[Sema|Index] Ignore the cache when loading a system module for indexing

Author: xymus

include/swift/AST/ASTContext.h

@@ -1140,9 +1140,12 @@ class ASTContext final {
   ///
   /// \param ModulePath The module's \c ImportPath which describes
   /// the name of the module being loaded, possibly including submodules.
-
+  /// \param AllowMemoryCached Should we allow reuse of an already loaded
+  /// module or force reloading from disk, defaults to true.
+  ///
   /// \returns The requested module, or NULL if the module cannot be found.
-  ModuleDecl *getModule(ImportPath::Module ModulePath);
+  ModuleDecl *
+  getModule(ImportPath::Module ModulePath, bool AllowMemoryCached = true);
 
   /// Attempts to load the matching overlay module for the given clang
   /// module into this ASTContext.

lib/AST/ASTContext.cpp

@@ -2192,10 +2192,6 @@ void ASTContext::addLoadedModule(ModuleDecl *M) {
 }
 
 void ASTContext::setIgnoreAdjacentModules(bool value) {
-  // Clear the cache if we expect a different view on the same modules.
-  if (IgnoreAdjacentModules != value)
-    getImpl().LoadedModules.clear();
-
   IgnoreAdjacentModules = value;
 }
 
@@ -2449,11 +2445,12 @@ bool ASTContext::canImportModule(ImportPath::Module ModuleName,
 }
 
 ModuleDecl *
-ASTContext::getModule(ImportPath::Module ModulePath) {
+ASTContext::getModule(ImportPath::Module ModulePath, bool AllowMemoryCached) {
   assert(!ModulePath.empty());
 
-  if (auto *M = getLoadedModule(ModulePath))
-    return M;
+  if (AllowMemoryCached)
+    if (auto *M = getLoadedModule(ModulePath))
+      return M;
 
   auto moduleID = ModulePath[0];
   if (PreModuleImportCallback)

lib/Index/IndexRecord.cpp

@@ -520,7 +520,9 @@ emitDataForSwiftSerializedModule(ModuleDecl *module,
     module->getASTContext().setIgnoreAdjacentModules(true);
 
     ImportPath::Module::Builder builder(module->getName());
-    auto reloadedModule = module->getASTContext().getModule(builder.get());
+    ASTContext &ctx = module->getASTContext();
+    auto reloadedModule = ctx.getModule(builder.get(),
+                                        /*AllowMemoryCached=*/false);
 
     if (reloadedModule) {
       module = reloadedModule;