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

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

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

[Message part 1 (text/plain, inline)]

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 );
    }

  }

}

[Message part 2 (text/html, inline)]

Message #8 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: turner25 <at> gmail.com
Cc: 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Mon, 16 Feb 2015 14:09:55 -0500

Simon wrote:

> Severity: important

Unless it leads to invalid code (eg Python-style languages), I tend to
think of indentation bugs as minor problems, since it's just cosmetic.
Why do you think this one is important?

Message #11 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Simon <turner25 <at> gmail.com>
To: Glenn Morris <rgm <at> gnu.org>
Cc: 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Mon, 16 Feb 2015 14:29:36 -0500

On Mon, Feb 16, 2015 at 2:09 PM, Glenn Morris <rgm <at> gnu.org> wrote:
> Simon wrote:
>
>> Severity: important
>
> Unless it leads to invalid code (eg Python-style languages), I tend to
> think of indentation bugs as minor problems, since it's just cosmetic.
> Why do you think this one is important?

I am inclined to follow your lead.  C++ code compiles without errors
as I mentioned.

The bug affects "c++-mode" and since c++-mode mostly (solely?) affects
cosmetics, then the bug makes c++-mode difficult to use.  In fact, I
have been searching for alternatives, in vain.

I would suggest keeping severity as "important" if this report can be
assigned more precisely to the "c++-mode" sub-package or group.  If
not, then you may downgrade to "minor" as you said.

Message #14 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Daniel Colascione <dancol <at> dancol.org>
To: Glenn Morris <rgm <at> gnu.org>, turner25 <at> gmail.com
Cc: 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Mon, 16 Feb 2015 13:03:08 -0800

[Message part 1 (text/plain, inline)]

On 02/16/2015 11:09 AM, Glenn Morris wrote:
> Simon wrote:
> 
>> Severity: important
> 
> Unless it leads to invalid code (eg Python-style languages), I tend to
> think of indentation bugs as minor problems, since it's just cosmetic.
> Why do you think this one is important?

Indentation bugs are infuriating because I use electric mode, which
means that even if I fix the indentation, the fixes are undone
automatically.

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Message #17 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Daniel Colascione <dancol <at> dancol.org>
To: turner25 <at> gmail.com, Glenn Morris <rgm <at> gnu.org>
Cc: 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Mon, 16 Feb 2015 13:38:39 -0800

[Message part 1 (text/plain, inline)]

On 02/16/2015 11:29 AM, Simon wrote:
> On Mon, Feb 16, 2015 at 2:09 PM, Glenn Morris <rgm <at> gnu.org> wrote:
>> Simon wrote:
>>
>>> Severity: important
>>
>> Unless it leads to invalid code (eg Python-style languages), I tend to
>> think of indentation bugs as minor problems, since it's just cosmetic.
>> Why do you think this one is important?
> 
> I am inclined to follow your lead.  C++ code compiles without errors
> as I mentioned.
> 
> The bug affects "c++-mode" and since c++-mode mostly (solely?) affects
> cosmetics, then the bug makes c++-mode difficult to use.  In fact, I
> have been searching for alternatives, in vain.
> 
> I would suggest keeping severity as "important" if this report can be
> assigned more precisely to the "c++-mode" sub-package or group.  If
> not, then you may downgrade to "minor" as you said.

OP, your best bet is to dive into cc-engine.el and fix it yourself.

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Message #20 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: turner25 <at> gmail.com
Cc: 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Tue, 17 Feb 2015 14:23:36 -0500

In Emacs, we traditionally reserve severity > normal for failure to
build, security issues etc. So I'll downgrade this to normal, but don't
worry, because I have seen very little evidence that the severity makes
any difference to whether something gets fixed. :), and :( too.

Message #25 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Simon <turner25 <at> gmail.com>
To: Glenn Morris <rgm <at> gnu.org>
Cc: 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Tue, 17 Feb 2015 14:39:09 -0500

> In Emacs, we traditionally reserve severity > normal for failure to
> build, security issues etc. So I'll downgrade this to normal, but don't
> worry, because I have seen very little evidence that the severity makes
> any difference to whether something gets fixed. :), and :( too.

Sounds good.  Thank you Glenn.

I hope someone can look into this within a year or two.  Ideally,
before C++17 becomes a reality and swizzles the syntax further with
its "concepts lite" and other features.

I also noticed some more strange indentation cases with nested
constructor initialization lists.  I'll be available to test any
improvements made and provide more test cases if needed.  Thanks
again.

Message #28 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefan <at> marxist.se>
To: Alan Mackenzie <acm <at> muc.de>
Cc: Simon <turner25 <at> gmail.com>, 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Mon, 23 Nov 2020 09:14:43 -0500

Simon <turner25 <at> gmail.com> writes:

> 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.

I had a look at the fairly long example provided here, and AFAICT, the
indentation is incorrect in the below cases (trimmed down from the
original).  Some of the examples of incorrect indentation were already
fixed.

Alan, could you perhaps take a look at this and see if this is something
that is fixable?  Thanks in advance.


#include <vector>
#include <functional>

namespace emacs_initlist_indentation_bug {
  struct DEF {
    int d, //
      e,   // indented from "int" + 2
      f;   //
  };
  struct GHI {
    int   //
    g,    // indented from "int" +0
      h,  // indented from "int" + 2
      i;  //
  };

  void f4 (int a, int b, int c)
  {
    std::vector<ABC> abcList2(                     // Source of
alignment for closing ")" below
      {{a+6,
        b+6,
        c+6}
      }                    //
                                                   ); /* Somehow, this
one aligns with first line's comment position!! */
  }

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

Message #31 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Alan Mackenzie <acm <at> muc.de>
Cc: Simon <turner25 <at> gmail.com>, 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Tue, 11 Mar 2025 09:54:20 -0700

Stefan Kangas <stefankangas <at> gmail.com> writes:

> Simon <turner25 <at> gmail.com> writes:
>
>> 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.
>
> I had a look at the fairly long example provided here, and AFAICT, the
> indentation is incorrect in the below cases (trimmed down from the
> original).  Some of the examples of incorrect indentation were already
> fixed.
>
> Alan, could you perhaps take a look at this and see if this is something
> that is fixable?  Thanks in advance.

Alan, any chance you could look into the below cases?  Thanks in advance.

> #include <vector>
> #include <functional>
>
> namespace emacs_initlist_indentation_bug {
>   struct DEF {
>     int d, //
>       e,   // indented from "int" + 2
>       f;   //
>   };
>   struct GHI {
>     int   //
>     g,    // indented from "int" +0
>       h,  // indented from "int" + 2
>       i;  //
>   };
>
>   void f4 (int a, int b, int c)
>   {
>     std::vector<ABC> abcList2(                     // Source of
> alignment for closing ")" below
>       {{a+6,
>         b+6,
>         c+6}
>       }                    //
>                                                    ); /* Somehow, this
> one aligns with first line's comment position!! */
>   }
>
>   lambda_initlist_bug.push_back(              //
>     [](int p)     // OK, text-book indentation
>     {             //
>       return p+p; //
>     }             //
>                                               );  /* Aligned with
> first comment! */
>   }
> }

Message #36 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Stefan Kangas <stefankangas <at> gmail.com>
Cc: Simon <turner25 <at> gmail.com>, 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Tue, 11 Mar 2025 20:15:35 +0000

Hello, Stefan.

On Tue, Mar 11, 2025 at 09:54:20 -0700, Stefan Kangas wrote:
> Stefan Kangas <stefankangas <at> gmail.com> writes:

> > Simon <turner25 <at> gmail.com> writes:

> >> 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.

> > I had a look at the fairly long example provided here, and AFAICT, the
> > indentation is incorrect in the below cases (trimmed down from the
> > original).  Some of the examples of incorrect indentation were already
> > fixed.

> > Alan, could you perhaps take a look at this and see if this is something
> > that is fixable?  Thanks in advance.

> Alan, any chance you could look into the below cases?  Thanks in advance.

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.

[ .... ]

-- 
Alan Mackenzie (Nuremberg, Germany).

Message #39 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Alan Mackenzie <acm <at> muc.de>
Cc: Simon <turner25 <at> gmail.com>, 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Tue, 11 Mar 2025 16:23:13 -0400

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!

Message #44 received at 19867-done <at> debbugs.gnu.org (full text, mbox):

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).

Message #47 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Alan Mackenzie <acm <at> muc.de>
Cc: Simon <turner25 <at> gmail.com>, 19867 <at> debbugs.gnu.org
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Wed, 9 Apr 2025 17:54:09 -0700

Alan Mackenzie <acm <at> muc.de> writes:

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

Thank you!

Message #50 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Alan Mackenzie <acm <at> muc.de>
Cc: Simon <turner25 <at> gmail.com>, 19867 <at> debbugs.gnu.org,
 Stefan Kangas <stefankangas <at> gmail.com>
Subject: bug#19867: c++-mode indentation issues with C++1x initializer lists 
Date: Thu, 17 Apr 2025 15:42:59 +0200

Thank you for fixing this. A minor oversight in the committed patch, in cc-align.el:

 351        (skip-syntax-backward " \t([{" (c-point 'boi))

This call should probably use `skip-char-backward`, because `\t`, `[`, and `{` aren't syntax chars.
It currently works by accident because of the ` ` and `(` syntax classes.

Message #53 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Mattias Engdegård <mattias.engdegard <at> gmail.com>
Cc: Simon <turner25 <at> gmail.com>, 19867 <at> debbugs.gnu.org,
 Stefan Kangas <stefankangas <at> gmail.com>
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Mon, 21 Apr 2025 20:35:22 +0000

Hello, Mattias.

On Thu, Apr 17, 2025 at 15:42:59 +0200, Mattias Engdegård wrote:
> Thank you for fixing this. A minor oversight in the committed patch, in cc-align.el:

>  351        (skip-syntax-backward " \t([{" (c-point 'boi))

> This call should probably use `skip-char-backward`, because `\t`, `[`, and `{` aren't syntax chars.
> It currently works by accident because of the ` ` and `(` syntax classes.

Thanks for spotting this and telling me about it.  I'll get around to
fixing it in the next few days.

-- 
Alan Mackenzie (Nuremberg, Germany).

Message #56 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Mattias Engdegård <mattias.engdegard <at> gmail.com>
Cc: Simon <turner25 <at> gmail.com>, 19867 <at> debbugs.gnu.org,
 Stefan Kangas <stefankangas <at> gmail.com>
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists
Date: Wed, 30 Apr 2025 18:58:26 +0000

Hello again, Mattias.

On Mon, Apr 21, 2025 at 20:35:22 +0000, Alan Mackenzie wrote:
> On Thu, Apr 17, 2025 at 15:42:59 +0200, Mattias Engdegård wrote:
> > Thank you for fixing this. A minor oversight in the committed patch, in cc-align.el:

> >  351        (skip-syntax-backward " \t([{" (c-point 'boi))

> > This call should probably use `skip-char-backward`, because `\t`, `[`, and `{` aren't syntax chars.
> > It currently works by accident because of the ` ` and `(` syntax classes.

> Thanks for spotting this and telling me about it.  I'll get around to
> fixing it in the next few days.

DONE.

-- 
Alan Mackenzie (Nuremberg, Germany).

Message #59 received at 19867 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Alan Mackenzie <acm <at> muc.de>
Cc: Simon <turner25 <at> gmail.com>, 19867 <at> debbugs.gnu.org,
 Stefan Kangas <stefankangas <at> gmail.com>
Subject: Re: bug#19867: c++-mode indentation issues with C++1x initializer
 lists 
Date: Thu, 15 May 2025 20:43:15 +0200

30 apr. 2025 kl. 20.58 skrev Alan Mackenzie <acm <at> muc.de>:

> DONE.

Thank you!

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