Copy a line, comment it and replace a word in copied line

Question

Libraries evolve all the time and I often face the situation where after an update some function name have changed and they return errors in the updated version of the library.

It's easy to replace all the instances of a word by another however I would like to keep track of the old version by commenting the line containing the old function name, as follows:

original line (which raises an error)

a line with old code

after:

// a line with old code
a line with new code

So far I did it manually: yy + p to copy the line, :%s/\<old code\>/new code/gc to replace with confirmation, then in the line I want to comment, esc + I + // + esc and I use the repeat command . to add my comment to the other appropriate lines. This is fine for few dozen lines of code but not for hundreds of lines, so I'd like to make this less manual.

The steps to be taken would be:

• search lines with the old code (old function name)
• copy the lines
• comment the original lines: add // (or other) in front of the line
• replace the old code in the uncommented line

Can this be done in a "vim-apprentice" friendly manner? More advanced methods will be welcome too.

Answer 1

Script

func! CoRep (pat, ...)
    let line_loc    = search (a:pat, 'nw')
    let line        = getline (line_loc)

    call setline (line_loc, '// '.line)

    let pair = 0
    while pair < a:0
        let pat = a:000[pair]
        let sub = a:000[pair+1]

        let line = substitute (line, pat, sub, '')
        let pair = pair + 2
    endwhile

    call append (line_loc, line)
endf

The arguments are:

1. First argument is a line pattern. Line is being searched down the cursor, wrapping to the top.
2. Other arguments are pairs of pattern and substitution strings (up to 9 pairs). Substitutions are applied to the entire line, in the same order, and stop at the first match.

Usage

Call from the command mode or map to leader-r (or any other key).

nnoremap <leader>r :CoRep 
command! -nargs=+ CoRep : call CoRep (<f-args>)

Update

Applies substitution to all matched lines at once

func! CoRepGlob (pat, ...)
    let origin = getcurpos()
    call cursor (1, 0)

    while 1
        let line_loc = search (a:pat, 'cW')
        if line_loc == 0
            break
        endif

        let line = getline (line_loc)
        call setline (line_loc, '// '.line)

        let pair = 0
        while pair < a:0
            let pat = a:000[pair]
            let sub = a:000[pair+1]

            let line = substitute (line, pat, sub, '')
            let pair = pair + 2
        endwhile

        call append (line_loc, line)
        call cursor (line_loc + 2, 0)
    endwhile

    call setpos ('.', origin)
endf

Answer 2

You can use capture groups in your replace and replace the original line with two lines. Here is an example with python changing print statements to have parentheses (python 2 --> python 3)

Original text:

print 'woo'

print 'woosh'

print 'wee'

print 'weesh'

Command:

:%s/print \(.*\)/#print \1 \rprint(\1)/g

Result:

#print 'woo' 
print('woo')

#print 'woosh' 
print('woosh')

#print 'wee' 
print('wee')

#print 'weesh' 
print('weesh')

If the command you are trying to replace is long this may be a poor solution

Answer 3

This is a very rough function, that should do what you want:

    " <range>CopyAndComment char/line/match/replace
    com! -range=% -nargs=+ CopyAndComment let wsv=winsaveview()|<line1>,<line2>call s:CopyAndComment(<q-args>)|call winrestview(wsv)

    function! s:CopyAndComment(args) range
        let arg=split(a:args, '/')
        if len(arg) > 4 || len(arg) < 3
            echoerr "Usage: <range>CopyAndComment char/line/match/replace"
            return
        endif
        if len(arg) == 3
            let com = split(getbufvar("%", '&cms', '# %s'), '%s')[0]
            call insert(arg, com, 0)
        endif
        let arg=map(arg, 'escape(v:val, "/#")')
        let s_replace_arg = '\="'.arg[0]. '".submatch(0).'.'"\n"'.'.substitute(submatch(0),"'.arg[2].'","'.arg[3].'","g")'
        exe a:firstline.','.a:lastline.'g/'.arg[1].'/s#.*#'.s_replace_arg.'#g'
    endfunc

This defines a command :CopyAndComment that takes one argument of the form comment/linematch/search/replace and it will use the linematch regex to find matching lines to copy. In each matching line, it will copy the line, add a comment char to the original line, and replace the newly created line according to the search/replace argument. You can leave out the firsts comment char, in which case the function will take the value from the &commentstring option and use that (only the first half of it) which defaults to /*.

Additionally, the command takes a range argument, so if you only want to replace in the lines 1-5, you would call it like 1,5CopyAndComment \#/line/foo/bar. If no range is given, it defaults to the whole file.

Internally the function works by sticking together a :g command with a :s command doing all those replacements. However quoting is really ugly, it took my a couple of minutes to twist my brain until I got that correct.

For your example you would then call it as :CopyAndComment \/\/ /line/old/new (note you have to escape the comment chars // as this is used as delimiter)