Add support for checking Fortran syntax with GCC. Mad respect for the mathematicians.

README.md

@@ -28,6 +28,7 @@ name. That seems to be the fairest way to arrange this table.
 | Bash | [-n flag](https://www.gnu.org/software/bash/manual/bash.html#index-set) |
 | Bourne Shell | [-n flag](http://linux.die.net/man/1/sh) |
 | D | [dmd](https://dlang.org/dmd-linux.html) |
+| Fortran | [gcc](https://gcc.gnu.org/) |
 | JavaScript | [eslint](http://eslint.org/), [jscs](http://jscs.info/), [jshint](http://jshint.com/) |
 | Python | [flake8](http://flake8.pycqa.org/en/latest/) |
 | Ruby   | [rubocop](https://github.com/bbatsov/rubocop) |

ale_linters/fortran/gcc.vim

@@ -0,0 +1,68 @@
+if exists('g:loaded_ale_linters_fortran_gcc')
+    finish
+endif
+
+let g:loaded_ale_linters_fortran_gcc = 1
+
+" Set this option to change the GCC options for warnings for Fortran.
+if !exists('g:ale_fortran_gcc_options')
+    let g:ale_fortran_gcc_options = '-Wall'
+endif
+
+function! ale_linters#fortran#gcc#Handle(buffer, lines)
+    " We have to match a starting line and a later ending line together,
+    " like so.
+    "
+    " :21.34:
+    " Error: Expected comma in I/O list at (1)
+    let line_marker_pattern = '^:\(\d\+\)\.\(\d\+\):$'
+    let message_pattern = '^\(Error\|Warning\): \(.\+\)$'
+    let looking_for_message = 0
+    let last_loclist_obj = {}
+
+    let output = []
+
+    for line in a:lines
+        if looking_for_message
+            let l:match = matchlist(line, message_pattern)
+        else
+            let l:match = matchlist(line, line_marker_pattern)
+        endif
+
+        if len(l:match) == 0
+            continue
+        endif
+
+        if looking_for_message
+            let looking_for_message = 0
+
+            " Now we have the text, we can set it and add the error.
+            let last_loclist_obj.text = l:match[2]
+            let last_loclist_obj.type = l:match[1] ==# 'Warning' ? 'W' : 'E'
+            call add(output, last_loclist_obj)
+        else
+            let last_loclist_obj = {
+            \   'bufnr': a:buffer,
+            \   'lnum': l:match[1] + 0,
+            \   'vcol': 0,
+            \   'col': l:match[2] + 0,
+            \   'nr': -1,
+            \}
+
+            " Start looking for the message and error type.
+            let looking_for_message = 1
+        endif
+    endfor
+
+    return output
+endfunction
+
+call ALEAddLinter('fortran', {
+\   'name': 'gcc',
+\   'output_stream': 'stderr',
+\   'executable': 'gcc',
+\   'command': 'gcc -S -x f95 -fsyntax-only -ffree-form '
+\       . g:ale_fortran_gcc_options
+\       . ' -',
+\   'callback': 'ale_linters#fortran#gcc#Handle',
+\})