Detect recursive default argument definition

[sepavloff]

Summary

If definition of default function argument uses itself, clang crashed,
because corresponding function parameter is not associated with the default
argument yet. With this fix clang emits appropriate error message.

This change fixes PR28105.

[majnemer]

LGTM

lib/Sema/SemaExpr.cpp

4570 ↗

(On Diff #60564)

I'd make this !Param->hasInit().

cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td

 def err_default_arg_makes_ctor_special : Error<
   "addition of default argument on redeclaration makes this constructor a "
   "%select{default|copy|move}0 constructor">;
 
 def err_use_of_default_argument_to_function_declared_later : Error<
   "use of default argument to function %0 that is declared later in class %1">;
 def note_default_argument_declared_here : Note<
   "default argument declared here">;
+def err_recursive_default_argument : Error<"recursive evaluation of default argument">;
 
 def ext_param_promoted_not_compatible_with_prototype : ExtWarn<
   "%diff{promoted type $ of K&R function parameter is not compatible with the "
   "parameter type $|promoted type of K&R function parameter is not compatible "
   "with parameter type}0,1 declared in a previous prototype">,
   InGroup<KNRPromotedParameter>;
 
 

cfe/trunk/lib/Sema/SemaExpr.cpp

if (Param->hasUninstantiatedDefaultArg()) {
 
     // Remember the instantiated default argument.
     Param->setDefaultArg(Result.getAs<Expr>());
     if (ASTMutationListener *L = getASTMutationListener()) {
       L->DefaultArgumentInstantiated(Param);
     }
   }
 
+  // If the default argument expression is not set yet, we are building it now.
+  if (!Param->hasInit()) {
+    Diag(Param->getLocStart(), diag::err_recursive_default_argument) << FD;
+    Param->setInvalidDecl();
+    return ExprError();
+  }
+
   // If the default expression creates temporaries, we need to
   // push them to the current stack of expression temporaries so they'll
   // be properly destroyed.
   // FIXME: We should really be rebuilding the default argument with new
   // bound temporaries; see the comment in PR5810.
   // We don't need to do that with block decls, though, because
   // blocks in default argument expression can never capture anything.
   if (isa<ExprWithCleanups>(Param->getInit())) {

cfe/trunk/test/SemaCXX/default2.cpp

class XX {
   void B() { A(); }
 };
 
 template <int I = (1 * I)> struct S {};  // expected-error-re {{use of undeclared identifier 'I'{{$}}}}
 S<1> s;
 
 template <int I1 = I2, int I2 = 1> struct T {};  // expected-error-re {{use of undeclared identifier 'I2'{{$}}}}
 T<0, 1> t;
+
+struct PR28105 {
+  PR28105 (int = 0, int = 0, PR28105 = 0);  // expected-error{{recursive evaluation of default argument}}
+};