[DNM, Incremental] Fix problem of priors injecting nodes for removed inputs into the graph.

Sources/SwiftDriver/IncrementalCompilation/ModuleDependencyGraph.swift

@@ -149,6 +149,15 @@ extension ModuleDependencyGraph {
       invalidatedNodes.formUnion(self.integrateExternal(.known(fed)))
     }
   }
+
+  /// If the priors were read from an invocation containing a subsuequently removed input,
+  /// the nodes defining decls from that input must be culled.
+  fileprivate func isForRemovedInput(_ node: Node) -> Bool {
+    guard let dependencySource = node.dependencySource else {
+      return false
+    }
+    return inputDependencySourceMap.inputIfKnown(for: dependencySource) == nil
+  }
 }
 
 // MARK: - Scheduling the first wave
@@ -528,7 +537,9 @@ extension ModuleDependencyGraph {
       private var identifiers: [String] = [""]
       private var currentDefKey: DependencyKey? = nil
       private var nodeUses: [(DependencyKey, Int)] = []
-      public private(set) var allNodes: [Node] = []
+      /// Use nodes in def-use links are seliarized by index, so keep an array of all nodes read.
+      /// But, don't keep nodes that are for reomved inputs.
+      public private(set) var potentiallyUsedNodes: [Node?] = []
 
       init?(_ info: IncrementalCompilationState.IncrementalDependencyAndInputSetup) {
         self.fileSystem = info.fileSystem
@@ -541,8 +552,11 @@ extension ModuleDependencyGraph {
 
       func finalizeGraph() -> ModuleDependencyGraph {
         for (dependencyKey, useID) in self.nodeUses {
+          guard let use = self.potentiallyUsedNodes[useID] else {
+            continue
+          }
           let isNewUse = self.graph.nodeFinder
-            .record(def: dependencyKey, use: self.allNodes[useID])
+            .record(def: dependencyKey, use: use)
           assert(isNewUse, "Duplicate use def-use arc in graph?")
         }
         return self.graph
@@ -561,7 +575,12 @@ extension ModuleDependencyGraph {
       mutating func didExitBlock() throws {}
 
       private mutating func finalize(node newNode: Node) {
-        self.allNodes.append(newNode)
+        if graph.isForRemovedInput(newNode) {
+          // Preserve the mapping of Int to Node for reconstructing def-use links.
+          self.potentiallyUsedNodes.append(nil)
+          return
+        }
+        self.potentiallyUsedNodes.append(newNode)
         let oldNode = self.graph.nodeFinder.insert(newNode)
         assert(oldNode == nil,
                "Integrated the same node twice: \(oldNode!), \(newNode)")

Tests/SwiftDriverTests/IncrementalCompilationTests.swift

@@ -796,22 +796,6 @@ extension IncrementalCompilationTests {
 
     graph.verifyGraph()
     if removeInputFromInvocation {
-      if afterRestoringBadPriors {
-        // FIXME: Fix the driver
-        // If you incrementally compile with a.swift and b.swift,
-        // at the end, the driver saves a serialized `ModuleDependencyGraph`
-        // contains nodes for declarations defined in both files.
-        // If you then later remove b.swift and recompile, the driver will
-        // see that a file was removed (via comparisons with the saved `BuildRecord`
-        // and will delete the saved priors. However, if for some reason the
-        // saved priors are not deleted, the driver will read saved priors
-        // containing entries for the deleted file. This test simulates that
-        // condition by restoring the deleted priors. The driver ought to be fixed
-        // to cull any entries for removed files from the deserialized priors.
-        print("*** WARNING: skipping checks, driver fails to cleaned out the graph ***",
-              to: &stderrStream); stderrStream.flush()
-        return graph
-      }
       graph.ensureOmits(sourceBasenameWithoutExt: removedInput)
       graph.ensureOmits(name: topLevelName)
     }