Revert "[RFC][C++20][Modules] Fix crash when function and lambda insi… (#108311)

…de loaded from different modules (#104512)"

This reverts commit d778689.

Author: pranavk

clang/include/clang/Serialization/ASTReader.h

@@ -1188,15 +1188,6 @@ 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 canonical declaration for lambda class from the
-  /// same module as enclosing function. This is required to correctly resolve
-  /// captured variables in the lambda. Without this, due to lazy
-  /// deserialization canonical declarations for the function and lambdas can
-  /// be from different modules and DeclRefExprs may refer to the AST nodes
-  /// that don't exist in the function.
-  SmallVector<GlobalDeclID, 4> PendingLambdas;
-
   using DataPointers =
       std::pair<CXXRecordDecl *, struct CXXRecordDecl::DefinitionData *>;
   using ObjCInterfaceDataPointers =

clang/lib/Serialization/ASTReader.cpp

@@ -9782,8 +9782,7 @@ void ASTReader::finishPendingActions() {
       !PendingDeducedVarTypes.empty() || !PendingIncompleteDeclChains.empty() ||
       !PendingDeclChains.empty() || !PendingMacroIDs.empty() ||
       !PendingDeclContextInfos.empty() || !PendingUpdateRecords.empty() ||
-      !PendingObjCExtensionIvarRedeclarations.empty() ||
-      !PendingLambdas.empty()) {
+      !PendingObjCExtensionIvarRedeclarations.empty()) {
     // If any identifiers with corresponding top-level declarations have
     // been loaded, load those declarations now.
     using TopLevelDeclsMap =
@@ -9928,11 +9927,6 @@ 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

@@ -1155,16 +1155,6 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
   for (unsigned I = 0; I != NumParams; ++I)
     Params.push_back(readDeclAs<ParmVarDecl>());
   FD->setParams(Reader.getContext(), Params);
-
-  // 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)
-      Reader.PendingLambdas.push_back(Record.readDeclID());
-  } else {
-    Record.skipInts(NumLambdas);
-  }
 }
 
 void ASTDeclReader::VisitObjCMethodDecl(ObjCMethodDecl *MD) {

clang/lib/Serialization/ASTWriterDecl.cpp

@@ -18,7 +18,6 @@
 #include "clang/AST/Expr.h"
 #include "clang/AST/OpenMPClause.h"
 #include "clang/AST/PrettyDeclStackTrace.h"
-#include "clang/AST/StmtVisitor.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Serialization/ASTReader.h"
 #include "clang/Serialization/ASTRecordWriter.h"
@@ -626,33 +625,6 @@ void ASTDeclWriter::VisitDeclaratorDecl(DeclaratorDecl *D) {
                                            : QualType());
 }
 
-static llvm::SmallVector<const Decl *, 2> collectLambdas(FunctionDecl *D) {
-  struct LambdaCollector : public ConstStmtVisitor<LambdaCollector> {
-    llvm::SmallVectorImpl<const Decl *> &Lambdas;
-
-    LambdaCollector(llvm::SmallVectorImpl<const Decl *> &Lambdas)
-        : Lambdas(Lambdas) {}
-
-    void VisitLambdaExpr(const LambdaExpr *E) {
-      VisitStmt(E);
-      Lambdas.push_back(E->getLambdaClass());
-    }
-
-    void VisitStmt(const Stmt *S) {
-      if (!S)
-        return;
-      for (const Stmt *Child : S->children())
-        if (Child)
-          Visit(Child);
-    }
-  };
-
-  llvm::SmallVector<const Decl *, 2> Lambdas;
-  if (D->hasBody())
-    LambdaCollector(Lambdas).VisitStmt(D->getBody());
-  return Lambdas;
-}
-
 void ASTDeclWriter::VisitFunctionDecl(FunctionDecl *D) {
   static_assert(DeclContext::NumFunctionDeclBits == 44,
                 "You need to update the serializer after you change the "
@@ -792,19 +764,6 @@ void ASTDeclWriter::VisitFunctionDecl(FunctionDecl *D) {
   Record.push_back(D->param_size());
   for (auto *P : D->parameters())
     Record.AddDeclRef(P);
-
-  // Store references to all lambda decls inside function to load them
-  // immediately after loading the function to make sure that canonical
-  // decls for lambdas will be from the same module.
-  if (D->isCanonicalDecl()) {
-    llvm::SmallVector<const Decl *, 2> Lambdas = collectLambdas(D);
-    Record.push_back(Lambdas.size());
-    for (const auto *L : Lambdas)
-      Record.AddDeclRef(L);
-  } else {
-    Record.push_back(0);
-  }
-
   Code = serialization::DECL_FUNCTION;
 }
 
@@ -2280,7 +2239,6 @@ getFunctionDeclAbbrev(serialization::DeclCode Code) {
   //
   // This is:
   //         NumParams and Params[] from FunctionDecl, and
-  //         NumLambdas, Lambdas[] from FunctionDecl, and
   //         NumOverriddenMethods, OverriddenMethods[] from CXXMethodDecl.
   //
   //  Add an AbbrevOp for 'size then elements' and use it here.