Summary:
The string constructors are not defined using optional parameters and are not recognize by the checker.
The constructor defined in the MSVC header is defined with 1 parameter. Therefore, patterns are not recognized by the checker.
The current patch add support to accept constructor with only one parameter.
Repro on a Visual Studio 14 installation with the following code:
```
void f1(const std::string &s) {
f1(s.c_str());
}
```
In the xstring.h header, the constructors are defined this way:
```
basic_string(const _Myt& _Right) [...]
basic_string(const _Myt& _Right, const _Alloc& _Al) [...]
```
The CXXConstructExpr to recognize only contains 1 parameter.
```
CXXConstructExpr 0x3f1a070 <C:\src\llvm\examples\test.cc:6:6, col:14> 'const std::string':'const class std::basic_string<char, struct std::char_traits<char>, class
std::allocator<char> >' 'void (const char *) __attribute__((thiscall))'
`-CXXMemberCallExpr 0x3f1a008 <col:6, col:14> 'const char *'
`-MemberExpr 0x3f19fe0 <col:6, col:8> '<bound member function type>' .c_str 0x3cc22f8
`-DeclRefExpr 0x3f19fc8 <col:6> 'const std::string':'const class std::basic_string<char, struct std::char_traits<char>, class std::allocator<char> >' lvalue ParmVar 0x3f19c80 's' 'const std::string &'
```
Reviewers: aaron.ballman, alexfh
Subscribers: aemerson
Differential Revision: http://reviews.llvm.org/D18285
llvm-svn: 264075
Etienne Bergeron