Add linting with eslint in NeoVim, with a few bugs.

.gitignore

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+/init.vim

LICENSE

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+Copyright (c) 2016, w0rp <devw0rp@gmail.com>
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

README.md

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+# ALE - Asynchronous Lint Engine
+
+ALE (Asynchronous Lint Engine) is a plugin for providing linting in NeoVim
+and Vim 8 while you edit your text files.
+
+ALE makes use of NeoVim and Vim 8 job control functions and timers to
+run linters on the contents of text buffers and return errors as
+text is changed in Vim. This allows for displaying warnings and
+errors in files being edited in Vim before file has been saved
+back to disk.
+
+**NOTE:** This Vim plugin has been written pretty quickly so far,
+and is still in rapid development. Documentation and stable APIs will
+follow later.
+
+## Known Bugs
+
+1. Warnings are cleared when a syntax error is hit with eslint.

ale_linters/javascript/eslint.vim

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+if exists('g:loaded_ale_linters_javascript_eslint')
+    finish
+endif
+
+let g:loaded_ale_linters_javascript_eslint = 1
+
+function! ale_linters#javascript#eslint#Handle(lines)
+    " Matches patterns line the following:
+    "
+    " <text>:47:14: Missing trailing comma. [Warning/comma-dangle]
+    " <text>:56:41: Missing semicolon. [Error/semi]
+    let pattern = '^<text>:\(\d\+\):\(\d\+\): \(.\+\) \[\(.\+\)/\(.\+\)\]'
+    let output = []
+
+    for line in a:lines
+        let match = matchlist(line, pattern)
+
+        if len(match) == 0
+            break
+        endif
+
+        " vcol is Needed to indicate that the column is a character.
+        call add(output, {
+        \   'bufnr': bufnr('%'),
+        \   'lnum': match[1] + 0,
+        \   'vcol': 0,
+        \   'col': match[2] + 0,
+        \   'text': match[3] . '(' . match[5] . ')',
+        \   'type': match[4] ==# 'Warning' ? 'W' : 'E',
+        \   'nr': -1,
+        \})
+    endfor
+
+    return output
+endfunction
+
+call ALEAddLinter('javascript', {
+\   'executable': 'eslint',
+\   'command': 'eslint -f unix --stdin',
+\   'callback': 'ale_linters#javascript#eslint#Handle',
+\})

plugin/ale/aaflags.vim

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+" This file sets up configuration settings for the ALE plugin.
+" Flags can be set in vimrc files and so on to disable particular features,
+" etc.
+
+if exists('g:loaded_ale_flags')
+    finish
+endif
+
+let g:loaded_ale_flags = 1
+
+" This flag can be set to 0 to disable linting when text is changed.
+if !exists('g:ale_lint_on_text_changed')
+    let g:ale_lint_on_text_changed = 1
+endif
+
+" This flag can be set with a number of milliseconds for delaying the
+" execution of a linter when text is changed. The timeout will be set and
+" cleared each time text is changed, so repeated edits won't trigger the
+" jobs for linting until enough time has passed after editing is done.
+if !exists('g:ale_lint_delay')
+    let g:ale_lint_delay = 100
+endif
+
+" This flag can be set to 0 to disable linting when the buffer is entered.
+if !exists('g:ale_lint_on_enter')
+    let g:ale_lint_on_enter = 1
+endif
+
+" This flag can be set to 0 to disable setting the loclist.
+if !exists('g:ale_set_loclist')
+    let g:ale_set_loclist = 1
+endif
+
+" This flag can be set to 0 to disable setting signs.
+if !exists('g:ale_set_signs')
+    let g:ale_set_signs = 1
+endif
+
+" This flag can be set to 0 to disable echoing when the cursor moves.
+if !exists('g:ale_echo_cursor')
+    let g:ale_echo_cursor = 1
+endif

plugin/ale/cursor.vim

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+if exists('g:loaded_ale_cursor')
+    finish
+endif
+
+let g:loaded_ale_cursor = 1
+
+" This function will perform a binary search to find a message from the
+" loclist to echo when the cursor moves.
+function! s:BinarySearch(loclist, line, column)
+    let min = 0
+    let max = len(a:loclist) - 1
+    let last_column_match = -1
+
+    while 1
+        if max < min
+            return last_column_match
+        endif
+
+        let mid = (min + max) / 2
+        let obj = a:loclist[mid]
+
+        " Binary search to get on the same line
+        if a:loclist[mid]['lnum'] < a:line
+            let min = mid + 1
+        elseif a:loclist[mid]['lnum'] > a:line
+            let max = mid - 1
+        else
+            let last_column_match = mid
+
+            " Binary search to get the same column, or near it
+            if a:loclist[mid]['col'] < a:column
+                let min = mid + 1
+            elseif a:loclist[mid]['col'] > a:column
+                let max = mid - 1
+            else
+                return mid
+            endif
+        endif
+    endwhile
+endfunction
+
+function! ale#cursor#TruncatedEcho(message)
+    let message = a:message
+    " Change tabs to spaces.
+    let message = substitute(message, "\t", ' ', 'g')
+    " Remove any newlines in the message.
+    let message = substitute(message, "\n", '', 'g')
+
+    let truncated_message = join(split(message, '\zs')[:&columns - 2], '')
+
+    " Echo the message truncated to fit without creating a prompt.
+    echo truncated_message
+endfunction
+
+function! ale#cursor#EchoCursorWarning()
+    let pos = getcurpos()
+
+    let index = s:BinarySearch(b:ale_loclist, pos[1], pos[2])
+
+    if index >= 0
+        call ale#cursor#TruncatedEcho(b:ale_loclist[index]['text'])
+    else
+        echo
+    endif
+endfunction
+
+if g:ale_echo_cursor
+    augroup ALECursorGroup
+        autocmd!
+        autocmd CursorMoved * call ale#cursor#EchoCursorWarning()
+    augroup END
+endif

plugin/ale/sign.vim

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+if exists('g:loaded_ale_sign')
+    finish
+endif
+
+let g:loaded_ale_sign = 1
+
+if !hlexists('ALEErrorSign')
+    highlight link ALErrorSign error
+endif
+
+if !hlexists('ALEWarningSign')
+    highlight link ALEWarningSign todo
+endif
+
+if !hlexists('ALEError')
+    highlight link ALEError SpellBad
+endif
+
+if !hlexists('ALEWarning')
+    highlight link ALEWarning SpellCap
+endif
+
+" Signs show up on the left for error markers.
+sign define ALEErrorSign text=>> texthl=ALEErrorSign
+sign define ALEWarningSign text=-- texthl=ALEWarningSign
+
+" This function will set the signs which show up on the left.
+function! ale#sign#SetSigns(loclist)
+    sign unplace *
+
+    for i in range(0, len(a:loclist) - 1)
+        let obj = a:loclist[i]
+        let name = obj['type'] ==# 'W' ? 'ALEWarningSign' : 'ALEErrorSign'
+
+        let sign_line = 'sign place ' . (i + 1)
+            \. ' line=' . obj['lnum']
+            \. ' name=' . name
+            \. ' buffer=' . obj['bufnr']
+
+        exec sign_line
+    endfor
+endfunction