[AST][RecoveryExpr] Fix a crash: don't attach error-type base specifiers.

[hokein]

Summary

otherwise we'll run into code path which expects a good base specifiers,
and lead to crashes.

The crash only occurs in template instantiations (in non-template case,
the bad base specifiers are dropped during parsing.)

crash stacktrace:

clang: llvm-project/clang/lib/Sema/SemaInit.cpp:7864: clang::ExprResult clang::InitializationSequence::Perform(clang::Sema &, const clang::InitializedEntity &, const clang::InitializationKind &, clang::MultiExprArg, clang::QualType *): Assertion `Kind.getKind() == InitializationKind::IK_Copy || Kind.isExplicitCast() || Kind.getKind() == InitializationKind::IK_DirectList' failed.
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
#14 clang::InitializationSequence::Perform(clang::Sema&, clang::InitializedEntity const&, clang::InitializationKind const&, llvm::MutableArrayRef<clang::Expr*>, clang::QualType*) llvm-project/clang/lib/Sema/SemaInit.cpp:7889:12
#15 BuildImplicitBaseInitializer(clang::Sema&, clang::CXXConstructorDecl*, ImplicitInitializerKind, clang::CXXBaseSpecifier*, bool, clang::CXXCtorInitializer*&) llvm-project/clang/lib/Sema/SemaDeclCXX.cpp:4563:24
#16 clang::Sema::SetCtorInitializers(clang::CXXConstructorDecl*, bool, llvm::ArrayRef<clang::CXXCtorInitializer*>) llvm-project/clang/lib/Sema/SemaDeclCXX.cpp:5090:11
#17 clang::Sema::ActOnMemInitializers(clang::Decl*, clang::SourceLocation, llvm::ArrayRef<clang::CXXCtorInitializer*>, bool) llvm-project/clang/lib/Sema/SemaDeclCXX.cpp:5404:3
#18 llvm::SmallVectorTemplateCommon<clang::CXXCtorInitializer*, void>::isSmall() const llvm-project/llvm/include/llvm/ADT/SmallVector.h:124:39
#19 llvm::SmallVectorImpl<clang::CXXCtorInitializer*>::~SmallVectorImpl() llvm-project/llvm/include/llvm/ADT/SmallVector.h:381:16
#20 llvm::SmallVector<clang::CXXCtorInitializer*, 4u>::~SmallVector() llvm-project/llvm/include/llvm/ADT/SmallVector.h:891:3
#21 clang::Sema::InstantiateMemInitializers(clang::CXXConstructorDecl*, clang::CXXConstructorDecl const*, clang::MultiLevelTemplateArgumentList const&) llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:5391:1
#22 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:4699:13
#23 clang::FunctionDecl::isDefined() const llvm-project/clang/include/clang/AST/Decl.h:2035:12
#24 clang::Sema::PerformPendingInstantiations(bool) llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:5956:23
#25 llvm::TimeTraceScope::~TimeTraceScope() llvm-project/llvm/include/llvm/Support/TimeProfiler.h:86:9
#26 clang::Sema::ActOnEndOfTranslationUnitFragment(clang::Sema::TUFragmentKind) llvm-project/clang/lib/Sema/Sema.cpp:958:3
#27 clang::Sema::ActOnEndOfTranslationUnit() llvm-project/clang/lib/Sema/Sema.cpp:999:9
#28 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, bool) llvm-project/clang/lib/Parse/Parser.cpp:657:15

[hokein]

clang/test/SemaCXX/invalid-template-base-specifier.cpp

7

to explain what's happening here:

• when parsing this primary template class decl, we'll keep this base specifier (whose type is a normal dependent type, DecltypeType 'decltype(Foo(T()))' dependent)
• later clang instantiates Crash<int> (creating a ClassTemplateSpecializationDecl), which will subst the base specifier with an instantiated base specifier (the type is DecltypeType decltype(<recovery-expr>(Foo, int())) ), and the instantiated specifier is passed the sanity checks (CheckBaseSpecifier), and gets attached to the ClassTemplateSpecializationDecl.

[sammccall]

clang/lib/Sema/SemaDeclCXX.cpp

2430

I think this is fine, just "// already emitted this error" or so

clang/lib/Sema/SemaDeclCXX.cpp

 /// and returns NULL otherwise.
 CXXBaseSpecifier *
 Sema::CheckBaseSpecifier(CXXRecordDecl *Class,
                          SourceRange SpecifierRange,
                          bool Virtual, AccessSpecifier Access,
                          TypeSourceInfo *TInfo,
                          SourceLocation EllipsisLoc) {
   QualType BaseType = TInfo->getType();
-
+  if (BaseType->containsErrors()) {
+    // Already emitted a diagnostic when parsing the error type.
+    return nullptr;
+  }
   // C++ [class.union]p1:
   //   A union shall not have base classes.
   if (Class->isUnion()) {
     Diag(Class->getLocation(), diag::err_base_clause_on_union)
       << SpecifierRange;
     return nullptr;
   }
 

clang/test/SemaCXX/invalid-template-base-specifier.cpp

+// RUN: %clang_cc1 -frecovery-ast -verify %s
+
+bool Foo(int *); // expected-note {{candidate function not viable}}
+
+template <typename T>
+struct Crash : decltype(Foo(T())) { // expected-error {{no matching function for call to 'Foo'}}
+  Crash(){};
+};
+
+void test() { Crash<int>(); } // expected-note {{in instantiation of template class}}