[NFC] Differential Incremental External Dependencies in DependencyTracker

Also perform the plumbing necessary to convince the rest of the compiler that they're just ordinary external dependencies. In particular, we will still emit these depenencies into .d files, and code completion will still index them.

Author: CodaFi

include/swift/AST/ModuleLoader.h

@@ -75,6 +75,9 @@ enum class IntermoduleDepTrackingMode {
 /// implemented in terms of a wrapped clang::DependencyCollector.
 class DependencyTracker {
   std::shared_ptr<clang::DependencyCollector> clangCollector;
+  SmallVector<std::string, 8> incrementalDeps;
+  llvm::StringSet<> incrementalDepsUniquer;
+
 public:
   explicit DependencyTracker(
       IntermoduleDepTrackingMode Mode,
@@ -87,9 +90,19 @@ class DependencyTracker {
   /// No path canonicalization is done.
   void addDependency(StringRef File, bool IsSystem);
 
+  /// Adds a file as an incremental dependency.
+  ///
+  /// No additional canonicalization or adulteration of the file path in
+  /// \p File is performed.
+  void addIncrementalDependency(StringRef File);
+
   /// Fetches the list of dependencies.
   ArrayRef<std::string> getDependencies() const;
 
+  /// Fetches the list of dependencies that are known to have incremental swift
+  /// dependency information embedded inside of them.
+  ArrayRef<std::string> getIncrementalDependencies() const;
+
   /// Return the underlying clang::DependencyCollector that this
   /// class wraps.
   std::shared_ptr<clang::DependencyCollector> getClangCollector();

include/swift/Basic/Statistics.def

@@ -114,6 +114,7 @@ FRONTEND_STATISTIC(AST, NumASTBytesAllocated)
 /// Number of file-level dependencies of this frontend job, as tracked in the
 /// AST context's dependency collector.
 FRONTEND_STATISTIC(AST, NumDependencies)
+FRONTEND_STATISTIC(AST, NumIncrementalDependencies)
 
 /// Number of top-level, dynamic, and member names referenced in this frontend
 /// job's source file, as tracked by the AST context's referenced-name tracker.

lib/AST/ModuleLoader.cpp

@@ -50,11 +50,22 @@ DependencyTracker::addDependency(StringRef File, bool IsSystem) {
                                      /*IsMissing=*/false);
 }
 
+void DependencyTracker::addIncrementalDependency(StringRef File) {
+  if (incrementalDepsUniquer.insert(File).second) {
+    incrementalDeps.emplace_back(File.str());
+  }
+}
+
 ArrayRef<std::string>
 DependencyTracker::getDependencies() const {
   return clangCollector->getDependencies();
 }
 
+ArrayRef<std::string>
+DependencyTracker::getIncrementalDependencies() const {
+  return incrementalDeps;
+}
+
 std::shared_ptr<clang::DependencyCollector>
 DependencyTracker::getClangCollector() {
   return clangCollector;

lib/FrontendTool/FrontendTool.cpp

@@ -209,6 +209,12 @@ static bool emitMakeDependenciesIfNeeded(DiagnosticEngine &diags,
     dependencyString.push_back(' ');
     dependencyString.append(frontend::utils::escapeForMake(path, buffer).str());
   }
+  auto incrementalDependencyPaths =
+      reversePathSortedFilenames(depTracker->getIncrementalDependencies());
+  for (auto const &path : incrementalDependencyPaths) {
+    dependencyString.push_back(' ');
+    dependencyString.append(frontend::utils::escapeForMake(path, buffer).str());
+  }
 
   // FIXME: Xcode can't currently handle multiple targets in a single
   // dependency line.
@@ -1176,6 +1182,7 @@ static void countASTStats(UnifiedStatsReporter &Stats,
 
   if (auto *D = Instance.getDependencyTracker()) {
     C.NumDependencies = D->getDependencies().size();
+    C.NumIncrementalDependencies = D->getIncrementalDependencies().size();
   }
 
   for (auto SF : Instance.getPrimarySourceFiles()) {

lib/IDE/CompletionInstance.cpp

@@ -198,6 +198,10 @@ forEachDependencyUntilTrue(CompilerInstance &CI, unsigned excludeBufferID,
     if (callback(dep))
       return true;
   }
+  for (auto &dep : CI.getDependencyTracker()->getIncrementalDependencies()) {
+    if (callback(dep))
+      return true;
+  }
 
   return false;
 }