tracing: Add vim script to enable folding for function_graph traces

" Enable folding for ftrace function_graph traces.

"

" To use, :source this file while viewing a function_graph trace, or use vim's

" -S option to load from the command-line together with a trace.  You can then

" use the usual vim fold commands, such as "za", to open and close nested

" functions.  While closed, a fold will show the total time taken for a call,

" as would normally appear on the line with the closing brace.  Folded

" functions will not include finish_task_switch(), so folding should remain

" relatively sane even through a context switch.

"

" Note that this will almost certainly only work well with a

" single-CPU trace (e.g. trace-cmd report --cpu 1).

function! FunctionGraphFoldExpr(lnum)

  let line = getline(a:lnum)

  if line[-1:] == '{'

    if line =~ 'finish_task_switch() {$'

      return '>1'

    endif

    return 'a1'

  elseif line[-1:] == '}'

    return 's1'

  else

    return '='

  endif

endfunction

function! FunctionGraphFoldText()

  let s = split(getline(v:foldstart), '|', 1)

  if getline(v:foldend+1) =~ 'finish_task_switch() {$'

    let s[2] = ' task switch  '

  else

    let e = split(getline(v:foldend), '|', 1)

    let s[2] = e[2]

  endif

  return join(s, '|')

endfunction

setlocal foldexpr=FunctionGraphFoldExpr(v:lnum)

setlocal foldtext=FunctionGraphFoldText()

setlocal foldcolumn=12

setlocal foldmethod=expr