[Sema] Avoids an assertion failure when an invalid conversion declaration is used

[Mordante]

Summary

When using a user-defined conversion function template with a deduced return type the compiler gives a set of warnings:

bug.cc:252:44: error: cannot specify any part of a return type in the declaration of a conversion function; use an alias template to declare a conversion to 'auto (Ts &&...) const'
  template <typename... Ts> operator auto()(Ts &&... xs) const;
                                           ^~~~~~~~~~~~~~~~~~~
bug.cc:252:29: error: conversion function cannot convert to a function type
  template <typename... Ts> operator auto()(Ts &&... xs) const;
                            ^
error: pointer to function type cannot have 'const' qualifier

after which it triggers an assertion failure. It seems the last error is incorrect and doesn't have any location information. This patch stops the compilation after the second warning.

Fixes bug 31422.

[Mordante]

Ping

[rsmith]

clang/test/Sema/conversion_function_to_function.cpp

1 ↗

(On Diff #210171)

Use %clang_cc1 -verify instead of not %clang_cc1 | FileCheck

1 ↗

(On Diff #210171)

This test should also live in test/SemaCXX, not test/Sema, because it's C++-specific.

9 ↗

(On Diff #210171)

(You don't need this final CHECK line: not %clang_cc1 still fails if clang crashes.)

[Mordante]

Addresses the review remarks:

• Moved the unit test to SemaCXX (also use the PR as name of the file)
• Change the unit test to use -verify instead of FileCheck

[rsmith]

LGTM

[Mordante]

Thanks for the review. Can you commit the patch since I don't have commit access?

cfe/trunk/lib/Sema/SemaDecl.cpp

static FunctionDecl *CreateNewFunctionDecl(Sema &SemaRef, Declarator &D,
   } else if (Name.getNameKind() == DeclarationName::CXXConversionFunctionName) {
     if (!DC->isRecord()) {
       SemaRef.Diag(D.getIdentifierLoc(),
            diag::err_conv_function_not_member);
       return nullptr;
     }
 
     SemaRef.CheckConversionDeclarator(D, R, SC);
+    if (D.isInvalidType())
+      return nullptr;
+
     IsVirtualOkay = true;
     return CXXConversionDecl::Create(
         SemaRef.Context, cast<CXXRecordDecl>(DC), D.getBeginLoc(), NameInfo, R,
         TInfo, isInline, ExplicitSpecifier, ConstexprKind, SourceLocation());
 
   } else if (Name.getNameKind() == DeclarationName::CXXDeductionGuideName) {
     SemaRef.CheckDeductionGuideDeclarator(D, R, SC);
 

cfe/trunk/test/SemaCXX/PR31422.cpp

+// RUN: %clang_cc1 -std=c++14 -fsyntax-only -verify %s
+
+// expected-error@+3 {{cannot specify any part of a return type in the declaration of a conversion function; use an alias template to declare a conversion to 'auto (Ts &&...) const'}}
+// expected-error@+2 {{conversion function cannot convert to a function type}}
+struct S {
+  template <typename... Ts> operator auto()(Ts &&... xs) const;
+};