src/NLog/Internal/FileInfoHelper.cs (1)

50-57: Windows edge-case: extremely old (pre-1980) timestamps

The Year < 1980 fallback is disabled on Win32. On odd filesystems (e.g., certain SMB shares), CreationTimeUtc could be 1601-01-01 and propagate through, potentially skewing archive scheduling/cleanup. If intentional, consider a brief comment stating why Windows is excluded; otherwise, consider allowing the fallback when Year < 1980 regardless of OS.

src/NLog/Targets/FileAppenders/ExclusiveFileLockingAppender.cs (1)

111-113: Remove stale MinValue sentinel branch

LookupValidFileCreationTimeUtc now always returns a non-null DateTime. The MinValue check is redundant and the else-path won’t trigger in practice.

-                    var fileBirthTimeUtc = FileInfoHelper.LookupValidFileCreationTimeUtc(fileInfo);
-                    var fileBirthTime = fileBirthTimeUtc != DateTime.MinValue ? NLog.Time.TimeSource.Current.FromSystemTime(fileBirthTimeUtc) : OpenStreamTime;
+                    var fileBirthTimeUtc = FileInfoHelper.LookupValidFileCreationTimeUtc(fileInfo);
+                    var fileBirthTime = NLog.Time.TimeSource.Current.FromSystemTime(fileBirthTimeUtc);

src/NLog/Targets/FileArchiveHandlers/BaseFileArchiveHandler.cs (1)

252-256: Log message label nit: variable is local-date based

currentDateUtc is actually local date (TimeSource.Current.Time.Date). Consider renaming the variable or log label for clarity. Optional.

src/NLog/Targets/FileAppenders/MinimalFileLockingAppender.cs (1)

83-93: Harden against TOCTOU/IO exceptions when probing FileInfo (mirror FileLastModified’s try/catch)

CreationTime/Length can throw (e.g., racey deletes, permission issues). FileLastModified already logs and falls back; NextArchiveTime should do the same to avoid breaking logging on metadata failures.

@@
-                if (_nextArchiveTime < NLog.Time.TimeSource.Current.Time.AddMinutes(1) || _lastFileBirthTimeUtc == DateTime.MinValue)
-                {
-                    var fileInfo = new FileInfo(_filePath);
-                    var fileBirthTimeUtc = (fileInfo.Exists && fileInfo.Length != 0) ? FileInfoHelper.LookupValidFileCreationTimeUtc(fileInfo) : DateTime.MinValue;
-                    if (fileBirthTimeUtc == DateTime.MinValue || _lastFileBirthTimeUtc < fileBirthTimeUtc)
-                    {
-                        var fileBirthTime = fileBirthTimeUtc != DateTime.MinValue ? NLog.Time.TimeSource.Current.FromSystemTime(fileBirthTimeUtc) : OpenStreamTime;
-                        _nextArchiveTime = FileTarget.CalculateNextArchiveEventTime(_fileTarget.ArchiveEvery, fileBirthTime);
-                        _lastFileBirthTimeUtc = fileBirthTimeUtc;
-                    }
-                }
+                if (_nextArchiveTime < NLog.Time.TimeSource.Current.Time.AddMinutes(1) || _lastFileBirthTimeUtc == DateTime.MinValue)
+                {
+                    try
+                    {
+                        var fileInfo = new FileInfo(_filePath);
+                        var fileBirthTimeUtc = (fileInfo.Exists && fileInfo.Length != 0)
+                            ? FileInfoHelper.LookupValidFileCreationTimeUtc(fileInfo)
+                            : DateTime.MinValue;
+                        if (fileBirthTimeUtc == DateTime.MinValue || _lastFileBirthTimeUtc < fileBirthTimeUtc)
+                        {
+                            var fileBirthTime = fileBirthTimeUtc != DateTime.MinValue ? NLog.Time.TimeSource.Current.FromSystemTime(fileBirthTimeUtc) : OpenStreamTime;
+                            _nextArchiveTime = FileTarget.CalculateNextArchiveEventTime(_fileTarget.ArchiveEvery, fileBirthTime);
+                            _lastFileBirthTimeUtc = fileBirthTimeUtc;
+                        }
+                    }
+                    catch (Exception ex)
+                    {
+                        NLog.Common.InternalLogger.Error(ex, "{0}: Failed to lookup FileInfo.CreationTimeUtc for file: {1}", _fileTarget, _filePath);
+                        if (ex.MustBeRethrown())
+                            throw;
+                        // Fall back to OpenStreamTime on probe failure
+                        if (_lastFileBirthTimeUtc != DateTime.MinValue)
+                        {
+                            _lastFileBirthTimeUtc = DateTime.MinValue;
+                            _nextArchiveTime = FileTarget.CalculateNextArchiveEventTime(_fileTarget.ArchiveEvery, OpenStreamTime);
+                        }
+                    }
+                }

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Plan: Pro

src/NLog/Internal/FileInfoHelper.cs (2)

50-55: Replace magic number 1980 with a named constant

This improves readability and documents intent (FAT epoch / “likely invalid birthtime”).

Apply within this block:

-            if (fileCreationTime.Year < 1980 && !PlatformDetector.IsWin32)
+            if (!PlatformDetector.IsWin32 && fileCreationTime.Year < MinReliableBirthYear)
             {
                 // Non-Windows-FileSystems doesn't always provide correct CreationTime/BirthTime
                 fileCreationTime = fallback(fileInfo);
-                if (finalFallback != null && fileCreationTime.Year < 1980)
+                if (finalFallback != null && fileCreationTime.Year < MinReliableBirthYear)
                 {
                     fileCreationTime = finalFallback(fileInfo);
                 }

And add near the top of the class:

// Consider values before this year as “unreliable” on non-Windows FS
private const int MinReliableBirthYear = 1980;

---

46-60: Remove unused finalFallback parameter and branch
The generic method is only ever called with two arguments (finalFallback always defaults to null), so the finalFallback check never runs. Drop the Func<T, DateTime>? finalFallback = null parameter and the inner if (finalFallback != null …) block.

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Review profile: CHILL

Plan: Pro

src/NLog/Internal/FileInfoHelper.cs (1)

41-41: Name the threshold as a DateTime to avoid repeated Year checks (optional)

Consider adding a MinReliableBirthDateUtc = new DateTime(1980,1,1,0,0,0,DateTimeKind.Utc) and comparing with < MinReliableBirthDateUtc to improve intent and avoid magic number/year comparisons.

- internal const int MinReliableBirthYear = 1980;
+ internal const int MinReliableBirthYear = 1980;
+ internal static readonly DateTime MinReliableBirthDateUtc = new DateTime(1980, 1, 1, 0, 0, 0, DateTimeKind.Utc);

And then:

- if (fileCreationTime.Year < MinReliableBirthYear && !PlatformDetector.IsWin32)
+ if (fileCreationTime < MinReliableBirthDateUtc && !PlatformDetector.IsWin32)

src/NLog/Targets/FileAppenders/MinimalFileLockingAppender.cs (1)

86-86: Minor: guard branch can avoid unnecessary FileInfo allocation

You allocate FileInfo regardless; micro-opt: check _lastFileBirthTimeUtc/date guard first, then allocate only when needed. Low impact, feel free to ignore.

tests/NLog.UnitTests/Targets/FileTargetTests.cs (1)

1105-1113: Make the extra 500ms wait conditional (optional)

After the polling loop, the unconditional Thread.Sleep(500) lengthens the test. Sleep only if the loop exhausted all attempts, or switch to SpinWait.SpinUntil with a timeout.

-                        for (int i = 0; i < 100; ++i)
+                        var completed = false;
+                        for (int i = 0; i < 100; ++i)
                         {
                             var fileInfo = new FileInfo(logFile);
                             if (fileInfo.Exists && fileInfo.Length > 0)
-                                break;
+                            { completed = true; break; }
                             Thread.Sleep(50);
                         }
-                        Thread.Sleep(500);
+                        if (!completed)
+                            Thread.Sleep(500);

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Review profile: CHILL

Plan: Pro