GNU bug report logs - #19867
c++-mode indentation issues with C++1x initializer lists

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: turner25 <at> gmail.com
Subject: bug#19867: closed (Re: bug#19867: c++-mode indentation issues
 with C++1x initializer lists)
Date: Thu, 27 Mar 2025 10:43:04 +0000

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Your bug report

#19867: c++-mode indentation issues with C++1x initializer lists

which was filed against the emacs,cc-mode package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 19867 <at> debbugs.gnu.org.

-- 
19867: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=19867
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Alan Mackenzie <acm <at> muc.de>
To: Stefan Kangas <stefankangas <at> gmail.com>
Cc: acm <at> muc.de, Simon <turner25 <at> gmail.com>, 19867-done <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Thu, 27 Mar 2025 10:42:35 +0000

Hello, Stefan.

On Tue, Mar 11, 2025 at 16:23:13 -0400, Stefan Kangas wrote:
> Alan Mackenzie <acm <at> muc.de> writes:

> > Yes, I'll do this.  Sorry I never replied to your post in 2020.  I
> > started looking at the bug then, but somehow didn't get very far with it.
> > Maybe it was because there were so many individual glitches in the
> > report.  Thanks for distilling the cases which still remain unfixed.

> Thanks!

I've just committed a fix (a ~700 line patch ;-), so I think this bug is
finally solved.

I'm closing the bug with this post.

-- 
Alan Mackenzie (Nuremberg, Germany).

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From: Simon <turner25 <at> gmail.com>
To: submit <at> debbugs.gnu.org
Subject: c++-mode indentation issues with C++1x initializer lists
Date: Sat, 14 Feb 2015 12:50:31 -0500

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Package: emacs
Version: 24.4.1
Severity: important

Related: c++-mode


Initializer lists use curly braces, but their contents do not indent
properly with emacs' c++-mode.
In short, one may use an initializer list to declare and initialize a
vector of integers as such:
  std::vector<int> Foo( { 1, 2, 3, 4, 5 } );

Problems arise when the elements of the list span on multiple line and it
gets even worse when the elements are lambda-expressions and nested
initializer lists.
The following code illustrate most cases and related situations.  The code
below compiles without error or warning with gcc 4.8.3.


In case email systems mess with the spaces, the code below is available at
this URL as well:
http://next.n32.ca/emacs_initlist_indentation_bug.txt

#include <vector>
#include <functional>

namespace emacs_initlist_indentation_bug {

  struct ABC {
    int a;  // OK, text-book indentation
    int b;  //
    int c;  //
  };

  struct DEF {
    int d, //
      e,   // indented from "int" + 2
      f;   //
  };

  struct GHI {
    int   //
    g,    // indented from "int" +0
      h,  // indented from "int" + 2
      i;  //
  };

  int f1 ( int a,  // Indentation OK in function declaration context
	   int b,  //
	   int c   //
	   )       // Notice how the ")" is indented
  {

    if(a>0){

      return a+  // while out-of-topic, this probably pinpoints
	b+       // what's going on internally
	c;       //

    } else if(a<0) {

      return (a+  // these are well aligned
	      b+  //
	      c); //

    } else {

      return
	(a+  // these are well aligned
	 b+  //
	 c); //

    }
  }

  void f2 (const ABC& abc)
  {
    f1(abc.a,  // Indentation OK in function call context
       abc.b,  //
       abc.c); //
  }

  void f3 (int a, int b, int c)
  {
    f1( f1( a+1,    // Indentation OK, text-book example, perfect!
	    b+1,    //
	    c+1 ),  //
	f1( a+2,    //
	    b+2,    //
	    c+2 ),  //
	f1( a+3,    //
	    b+3,    //
	    c+3 )   //
	);          //
  }

  void f4 (int a, int b, int c)
  {
    f2({a+1,     // note "{" on same line as "("
	  b+1,   // indented after "{" + 2
	  c+1}   //
      );         // Bad! ")" indented underneath "(" instead of
argument (ie. "{")

    f2(
       {a+2,     // note "{" on different line as "("
	   b+2,  // indented after "{" + 3 !!!
	   c+2}  //
       );        // OK, ")" indented underneath "{"

    // Below are some typical indentation I'm getting these days.
    // The only difference is in the newline on first line (and numerics)

    std::vector<ABC> abcList1({{a+1, //
	    b+1,                     //
	    c+1},                    //
	  {a+2,                      //
	      b+2,                   //
	      c+2},                  //
	    {a+3,                    //
		b+3,                 //
		c+3}                 //
      }                              //
      );                             //

    std::vector<ABC> abcList2(                     // Source of
alignment for closing ")" below
			      {{a+4,               //
				    b+4,           //
				    c+4},          //
				  {a+5,            //
				      b+5,         //
				      c+5},        //
				    {a+6,          //
					b+6,       //
					c+6}       //
			      }                    //
						   ); /* Somehow, this one aligns with first line's comment position!! */

  }


  void f5 ()
  {
    int foo = 0;
    std::vector< std::function<int(int)> >
      lambda_initlist_bug({    //
	  [foo](int x)         //
	    {                  // BAD, too indented by 2 positions
	      return x+x;      //
	    },                 //
	    [foo](int y)       //
	      {                // BAD, too indented by 2 positions
		return y+y;    //
	      },               //
	      [foo](int z)     //
		{              // BAD, too indented by 2 positions
		  return z+z;  //
		}              //
	}
	);

    lambda_initlist_bug.push_back(              //
				  [](int p)     // OK, text-book indentation
				  {             //
				    return p+p; //
				  }             //
						);  /* Aligned with first comment! */

    for(auto f_lambda : lambda_initlist_bug){
      f_lambda( 123 );
    }

  }

}

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