Working with line continuations (\).

Question

When working in the C language, sometimes you have to write multi line macros like the following.

#define SOME_FUNCTION_LIKE_MACRO(a,b)     \
   foo(a);                                \
   bar(b);                                \
   baz(a+b);

Typically, after a few iterations of editing your code, the backslashes end up unaligned like:

#define SOME_FUNCTION_LIKE_MACRO(a,b)             \
   foo(a);                 \
   bar(b);                                  \
   baz(a+b);

And it drives me crazy. I always end up wasting a lot of time manually aligning them.

Is there a plugin/mapping/function/whatever for automatically aligning the line continuation characters? Something like select lines in visual line mode, hit a key combination and voila, you have aligned backslashes at the end.

Answer 1

Plugin vim-lion

by Tom McDonald

Install and add following line to your vimrc:

let g:lion_squeeze_spaces = 1

Now you can change

#define SOME_FUNCTION_LIKE_MACRO(a,b)             \
   foo(a);                 \
   bar(b);                                  \
   baz(a+b);

by pressing glip\ to

#define SOME_FUNCTION_LIKE_MACRO(a,b) \
   foo(a);                            \
   bar(b);                            \
   baz(a+b);

Alternatives to vim-lion

Vim-lion is a very small plugin (190 sloc) and has a few limitations (see example given by the plugin Align). There are more feature rich alternatives:

• vim-easy-align (#4520) by Junegunn Choi. It has no default rule for \. However, it is not difficult to define one:

  let g:easy_align_delimiters = {
    \ '\': {
    \     'pattern': '\\$',
    \ },
    \ }
  

  With the default mapping ga you can re-align your code now with gaip\. Note, ga overwrites a builtin mapping (:h ga) (and competes with vim-characterize). The choice gl of vim-lion might be better:

  xmap gl <Plug>(EasyAlign)
  nmap gl <Plug>(EasyAlign)
  

• Tabular by Matt Wozniski. By default no mappings exist, only the command :Tab[ularize] /\\$<CR>. Note that you do not need a visual selection or to specify a range before :[range]Tab[ularize] (but you can), Tabular tries to be smart to figure out the correct range (:h :Tabularize). See e.g. this vimcast for an introduction and suggestions for mappings. You can also use following from the plugin Align

  if exists(":Tabularize")
    nmap <Leader>tml :Tabularize /\\$<CR>
    vmap <Leader>tml :Tabularize /\\$<CR>
  endif
  

• Align (#294) by DrChip (Charles Campbell) with default mapping \tml. From the documentation:

  Original: illustrates aligning multi-line continuation marks

  one \
  two three \
  four five six \
  seven \\ \
  eight \nine \
  ten \
  

  Becomes:

  one           \
  two three     \
  four five six \
  seven \\      \
  eight \nine   \
  ten           \
  

  Note, vim-lion struggles with this example. My vim-easy-align and Tabular proposals work fine.

I personally use vim-easy-align with the mapping gl.

Answer 2

I came up with this a few minutes after asking the question here.

You hit if you want to add backslashes at the end of a line, or multiple selected lines. You hit \ if you want to align all backslashes in the whole file or in the selected lines.

" Aligns backslash characters at the end of lines. 
" Useful when writing multiline macros or multiline strings.
function AlignBackslash()
  :silent! s@\s\+\\$@ \\@
  :silent! s/s*\\$/\=repeat(' ', 80-col('.')).'\'
  :let @/ = ""
endfunction

function RemoveDuplicateBackslash()
  :silent! s/\\\\$/\\/g
endfunction

" In normal mode align the whole file. 
nmap \\ mxggVG:call RemoveDuplicateBackslash()<cr>ggVG:call AlignBackslash()<cr>'x

" In visual select mode align selected lines.
vmap \\ :call RemoveDuplicateBackslash()<cr>gv:call AlignBackslash()<cr>

" Insert backslash at the end of current line and align it
nmap <c-\> A\<esc>:call AlignBackslash()<cr>

" Insert backslash at the end of selected lines and align them
vmap <c-\> :norm A\<esc>gv:call AlignBackslash()<cr>