612.2 ns
| 1,125.69 ns | 940.00 ns | 8.5449 | 143840 B |
| ProjectItemInstance_AllDefiningProjectModifiers_Once | 1.559 μs |
0.0047 μs | 0.0040 μs | 0.0572 | 976 B |
| ProjectItemInstance_DefiningProjectDirectory_Repeated | 9.092 μs |
0.0654 μs | 0.0580 μs | 0.4883 | 8304 B |
|
ProjectItemInstance_DefiningProjectNameExtension_AllItems_SingleProject
| 12.515 μs | 0.0297 μs | 0.0263 μs | 0.5188 | 8864 B |
| ProjectItemInstance_DefiningProjectFullPath_AllItems_MultiProject |
35.245 μs | 0.0405 μs | 0.0379 μs | - | 64 B |
|
ProjectItemInstance_DefiningProjectDirectory_AllItems_MultiProject_Repeated
| 878.931 μs | 3.1495 μs | 2.7919 μs | 48.8281 | 824640 B |
| TaskItem_AllDefiningProjectModifiers_Once | 1.430 μs | 0.0027 μs |
0.0023 μs | 0.0534 | 912 B |
| TaskItem_DefiningProjectNameExtension_AllItems | 11.628 μs | 0.0289 μs
| 0.0241 μs | 0.5188 | 8800 B |
| TaskItem_DefiningProjectDirectory_Repeated | 9.121 μs | 0.0192 μs |
0.0170 μs | 0.4883 | 8240 B |

### .NET Framework 4.8.1

| Method | Mean | Error | StdDev | Gen0 | Allocated |
|---------------------------------------------
|-------------:|-----------:|----------:|-------:|----------:|
| IsItemSpecModifier_AllModifiers | 227.45 ns | 0.297 ns | 0.264 ns | -
| - |
| IsDerivableItemSpecModifier_RecursiveDir | 10.49 ns | 0.019 ns | 0.018
ns | - | - |
| GetItemSpecModifier_FullPath | 1,267.45 ns | 0.844 ns | 0.705 ns | - |
- |
| GetItemSpecModifier_Directory | 2,433.43 ns | 7.400 ns | 6.560 ns |
0.0954 | 517 B |
| GetItemSpecModifier_ModifiedTime | 41,881.06 ns | 111.954 ns | 93.487
ns | 0.1221 | 878 B |
| GetItemSpecModifier_DefiningProjectDirectory | 5,467.24 ns | 8.295 ns
| 6.926 ns | 0.1602 | 857 B |
| TaskItem_AllDerivableModifiers_Once | 5.322 μs | 0.0354 μs | 0.0331 μs
| 0.3662 | 1923 B |
| TaskItem_FilenameAndExtension_Repeated | 10.238 μs | 0.0108 μs |
0.0101 μs | 0.1373 | 761 B |
| TaskItem_Filename_ManyItems | 110.078 μs | 0.1367 μs | 0.1212 μs |
2.3193 | 12379 B |
| TaskItem_FullPathDerivedModifiers_Repeated | 26.619 μs | 0.1695 μs |
0.1585 μs | 2.1973 | 11578 B |
| ProjectItemInstance_AllDerivableModifiers_Once | 5.525 μs | 0.0311 μs
| 0.0276 μs | 0.3662 | 1959 B |
| ProjectItemInstance_FilenameExtension_AllItems | 216.406 μs | 0.2767
μs | 0.2160 μs | 2.9297 | 16422 B |
| ProjectItemInstance_FilenameExtension_AllItems_Repeated | 2,161.623 μs
| 10.4073 μs | 9.2258 μs | 31.2500 | 164225 B |
| ProjectItemInstance_AllDefiningProjectModifiers_Once | 9.808 μs |
0.0177 μs | 0.0165 μs | 0.2594 | 1418 B |
| ProjectItemInstance_DefiningProjectDirectory_Repeated | 64.204 μs |
0.3983 μs | 0.3726 μs | 2.3193 | 12616 B |
|
ProjectItemInstance_DefiningProjectNameExtension_AllItems_SingleProject
| 131.504 μs | 0.3383 μs | 0.3165 μs | 2.1973 | 12456 B |
| ProjectItemInstance_DefiningProjectFullPath_AllItems_MultiProject |
173.171 μs | 0.7242 μs | 0.5654 μs | - | 38 B |
|
ProjectItemInstance_DefiningProjectDirectory_AllItems_MultiProject_Repeated
| 6,399.063 μs | 71.6927 μs | 67.0614 μs | 234.3750 | 1242225 B |
| TaskItem_AllDefiningProjectModifiers_Once | 8.636 μs | 0.0177 μs |
0.0147 μs | 0.2594 | 1382 B |
| TaskItem_DefiningProjectNameExtension_AllItems | 126.982 μs | 0.2250
μs | 0.2104 μs | 2.1973 | 12420 B |
| TaskItem_DefiningProjectDirectory_Repeated | 58.025 μs | 0.1388 μs |
0.1299 μs | 2.3804 | 12579 B |

## Final Benchmark Results

### .NET 10.0

| Method | Mean | Error | StdDev | Gen0 | Allocated |
|---------------------------------------------
|--------------:|------------:|------------:|-------:|----------:|
| IsItemSpecModifier_AllModifiers | 38.4923 ns | 0.5501 ns | 0.5145 ns |
- | - |
| IsDerivableItemSpecModifier_RecursiveDir | 0.0000 ns | 0.0000 ns |
0.0000 ns | - | - |
| GetItemSpecModifier_FullPath | 260.1019 ns | 0.3623 ns | 0.3212 ns | -
| - |
| GetItemSpecModifier_Directory | 413.2121 ns | 1.9441 ns | 1.8185 ns |
0.0224 | 376 B |
| GetItemSpecModifier_ModifiedTime | 30,272.3116 ns | 408.0450 ns |
381.6855 ns | - | 176 B |
| GetItemSpecModifier_DefiningProjectDirectory | 72.3691 ns | 0.0289 ns
| 0.0270 ns | - | - |
| TaskItem_AllDerivableModifiers_Once | 87.41 ns | 0.226 ns | 0.200 ns |
- | - |
| TaskItem_FilenameAndExtension_Repeated | 173.68 ns | 1.812 ns | 1.695
ns | - | - |
| TaskItem_Filename_ManyItems | 1,856.79 ns | 1.128 ns | 0.942 ns | - |
- |
| TaskItem_FullPathDerivedModifiers_Repeated | 321.57 ns | 0.301 ns |
0.267 ns | - | - |
| ProjectItemInstance_AllDerivableModifiers_Once | 143.78 ns | 0.493 ns
| 0.462 ns | 0.0038 | 64 B |
| ProjectItemInstance_FilenameExtension_AllItems | 5,343.30 ns | 4.955
ns | 4.138 ns | - | 64 B |
| ProjectItemInstance_FilenameExtension_AllItems_Repeated | 67,028.30 ns
| 252.985 ns | 224.264 ns | - | 640 B |
| ProjectItemInstance_AllDefiningProjectModifiers_Once | 459.4 ns | 0.34
ns | 0.31 ns | 0.0038 | 64 B |
| ProjectItemInstance_DefiningProjectDirectory_Repeated | 1,020.5 ns |
0.56 ns | 0.47 ns | 0.0038 | 64 B |
|
ProjectItemInstance_DefiningProjectNameExtension_AllItems_SingleProject
| 20,091.0 ns | 17.96 ns | 16.80 ns | - | 64 B |
| ProjectItemInstance_DefiningProjectFullPath_AllItems_MultiProject |
9,946.7 ns | 5.28 ns | 4.68 ns | - | 64 B |
|
ProjectItemInstance_DefiningProjectDirectory_AllItems_MultiProject_Repeated
| 103,960.5 ns | 57.74 ns | 48.21 ns | - | 640 B |
| TaskItem_AllDefiningProjectModifiers_Once | 400.5 ns | 0.15 ns | 0.12
ns | - | - |
| TaskItem_DefiningProjectNameExtension_AllItems | 19,150.3 ns | 11.55
ns | 10.24 ns | - | - |
| TaskItem_DefiningProjectDirectory_Repeated | 970.8 ns | 0.62 ns | 0.55
ns | - | - |

### .NET Framework 4.8.1

| Method | Mean | Error | StdDev | Gen0 | Allocated |
|---------------------------------------------
|-------------:|-----------:|----------:|-------:|----------:|
| IsItemSpecModifier_AllModifiers | 106.532 ns | 0.4289 ns | 0.4012 ns |
- | - |
| IsDerivableItemSpecModifier_RecursiveDir | 5.067 ns | 0.0031 ns |
0.0024 ns | - | - |
| GetItemSpecModifier_FullPath | 1,331.138 ns | 1.4666 ns | 1.3001 ns |
- | - |
| GetItemSpecModifier_Directory | 2,471.887 ns | 4.2333 ns | 3.7527 ns |
0.0954 | 517 B |
| GetItemSpecModifier_ModifiedTime | 44,773.794 ns | 405.2647 ns |
359.2566 ns | 0.1221 | 878 B |
| GetItemSpecModifier_DefiningProjectDirectory | 156.840 ns | 0.2242 ns
| 0.1987 ns | - | - |
| TaskItem_AllDerivableModifiers_Once | 507.2 ns | 1.19 ns | 1.11 ns | -
| - |
| TaskItem_FilenameAndExtension_Repeated | 664.7 ns | 0.39 ns | 0.35 ns
| - | - |
| TaskItem_Filename_ManyItems | 6,916.2 ns | 4.03 ns | 3.77 ns | - | - |
| TaskItem_FullPathDerivedModifiers_Repeated | 2,261.6 ns | 3.34 ns |
2.96 ns | - | - |
| ProjectItemInstance_AllDerivableModifiers_Once | 688.6 ns | 1.01 ns |
0.94 ns | 0.0067 | 36 B |
| ProjectItemInstance_FilenameExtension_AllItems | 20,366.3 ns | 11.28
ns | 10.56 ns | - | 36 B |
| ProjectItemInstance_FilenameExtension_AllItems_Repeated | 202,570.4 ns
| 271.12 ns | 240.34 ns | - | 362 B |
| ProjectItemInstance_AllDefiningProjectModifiers_Once | 1,153.5 ns |
13.83 ns | 12.26 ns | 0.0057 | 36 B |
| ProjectItemInstance_DefiningProjectDirectory_Repeated | 2,795.7 ns |
17.33 ns | 16.21 ns | 0.0038 | 36 B |
|
ProjectItemInstance_DefiningProjectNameExtension_AllItems_SingleProject
| 46,236.9 ns | 105.16 ns | 93.22 ns | - | 36 B |
| ProjectItemInstance_DefiningProjectFullPath_AllItems_MultiProject |
28,362.1 ns | 34.50 ns | 30.58 ns | - | 36 B |
|
ProjectItemInstance_DefiningProjectDirectory_AllItems_MultiProject_Repeated
| 282,316.9 ns | 1,944.00 ns | 1,818.42 ns | - | 364 B |
| TaskItem_AllDefiningProjectModifiers_Once | 965.3 ns | 5.43 ns | 4.53
ns | - | - |
| TaskItem_DefiningProjectNameExtension_AllItems | 42,707.8 ns | 179.84
ns | 168.23 ns | - | - |
| TaskItem_DefiningProjectDirectory_Repeated | 2,539.1 ns | 9.64 ns |
8.05 ns | - | - |

Fixes #13425

### Context
Blazor WASM builds (and other projects) fail under /mt mode on Unix with
`DirectoryNotFoundException` because paths contain unresolved
backslashes, e.g.:
```
obj\Debug/net8.0/Net8BlazorWasmApp.csproj.AssemblyReference.cache
```

The root cause is in `FileUtilities.LooksLikeUnixFilePath`. This method
checks whether the value looks like a unix path by checking whether the
first path segment (e.g., obj) actually exists as a directory. It is
used in `FileUtilities.MaybeAdjustFilePath` which decides whether a
string with backslashes should be normalized to forward slashes.
However, `LooksLikeUnixFilePath`, when base directory is not passed to
the method, relies on CWD for the directory existence check. This breaks
in /mt mode.

### Changes Made
Use `CurrentThreadWorkingDirectory` for resolving the absolute path to
check for existence, when base path is not provided.

### Testing
- Tested on local repro, this fixes the original issue.
- Unit test.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Fixes #12867

### Context
Building large repos (e.g., Roslyn) in multi-threaded mode crashes
intermittently:

error MSB4061: The "CombineTargetFrameworkInfoProperties" task could not
be instantiated...
Operations that change non-concurrent collections must have exclusive
access. A concurrent update was performed on this collection and
corrupted its state.

Root Cause
`AssemblyTaskFactory` instances are shared across thread nodes — they're
cached in `TaskRegistry._taskFactoryWrapperInstance`. `TaskRegistry`
itself is shared across thread nodes by design. In mt builds, multiple
projects call `CreateTaskInstance()` on the same `AssemblyTaskFactory`
instance concurrently from different threads. This exposed two
thread-safety issues:

 1. `_taskLoggingContext` field race (crash-causing)

Race condition example: When Thread A (Project A) and Thread B (Project
B) concurrently call `CreateTaskInstance()`:
   1. Thread A sets `_taskLoggingContext = contextA`
   2. Thread B overwrites `_taskLoggingContext = contextB`
3. Thread A reads `_taskLoggingContext` for `TrackTaskSubclassing` →
gets `contextB` → writes to Project B's ProjectTelemetry
   4. Thread B also writes to Project B's ProjectTelemetry
   5. Two threads mutate the same Dictionary<string, int> → crash

The `ProjectTelemetry` in turn is not supposed to be accessed from
multiple threads - only one thread node should build a project. It does
not need to be thread-safe.

`_taskLoggingContext` field existed so that `ErrorLoggingDelegate` (a
named method passed as a callback to `TaskLoader.CreateTask()`) could
access the logging context, but it is not really required. For mt mode
support, there should not be mutable fields in `AssemblyTaskFactory`
that relate to a specific task.

  2. `_tasksAndAppDomains` dictionary (in .NET Framework)

`Dictionary<ITask, AppDomain>` is not safe for concurrent structural
mutations. While each thread operates on different keys (unique ITask
instances), concurrent add/remove on different keys still corrupts a
plain Dictionary.

### Changes Made
- Removed `_taskLoggingContext` field entirely. 
- Changed `_tasksAndAppDomains` from `Dictionary<ITask, AppDomain>` to
`ConcurrentDictionary<ITask, AppDomain>`
Note that lock contention should be negligible, as each thread would add
and clean-up its own set of keys.

### Testing
Existing unit tests

updates the process to be aligned with rolling VS updates and provides
agent to assist with activities so dev does not have to do the commands

---------

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Rainer Sigwald <raines@microsoft.com>

…13443)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…wn (#13450)

## Summary

Fix a race condition crash (access violation 0xC0000005 /
NullReferenceException) in `LoggingService.ProcessLoggingEvent` when the
method is called after the logging service has been shut down.

## Problem

`ProcessLoggingEvent` directly accesses `_eventQueue`, `_dequeueEvent`,
and `_enqueueEvent` without any shutdown guard. During
`ShutdownComponent()`, `CleanLoggingEventProcessing()` disposes and
nullifies all of these fields. If an external callback (e.g.,
`Process.Exited` from a `ProjectCachePlugin`) attempts to log a message
after shutdown has completed, the null field access causes an
unrecoverable crash.

### Reproduction Scenario

1. A build runs with a `ProjectCachePlugin`
2. The build completes and `LoggingService.ShutdownComponent()` is
called
3. The cache plugin's external process exits, triggering
`Process.OnExited` on a ThreadPool thread
4. The callback logs "Project cache service process exited" via
`LoggingServiceToPluginLoggerAdapter.LogMessage`
5. This calls `ProcessLoggingEvent()` which accesses `_eventQueue.Count`
→ **null reference crash**

### Debugger Evidence

```
_serviceState = Shutdown
_eventQueue = null
_dequeueEvent = null
_enqueueEvent = null
_emptyQueueEvent = null
_loggingEventProcessingCancellation = null

buildEvent.Message = "Project cache service process exited"
Call: System.Diagnostics.Process.OnExited -> ProjectCachePlugin.dll -> LoggingServiceToPluginLoggerAdapter.LogMessage
```

## Root Cause

`ProcessLoggingEvent` lacked two protections that already exist
elsewhere in the codebase:

1. **Shutdown state guard** - Other public methods (`RegisterLogger`,
`RegisterDistributedLogger`, `InitializeNodeLoggers`,
`InitializeComponent`) all check `_serviceState !=
LoggingServiceState.Shutdown`. `ProcessLoggingEvent` did not.

2. **Local field capture** - The `LoggingEventProc` queue pump thread
already captures `_eventQueue`, `_dequeueEvent`, `_emptyQueueEvent`, and
`_enqueueEvent` into local variables to prevent races with
`CleanLoggingEventProcessing()`. `ProcessLoggingEvent` accessed the
fields directly.

## Fix

Three layers of defense, all following patterns already established in
the same file:

1. **Early return** when `_serviceState == LoggingServiceState.Shutdown`
- silently drops the event, since the service is no longer operational.
2. **Capture fields to locals** before use - prevents null dereference
if `CleanLoggingEventProcessing()` runs concurrently between the state
check and the field reads.
3. **Null-check the captured locals** - second defense against the
TOCTOU race between step 1 and step 2.

## Risk

**Low.** The fix only adds early-exit guards - no behavioral change for
the normal (non-shutdown) code path. The patterns used are already
established in the same file.