Toggle hidden attribute to highlight syntax in VIM

Question

I currently have a syntax file that parses a log file very similar to the following [this is for syslog]:

syn match   syslogText  /.*$/
syn match   syslogFacility  /.\{-1,}:/  nextgroup=syslogText skipwhite
syn match   syslogHost  /\S\+/  nextgroup=syslogFacility,syslogText skipwhite
syn match   syslogDate  /^.\{-}\d\d:\d\d:\d\d/  nextgroup=syslogHost skipwhite

Using a map, I would like to switch whether a given group is hidden (say, syslogHost) or not. Is there a way to do something like the following pseudocode:

map <leader>ch :syn match syslogHost conceal!

and thereby switch the definition of syslogHost between:

syn match   syslogHost  /\S\+/  nextgroup=syslogFacility,syslogText skipwhite

and

syn match   syslogHost  /\S\+/  nextgroup=syslogFacility,syslogText skipwhite conceal

Thank.

Answer 1

I think the only way to do this is with a function:

map <leader>ch :call ToggleGroupConceal('sysLogHost')<CR>

function! ToggleGroupConceal(group)
    " Get the existing syntax definition
    redir => syntax_def
    exe 'silent syn list' a:group
    redir END
    " Split into multiple lines
    let lines = split(syntax_def, "\n")
    " Clear the existing syntax definitions
    exe 'syn clear' a:group
    for line in lines
            " Only parse the lines that mention the desired group
            " (so don't try to parse the "--- Syntax items ---" line)
        if line =~ a:group
                    " Get the required bits (the syntax type and the full definition)
            let matcher = a:group . '\s\+xxx\s\+\(\k\+\)\s\+\(.*\)'
            let type = substitute(line, matcher, '\1', '')
            let definition = substitute(line, matcher, '\2', '')
                    " Either add or remove 'conceal' from the definition
            if definition =~ 'conceal'
                let definition = substitute(definition, ' conceal\>', '', '')
                exe 'syn' type a:group definition
            else
                exe 'syn' type a:group definition 'conceal'
            endif
        endif
    endfor
endfunction

Answer 2

Here is a modification for the original version of @DrAl, which works with both match syntactic groups and regions.

" function to toggle conceal attribute for a syntax group
function! ToggleGroupConceal(group)
    " Get the existing syntax definition for specified group
    redir => syntax_def
    exe 'silent syn list' a:group
    redir END
    " Split into multiple lines
    let lines = split(syntax_def, "\n")
    " Clear the existing syntax definitions
    exe 'syn clear' a:group
    for line in lines
        " Only parse lines that contain the desired group definition
        " (skip "--- Syntax items ---" line and 'links to' lines)
        if line =~ a:group
            "echo 'line = ' . line
            " need to handle match and region types separately since type
            " isn't specified for regions in the syn list output like it is
            " for matches.
            let type = substitute(line, '\v' . a:group . '\s+xxx\s+(\k+)\s+(.*)', '\1', '')
            if type == 'match'
                " get args as everything after 'xxx match'
                let args = substitute(line, '\v' . a:group . '\s+xxx\s+(\k+)\s+(.*)', '\2', '')
            else
                " get args as everything after 'xxx'
                let args = substitute(line, '\v' . a:group . '\s+xxx\s+(.*)', '\1', '')
                if args =~ 'start' && args =~ 'end'
                    let type = 'region'
                endif
            endif
            "echo '    type = ' . type
            "echo '    args = ' . args
            " Either add or remove 'conceal' from the definition
            if args =~ 'conceal'
                exe 'syn' type a:group substitute(args, ' conceal', '', '')
            else
                exe 'syn' type a:group args 'conceal'
            endif
        endif
    endfor
endfunction

Answer 3

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