[ScanDependency] Respect working directory set inside invocation

Teach scanner to respect the working directory set in the invocation
through scanner C API.

Also add test infrastructure to testing scanner from C API. Break up
DependencyScan lib into two so the swift-scan-test and remain small
without understanding swift AST.

rdar://127626011

Author: cachemeifyoucan

include/swift/DependencyScan/DependencyScanJSON.h

@@ -0,0 +1,30 @@
+//===-------------- DependencyScanImpl.h - Swift Compiler -----------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// Implementation details of the dependency scanning C API
+//
+//===----------------------------------------------------------------------===//
+#ifndef SWIFT_DEPENDENCY_SCAN_JSON_H
+#define SWIFT_DEPENDENCY_SCAN_JSON_H
+
+#include "swift-c/DependencyScan/DependencyScan.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace swift::dependencies {
+
+void writePrescanJSON(llvm::raw_ostream &out,
+                      swiftscan_import_set_t importSet);
+void writeJSON(llvm::raw_ostream &out,
+               swiftscan_dependency_graph_t fullDependencies);
+} // namespace swift::dependencies
+
+#endif // SWIFT_DEPENDENCY_SCAN_JSON_H

include/swift/DependencyScan/DependencyScanningTool.h

@@ -87,14 +87,15 @@ class DependencyScanningTool {
   /// occurred, \c swiftscan_dependency_result_t otherwise.
   llvm::ErrorOr<swiftscan_dependency_graph_t>
   getDependencies(ArrayRef<const char *> Command,
-                  const llvm::StringSet<> &PlaceholderModules);
+                  const llvm::StringSet<> &PlaceholderModules,
+                  StringRef WorkingDirectory);
 
   /// Collect the set of imports for the input module
   ///
   /// \returns a \c StringError with the diagnostic output if errors
   /// occurred, \c swiftscan_prescan_result_t otherwise.
   llvm::ErrorOr<swiftscan_import_set_t>
-  getImports(ArrayRef<const char *> Command);
+  getImports(ArrayRef<const char *> Command, StringRef WorkingDirectory);
 
   /// Collect the full module dependency graph for the input collection of
   /// module names (batch inputs) and output them to the
@@ -104,7 +105,8 @@ class DependencyScanningTool {
   std::vector<llvm::ErrorOr<swiftscan_dependency_graph_t>>
   getDependencies(ArrayRef<const char *> Command,
                   const std::vector<BatchScanInput> &BatchInput,
-                  const llvm::StringSet<> &PlaceholderModules);
+                  const llvm::StringSet<> &PlaceholderModules,
+                  StringRef WorkingDirectory);
 
   /// Writes the current `SharedCache` instance to a specified FileSystem path.
   void serializeCache(llvm::StringRef path);
@@ -121,13 +123,15 @@ class DependencyScanningTool {
   /// Using the specified invocation command, instantiate a CompilerInstance
   /// that will be used for this scan.
   llvm::ErrorOr<ScanQueryInstance>
-  initCompilerInstanceForScan(ArrayRef<const char *> Command);
+  initCompilerInstanceForScan(ArrayRef<const char *> Command,
+                              StringRef WorkingDirectory);
 
 private:
   /// Using the specified invocation command, initialize the scanner instance
   /// for this scan. Returns the `CompilerInstance` that will be used.
   llvm::ErrorOr<ScanQueryInstance>
-  initScannerForAction(ArrayRef<const char *> Command);
+  initScannerForAction(ArrayRef<const char *> Command,
+                       StringRef WorkingDirectory);
 
   /// Shared cache of module dependencies, re-used by individual full-scan queries
   /// during the lifetime of this Tool.

lib/DependencyScan/CMakeLists.txt

@@ -1,16 +1,20 @@
-
+add_swift_host_library(swiftDependencyScanImpl STATIC
+  DependencyScanJSON.cpp
+  StringUtils.cpp)
 
 add_swift_host_library(swiftDependencyScan STATIC
   DependencyScanningTool.cpp
   ModuleDependencyCacheSerialization.cpp
-  ModuleDependencyScanner.cpp  
-  ScanDependencies.cpp
-  StringUtils.cpp)
+  ModuleDependencyScanner.cpp
+  ScanDependencies.cpp)
 
 target_link_libraries(swiftDependencyScan INTERFACE
   clangBasic)
 
 target_link_libraries(swiftDependencyScan PRIVATE
-    swiftClangImporter
-    swiftAST
-    swiftSerialization)
+  swiftClangImporter
+  swiftAST
+  swiftSerialization)
+
+target_link_libraries(swiftDependencyScan PUBLIC
+  swiftDependencyScanImpl)