Add erlc lint for Erlang (#248) (#255)

* Add erlc lint for Erlang (#248)

* Ignore certain errors in Erlang .hrl files (#248)

A .hrl file does not need to have a -module definition. Additionally, it
is common to have unused elements in such a file, as the entities will
be used in a file including the header.

* Address change requests to Erlang linter

1 files changed, 89 insertions, 0 deletions

diff --git a/ale_linters/erlang/erlc.vim b/ale_linters/erlang/erlc.vim
new file mode 100644
index 00000000..0e3cc2fa
--- /dev/null
+++ b/ale_linters/erlang/erlc.vim
@@ -0,0 +1,89 @@
+" Author: Magnus Ottenklinger - https://github.com/evnu
+
+function! ale_linters#erlang#erlc#Handle(buffer, lines)
+  " Matches patterns like the following:
+  "
+  " error.erl:4: variable 'B' is unbound
+  " error.erl:3: Warning: function main/0 is unused
+  " error.erl:4: Warning: variable 'A' is unused
+  let l:pattern = '\v^([^:]+):(\d+): (Warning: )?(.+)$'
+
+  " parse_transforms are a special case. The error message does not indicate a location:
+  " error.erl: undefined parse transform 'some_parse_transform'
+  let l:pattern_parse_transform = '\v(undefined parse transform .*)$'
+  let l:output = []
+
+  let l:pattern_no_module_definition = '\v(no module definition)$'
+  let l:pattern_unused = '\v(.* is unused)$'
+
+  let l:is_hrl = fnamemodify(bufname(a:buffer), ':e') ==# 'hrl'
+
+  for l:line in a:lines
+    let l:match = matchlist(l:line, l:pattern)
+
+    " Determine if the output indicates an error. We distinguish between two cases:
+    "
+    " 1) normal errors match l:pattern
+    " 2) parse_transform errors match l:pattern_parse_transform
+    "
+    " If none of the patterns above match, the line can be ignored
+    if len(l:match) == 0 " not a 'normal' warning or error
+
+        let l:match_parse_transform = matchlist(l:line, l:pattern_parse_transform)
+
+        if len(l:match_parse_transform) == 0 " also not a parse_transform error
+            continue
+        endif
+
+        call add(l:output, {
+        \   'bufnr': a:buffer,
+        \   'lnum': 0,
+        \   'vcol': 0,
+        \   'col': 0,
+        \   'type': 'E',
+        \   'text': l:match_parse_transform[0],
+        \   'nr': -1,
+        \})
+        continue
+    endif
+
+    let l:line = l:match[2]
+    let l:warning_or_text = l:match[3]
+    let l:text = l:match[4]
+
+    " If this file is a header .hrl, ignore the following expected messages:
+    " - 'no module definition'
+    " - 'X is unused'
+    if l:is_hrl &&
+                \ (match(l:text, l:pattern_no_module_definition) != -1 ||
+                \  match(l:text, l:pattern_unused) != -1)
+        continue
+    endif
+
+    if !empty(l:warning_or_text)
+        let l:type = 'W'
+    else
+        let l:type = 'E'
+    endif
+
+    " vcol is Needed to indicate that the column is a character.
+    call add(l:output, {
+    \   'bufnr': a:buffer,
+    \   'lnum': l:line,
+    \   'vcol': 0,
+    \   'col': 0,
+    \   'type': l:type,
+    \   'text': l:text,
+    \   'nr': -1,
+    \})
+  endfor
+
+  return l:output
+endfunction
+
+call ale#linter#Define('erlang', {
+\   'name': 'erlc',
+\   'executable': 'erlc',
+\   'command': g:ale#util#stdin_wrapper . ' .erl erlc '
+\               . get(g:, 'ale_erlang_erlc_flags', ''),
+\   'callback': 'ale_linters#erlang#erlc#Handle' })