Plumb Module Fingerprints Into ModuleDepGraphFactory

Author: CodaFi

include/swift/AST/AbstractSourceFileDepGraphFactory.h

@@ -87,6 +87,12 @@ class AbstractSourceFileDepGraphFactory {
 
   void addAUsedDecl(const DependencyKey &def, const DependencyKey &use);
 
+  /// Add an external dependency node to the graph. If the provided fingerprint
+  /// is not \c None, it is added to the def key.
+  void addAnExternalDependency(const DependencyKey &def,
+                               const DependencyKey &use,
+                               Optional<Fingerprint> dependencyFingerprint);
+
   static Optional<Fingerprint>
   getFingerprintIfAny(std::pair<const NominalTypeDecl *, const ValueDecl *>) {
     return None;

lib/AST/AbstractSourceFileDepGraphFactory.cpp

@@ -108,3 +108,16 @@ void AbstractSourceFileDepGraphFactory::addAUsedDecl(
   assert(useNode->getIsProvides() && "Use (using node) must be a provides");
   g.addArc(defNode, useNode);
 }
+
+void AbstractSourceFileDepGraphFactory::addAnExternalDependency(
+    const DependencyKey &defKey, const DependencyKey &useKey,
+    Optional<Fingerprint> maybeFP) {
+  auto *defNode = g.findExistingNodeOrCreateIfNew(defKey, maybeFP,
+                                                  false /* = !isProvides */);
+
+  auto nullableUse = g.findExistingNode(useKey);
+  assert(nullableUse.isNonNull() && "Use must be an already-added provides");
+  auto *useNode = nullableUse.get();
+  assert(useNode->getIsProvides() && "Use (using node) must be a provides");
+  g.addArc(defNode, useNode);
+}

lib/AST/FrontendSourceFileDepGraphFactory.cpp

@@ -499,19 +499,10 @@ void FrontendSourceFileDepGraphFactory::addAllUsedDecls() {
 
 ModuleDepGraphFactory::ModuleDepGraphFactory(const ModuleDecl *Mod,
                                              bool emitDot)
-    : AbstractSourceFileDepGraphFactory(Mod->getASTContext().hadError(),
-                                        Mod->getNameStr(), Fingerprint::ZERO(),
-                                        emitDot, Mod->getASTContext().Diags),
-
-      Mod(Mod) {
-  // Since a fingerprint only summarizes the state of the module but not
-  // the state of its fingerprinted sub-declarations, and since a module
-  // contains no state other than sub-declarations, its fingerprint does not
-  // matter and can just be some arbitrary value. Should it be the case that a
-  // change in a declaration that does not have a fingerprint must cause
-  // a rebuild of a file outside of the module, this assumption will need
-  // to be revisited.
-}
+    : AbstractSourceFileDepGraphFactory(
+          Mod->getASTContext().hadError(), Mod->getNameStr(),
+          Mod->getFingerprint(), emitDot, Mod->getASTContext().Diags),
+      Mod(Mod) {}
 
 void ModuleDepGraphFactory::addAllDefinedDecls() {
   // TODO: express the multiple provides and depends streams with variadic