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

[Simon]

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 );
    }
  
  }

}