[C++ PATCH] c++/92878 - Parenthesized init of aggregates in new-expression.

[Jason Merrill]

On 12/10/19 2:13 PM, Marek Polacek wrote:
> Ville pointed out that our paren init of aggregates doesn't work for
> 
>    auto a = new A(1, 2, 3);
> 
> and I think it should:
> 
> A new-expression that creates an object of type T initializes that object
> as follows:
> ...
> -- Otherwise, the new-initializer is interpreted according to the
>     initialization rules of [dcl.init] for direct-initialization.
> 
> so I think it follows that we should perform dcl.init#17.6.2.2.
> 
> This doesn't work with new[]; we have:
>    error ("parenthesized initializer in array new");
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?

OK.

> 2019-12-10  Marek Polacek  <polacek@redhat.com>
> 
> 	PR c++/92878 - Parenthesized init of aggregates in new-expression.
> 	* init.c (build_new_1): Handle parenthesized initialization of
> 	aggregates in new-expression.
> 
> 	* g++.dg/cpp2a/paren-init20.C: New test.
> 
> diff --git gcc/cp/init.c gcc/cp/init.c
> index e40afe27e1a..b0331b8ba53 100644
> --- gcc/cp/init.c
> +++ gcc/cp/init.c
> @@ -3608,10 +3608,22 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
>   	      tree ie;
>   
>   	      /* We are processing something like `new int (10)', which
> -		 means allocate an int, and initialize it with 10.  */
> +		 means allocate an int, and initialize it with 10.
>   
> -	      ie = build_x_compound_expr_from_vec (*init, "new initializer",
> -						   complain);
> +		 In C++20, also handle `new A(1, 2)'.  */
> +	      if (cxx_dialect >= cxx2a
> +		  && AGGREGATE_TYPE_P (type)
> +		  && (*init)->length () > 1)
> +		{
> +		  ie = build_tree_list_vec (*init);
> +		  ie = build_constructor_from_list (init_list_type_node, ie);
> +		  CONSTRUCTOR_IS_DIRECT_INIT (ie) = true;
> +		  CONSTRUCTOR_IS_PAREN_INIT (ie) = true;
> +		  ie = digest_init (type, ie, complain);
> +		}
> +	      else
> +		ie = build_x_compound_expr_from_vec (*init, "new initializer",
> +						     complain);
>   	      init_expr = cp_build_modify_expr (input_location, init_expr,
>   						INIT_EXPR, ie, complain);
>   	    }
> diff --git gcc/testsuite/g++.dg/cpp2a/paren-init20.C gcc/testsuite/g++.dg/cpp2a/paren-init20.C
> new file mode 100644
> index 00000000000..05da7604686
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp2a/paren-init20.C
> @@ -0,0 +1,54 @@
> +// PR c++/92878 - Parenthesized init of aggregates in new-expression.
> +// { dg-do compile { target c++2a } }
> +// Test new TYPE(...).
> +
> +int f ();
> +
> +struct A
> +{
> +  int a;
> +  int b;
> +};
> +
> +void
> +fn_A ()
> +{
> +  int i = 0;
> +  auto y = new A(1, 2);
> +  auto x = new A(++i, ++i);
> +  auto z = new A(1, { ++i });
> +  auto u = new A(1, f());
> +}
> +
> +struct B
> +{
> +  int a;
> +  int b;
> +  int c = 42;
> +};
> +
> +void
> +fn_B ()
> +{
> +  int i = 0;
> +  auto y = new B(1, 2);
> +  auto x = new B(++i, ++i);
> +  auto z = new B(1, { ++i });
> +  auto u = new B(1, f());
> +}
> +
> +struct C
> +{
> +  int a;
> +  int b = 10;
> +};
> +
> +void
> +fn_C ()
> +{
> +  int i = 0;
> +  auto y = new C(1);
> +  auto x = new C(++i);
> +  auto z = new C({ ++i });
> +  auto u = new C(f());
> +}
>