Clean up the cache folder before saving

Author: davidwengier

src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/RemoteMefComposition.cs

@@ -120,6 +120,8 @@ private static async Task TrySaveCachedExportProviderAsync(CachedComposition cac
             var cacheDirectory = Path.GetDirectoryName(compositionCacheFile).AssumeNotNull();
             var directoryInfo = Directory.CreateDirectory(cacheDirectory);
 
+            CleanCacheDirectory(directoryInfo, cancellationToken);
+
             var tempFilePath = Path.Combine(cacheDirectory, Path.GetRandomFileName());
             using (var cacheStream = new FileStream(compositionCacheFile, FileMode.Create, FileAccess.Write, FileShare.None, bufferSize: 4096, useAsync: true))
             {
@@ -134,6 +136,25 @@ private static async Task TrySaveCachedExportProviderAsync(CachedComposition cac
         }
     }
 
+    private static void CleanCacheDirectory(DirectoryInfo directoryInfo, CancellationToken cancellationToken)
+    {
+        try
+        {
+            // Delete any existing cached files.
+            foreach (var fileInfo in directoryInfo.EnumerateFiles())
+            {
+                // Failing to delete any file is fine, we'll just try again the next VS session in which we attempt
+                // to write a new cache
+                fileInfo.Delete();
+                cancellationToken.ThrowIfCancellationRequested();
+            }
+        }
+        catch (Exception)
+        {
+            // We ignore all errors when cleaning the cache directory, because we'll try again if the cache is corrupt.
+        }
+    }
+
     [return: NotNullIfNotNull(nameof(cacheDirectory))]
     private static string? GetCompositionCacheFile(string? cacheDirectory)
     {

src/Razor/test/Microsoft.CodeAnalysis.Remote.Razor.Test/RemoteMefCompositionTest.cs

@@ -62,4 +62,29 @@ public async Task CorruptCacheFileIsOverwritten()
         Assert.Single(Directory.GetFiles(cacheDirectory));
         Assert.True(new FileInfo(cacheFile).Length > 35);
     }
+
+    [Fact]
+    public async Task CleansOldCacheFiles()
+    {
+        using var tempRoot = new TempRoot();
+        var cacheDirectory = tempRoot.CreateDirectory().Path;
+        Directory.CreateDirectory(cacheDirectory);
+
+        File.WriteAllText(Path.Combine(cacheDirectory, Path.GetRandomFileName()), "");
+        File.WriteAllText(Path.Combine(cacheDirectory, Path.GetRandomFileName()), "");
+        File.WriteAllText(Path.Combine(cacheDirectory, Path.GetRandomFileName()), "");
+        File.WriteAllText(Path.Combine(cacheDirectory, Path.GetRandomFileName()), "");
+
+        Assert.Equal(4, Directory.GetFiles(cacheDirectory).Length);
+
+        var cacheFile = RemoteMefComposition.TestAccessor.GetCacheCompositionFile(cacheDirectory);
+
+        var exportProvider = await RemoteMefComposition.CreateExportProviderAsync(cacheDirectory, DisposalToken);
+
+        Assert.NotNull(RemoteMefComposition.TestAccessor.SaveCacheFileTask);
+        await RemoteMefComposition.TestAccessor.SaveCacheFileTask;
+
+        Assert.Single(Directory.GetFiles(cacheDirectory));
+        Assert.True(new FileInfo(cacheFile).Length > 35);
+    }
 }