Tolerate dependencies outside the repo when adding to cache (#82)

src/Common/Fingerprinting/FingerprintFactory.cs

@@ -35,19 +35,22 @@ public sealed class FingerprintFactory : IFingerprintFactory
     private readonly List<FingerprintEntry> _pluginSettingsFingerprintEntries;
     private readonly PluginSettings _pluginSettings;
     private readonly PathNormalizer _pathNormalizer;
+    private readonly string _repoRoot;
 
     public FingerprintFactory(
         IContentHasher contentHasher,
         IInputHasher inputHasher,
         INodeContextRepository nodeRepository,
         PluginSettings pluginSettings,
-        PathNormalizer pathNormalizer)
+        PathNormalizer pathNormalizer,
+        string repoRoot)
     {
         _contentHasher = contentHasher;
         _inputHasher = inputHasher;
         _nodeContextRepository = nodeRepository;
         _pluginSettings = pluginSettings;
         _pathNormalizer = pathNormalizer;
+        _repoRoot = repoRoot;
 
         _pluginSettingsFingerprintEntries = new List<FingerprintEntry>()
         {
@@ -119,6 +122,11 @@ void AddSettingToFingerprint(IReadOnlyCollection<Glob>? patterns, string setting
                 {
                     if (!_nodeContextRepository.TryGetNodeContext(dependencyNode.ProjectInstance, out NodeContext? dependency))
                     {
+                        if (!dependencyNode.ProjectInstance.FullPath.IsUnderDirectory(_repoRoot))
+                        {
+                            continue;
+                        }
+
                         return null;
                     }
 

src/Common/MSBuildCachePluginBase.cs

@@ -197,12 +197,13 @@ protected virtual IFingerprintFactory CreateFingerprintFactory()
             || InputHasher == null
             || _nodeContextRepository == null
             || Settings == null
-            || _pathNormalizer == null)
+            || _pathNormalizer == null
+            || _repoRoot == null)
         {
             throw new InvalidOperationException();
         }
 
-        return new FingerprintFactory(ContentHasher, InputHasher, _nodeContextRepository, Settings, _pathNormalizer);
+        return new FingerprintFactory(ContentHasher, InputHasher, _nodeContextRepository, Settings, _pathNormalizer, _repoRoot);
     }
 
     protected abstract Task<ICacheClient> CreateCacheClientAsync(PluginLoggerBase logger, CancellationToken cancellationToken);
@@ -442,6 +443,15 @@ private async Task HandleProjectFinishedInnerAsync(FileAccessContext fileAccessC
         {
             if (!_nodeContextRepository.TryGetNodeContext(dependencyNode.ProjectInstance, out NodeContext? dependencyNodeContext))
             {
+                // If the dependency is outside the repository, we exclude it (see Parser) so we won't ever find a NodeContext.
+                // The choices at this point are to either to return and not add cached outputs (this project is not cacheable),
+                // or to just ignore the project and risk an under-build. We're choosing to accept the risk since we've already
+                // accepted it for input files outside the repo during fingerprinting. 
+                if (!dependencyNode.ProjectInstance.FullPath.IsUnderDirectory(_repoRoot))
+                {
+                    continue;
+                }
+
                 return;
             }