[CAS] Allow SwiftDependencyScanningService be shared

When the CASOptions are the same, SwiftDependencyScanningService can be
shared with multiple swift driver invocation for scanning.

Author: cachemeifyoucan

include/swift/AST/ModuleDependencies.h

@@ -20,6 +20,7 @@
 
 #include "swift/Basic/LLVM.h"
 #include "swift/AST/Import.h"
+#include "clang/CAS/CASOptions.h"
 #include "clang/Tooling/DependencyScanning/DependencyScanningService.h"
 #include "clang/Tooling/DependencyScanning/DependencyScanningTool.h"
 #include "llvm/ADT/ArrayRef.h"
@@ -767,6 +768,9 @@ class SwiftDependencyScanningService {
     ModuleDependenciesKindMap ModuleDependenciesMap;
   };
 
+  /// The CASOption created the Scanning Service if used.
+  llvm::Optional<clang::CASOptions> CASOpts;
+
   /// The persistent Clang dependency scanner service
   Optional<clang::tooling::dependencies::DependencyScanningService>
       ClangScanningService;
@@ -863,7 +867,7 @@ class SwiftDependencyScanningService {
   void overlaySharedFilesystemCacheForCompilation(CompilerInstance &Instance);
 
   /// Setup caching service.
-  void setupCachingDependencyScanningService(CompilerInstance &Instance);
+  bool setupCachingDependencyScanningService(CompilerInstance &Instance);
 private:
   /// Enforce clients not being allowed to query this cache directly, it must be
   /// wrapped in an instance of `ModuleDependenciesCache`.

lib/AST/ModuleDependencies.cpp

@@ -417,12 +417,25 @@ void SwiftDependencyScanningService::overlaySharedFilesystemCacheForCompilation(
   Instance.getSourceMgr().setFileSystem(depFS);
 }
 
-void SwiftDependencyScanningService::setupCachingDependencyScanningService(
+bool SwiftDependencyScanningService::setupCachingDependencyScanningService(
     CompilerInstance &Instance) {
   if (!Instance.getInvocation().getFrontendOptions().EnableCAS)
-    return;
+    return false;
+
+  if (CASOpts) {
+    // If CASOption matches, the service is initialized already.
+    if (*CASOpts == Instance.getInvocation().getFrontendOptions().CASOpts)
+      return false;
+
+    // CASOption mismatch, return error.
+    Instance.getDiags().diagnose(
+        SourceLoc(), diag::error_cas,
+        "conflicting CAS options used in scanning service");
+    return true;
+  }
 
   // Setup CAS.
+  CASOpts = Instance.getInvocation().getFrontendOptions().CASOpts;
   CAS = Instance.getSharedCASInstance();
 
   // Add SDKSetting file.
@@ -456,7 +469,7 @@ void SwiftDependencyScanningService::setupCachingDependencyScanningService(
   if (!CachingFS) {
     Instance.getDiags().diagnose(SourceLoc(), diag::error_cas,
                                  toString(CachingFS.takeError()));
-    return;
+    return true;
   }
   CacheFS = std::move(*CachingFS);
 
@@ -474,6 +487,8 @@ void SwiftDependencyScanningService::setupCachingDependencyScanningService(
       Instance.getSharedCASInstance(), Instance.getSharedCacheInstance(),
       UseClangIncludeTree ? nullptr : CacheFS,
       /* ReuseFileManager */ false, /* OptimizeArgs */ false);
+
+  return false;
 }
 
 SwiftDependencyScanningService::ContextSpecificGlobalCacheState *

lib/DependencyScan/DependencyScanningTool.cpp

@@ -279,7 +279,8 @@ DependencyScanningTool::initCompilerInstanceForScan(
   }
 
   // Setup the caching service after the instance finishes setup.
-  ScanningService->setupCachingDependencyScanningService(*Instance);
+  if (ScanningService->setupCachingDependencyScanningService(*Instance))
+    return std::make_error_code(std::errc::invalid_argument);
 
   (void)Instance->getMainModule();
 

lib/DependencyScan/ScanDependencies.cpp

@@ -1764,7 +1764,9 @@ bool swift::dependencies::scanDependencies(CompilerInstance &instance) {
     deserializeDependencyCache(instance, service);
   // Wrap the filesystem with a caching `DependencyScanningWorkerFilesystem`
   service.overlaySharedFilesystemCacheForCompilation(instance);
-  service.setupCachingDependencyScanningService(instance);
+  if (service.setupCachingDependencyScanningService(instance))
+    return true;
+
   ModuleDependenciesCache cache(service,
                                 instance.getMainModule()->getNameStr().str(),
                                 instance.getInvocation().getModuleScanningHash());
@@ -1832,7 +1834,9 @@ bool swift::dependencies::batchScanDependencies(
 
   SwiftDependencyScanningService singleUseService;
   singleUseService.overlaySharedFilesystemCacheForCompilation(instance);
-  singleUseService.setupCachingDependencyScanningService(instance);
+  if (singleUseService.setupCachingDependencyScanningService(instance))
+    return true;
+
   ModuleDependenciesCache cache(singleUseService,
                                 instance.getMainModule()->getNameStr().str(),
                                 instance.getInvocation().getModuleScanningHash());