[LLVMbugs] [Bug 12167] New: template instantiation of single-element braced casts drops the cast

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12167

             Bug #: 12167
           Summary: template instantiation of single-element braced casts
                    drops the cast
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++0x
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: richard-llvm at metafoo.co.uk
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu,
                    sebastian.redl at getdesigned.at
    Classification: Unclassified


Clang rejects this:

template<int N> struct string {};

struct X {
  X(const char v);
  template<typename T> bool operator()(T) const;
};

template<int N, class Comparator> bool g(const string<N>& s, Comparator f) {
return f(s); }
template<int N> bool f(const string<N> &s) { return g(s, X{'x'}); }

bool s = f(string<1>());


Errors:


tmp.cpp:11:10: error: called object type 'int' is not a function or function
pointer
  return f(s);
         ^
tmp.cpp:16:10: note: in instantiation of function template specialization 'g<1,
char>' requested here
  return g(s, X{'x'});
         ^
tmp.cpp:19:10: note: in instantiation of function template specialization
'f<1>' requested here
bool s = f(string<1>());
         ^


Note that we instantiate 'g<1, char>' not 'g<1, X>'. The body of the f template
looks like this:


(CompoundStmt 0x4df4160 <tmp.cpp:9:44, col:67>
  (ReturnStmt 0x4df4140 <col:46, col:64>
    (CallExpr 0x4df4108 <col:53, col:64> '<dependent type>'
      (UnresolvedLookupExpr 0x4df3af0 <col:53> '<overloaded function type>'
lvalue (ADL) = '1' 0x4df14d0)
      (DeclRefExpr 0x4df3b48 <col:55> 'const string<N>' lvalue ParmVar
0x4df3900 's' 'const string<N> &')
      (CXXConstructExpr 0x4df3f80 <col:58, col:60> 'struct X''void (const
char)'
        (CharacterLiteral 0x4df3b80 <col:60> 'char' 120)))))

... but it instantiates to this ...

(CompoundStmt 0x4df6288 <tmp.cpp:9:44, col:67>
  (ReturnStmt 0x4df6268 <col:46, col:64>
    (CallExpr 0x4df6230 <col:53, col:64> '_Bool'
      (ImplicitCastExpr 0x4df6218 <col:53> '_Bool (*)(const string<1> &, char)'
<FunctionToPointerDecay>
        (DeclRefExpr 0x4df6190 <col:53> '_Bool (const string<1> &, char)'
lvalue Function 0x4df6050 'g' '_Bool (const string<1> &, char)'
(FunctionTemplate 0x4df14d0 'g')))
      (DeclRefExpr 0x4df5cb8 <col:55> 'const string<1>':'const struct
string<1>' lvalue ParmVar 0x4df5950 's' 'const string<1> &')
      (CharacterLiteral 0x4df3b80 <col:60> 'char' 120))))

The CXXConstructExpr has *gone*. TreeTransform.h says:

  // CXXConstructExprs are always implicit, so when we have a
  // 1-argument construction we just transform that argument.

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