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pythonvimidemultilinefolding

Python multi-line strings breaks Vim's indent folding

Python's string-literal juxtaposition makes multi-line strings much easier and prettier to write, but when I'm four or five indents deep and want to use the entire row (leading whitespace does not matter), Vim's foldmethod=indent breaks down.

For example:

def getQuotation():
    print "Fetching quotation from the absolutely useless function."
    return ("Four score and seven years ago our fathers brought forth, "
"upon this continent, a new nation, conceived in liberty, and dedicated "
"to the proposition that \"all men are created equal\"")

should be folded as this:

def getQuotation():
+--  4 lines: print "Fetching quotation from the absolutely useless function."--

but instead I get this:

def getQuotation():
+--  2 lines: print "Fetching quotation from the absolutely useless function."--
"upon this continent, a new nation, conceived in liberty, and dedicated "
"to the proposition that \"all men are created equal\"")

I tried setting foldignore=\", but to no avail. Vim's help foldignore offers this to say on the subject:

Used only when 'foldmethod' is "indent". Lines starting with characters in 'foldignore' will get their fold level from surrounding lines. White space is skipped before checking for this character.

Is there something obvious that I'm missing, or will I have to resort to foldmethod=expr, base the foldlevel on the indent, and except the corner cases myself?

EDIT: I've made at least some headway; it turns out that if I add a non-empty line after the strings and "refresh" the indent with set fdm=indent, then the block folds as it's supposed to. Even an empty comment (#) is enough.

Solution

  • Is there something obvious that I'm missing, or will I have to resort to foldmethod=expr, base the foldlevel on the indent, and except the corner cases myself?

    Short answer: you can't do this with foldmethod=indent, but I found something you can use with foldmethod=expr, so no need to reinvent the wheel. See the long answer.

    Long answer

    Just a brief review of how foldmethod=indent works...

    • Look for text shifted shiftwidth with whitespace from the edge of the page
    • Insert a new foldlevel
    • De-indenting takes you down foldlevels

    Since the text you have is justified at the edge of the screen, anything involving shiftwidth is eventually broken unless you hack it up as you did.

    I looked at several different .vimrc configurations before I found something that would work. For a cleaner solution than foldmethod=indent, use foldmethod=expr with the ~/.vimrc I have below. I found it in jneb's bitbucket python-fold repo

    As a test, I built a few more cases into your example...

    class testclass(object):
    def __init__(self):
        self.testit = None
    def __repr__(self):
        return "guacamole"

def foobarme():
    assert False
    return 42

def getQuotation():
    print "Fetching quotation from the absolutely useless function."
    return ("Four score and seven years ago our fathers brought forth, "
"upon this continent, a new nation, conceived in liberty, and dedicated "
"to the proposition that \"all men are created equal\"")

    Using python-fold at the bottom of my ~/.vimrc yields:

    jneb_folded

    And when I hit zR to unfold:

    jneb_unfolded

    FYI, I use Dmitry Vasiliev's python.vim in ~/.vim/syntax/python.vim for python syntax highlights.

    I copied jneb's vim script below in case the bitbucket repo disappears...

    " Fold routines for python code, version 3.2
" Source: http://www.vim.org/scripts/script.php?script_id=2527
" Last Change: 2009 Feb 25
" Author: Jurjen Bos
" Bug fixes and helpful comments: Grissiom, David Froger, Andrew McNabb

" Principles:
" - a def/class starts a fold
" a line with indent less than the previous def/class ends a fold
" empty lines and comment lines are linked to the previous fold
" comment lines outside a def/class are never folded
" other lines outside a def/class are folded together as a group
" for algorithm, see bottom of script

" - optionally, you can get empty lines between folds, see (***)
" - another option is to ignore non-python files see (**)
" - you can also modify the def/class check,
"    allowing for multiline def and class definitions see (*)

" Note for vim 7 users:
" Vim 6 line numbers always take 8 columns, while vim 7 has a numberwidth variable
" you can change the 8 below to &numberwidth if you have vim 7,
" this is only really useful when you plan to use more than 8 columns (i.e. never)

" Note for masochists trying to read this:
" I wanted to keep the functions short, so I replaced occurences of
" if condition
"     statement
" by
" if condition | statement
" wherever I found that useful

" (*)
" class definitions are supposed to ontain a colon on the same line.
" function definitions are *not* required to have a colon, to allow for multiline defs.
" I you disagree, use instead of the pattern '^\s*\(class\s.*:\|def\s\)'
" to enforce : for defs:                     '^\s*\(class\|def\)\s.*:'
" you'll have to do this in two places.
let s:defpat = '^\s*\(@\|class\s.*:\|def\s\)'

" (**) Ignore non-python files
" Commented out because some python files are not recognized by Vim
"if &filetype != 'python'
"    finish
"endif

setlocal foldmethod=expr
setlocal foldexpr=GetPythonFold(v:lnum)
setlocal foldtext=PythonFoldText()

function! PythonFoldText()
  let fs = v:foldstart
  while getline(fs) =~ '^\s*@' | let fs = nextnonblank(fs + 1)
  endwhile
  let line = getline(fs)
  let nnum = nextnonblank(fs + 1)
  let nextline = getline(nnum)
  "get the document string: next line is ''' or """
  if nextline =~ "^\\s\\+[\"']\\{3}\\s*$"
      let line = line . " " . matchstr(getline(nextnonblank(nnum + 1)), '^\s*\zs.*\ze$')
  "next line starts with qoutes, and has text
  elseif nextline =~ "^\\s\\+[\"']\\{1,3}"
      let line = line." ".matchstr(nextline, "^\\s\\+[\"']\\{1,3}\\zs.\\{-}\\ze['\"]\\{0,3}$")
  elseif nextline =~ '^\s\+pass\s*$'
    let line = line . ' pass'
  endif
  "compute the width of the visible part of the window (see Note above)
  let w = winwidth(0) - &foldcolumn - (&number ? 8 : 0)
  let size = 1 + v:foldend - v:foldstart
  "compute expansion string
  let spcs = '................'
  while strlen(spcs) < w | let spcs = spcs . spcs
  endwhile
  "expand tabs (mail me if you have tabstop>10)
  let onetab = strpart('          ', 0, &tabstop)
  let line = substitute(line, '\t', onetab, 'g')
  return strpart(line.spcs, 0, w-strlen(size)-7).'.'.size.' lines'
endfunction

function! GetBlockIndent(lnum)
    " Auxiliary function; determines the indent level of the surrounding def/class
    " "global" lines are level 0, first def &shiftwidth, and so on
    " scan backwards for class/def that is shallower or equal
    let ind = 100
    let p = a:lnum+1
    while indent(p) >= 0
        let p = p - 1
        " skip empty and comment lines
        if getline(p) =~ '^$\|^\s*#' | continue
        " zero-level regular line
        elseif indent(p) == 0 | return 0
        " skip deeper or equal lines
        elseif indent(p) >= ind || getline(p) =~ '^$\|^\s*#' | continue
        " indent is strictly less at this point: check for def/class
        elseif getline(p) =~ s:defpat && getline(p) !~ '^\s*@'
            " level is one more than this def/class
            return indent(p) + &shiftwidth
        endif
        " shallower line that is neither class nor def: continue search at new level
        let ind = indent(p)
    endwhile
    "beginning of file
    return 0
endfunction

" Clever debug code, use to display text for a given moment the statement is executed:
" call PrintIfCount(6, "Line: ".a:lnum.", indent: ".ind.", previous indent: ".pind)
let s:counter=0
function! PrintIfCount(n,t)
    "Print text the nth time this function is called
    let s:counter = s:counter+1
    if s:counter==a:n | echo a:t
    endif
endfunction

function! GetPythonFold(lnum)
    " Determine folding level in Python source (see "higher foldlevel theory" below)
    let line = getline(a:lnum)
    let ind = indent(a:lnum)
    " Case D***: class and def start a fold
    " If previous line is @, it is not the first
    if line =~ s:defpat && getline(prevnonblank(a:lnum-1)) !~ '^\s*@'
        " let's see if this range of 0 or more @'s end in a class/def
        let n = a:lnum
        while getline(n) =~ '^\s*@' | let n = nextnonblank(n + 1)
        endwhile
        " yes, we have a match: this is the first of a real def/class with decorators
        if getline(n) =~ s:defpat
            return ">".(ind/&shiftwidth+1)
        endif
    " Case E***: empty lines fold with previous
    " (***) change '=' to -1 if you want empty lines/comment out of a fold
    elseif line == '' | return '='
    endif
    " now we need the indent from previous
    let p = prevnonblank(a:lnum-1)
    while p>0 && getline(p) =~ '^\s*#' | let p = prevnonblank(p-1)
    endwhile
    let pind = indent(p)
    " If previous was definition: count as one level deeper
    if getline(p) =~ s:defpat && getline(prevnonblank(a:lnum - 1)) !~ '^\s*@'
        let pind = pind + &shiftwidth
    " if begin of file: take zero
    elseif p==0 | let pind = 0
    endif
    " Case S*=* and C*=*: indent equal
    if ind>0 && ind==pind | return '='
    " Case S*>* and C*>*: indent increase
    elseif ind>pind | return '='
    " All cases with 0 indent
    elseif ind==0
        " Case C*=0*: separate global code blocks
        if pind==0 && line =~ '^#' | return 0
        " Case S*<0* and S*=0*: global code
        elseif line !~'^#'
            " TODO: here we need to check GetBlockIndent(a:lnum) for version 3.3
            " Case S*<0*: new global statement if/while/for/try/with
            if 0<pind && line!~'^else\s*:\|^except.*:\|^elif.*:\|^finally\s*:' | return '>1'
            " Case S*=0*, after level 0 comment
            elseif 0==pind && getline(prevnonblank(a:lnum-1)) =~ '^\s*#' | return '>1'
            " Case S*=0*, other, stay 1
            else | return '='
            endif
        endif
        " Case C*<0= and C*<0<: compute next indent
        let n = nextnonblank(a:lnum+1)
        while n>0 && getline(n) =~'^\s*#' | let n = nextnonblank(n+1)
        endwhile
        " Case C*<0=: split definitions
        if indent(n)==0 | return 0
        " Case C*<0<: shallow comment
        else | return -1
        end
    endif
    " now we really need to compute the actual fold indent
    " do the hard computation
    let blockindent = GetBlockIndent(a:lnum)
    " Case SG<* and CG<*: global code, level 1
    if blockindent==0 | return 1
    endif
    " now we need the indent from next
    let n = nextnonblank(a:lnum+1)
    while n>0 && getline(n) =~'^\s*#' | let n = nextnonblank(n+1)
    endwhile
    let nind = indent(n)
    " Case CR<= and CR<>
    endif
    if line =~ '^\s*#' && ind>=nind | return -1
    " Case CR<<: return next indent
    elseif line =~ '^\s*#' | return nind / &shiftwidth
    " Case SR<*: return actual indent
    else | return blockindent / &shiftwidth
    endif
endfunction

" higher foldlevel theory
" There are five kinds of statements: S (code), D (def/class), E (empty), C (comment)

" Note that a decorator statement (beginning with @) counts as definition,
" but that of a sequence of @,@,@,def only the first one counts
" This means that a definiion only counts if not preceded by a decorator

" There are two kinds of folds: R (regular), G (global statements)

" There are five indent situations with respect to the previous non-emtpy non-comment line:
" > (indent), < (dedent), = (same); < and = combine with 0 (indent is zero)
" Note: if the previous line is class/def, its indent is interpreted as one higher

" There are three indent situations with respect to the next (non-E non-C) line:
" > (dedent), < (indent), = (same)

" Situations (in order of the script):
" stat  fold prev   next
" SDEC  RG   ><=00  ><=
" D     *    *      *     begin fold level if previous is not @: '>'.ind/&sw+1
" E     *    *      *     keep with previous: '='
" S     *    =      *     stays the same: '='
" C     *    =      *     combine with previous: '='
" S     *    >      *     stays the same: '='
" C     *    >      *     combine with previous: '='
" C     *    =0     *     separate blocks: 0
" S     *    <0     *     becomes new level 1: >1 (except except/else: 1)
" S     *    =0     *     stays 1: '=' (after level 0 comment: '>1')
" C     *    <0     =     split definitions: 0
" C     *    <0     <     shallow comment: -1
" C     *    <0     >     [never occurs]
" S     G    <      *     global, not the first: 1
" C     G    <      *     indent isn't 0: 1
" C     R    <      =     foldlevel as computed for next line: -1
" C     R    <      >     foldlevel as computed for next line: -1
" S     R    <      *     compute foldlevel the hard way: use function
" C     R    <      <     foldlevel as computed for this line: use function