[PATCH] Fix parsing comma in default arguments.

[Olivier Goffart]

On Wednesday 12 June 2013 14:39:04 Richard Smith wrote:
> I've had a look at this before. Here are some testcases for you:
> 
> Index: test/Parser/cxx-ambig-init-templ.cpp
> ===================================================================
> --- test/Parser/cxx-ambig-init-templ.cpp        (revision 0)
> +++ test/Parser/cxx-ambig-init-templ.cpp        (revision 0)
> @@ -0,0 +1,57 @@
> +// RUN: %clang_cc1 -std=c++11 -verify %s
> +
> +template<int> struct c { c(int) = delete; typedef void val; };
> +
> +int val;
> +struct S {
> +  int k1 = a < b < c, d > ::val, e1;
> +  int k2 = a < b, c < d > ::val, e2;
> +  int k3 = b < a < c, d > ::val, e3;
> +  int k4 = b < c, x, y = d > ::val, e4;
> +  int k5 = T1 < b, &S::operator=(int); // expected-warning
> {{qualification}} 

that is an error instead of a warning for me, so i removed the extra 
qualification

> +  int k6 = T2 < b, &S::operator= >::val;
> +  int k7 = T1 < b, &S::operator>(int); // expected-warning
> {{qualification}} 

Same here.

> +  int k8 = T2 < b, &S::operator> >::val;
> +  int k9 = T3 < a < b, c >> (d), e5 = 1 > (e4);
> +
> +  void f(
> +    int k1 = a < b < c, d > ::val,
> +    int k3 = b < a < c, d > ::val,
> +    int k4 = b < c, int x = 0 > ::val,
> +    int k5 = a < b, T3 < int > >(),

T3<int>  is not int,  and a is not an int

> +    int k6 = c < b, T3 < int > x,

'x is a duplicate argument, missing a default value, and T3 must be declared 
before

> +
> +    int k2 = a < b, c < d > ::val, // 'a' must be a template
> (otherwise we're missing a default arg)
> +    int k7 = a < b, c < d > (n) // 'a' must be a template (otherwise
> we're missing a default arg)

there is no 'n' and 'a' don't  convert to int

> +  );
> +
> +  template<int, int=0> struct a { static const int val = 0; };
> +  static const int b = 0, c = 1, d = 2;
> +
> +  static const int T1 = 4;
> +  template<int, int &(S::*)(int)> struct T2 { static const int val = 0; };
> +
> +  template<typename> struct T3 { T3(int); operator int(); };
> +};
> +
> +namespace CWG325 {
> +
> +  template <int A, typename B> struct T { static int i; operator int(); };
> +  class C {
> +    int Foo (int i = T<1, int>::i);
> +  };
> +
> +  class D {
> +    int Foo (int i = T<1, int>::i);
> +    template <int A, typename B> struct T {static int i;};
> +  };
> +
> +  const int a = 0;
> +  typedef int b;
> +  T<a,b> c;
> +  struct E {
> +    int n = T<a,b>(c);
> +  };
> +
> +}
> 
> I don't see any handling of "operator<", "operator>", "operator,",
> "operator=" in your patch, so I assume it doesn't handle those cases
> properly. (That should be straightforward to fix.)

Right, I have forgotten that.

> Essentially, there are two different tricks we need in order to fully
> disambiguate these cases with no name lookup:
> 
> 1) For an in-class function declaration, if we are in a default
> argument, every parameter after the current parameter must also have a
> default argument, and a template argument cannot contain a top-level
> '='. So if we see a '=', we know we're back to a parameter, and can
> back up to the comma at the start of that parameter.

This was basically what i implemented before
 
> 2) For an in-class default initializer for a data member, any '=' must
> be part of a new data member, and otherwise any '<' or '>' must be
> part of the same initializer (because a declarator cannot contain a
> '<' or '>').

Yes, the previous patch did not really work well with NSDMI.

Too be honnest I was mostly focussed on getting the default argument working 
since it was the problem i had on the project I was working with.

Now it is implemented using a similar way.

I can still think about some broken cases, but I think they are corner case 
and they do not deserve to be fixed:
 int i = 0 < 1,   vector<string>::*j;


Also a template argument can contains = for example in this case:
 struct S {constexpr S(){}; constexpr int operator=(int) const {return 5;}};
 template <int> struct A {};
 constexpr S s;
 A<s=4> a;

But, while GCC accept this code, clang currently reject it.  But that's 
another bug

-- 
Olivier
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