refactor how we represent and store checkers using python as a demo

Add 2 classes: SyntasticChecker and SyntasticRegistry.

SyntasticChecker represents a checker. It holds funcrefs to the checker
func, the highlight regex func and a new `isAvailable()` func (that
essentially just checks if the checker exe is installed)

SyntasticRegistry is responsible for:
* loading checkers
* storing checkers
* fetching the checkers to use according to availability and the users
  settings

Motivation/benefits:
* in the current system only one checker can be loaded per filetype
* syntax checkers cant be "chained" together
* the system is hard to add features to since fundamental concepts like
  syntax checkers and location lists arent represented explicitly

Things left to do:
* add a call to g:SyntasticRegistry.CreateAndRegisterChecker() to all
  checkers
* add an `isAvailable` function to all checkers
* move all checkers into `syntax_checkers/filetype/checkername.vim` -
  g:SyntasticRegistry assumes this layout, and its a good idea anyway
  for consistency and it makes it easier for users to add their own
  checkers

Things to do after all of the above:
* add a LocationList class and move all the filtering functions onto it
* possibly add an Error class that wraps up each item in a loc list

Random notes:
* with the new system you can select the checkers to use with e.g.
    `let g:syntastic_python_checkers=['flake8', 'pylint']`
  This will try flake8 first, and if no errors are detected it will move
  onto pylint.

plugin/syntastic.vim

@@ -17,6 +17,8 @@ if exists("g:loaded_syntastic_plugin")
 endif
 let g:loaded_syntastic_plugin = 1
 
+runtime plugin/syntastic/*.vim
+
 let s:running_windows = has("win16") || has("win32")
 
 if !exists("g:syntastic_enable_signs")
@@ -103,6 +105,8 @@ if !exists("g:syntastic_loc_list_height")
     let g:syntastic_loc_list_height = 10
 endif
 
+let s:registry = g:SyntasticRegistry.Instance()
+
 command! SyntasticToggleMode call s:ToggleMode()
 command! SyntasticCheck call s:UpdateErrors(0) <bar> call s:Redraw()
 command! Errors call s:ShowLocList()
@@ -199,15 +203,22 @@ function! s:CacheErrors()
         "functions legally for filetypes like "gentoo-metadata"
         let fts = substitute(&ft, '-', '_', 'g')
         for ft in split(fts, '\.')
-            if SyntasticCheckable(ft)
-                let errors = SyntaxCheckers_{ft}_GetLocList()
+            let checkers = s:registry.getActiveCheckers(ft)
+            for checker in checkers
+                let errors = checker.getLocList()
+
+                if !empty(errors)
                     "keep only lines that effectively match an error/warning
                     let errors = s:FilterLocList({'valid': 1}, errors)
                     "make errors have type "E" by default
                     call SyntasticAddToErrors(errors, {'type': 'E'})
                     call extend(s:LocList(), errors)
+
+                    "only get errors from one checker at a time
+                    break
                 endif
             endfor
+        endfor
     endif
 endfunction
 
@@ -531,18 +542,7 @@ endfunction
 "check if a syntax checker exists for the given filetype - and attempt to
 "load one
 function! SyntasticCheckable(ft)
-    "users can just define a syntax checking function and it will override the
-    "syntastic default
-    if exists("*SyntaxCheckers_". a:ft ."_GetLocList")
-        return 1
-    endif
-
-    if !exists("g:loaded_" . a:ft . "_syntax_checker")
-        exec "runtime syntax_checkers/" . a:ft . ".vim"
-        let {"g:loaded_" . a:ft . "_syntax_checker"} = 1
-    endif
-
-    return exists("*SyntaxCheckers_". a:ft ."_GetLocList")
+    return s:registry.checkable(a:ft)
 endfunction
 
 "the args must be arrays of the form [major, minor, macro]

plugin/syntastic/checker.vim

@@ -0,0 +1,47 @@
+if exists("g:loaded_syntastic_checker")
+    finish
+endif
+let g:loaded_syntastic_checker=1
+
+let g:SyntasticChecker = {}
+
+" Public methods {{{1
+
+function! g:SyntasticChecker.New(args)
+    let newObj = copy(self)
+
+    let newObj._locListFunc = a:args['loclistFunc']
+    let newObj._isAvailableFunc = a:args['isAvailableFunc']
+    let newObj._filetype = a:args['filetype']
+    let newObj._name = a:args['name']
+
+    let newObj._highlightRegexFunc = get(a:args, 'highlightRegexFunc', '')
+
+    return newObj
+endfunction
+
+function! g:SyntasticChecker.filetype()
+    return self._filetype
+endfunction
+
+function! g:SyntasticChecker.name()
+    return self._name
+endfunction
+
+function! g:SyntasticChecker.getLocList()
+    return self._locListFunc()
+endfunction
+
+function! g:SyntasticChecker.getHighlightRegexFor(error)
+    if empty(self._highlightRegexFunc)
+        return []
+    endif
+
+    return self._highlightRegexFunc(error)
+endfunction
+
+function! g:SyntasticChecker.isAvailable()
+    return self._isAvailableFunc()
+endfunction
+
+" vim: set sw=4 sts=4 et fdm=marker:

plugin/syntastic/registry.vim

@@ -0,0 +1,80 @@
+if exists("g:loaded_syntastic_registry")
+    finish
+endif
+let g:loaded_syntastic_registry=1
+
+let g:SyntasticRegistry = {}
+
+" Public methods {{{1
+
+function! g:SyntasticRegistry.Instance()
+    if !exists('s:SyntasticRegistryInstance')
+        let s:SyntasticRegistryInstance = copy(self)
+        let s:SyntasticRegistryInstance._checkerMap = {}
+    endif
+
+    return s:SyntasticRegistryInstance
+endfunction
+
+function! g:SyntasticRegistry.CreateAndRegisterChecker(args)
+    let checker = g:SyntasticChecker.New(a:args)
+    let registry = g:SyntasticRegistry.Instance()
+    call registry.registerChecker(checker)
+endfunction
+
+function! g:SyntasticRegistry.registerChecker(checker)
+    let ft = a:checker.filetype()
+
+    if !has_key(self._checkerMap, ft)
+        let self._checkerMap[ft] = []
+    endif
+
+    call add(self._checkerMap[ft], a:checker)
+endfunction
+
+function! g:SyntasticRegistry.checkable(filetype)
+    return !empty(self.getActiveCheckers(a:filetype))
+endfunction
+
+function! g:SyntasticRegistry.getActiveCheckers(filetype)
+    let allCheckers = copy(self._checkersFor(a:filetype))
+
+    "only use checkers the user has specified
+    if exists("g:syntastic_" . a:filetype . "_checkers")
+        let whitelist = g:syntastic_{a:filetype}_checkers
+        call filter(allCheckers, "index(whitelist, v:val.name()) != -1")
+    endif
+
+    "only use available checkers
+    return filter(allCheckers, "v:val.isAvailable()")
+endfunction
+
+
+" Private methods {{{1
+
+function! g:SyntasticRegistry._checkersFor(filetype)
+    call self._loadCheckers(a:filetype)
+    if empty(self._checkerMap[a:filetype])
+        return []
+    endif
+
+    return self._checkerMap[a:filetype]
+endfunction
+
+function! g:SyntasticRegistry._loadCheckers(filetype)
+    if self._haveLoadedCheckers(a:filetype)
+        return
+    endif
+
+    exec "runtime! syntax_checkers/" . a:filetype . "/*.vim"
+
+    if !has_key(self._checkerMap, a:filetype)
+        let self._checkerMap[a:filetype] = []
+    endif
+endfunction
+
+function! g:SyntasticRegistry._haveLoadedCheckers(filetype)
+    return has_key(self._checkerMap, a:filetype)
+endfunction
+
+" vim: set sw=4 sts=4 et fdm=marker:

syntax_checkers/python/flake8.vim

@@ -5,7 +5,11 @@
 "             kstep <me@kstep.me>
 "
 "============================================================================
-function! SyntaxCheckers_python_GetHighlightRegex(i)
+function! SyntaxCheckers_python_flake8_IsAvailable()
+    return executable('flake8')
+endfunction
+
+function! SyntaxCheckers_python_flake8_GetHighlightRegex(i)
     if match(a:i['text'], 'is assigned to but never used') > -1
                 \ || match(a:i['text'], 'imported but unused') > -1
                 \ || match(a:i['text'], 'undefined name') > -1
@@ -21,11 +25,17 @@ function! SyntaxCheckers_python_GetHighlightRegex(i)
     return ''
 endfunction
 
-function! SyntaxCheckers_python_GetLocList()
+function! SyntaxCheckers_python_flake8_GetLocList()
     let makeprg = syntastic#makeprg#build({
                 \ 'exe': 'flake8',
-                \ 'args': g:syntastic_python_checker_args,
                 \ 'subchecker': 'flake8' })
     let errorformat = '%E%f:%l: could not compile,%-Z%p^,%E%f:%l:%c: %m,%W%f:%l: %m,%-G%.%#'
     return SyntasticMake({ 'makeprg': makeprg, 'errorformat': errorformat })
 endfunction
+
+call g:SyntasticRegistry.CreateAndRegisterChecker({
+    \ 'loclistFunc': function("SyntaxCheckers_python_flake8_GetLocList"),
+    \ 'highlightRegexFunc': function("SyntaxCheckers_python_flake8_GetHighlightRegex"),
+    \ 'filetype': 'python',
+    \ 'name': 'flake8',
+    \ 'isAvailableFunc': function("SyntaxCheckers_python_flake8_IsAvailable")} )

syntax_checkers/python/pyflakes.vim

@@ -6,7 +6,11 @@
 "             Parantapa Bhattacharya <parantapa@gmail.com>
 "
 "============================================================================
-function! SyntaxCheckers_python_GetHighlightRegex(i)
+function! SyntaxCheckers_python_pyflakes_IsAvailable()
+    return executable('pyflakes')
+endfunction
+
+function! SyntaxCheckers_python_pyflakes_GetHighlightRegex(i)
     if match(a:i['text'], 'is assigned to but never used') > -1
                 \ || match(a:i['text'], 'imported but unused') > -1
                 \ || match(a:i['text'], 'undefined name') > -1
@@ -22,16 +26,21 @@ function! SyntaxCheckers_python_GetHighlightRegex(i)
     return ''
 endfunction
 
-function! SyntaxCheckers_python_GetLocList()
+function! SyntaxCheckers_python_pyflakes_GetLocList()
     let makeprg = syntastic#makeprg#build({
                 \ 'exe': 'pyflakes',
                 \ 'args': g:syntastic_python_checker_args,
                 \ 'subchecker': 'pyflakes' })
     let errorformat = '%E%f:%l: could not compile,%-Z%p^,%E%f:%l:%c: %m,%E%f:%l: %m,%-G%.%#'
 
-    let errors = SyntasticMake({ 'makeprg': makeprg,
+    return SyntasticMake({ 'makeprg': makeprg,
                          \ 'errorformat': errorformat,
                          \ 'defaults': {'text': "Syntax error"} })
-
-    return errors
 endfunction
+
+call g:SyntasticRegistry.CreateAndRegisterChecker({
+    \ 'loclistFunc': function('SyntaxCheckers_python_pyflakes_GetLocList'),
+    \ 'highlightRegexFunc': function('SyntaxCheckers_python_pyflakes_GetHighlightRegex'),
+    \ 'filetype': 'python',
+    \ 'name': 'pyflakes',
+    \ 'isAvailableFunc': function('SyntaxCheckers_python_pyflakes_IsAvailable')} )

syntax_checkers/python/pylint.vim

@@ -4,7 +4,11 @@
 "Author:      Parantapa Bhattacharya <parantapa at gmail dot com>
 "
 "============================================================================
-function! SyntaxCheckers_python_GetLocList()
+function! SyntaxCheckers_python_pylint_IsAvailable()
+    return executable('pylint')
+endfunction
+
+function! SyntaxCheckers_python_pylint_GetLocList()
     let makeprg = syntastic#makeprg#build({
                 \ 'exe': 'pylint',
                 \ 'args': g:syntastic_python_checker_args. ' -f parseable -r n -i y',
@@ -18,5 +22,10 @@ endfunction
 function! s:MakeprgTail()
     return ' 2>&1 \| sed ''s_: \[\([RCW]\)_: \[W] \[\1_''' .
          \ ' \| sed ''s_: \[\([FE]\)_:\ \[E] \[\1_'''
-
 endfunction
+
+call g:SyntasticRegistry.CreateAndRegisterChecker({
+    \ 'loclistFunc': function('SyntaxCheckers_python_pylint_GetLocList'),
+    \ 'filetype': 'python',
+    \ 'name': 'pylint',
+    \ 'isAvailableFunc': function('SyntaxCheckers_python_pylint_IsAvailable')} )

syntax_checkers/python/python.vim

@@ -7,8 +7,11 @@
 " http://www.vim.org/scripts/download_script.php?src_id=1392
 "
 "============================================================================
+function! SyntaxCheckers_python_pyflakes_IsAvailable()
+    return executable('python')
+endfunction
 
-function! SyntaxCheckers_python_GetLocList()
+function! SyntaxCheckers_python_pyflakes_GetLocList()
     let l:path = shellescape(expand('%'))
     let l:cmd = "compile(open(" . l:path . ").read(), " . l:path . ", 'exec')"
     let l:makeprg = 'python -c "' . l:cmd . '"'
@@ -25,3 +28,9 @@ function! SyntaxCheckers_python_GetLocList()
 
     return SyntasticMake({ 'makeprg': l:makeprg, 'errorformat': l:errorformat })
 endfunction
+
+call g:SyntasticRegistry.CreateAndRegisterChecker({
+    \ 'loclistFunc': function('SyntaxCheckers_python_pyflakes_GetLocList'),
+    \ 'filetype': 'python',
+    \ 'name': 'python',
+    \ 'isAvailableFunc': function('SyntaxCheckers_python_pyflakes_IsAvailable')} )