[cfe-dev] Criticism over a clang tool to reorder fields on constructor declarations

[Philip Craig]

On Sun, Aug 19, 2012 at 1:52 PM, Victor Vicente de Carvalho
<victor.v.carvalho at gmail.com> wrote:
> Hi Manuel,
>
> my rewrite basing only in source replacements is complete, but now I'm
> facing some strange side effects on some files. Consider the example:
>
> header ----------
>
> #include <B.h> // B defines a simple class named B
>
> class A {
> public:
>   A();
>
>   float x;
>   B b;
> };
>
> source ---------------
>
> A::A() : x(0) {
> }
>
>
> the strange behavior that I'm having is that if in the header file "x" is
> declared before "b", when processing the source location for the initializer
> list on CXXConstructorDecl*, the source location for it get's completely
> wrong pointing to right before the constructor name: "A::". If i declare "b"
> before "x" then the source location points to "A::A() : " which was
> expected. Also, the method getNumCtorInitializers on this declaration is
> returning to me 2 ( should be 1 as only x is being initialized ), but if
> decide to initialize b I'm __still__ getting 2. Also, node that the class
> I'm parsing does not have a base class, and I'm providing the correct
> includes as the tool run fine and exits returning 0. I'm a bit lost here,
> any comments are welcome. I could upload on gist the current tool source,
> cmake and sample code I'm using to test it if someone is willing to try.
>
> I've also tried to dump the ast and verify it but the initalizer list is not
> showing up so I don't know what might be happening.

The AST for the constructor looks like this:

  CXXConstructorDecl <A.cc:2:1-3:1>
    NestedNameSpecifier <2:1-2> A::
      RecordType <2:1>
    DeclarationName <2:4> A
    FunctionProtoType <-6>
      BuiltinType void <>
    CXXCtorInitializer  <2:10-13>
      FieldDeclRef <2:10> A::x
      ImplicitCastExpr <2:12>
        IntegerLiteral <2:12> 0
    CXXCtorInitializer  <2:4>
      FieldDeclRef <2:4> A::b
    CompoundStmt <2:15-3:1>

Reversing the order of x and b just reverses the order of the two
CXXCtorInitializer in the AST.

So it looks like clang always creates implicit initializers for
members that aren't explicitly initialized, but it has no way of
flagging them as implicit. I don't know the expected way of
determining which are implicit, maybe checking for a NULL getInit().