In Sema::SubstExceptionSpec: Assertion `ESI.Type != EST_Uninstantiated' failed #42496
Description
| Bugzilla Link | 43151 |
| Version | trunk |
| OS | Linux |
| Attachments | Small reproducer for the bug, compile with -std=c++17. |
| CC | @AaronBallman,@riccibruno,@zygoloid |
Extended Description
Compiling the following code with -fsyntax-only -std=c++17 produces an assertion failure:
template<typename T>
struct X {
using self = X<T>;
template<bool noex>
void f() noexcept(noex)
{
auto x = &self::f<noex>;
}
};
void g()
{
X<int> x;
x.f<true>();
}The trace shows:
1. <eof> parser at end of file
2. template-crash.cpp:6:8: instantiating function definition 'X<int>::f<true>'
The issue disappears when removing -std=c++17, probably because the exception specification is not part of the type then.
The function is called from clang::Sema::SubstituteExplicitTemplateArguments, where we have EPI.ExceptionSpec.Type = clang::EST_Uninstantiated and EPI.ExceptionSpec.SourceDecl = Function. On the other hand, the type of EPI.ExceptionSpec.SourceTemplate has an ExceptionSpec with Type = clang::EST_DependentNoexcept. So it seems we should be passing that one to Sema::SubstExceptionSpec instead.
Indeed, the following seems to fix the assertion (and not introduce new issues):
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -3112,6 +3112,13 @@ Sema::SubstituteExplicitTemplateArguments(
// so substitution into the type must also substitute into the exception
// specification.
SmallVector<QualType, 4> ExceptionStorage;
+ if (EPI.ExceptionSpec.Type == EST_Uninstantiated) {
+ assert(Function == EPI.ExceptionSpec.SourceDecl);
+ const auto *TplType = EPI.ExceptionSpec.SourceTemplate->getType()
+ ->getAs<FunctionProtoType>();
+ EPI.ExceptionSpec = TplType->getExtProtoInfo().ExceptionSpec;
+ assert(EPI.ExceptionSpec.Type != EST_Uninstantiated);
+ }
if (getLangOpts().CPlusPlus17 &&
SubstExceptionSpec(
Function->getLocation(), EPI.ExceptionSpec, ExceptionStorage,But this seems like a hack, since in other instances the ExceptionSpec is already instantiated correctly.