[vim] Misc improvements to vimrc

* More verbose comments for obscure features
* Shorten .viminfo memory for privacy/security purposes
* Setup .viminfo for neovim
* Remove unused Q mapping
* Change ReflowParagraph() to gwip -> conserve cursor position
* Fix trailing spaces cleanup so that it doesn't pollute the undo tree
* Fix header/source swap function to work with both C and C++

aliases

@@ -24,6 +24,9 @@ fi
 if which nvim > /dev/null 2>&1; then
     alias vim='nvim'
 fi
+if [ -f "$HOME/howto/how_to" ]; then
+    alias howto="vim $HOME/howto/how_to"
+fi
 case $(uname -s) in
     Arch)
         alias redwm='cd ~/aur/dwm-git; updpkgsums; makepkg -fi --noconfirm; killall dwm'

vimrc

@@ -58,6 +58,7 @@ if has("unix") || has("mac")
 
     Plugin 'tikhomirov/vim-glsl'
     Plugin 'jamessan/vim-gnupg'
+    Plugin 'romainl/vim-cool'
     Plugin 'machakann/vim-highlightedyank'
     let g:highlightedyank_highlight_duration = 200
     "[Needed only with old vim versions]"
@@ -77,9 +78,10 @@ set number
 set relativenumber
 "[Hide/show the white-space and more invisible symbols]"
 set list
-set listchars=nbsp:¬,trail:-
-"set listchars+=tab:│\ ,
-set listchars+=tab:▸\ ,
+set listchars=tab:▸\ ,nbsp:¬,trail:-
+"             |       |      + Trailing spaces
+"             |       + Non breakable spaces
+"             + Tabulations: `tab xy`, x: first char, y: following chars
 set nojoinspaces
 "[Indent & Tab/mode-line settings]"
 set breakindent
@@ -106,7 +108,6 @@ set textwidth=0
 set modeline
 set modelines=1
 
-set history=200		" keep 200 lines of command line history
 set ruler		" show the cursor position all the time
 set showcmd		" display incomplete commands
 set laststatus=2
@@ -115,6 +116,8 @@ set noshowmode
 "[Command mode autocompletion]"
 set wildmenu
 set wildmode=longest:full,full
+"            `------------|---- First complete till longest common string, open wildmenu
+"                         `---- Then, complete next full match
 
 set ttimeout		" time out for key codes
 set ttimeoutlen=100	" wait up to 100ms after Esc for special key
@@ -126,6 +129,20 @@ set history=1000
 set nowritebackup
 set undolevels=5000
 
+"[Setup history file]"
+set viminfo=%,<0,'10,/16,:16,h,f0
+"           | |  |   |   |   | + file marks 0-9,A-Z 0=NOT stored
+"           | |  |   |   |   + disable 'hlsearch' loading viminfo
+"           | |  |   |   + command-line history saved
+"           | |  |   + search history saved
+"           | |  + files marks saved
+"           | + lines saved each register (old name for <, vi6.2): NOT STORED
+"           + save/restore buffer list
+if !has('nvim')
+    "[Declutter $HOME]"
+    set viminfo+=n~/.vim/cache/.viminfo
+endif
+
 " Show @@@ in the last line if it is truncated.
 set display=truncate
 "[Splitting rules]"
@@ -202,8 +219,6 @@ nnoremap <leader>o o<Esc>
 nnoremap <leader>O O<Esc>
 "[Clear search highlights]"
 nnoremap // :nohlsearch<CR>
-" Don't use Ex mode, use Q for formatting.
-map Q gq
 "[Reflow current paragraph]"
 "[http://stevelosh.com/blog/2010/09/coming-home-to-vim/]"
 nnoremap <silent> <leader>q :call ReflowParagraph()<CR>
@@ -242,14 +257,15 @@ endif
 "[Reflow current paragraph]"
 function! ReflowParagraph()
     let l:view = winsaveview()
-    normal gqip
+    normal gwip
     call winrestview(l:view)
 endfunction
 "[Remove tabs and spaces at the end of lines]"
 function! DeleteTrailingTWS()
-    if &ft =~ 'diff'
+    "[Do not clean up trailing spaces in binary mode or in diff files]"
+    if &binary || &ft =~ 'diff'
         return
-    end
+    endif
     let l:view = winsaveview()
     silent %s/[ \t]*$//g
     silent %s/\s\+$//ge
@@ -268,8 +284,12 @@ endfunction
 function! SwapExtension()
     let [rest, ext] = [expand('%:r'), expand('%:e')]
     if ext ==? 'h'
-        let ext = 'cpp'
-    elseif ext ==? 'cpp'
+        if filereadable(rest . '.c')
+            let ext = 'c'
+        elseif filereadable(rest . '.cpp')
+            let ext = 'cpp'
+        endif
+    elseif ext ==? 'cpp' || ext ==? 'c'
         let ext = 'h'
     "swap between vertex and fragment shader"
     elseif ext ==? 'vsh'
@@ -283,10 +303,9 @@ endfunction
 " Only do this part when compiled with support for autocommands.
 if has("autocmd")
 
-    " Enable file type detection.
-    " Use the default filetype settings, so that mail gets 'tw' set to 72,
-    " 'cindent' is on in C files, etc.
-    " Also load indent files, to automatically do language-dependent indenting.
+    " Enable file type detection. Use the default filetype settings, so that
+    " mail gets 'tw' set to 72, 'cindent' is on in C files, etc. Also load
+    " indent files, to automatically do language-dependent indenting.
     " Revert with ":filetype off".
     filetype plugin indent on
 
@@ -300,16 +319,20 @@ if has("autocmd")
         " (happens when dropping a file on gvim) and for a commit message (it's
         " likely a different one than last time).
         autocmd BufReadPost *
-            \ if line("'\"") >= 1 && line("'\"") <= line("$") && &ft !~# 'commit'
-            \ |   exe "normal! g`\""
-            \ | endif
+            \ if line("'\"") >= 1 && line("'\"") <= line("$") && &ft !~# 'commit' |
+                \ exe "normal! g`\"" |
+            \ endif
 
     augroup END
-    "
-    "[Do not clean up trailing spaces in binary mode]"
-    if !&binary
-        autocmd BufWritePre * call DeleteTrailingTWS()
-    endif
+
+    "[Try not to pollute the undo tree (https://vi.stackexchange.com/a/13401)]"
+    autocmd BufWritePre *
+        \ try |
+            \ undojoin |
+        \ catch /^Vim\%((\a\+)\)\=:E790/ |
+        \ finally |
+            \ call DeleteTrailingTWS() |
+        \ endtry
 
     if has("unix") || has("mac")
         autocmd BufWritePost * call ChangeScriptMode()