[Dependency Scanning] Always use a locking diagnostic consumer

Since we enabled parallel dependency scanning by-default, each individual scan needs a diagnostic consumer that is safe to use across many threads. Deprecate the 'Locking' sub-class, making its behavior the default in the base class.

Author: artemcm

include/swift/DependencyScan/DependencyScanningTool.h

@@ -40,6 +40,7 @@ class DependencyScanDiagnosticCollector : public DiagnosticConsumer {
     std::optional<ScannerImportStatementInfo::ImportDiagnosticLocationInfo> ImportLocation;
   };
   std::vector<ScannerDiagnosticInfo> Diagnostics;
+  llvm::sys::SmartMutex<true> ScanningDiagnosticConsumerStateLock;
 
   void handleDiagnostic(SourceManager &SM, const DiagnosticInfo &Info) override;
 
@@ -55,19 +56,6 @@ class DependencyScanDiagnosticCollector : public DiagnosticConsumer {
   }
 };
 
-/// Locking variant of the above diagnostic collector that guards accesses to
-/// its state with a lock.
-class LockingDependencyScanDiagnosticCollector
-    : public DependencyScanDiagnosticCollector {
-private:
-  void addDiagnostic(SourceManager &SM, const DiagnosticInfo &Info) override;
-  llvm::sys::SmartMutex<true> ScanningDiagnosticConsumerStateLock;
-
-public:
-  friend DependencyScanningTool;
-  LockingDependencyScanDiagnosticCollector() {}
-};
-
 /// Given a set of arguments to a print-target-info frontend tool query, produce the
 /// JSON target info.
 llvm::ErrorOr<swiftscan_string_ref_t> getTargetInfo(ArrayRef<const char *> Command,
@@ -118,7 +106,7 @@ class DependencyScanningTool {
   llvm::sys::SmartMutex<true> DependencyScanningToolStateLock;
 
   /// A shared consumer that accumulates encountered diagnostics.
-  LockingDependencyScanDiagnosticCollector CDC;
+  DependencyScanDiagnosticCollector CDC;
   llvm::BumpPtrAllocator Alloc;
   llvm::StringSaver Saver;
 };

lib/DependencyScan/DependencyScanningTool.cpp

@@ -74,6 +74,8 @@ void DependencyScanDiagnosticCollector::handleDiagnostic(SourceManager &SM,
 
 void DependencyScanDiagnosticCollector::addDiagnostic(
     SourceManager &SM, const DiagnosticInfo &Info) {
+  llvm::sys::SmartScopedLock<true> Lock(ScanningDiagnosticConsumerStateLock);
+
   // Determine what kind of diagnostic we're emitting.
   llvm::SourceMgr::DiagKind SMKind;
   switch (Info.Kind) {
@@ -129,12 +131,6 @@ void DependencyScanDiagnosticCollector::addDiagnostic(
   }
 }
 
-void LockingDependencyScanDiagnosticCollector::addDiagnostic(
-    SourceManager &SM, const DiagnosticInfo &Info) {
-  llvm::sys::SmartScopedLock<true> Lock(ScanningDiagnosticConsumerStateLock);
-  DependencyScanDiagnosticCollector::addDiagnostic(SM, Info);
-}
-
 swiftscan_diagnostic_set_t *mapCollectedDiagnosticsForOutput(
     const DependencyScanDiagnosticCollector *diagnosticCollector) {
   auto collectedDiagnostics = diagnosticCollector->getDiagnostics();
@@ -272,7 +268,8 @@ DependencyScanningTool::getDependencies(
     StringRef WorkingDirectory) {
   // There may be errors as early as in instance initialization, so we must ensure
   // we can catch those.
-  auto ScanDiagnosticConsumer = std::make_shared<DependencyScanDiagnosticCollector>();
+  auto ScanDiagnosticConsumer =
+    std::make_shared<DependencyScanDiagnosticCollector>();
 
   // The primary instance used to scan the query Swift source-code
   auto QueryContextOrErr = initCompilerInstanceForScan(Command,