[NFC] Refactor Reference Dependency Emission

Invert the responsibility of the entrypoint so that FrontendTool is directing the actual serialization work. The entrypoint now solely exists to construct a dependency graph.

While I'm here, prepare the way for serializing dependency graphs for modules by optimistically modeling a ModuleOrSourceFile input.

Author: CodaFi

include/swift/AST/FineGrainedDependencies.h

@@ -59,11 +59,14 @@ namespace swift {
 class DependencyTracker;
 class DiagnosticEngine;
 class FrontendOptions;
+class ModuleDecl;
 class SourceFile;
 
 /// Use a new namespace to help keep the experimental code from clashing.
 namespace fine_grained_dependencies {
 
+class SourceFileDepGraph;
+
 using StringVec = std::vector<std::string>;
 
 template <typename Element> using ConstPtrVec = std::vector<const Element *>;
@@ -343,11 +346,11 @@ class BiIndexedTwoStageMap {
 // MARK: Start of fine-grained-dependency-specific code
 //==============================================================================
 
-/// The entry point into this system from the frontend:
-/// Write out the .swiftdeps file for a frontend compilation of a primary file.
-bool emitReferenceDependencies(DiagnosticEngine &diags, SourceFile *SF,
-                               const DependencyTracker &depTracker,
-                               StringRef outputPath, bool alsoEmitDotFile);
+bool withReferenceDependencies(
+    llvm::PointerUnion<ModuleDecl *, SourceFile *> MSF,
+    const DependencyTracker &depTracker, StringRef outputPath,
+    bool alsoEmitDotFile, llvm::function_ref<bool(SourceFileDepGraph &&)>);
+
 //==============================================================================
 // MARK: Enums
 //==============================================================================

lib/AST/FrontendSourceFileDepGraphFactory.cpp

@@ -236,30 +236,20 @@ std::string DependencyKey::computeNameForProvidedEntity<
 // MARK: Entry point into frontend graph construction
 //==============================================================================
 
-bool fine_grained_dependencies::emitReferenceDependencies(
-    DiagnosticEngine &diags, SourceFile *const SF,
-    const DependencyTracker &depTracker,
-    StringRef outputPath,
-    const bool alsoEmitDotFile) {
-
-  // Before writing to the dependencies file path, preserve any previous file
-  // that may have been there. No error handling -- this is just a nicety, it
-  // doesn't matter if it fails.
-  llvm::sys::fs::rename(outputPath, outputPath + "~");
-
-  SourceFileDepGraph g = FrontendSourceFileDepGraphFactory(
-                             SF, outputPath, depTracker, alsoEmitDotFile)
-                              .construct();
-
-  bool hadError = writeFineGrainedDependencyGraphToPath(diags, outputPath, g);
-
-  // If path is stdout, cannot read it back, so check for "-"
-  assert(outputPath == "-" || g.verifyReadsWhatIsWritten(outputPath));
-
-  if (alsoEmitDotFile)
-    g.emitDotFile(outputPath, diags);
-
-  return hadError;
+bool fine_grained_dependencies::withReferenceDependencies(
+    llvm::PointerUnion<ModuleDecl *, SourceFile *> MSF,
+    const DependencyTracker &depTracker, StringRef outputPath,
+    bool alsoEmitDotFile,
+    llvm::function_ref<bool(SourceFileDepGraph &&)> cont) {
+  if (MSF.dyn_cast<ModuleDecl *>()) {
+    llvm_unreachable("Cannot construct dependency graph for modules!");
+  } else {
+    auto *SF = MSF.get<SourceFile *>();
+    SourceFileDepGraph g = FrontendSourceFileDepGraphFactory(
+                               SF, outputPath, depTracker, alsoEmitDotFile)
+                               .construct();
+    return cont(std::move(g));
+  }
 }
 
 //==============================================================================

lib/FrontendTool/FrontendTool.cpp

@@ -30,6 +30,7 @@
 #include "swift/AST/DiagnosticsSema.h"
 #include "swift/AST/FileSystem.h"
 #include "swift/AST/FineGrainedDependencies.h"
+#include "swift/AST/FineGrainedDependencyFormat.h"
 #include "swift/AST/GenericSignatureBuilder.h"
 #include "swift/AST/IRGenOptions.h"
 #include "swift/AST/IRGenRequests.h"
@@ -1370,6 +1371,35 @@ static bool dumpAST(CompilerInstance &Instance) {
   return Instance.getASTContext().hadError();
 }
 
+static bool emitReferenceDependencies(CompilerInstance &Instance,
+                                      SourceFile *const SF,
+                                      StringRef outputPath) {
+  const auto alsoEmitDotFile = Instance.getInvocation()
+                                   .getLangOptions()
+                                   .EmitFineGrainedDependencySourcefileDotFiles;
+
+  // Before writing to the dependencies file path, preserve any previous file
+  // that may have been there. No error handling -- this is just a nicety, it
+  // doesn't matter if it fails.
+  llvm::sys::fs::rename(outputPath, outputPath + "~");
+
+  using SourceFileDepGraph = fine_grained_dependencies::SourceFileDepGraph;
+  return fine_grained_dependencies::withReferenceDependencies(
+      SF, *Instance.getDependencyTracker(), outputPath, alsoEmitDotFile,
+      [&](SourceFileDepGraph &&g) -> bool {
+        const bool hadError =
+            fine_grained_dependencies::writeFineGrainedDependencyGraphToPath(
+                Instance.getDiags(), outputPath, g);
+
+        // If path is stdout, cannot read it back, so check for "-"
+        assert(outputPath == "-" || g.verifyReadsWhatIsWritten(outputPath));
+
+        if (alsoEmitDotFile)
+          g.emitDotFile(outputPath, Instance.getDiags());
+        return hadError;
+      });
+}
+
 static void emitReferenceDependenciesForAllPrimaryInputsIfNeeded(
     CompilerInstance &Instance) {
   const auto &Invocation = Instance.getInvocation();
@@ -1384,13 +1414,11 @@ static void emitReferenceDependenciesForAllPrimaryInputsIfNeeded(
     const std::string &referenceDependenciesFilePath =
         Invocation.getReferenceDependenciesFilePathForPrimary(
             SF->getFilename());
-    if (!referenceDependenciesFilePath.empty()) {
-      const auto LangOpts = Invocation.getLangOptions();
-      (void)fine_grained_dependencies::emitReferenceDependencies(
-          Instance.getDiags(), SF, *Instance.getDependencyTracker(),
-          referenceDependenciesFilePath,
-          LangOpts.EmitFineGrainedDependencySourcefileDotFiles);
+    if (referenceDependenciesFilePath.empty()) {
+      continue;
     }
+
+    emitReferenceDependencies(Instance, SF, referenceDependenciesFilePath);
   }
 }
 static void