Inheriting from variadic types messes up template member function indentation in Emacs

Question

Unpacking Ts in inheritance adds extra indentation to template member function void bar(). How can I get rid of that extra indentation?

template <typename ...Ts>
struct Foo: public Ts...
{
    Foo()
    {
    }

    template <typename U>
        void bar()
    {
    }
};

Non-unpacked inheritance works well:

template <typename T, typename U>
struct Foo: public T, public U
{
    Foo()
    {
    }

    template <typename S>
    void bar()
    {
    }
};

My .emacs:

; Replace highlighted text
(delete-selection-mode 1)


(defun bb-cpp-style()
  (c-set-style "linux")
  (setq indent-tabs-mode nil)
  (setq tab-width 4)
  (setq c-basic-offset 4)

  (c-set-offset 'case-label '+)
  (c-set-offset 'statement-case-intro '+)
  (c-set-offset 'statement-case-open '0)

  (c-set-offset 'inlambda 'c-lineup-inexpr-block) ;
  (c-set-offset 'inline-open '0) ;

)

(add-hook 'c++-mode-hook 'bb-cpp-style)

; treat .h as c++
(add-to-list 'auto-mode-alist '("\\.h\\'" . c++-mode))

Expected:

template <typename ...Ts>
struct Foo: public Ts...
{
    Foo()
    {
    }

    template <typename U>
    void bar()
    {
    }
};

Answer 1

The cc-mode syntactic element associated with the offending line is statement-cont. You can see the syntactic info with the functions c-show-syntactic-information and c-syntactic-information-on-region. Maybe there is some issue with how those elements are parsed since that line is given different syntactic designations in your two versions of the code - I dont know.

You could try adding a custom indentation rule for statement-cont that says to add no indentation to a statement-cont when it isn't an assignment (note: c-lineup-assignments doesn't add indentation to continuations following a line with = at the end of the line). This is simple:

(defun my-lineup-statement (langelem)
  (or (c-lineup-assignments langelem) 0))

And call (c-set-offset 'statement-cont #'my-lineup-statement) in the buffer to test it out (or add it to your mode hook). That should fix the indent in the case you've shown.

I tested it briefly on a couple files and the only other side-effect of this change I noticed was that it removed the indentation of the continued statement following a naked =, as in

int x =
1;  // before adding 'my-lineup-assignments this usually indented (depending on chosen c style)

There might be other cases where you want statement-cont elements to get indented.