Adding an implemented UNO interface

[Lionel Élie Mamane <lionel@xxxxxxxxx>]

Context
https://gerrit.libreoffice.org/c/core/+/155950/5/connectivity/source/inc/java/sql/Connection.hxx

Given the following code:

typedef ::cppu::WeakComponentImplHelper2 <
	      css::Baz,
	      css::qux >  bar_BASE;


class bar : public bar_BASE
{
   ...
}

to implement css:corge, one would just change the bar_BASE typedef to:

typedef ::cppu::WeakComponentImplHelper3 <
	      css::Baz,
	      css::qux,
	      css::corge >  bar_BASE;


But now consider:

#include <grault.hxx>
/* grault .hxx contains:
 *
 * typedef ::cppu::WeakComponentImplHelper2 <
 * 	      css::Baz,
 * 	      css::qux >  grault_BASE;
 *
 * class grault : public grault_BASE { ... }
 */

typedef grault bar_BASE;


_and_ I can't touch the definition of "grault" in grault.hxx because
it is used by other classes in other files. Now, how does one add
implementation of css:corge? Can one just nest them and do:

typedef ::cppu::WeakComponentImplHelper2 <
             grault,
	     css::corge >  bar_BASE;


>From reading existing code, I get the impression that one _cannot_
do:

typedef ::cppu::WeakComponentImplHelper2 <
	      css::Baz,
	      css::qux >  grault;

typedef grault bar_BASE;

class bar : public bar_BASE,
      	    public ::cppu::WeakComponentImplHelper1 < css::corge >