Don't cache known-broken compositions (#80021)

Right now we have an issue where users are getting broken MEF
compositions cached on their machines, so subsequent launches of the
product are operating on a broken composition. It's not "broken" in the
sense that "the cache cannot be loaded" but rather the content of the
cache is just missing most of our MEF parts. As a defense-in-depth
change to deal with potential transient issues, let's not cache
compositions we know are bad.

Author: jasonmalinowski

src/Workspaces/Remote/Core/ExportProviderBuilder.cs

@@ -87,12 +87,13 @@ private async Task<IExportProviderFactory> GetCompositionConfigurationAsync(Canc
         // Assemble the parts into a valid graph.
         var config = CompositionConfiguration.Create(catalog);
 
-        // Verify we only have expected errors.
-
-        ReportCompositionErrors(config, catalog);
-
-        // Try to cache the composition.
-        _ = WriteCompositionCacheAsync(compositionCacheFile, config, cancellationToken).ReportNonFatalErrorAsync();
+        // Check if we have errors, and report them accordingly.
+        if (!CheckForAndReportCompositionErrors(config, catalog))
+        {
+            // There weren't any errors in the composition, so let's cache it. If there were errors, those errors might have been temporary and we don't want
+            // to end up in a permanently broken case.
+            _ = WriteCompositionCacheAsync(compositionCacheFile, config, cancellationToken).ReportNonFatalErrorAsync();
+        }
 
         // Prepare an ExportProvider factory based on this graph.
         return config.CreateExportProviderFactory();
@@ -182,10 +183,14 @@ protected virtual void PerformCacheDirectoryCleanup(DirectoryInfo directoryInfo,
 
     protected abstract bool ContainsUnexpectedErrors(IEnumerable<string> erroredParts);
 
-    private void ReportCompositionErrors(CompositionConfiguration configuration, ComposableCatalog catalog)
+    /// <returns>True if there was an unexpected composition error, false otherwise.</returns>
+    private bool CheckForAndReportCompositionErrors(CompositionConfiguration configuration, ComposableCatalog catalog)
     {
+        var hasErrors = false;
+
         foreach (var exception in catalog.DiscoveredParts.DiscoveryErrors)
         {
+            hasErrors = true;
             LogError($"Encountered exception in the MEF composition: {exception.Message}");
         }
 
@@ -194,6 +199,8 @@ private void ReportCompositionErrors(CompositionConfiguration configuration, Com
 
         if (ContainsUnexpectedErrors(erroredParts))
         {
+            hasErrors = true;
+
             try
             {
                 configuration.ThrowOnErrors();
@@ -204,5 +211,7 @@ private void ReportCompositionErrors(CompositionConfiguration configuration, Com
                 LogError($"Encountered errors in the MEF composition: {ex.Message}{Environment.NewLine}{ex.ErrorsAsString}");
             }
         }
+
+        return hasErrors;
     }
 }