[fix] Fix HTML logger parallel file collision

.github/copilot-instructions.md

@@ -28,3 +28,87 @@ Anytime you add a new localization resource, you MUST:
 - Add a corresponding entry in the localization resource file.
 - Add an entry in all `*.xlf` files related to the modified `.resx` file.
 - Do not modify existing entries in '*.xlf' files unless you are also modifying the corresponding `.resx` file.
+
+## Build & Test Commands
+
+### Full Build
+
+```bash
+# Windows
+build.cmd
+# Unix
+./build.sh
+```
+
+### Building a Specific Project
+
+```bash
+dotnet build src/<ProjectName>/<ProjectName>.csproj --no-restore
+```
+
+### Running Unit Tests for a Specific Project
+
+```bash
+# Run all TFMs
+dotnet test test/<TestProjectName>/<TestProjectName>.csproj --no-build
+
+# Run a specific TFM
+dotnet test test/<TestProjectName>/<TestProjectName>.csproj --no-build -f net9.0
+
+# Run a specific test
+dotnet test test/<TestProjectName>/<TestProjectName>.csproj --no-build -f net9.0 --filter "TestMethodName"
+```
+
+### Key Test Projects
+
+| Component | Test Project |
+|---|---|
+| TRX Logger | `test/Microsoft.TestPlatform.Extensions.TrxLogger.UnitTests` |
+| HTML Logger | `test/Microsoft.TestPlatform.Extensions.HtmlLogger.UnitTests` |
+| Object Model | `test/Microsoft.TestPlatform.ObjectModel.UnitTests` |
+| Cross-Platform Engine | `test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests` |
+| Client | `test/Microsoft.TestPlatform.Client.UnitTests` |
+
+## Repository Structure
+
+- `src/` — Production source code
+  - `Microsoft.TestPlatform.Extensions.TrxLogger/` — TRX file logger (generates `.trx` test result files)
+  - `Microsoft.TestPlatform.Extensions.HtmlLogger/` — HTML logger (generates `.html` test reports via XML→XSLT transform)
+  - `Microsoft.TestPlatform.ObjectModel/` — Shared object model (TestCase, TestResult, etc.)
+  - `Microsoft.TestPlatform.Common/` — Common utilities
+  - `Microsoft.TestPlatform.CrossPlatEngine/` — Test execution engine
+  - `vstest.console/` — CLI console runner
+- `test/` — Unit tests (mirrors `src/` structure with `.UnitTests` suffix)
+- `eng/` — Build infrastructure
+- `scripts/` — Helper scripts
+
+## Logger Architecture Notes
+
+### TRX Logger (`src/Microsoft.TestPlatform.Extensions.TrxLogger/`)
+
+- **`TrxLogger.cs`** — Main logger class. Flow: `TestRunCompleteHandler` → compose XML DOM → `ReserveTrxFilePath` → `AdjustRunDeploymentRootForTrxSubdirectory` → `PopulateTrxFile`.
+- **`Utility/Converter.cs`** — Converts VSTest object model to TRX object model. Handles file attachments.
+- **`Utility/TrxFileHelper.cs`** — File path utilities. Use `MakePathRelative()` instead of `Path.GetRelativePath()` (netstandard2.0 compat).
+- Tests use `TestableTrxLogger` which overrides `PopulateTrxFile` to capture TRX file path.
+
+### HTML Logger (`src/Microsoft.TestPlatform.Extensions.HtmlLogger/`)
+
+- **`HtmlLogger.cs`** — Main logger. Creates temp XML, transforms to HTML via XSLT, deletes XML.
+- **`HtmlTransformer.cs`** — XSLT transformation from XML to HTML.
+- Temp XML filenames use millisecond-precision timestamps for cross-process uniqueness. File creation uses `FileMode.CreateNew` for atomicity.
+- Tests mock `IFileHelper`, `IHtmlTransformer`, and `XmlObjectSerializer`.
+
+## Analyzer Rules
+
+The codebase enforces strict code analysis rules as errors:
+- **CA1305**: Always provide `IFormatProvider` (e.g., `CultureInfo.InvariantCulture`) for `ToString()` calls.
+- **CA1837**: Use `Environment.ProcessId` instead of `Process.GetCurrentProcess().Id` (net5.0+ only; suppress for net48 targets).
+- Source projects target `netstandard2.0`/`net462` — many modern APIs are unavailable. Always check TFM compatibility.
+
+## Task Completion Jingle
+
+When you finish a task (right before calling `task_complete`), play a short celebratory jingle so the user knows you're done:
+
+```powershell
+[console]::beep(500,300); [console]::beep(600,300); [console]::beep(700,300); [console]::beep(600,300); [console]::beep(800,500)
+```

.github/skills/vstest-build-test/SKILL.md

@@ -143,3 +143,26 @@ After building with `--pack` / `-pack`, validate vstest.console changes by unzip
 - If build fails asking for .NET 4.6 targeting pack, install it from [Microsoft Downloads](https://www.microsoft.com/download/details.aspx?id=48136)
 - Enable verbose diagnostics: see `docs/diagnose.md`
 - For debugging, add `Debugger.Launch` at process entry points (testhost.exe, vstest.console.exe)
+
+## Logger-Specific Notes
+
+### TRX Logger (`src/Microsoft.TestPlatform.Extensions.TrxLogger/`)
+
+- **Key files:** `TrxLogger.cs` (main), `Utility/Converter.cs` (attachment handling), `Utility/TrxFileHelper.cs` (path utils)
+- **Flow:** `TestRunCompleteHandler` → compose XML DOM → `ReserveTrxFilePath` → `AdjustRunDeploymentRootForTrxSubdirectory` → `PopulateTrxFile`
+- **Test helper:** `TestableTrxLogger` overrides `PopulateTrxFile` to capture TRX file path. Call `MakeTestRunComplete()` to trigger the full flow.
+- **Important:** Targets netstandard2.0 — use `TrxFileHelper.MakePathRelative()` instead of `Path.GetRelativePath()`
+
+### HTML Logger (`src/Microsoft.TestPlatform.Extensions.HtmlLogger/`)
+
+- **Key files:** `HtmlLogger.cs` (main), `HtmlTransformer.cs` (XSLT)
+- **Flow:** `TestRunCompleteHandler` → `PopulateHtmlFile` → create temp XML → serialize → XSLT to HTML → delete XML
+- **Temp XML naming:** `TestResult_{user}_{machine}_{timestamp}.xml` — timestamp has millisecond precision; on collisions a `[n]` suffix is appended
+- **File creation:** Uses `FileMode.CreateNew` for atomic creation with retry on collision
+- **Tests:** Mock `IFileHelper`, `IHtmlTransformer`, and `XmlObjectSerializer`
+
+### Analyzer Pitfalls
+
+- **CA1305:** Always provide `IFormatProvider` (e.g., `CultureInfo.InvariantCulture`) for `ToString()` calls
+- **CA1837 (Environment.ProcessId):** Prefer `Environment.ProcessId` on net5.0+; for this repo (targeting `netstandard2.0`), continue using the existing PID retrieval (e.g., `Process.GetCurrentProcess().Id`) and suppress CA1837 with a brief justification comment.
+- Source targets `netstandard2.0` — many modern APIs (`Path.GetRelativePath`, `Environment.ProcessId`) are NOT available here; plan any migrations accordingly.

src/Microsoft.TestPlatform.Extensions.HtmlLogger/HtmlLogger.cs

@@ -33,7 +33,6 @@ public class HtmlLogger : ITestLoggerWithParameters
     private readonly IFileHelper _fileHelper;
     private readonly XmlObjectSerializer _xmlSerializer;
     private readonly IHtmlTransformer _htmlTransformer;
-    private static readonly object FileCreateLockObject = new();
     private Dictionary<string, string?>? _parametersDictionary;
 
     public HtmlLogger()
@@ -345,18 +344,21 @@ private void PopulateHtmlFile()
 
     private string GenerateUniqueFilePath(string fileName, string fileExtension)
     {
-        string fullFilePath;
         for (short i = 0; i < short.MaxValue; i++)
         {
             var fileNameWithIter = i == 0 ? fileName : Path.GetFileNameWithoutExtension(fileName) + $"[{i}]";
-            fullFilePath = Path.Combine(TestResultsDirPath!, $"TestResult_{fileNameWithIter}.{fileExtension}");
-            lock (FileCreateLockObject)
+            var fullFilePath = Path.Combine(TestResultsDirPath!, $"TestResult_{fileNameWithIter}.{fileExtension}");
+
+            try
             {
-                if (!File.Exists(fullFilePath))
-                {
-                    using var _ = File.Create(fullFilePath);
-                    return fullFilePath;
-                }
+                // Use FileMode.CreateNew for atomic "create if not exists" to avoid
+                // cross-process race conditions when multiple vstest processes run in parallel.
+                using var _ = new FileStream(fullFilePath, FileMode.CreateNew, FileAccess.Write, FileShare.None);
+                return fullFilePath;
+            }
+            catch (IOException) when (File.Exists(fullFilePath))
+            {
+                // File already exists (another process created it), try next iteration.
             }
         }
 
@@ -365,7 +367,7 @@ private string GenerateUniqueFilePath(string fileName, string fileExtension)
 
     private static string FormatDateTimeForRunName(DateTime timeStamp)
     {
-        return timeStamp.ToString("yyyyMMdd_HHmmss", DateTimeFormatInfo.InvariantInfo);
+        return timeStamp.ToString("yyyyMMdd_HHmmss.fffffff", DateTimeFormatInfo.InvariantInfo);
     }
 
     /// <summary>

test/Microsoft.TestPlatform.Extensions.HtmlLogger.UnitTests/HtmlLoggerTests.cs

@@ -591,6 +591,45 @@ public void TestCompleteHandlerShouldNotDivideByZeroWhenThereAre0TestResults()
         Assert.AreEqual(0, _htmlLogger.TestRunDetails.Summary.PassPercentage);
     }
 
+    [TestMethod]
+    public void XmlFilePathShouldContainMillisecondTimestampForCrossProcessUniqueness()
+    {
+        // Verifies fix for https://github.com/microsoft/vstest/issues/15404
+        // The temp XML file name should use millisecond-precision timestamps to avoid
+        // collisions when multiple vstest processes run in parallel.
+        string? createdFilePath = null;
+        try
+        {
+            _htmlLogger.TestRunCompleteHandler(new object(), new TestRunCompleteEventArgs(null, false, true, null, null, null, TimeSpan.Zero));
+
+            Assert.IsNotNull(_htmlLogger.XmlFilePath);
+            createdFilePath = _htmlLogger.XmlFilePath;
+
+            // The filename should match the pattern with milliseconds: yyyyMMdd_HHmmssfff
+            // e.g., TestResult_user_MACHINE_20260304_153012345.xml
+            // The time part (HHmmssfff) should be 9 chars; previously it was 6 chars (HHmmss).
+            var fileName = Path.GetFileNameWithoutExtension(_htmlLogger.XmlFilePath);
+            var parts = fileName.Split('_');
+            // The last part is the time portion, possibly with an iteration suffix like [7]
+            var timePart = parts[parts.Length - 1];
+            var bracketIdx = timePart.IndexOf('[');
+            if (bracketIdx >= 0)
+            {
+                timePart = timePart.Substring(0, bracketIdx);
+            }
+
+            Assert.AreEqual(9, timePart.Length,
+                $"Time portion of timestamp should be 9 chars (HHmmssfff) but was '{timePart}' (length {timePart.Length}) in path: '{_htmlLogger.XmlFilePath}'");
+        }
+        finally
+        {
+            if (!string.IsNullOrEmpty(createdFilePath) && File.Exists(createdFilePath))
+            {
+                File.Delete(createdFilePath);
+            }
+        }
+    }
+
     private static TestCase CreateTestCase(string testCaseName)
     {
         return new TestCase(testCaseName, new Uri("some://uri"), "DummySourceFileName");