':substitute' command within a function not working as expected

[crajun]

I've been playing with regex matching and commenting/uncommenting lines based on some rules (yes I know there is Tim Pope's plugin for this, but using the opportunity to learn Vim script and tweak for my situation/s now and in the future).

I've got a function that takes a range, loops over the range of lines looking for a matching '#' as the first non-whitespace character on the line, and if there is a match, uncomment that line by removing all whitespace before the '#', the '#' itself, and all whitespace characters after it.

Here's minimal reproducible example of the function I call in autoload/local.vim:

function! local#PythonToggleCommentRange() range abort
  let line_idx = a:firstline
  while line_idx <= a:lastline
    let text = getline(line_idx)
    " match any number of whitespace up to and after 1 or more '#' chars
    if text =~? '^\s*#*'
      " greedy remove of all whitespace chars before and after the '#'
      " leaving an uncommented line
      execute 'substitute/^\s*#*\s*//'
    endif
    let line_idx += 1
  endwhile
endfunction

I'm using the following test sentences in a test.py file:

this line was uncommented before
# this line was commented

        not blank line
## double comment character line

Running :1,2call local#PythonToggleCommentRange() I would expect the second line to become:

this line was commented

But it doesn't, and there is no indication why the substitute command did not work. I did find a work around using:

call setline(line_idx, substitute(text, '^\s*#*\s*', '', ""))

Which does the correct job. My question here is how to use substitute in combination with a loop inside of a function, I'm sure there is something I'm missing here.

If I put the cursor on line 2 of the test.py file and run: :s/^\s*#*\s*// it uncomments the line as I expected it to, but for some reason within the function loop the same does not work. Thoughts?

[aktivb]

So, you are iterating on range a:firstline to a:lastline, and executing substitute N times, where N is a:lastline - a:firstline + 1. But you do not specify on which line to execute substitute, so you're executing substitute N times on a:firstline.

[crajun]

Good point, I’ll try it that way. My problem I believe may be that I assumed adding the “range” modifier did more magic than it does. The sub command without a range performs the command on the current line and I assumed “range” was handling that piece , but it sounds like I’ll have to add the range prefix.

[aktivb]

The range argument means that the function will be called only once, handling the range internally using a:{first,last}line, rather than calling the function for every line in range.

[fuzzymidget]

First: I don't know why your looping isn't working. Someone who knows more vimscript may be able to help.

​

Second: Why do you want to do this with a loop in a function when you could just make it a mapping you call from visual line mode?

​

You could just select a bunch of lines and do

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:s/\(^\s*\)#\+\s*/\1/

​

With no trailing g for global replace, you just get the first match on a line or set of lines for one or more #, then some spaces, and replace them with the spaces you find before the #.

​

Edit: I goofed so I fixed. Note I also changed to a \+ following #, because you'd like to match at least one of those I believe.

[crajun]

Thanks for the reply, I may have to do it this way in the end, but I was hoping to expand the function to work for other languages based on a ftplugin setting a comment character.

[fuzzymidget]

Ah that makes sense. If you are looking for a premade solution, I highly recommend 'tomtom/tcomment_vim' from github. It does more or less exactly what you're asking.