[Dependency Scanning] Factor out import prescan into separate utility

Author: artemcm

include/swift/DependencyScan/ScanDependencies.h

@@ -28,41 +28,46 @@ class ModuleDependenciesCache;
 namespace dependencies {
 
 struct BatchScanInput {
-  StringRef moduleName;
-  StringRef arguments;
-  StringRef outputPath;
+  llvm::StringRef moduleName;
+  llvm::StringRef arguments;
+  llvm::StringRef outputPath;
   bool isSwift;
 };
 
+// MARK: swift-frontend -scan-dependencies entry points
 /// Scans the dependencies of the main module of \c instance and writes out
 /// the resulting JSON according to the instance's output parameters.
 /// This method is used for swift-frontend invocations in dependency scanning mode
 /// (-scan-dependencies), where the module dependency cache is not shared.
-bool scanAndOutputDependencies(CompilerInstance &instance);
-
-/// Scans the dependencies of the main module of \c instance.
-bool scanDependencies(CompilerInstance &instance,
-                      ModuleDependenciesCache &cache,
-                      llvm::raw_ostream &out);
+bool scanDependencies(CompilerInstance &instance);
 
 /// Batch scan the dependencies for modules specified in \c batchInputFile.
 bool batchScanDependencies(CompilerInstance &instance,
-                                 llvm::StringRef batchInputFile);
+                           llvm::StringRef batchInputFile);
+
+/// Identify all imports in the translation unit's module.
+bool prescanMainModuleDependencies(CompilerInstance &instance);
 
 
+// MARK: dependency scanning execution
+/// Scans the dependencies of the main module of \c instance.
+bool performModuleScan(CompilerInstance &instance,
+                       ModuleDependenciesCache &cache,
+                       llvm::raw_ostream &out);
+
 /// Batch scan the dependencies for modules specified in \c batchInputFile.
-bool executeBatchModuleScan(CompilerInstance &instance,
+bool performBatchModuleScan(CompilerInstance &instance,
                             ModuleDependenciesCache &cache,
                             llvm::StringSaver &saver,
                             const std::vector<BatchScanInput> &BatchInput);
 
 /// Scan for dependencies of a module with a specified name, producing the resulting output
 /// at the specified output path.
-bool executeSingleModuleScan(CompilerInstance &instance,
-                             ModuleDependenciesCache &cache,
-                             StringRef moduleName,
-                             bool isClang,
-                             StringRef outputPath);
+bool scanBatchModuleEntry(CompilerInstance &instance,
+                          ModuleDependenciesCache &cache,
+                          llvm::StringRef moduleName,
+                          bool isClang,
+                          llvm::StringRef outputPath);
 
 } // end namespace dependencies
 } // end namespace swift

lib/DependencyScan/DependencyScanningTool.cpp

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "swift/DependencyScan/DependencyScanningTool.h"
+#include "swift/DependencyScan/ModuleInfo.h"
 #include "swift/AST/DiagnosticEngine.h"
 #include "swift/AST/DiagnosticsFrontend.h"
 #include "swift/Basic/LLVMInitialize.h"
@@ -38,7 +39,7 @@ llvm::ErrorOr<std::string> DependencyScanningTool::getDependencies(
 
   std::string JSONOutput;
   llvm::raw_string_ostream OSS(JSONOutput);
-  scanDependencies(*Instance.get(), *SharedCache, OSS);
+  performModuleScan(*Instance.get(), *SharedCache, OSS);
   OSS.flush();
 
   // TODO: swiftch to an in-memory representation
@@ -55,7 +56,7 @@ std::error_code DependencyScanningTool::getDependencies(
     return EC;
   auto Instance = std::move(*InstanceOrErr);
 
-  executeBatchModuleScan(*Instance.get(), *SharedCache, Saver, BatchInput);
+  performBatchModuleScan(*Instance.get(), *SharedCache, Saver, BatchInput);
   return std::error_code();
 }