[PATCH] Warn, if parameter is used in ctor body after being used for move-construct

[Ismail Pazarbasi]

Hi rsmith, dblaikie,

If a member of type unique_ptr or shared_ptr is move-constructed from
a parameter in ctor-init, the parameter will be left with nullptr at
the completion of member's initialization. If the parameter's and
member's names are the same, use of member's name in the constructor
body will not refer to the member, but to the parameter.

  #include <memory>
  struct X {
    int v;
    X() : v() { }
    int f() { return v + 42; }
  };

  struct Y {
    std::unique_ptr<X> p;
    int x;
    explicit Y(std::unique_ptr<X> p)
      : p{std::move(p)} {
      x = p->f();  // 'p' is nullptr
      decltype(p->f()) v = x; // ignore unevaluated context
    }
    int f() const { return x; }
  };

  int main() {
    std::unique_ptr<X> p(new X);
    Y y(std::move(p));
    return y.f();
  }

http://reviews.llvm.org/D10425

Files:
  include/clang/Basic/DiagnosticGroups.td
  include/clang/Basic/DiagnosticSemaKinds.td
  lib/Sema/SemaDecl.cpp
  test/SemaCXX/rval-references.cpp

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