Delay loading lambdas

Author: dmpolukhin

clang/include/clang/Serialization/ASTReader.h

@@ -1188,6 +1188,11 @@ class ASTReader
   /// once recursing loading has been completed.
   llvm::SmallVector<NamedDecl *, 16> PendingOdrMergeChecks;
 
+  /// Lambdas that need to be loaded right after the function they belong to.
+  /// It is required to have the right canonical declaration for lambda class
+  /// from the same module as the function.
+  SmallVector<GlobalDeclID, 4> PendingLambdas;
+
   using DataPointers =
       std::pair<CXXRecordDecl *, struct CXXRecordDecl::DefinitionData *>;
   using ObjCInterfaceDataPointers =

clang/lib/Serialization/ASTReader.cpp

@@ -9782,7 +9782,8 @@ void ASTReader::finishPendingActions() {
       !PendingDeducedVarTypes.empty() || !PendingIncompleteDeclChains.empty() ||
       !PendingDeclChains.empty() || !PendingMacroIDs.empty() ||
       !PendingDeclContextInfos.empty() || !PendingUpdateRecords.empty() ||
-      !PendingObjCExtensionIvarRedeclarations.empty()) {
+      !PendingObjCExtensionIvarRedeclarations.empty() ||
+      !PendingLambdas.empty()) {
     // If any identifiers with corresponding top-level declarations have
     // been loaded, load those declarations now.
     using TopLevelDeclsMap =
@@ -9927,6 +9928,11 @@ void ASTReader::finishPendingActions() {
       }
       PendingObjCExtensionIvarRedeclarations.pop_back();
     }
+
+    // Load any pendiong lambdas.
+    for (auto ID : PendingLambdas)
+      GetDecl(ID);
+    PendingLambdas.clear();
   }
 
   // At this point, all update records for loaded decls are in place, so any

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -1156,11 +1156,12 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
     Params.push_back(readDeclAs<ParmVarDecl>());
   FD->setParams(Reader.getContext(), Params);
 
-  // For the first decl read all lambdas inside, otherwise skip them.
+  // For the first decl add all lambdas inside for loading them later,
+  // otherwise skip them.
   unsigned NumLambdas = Record.readInt();
   if (FD->isFirstDecl()) {
     for (unsigned I = 0; I != NumLambdas; ++I)
-      readDecl();
+      Reader.PendingLambdas.push_back(Record.readDeclID());
   } else {
     (void)Record.readIntArray(NumLambdas);
   }

clang/test/Headers/crash-instantiated-in-scope-cxx-modules2.cpp

@@ -23,7 +23,6 @@ struct B {
     });
   }
 };
-
 // expected-no-diagnostics
 
 //--- main.cpp