Fix awk linter and security concerns. (#1411)

* Fixed (g)awk linter

 * Made it secure, albeit less useful.
 * Added gawk handler; the cpplint one was not working?
 * Added gawk handler test.
 * added warning to gawk handler.
 * added gawk command callback test
 * added comment about --source

* added back optional commandline option

ale_linters/awk/gawk.vim

@@ -12,7 +12,11 @@ function! ale_linters#awk#gawk#GetExecutable(buffer) abort
 endfunction
 
 function! ale_linters#awk#gawk#GetCommand(buffer) abort
+    " note the --source 'BEGIN ...' is to prevent
+    " gawk from attempting to execute the body of the script
+    " it is linting.
     return ale_linters#awk#gawk#GetExecutable(a:buffer)
+    \   . " --source 'BEGIN { exit } END { exit 1 }'"
     \   . ' ' . ale#Var(a:buffer, 'awk_gawk_options')
     \   . ' ' . '-f %t --lint /dev/null'
 endfunction
@@ -21,6 +25,6 @@ call ale#linter#Define('awk', {
 \   'name': 'gawk',
 \   'executable_callback': 'ale_linters#awk#gawk#GetExecutable',
 \   'command_callback': 'ale_linters#awk#gawk#GetCommand',
-\   'callback': 'ale#handlers#cpplint#HandleCppLintFormat',
+\   'callback': 'ale#handlers#gawk#HandleGawkFormat',
 \   'output_stream': 'both'
 \})

autoload/ale/handlers/gawk.vim

@@ -0,0 +1,25 @@
+" Author: Anthony DeDominic <adedomin@gmail.com>
+" Description: Handle output from gawk's --lint option
+
+function! ale#handlers#gawk#HandleGawkFormat(buffer, lines) abort
+    " Look for lines like the following:
+    " gawk: /tmp/v0fddXz/1/something.awk:1: ^ invalid char ''' in expression
+    let l:pattern = '^.\{-}:\(\d\+\):\s\+\(warning:\|\^\)\s*\(.*\)'
+    let l:output = []
+
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        let l:ecode = 'E'
+        if l:match[2] is? 'warning:'
+            let l:ecode = 'W'
+        endif
+        call add(l:output, {
+        \   'lnum': l:match[1] + 0,
+        \   'col': 0,
+        \   'text': l:match[3],
+        \   'code': 0,
+        \   'type': l:ecode,
+        \})
+    endfor
+
+    return l:output
+endfunction

test/command_callback/test_gawk_command_callback.vader

@@ -0,0 +1,40 @@
+Before:
+  Save g:ale_awk_gawk_executable
+  Save g:ale_awk_gawk_options
+  unlet! g:ale_awk_gawk_executable
+  unlet! g:ale_awk_gawk_options
+
+  runtime ale_linters/awk/gawk.vim
+
+After:
+  Restore
+  unlet! b:command_tail
+  unlet! b:ale_awk_gawk_executable
+  unlet! b:ale_awk_gawk_options
+
+  call ale#linter#Reset()
+
+Execute(The executable should be used in the command):
+  AssertEqual
+  \ 'gawk'
+    \ . " --source 'BEGIN { exit } END { exit 1 }'"
+    \ . '  ' . '-f %t --lint /dev/null',
+  \ ale_linters#awk#gawk#GetCommand(bufnr(''))
+
+  let b:ale_awk_gawk_executable = '/other/gawk'
+
+  AssertEqual
+  \ '/other/gawk'
+    \ . " --source 'BEGIN { exit } END { exit 1 }'"
+    \ . '  ' . '-f %t --lint /dev/null',
+  \ ale_linters#awk#gawk#GetCommand(bufnr(''))
+
+  let b:ale_awk_gawk_executable = 'gawk'
+  let b:ale_awk_gawk_options = '--something'
+
+  AssertEqual
+  \ 'gawk'
+    \ . " --source 'BEGIN { exit } END { exit 1 }'"
+    \ . ' --something'
+    \ . ' ' . '-f %t --lint /dev/null',
+  \ ale_linters#awk#gawk#GetCommand(bufnr(''))

test/handler/test_gawk_handler.vader

@@ -0,0 +1,39 @@
+Before:
+  runtime ale_linters/awk/gawk.vim
+
+After:
+  call ale#linter#Reset()
+
+Execute(gawk syntax errors should be parsed correctly):
+
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 1,
+  \     'col': 0,
+  \     'text': "invalid char ''' in expression",
+  \     'code': 0,
+  \     'type': 'E',
+  \   },
+  \   {
+  \     'lnum': 5,
+  \     'col': 0,
+  \     'text': 'unterminated string',
+  \     'code': 0,
+  \     'type': 'E',
+  \   },
+  \   {
+  \     'lnum': 10,
+  \     'col': 0,
+  \     'text': "escape sequence `\u' treated as plain `u'",
+  \     'code': 0,
+  \     'type': 'W',
+  \   },
+  \ ],
+  \ ale#handlers#gawk#HandleGawkFormat(347, [
+  \   "gawk: something.awk:1: BEGIN { system('touch aaaaaaaaa') }",
+  \   "gawk: something.awk:1:                ^ invalid char ''' in expression",
+  \   'gawk: something.awk:5: { x = "aaaaaaaaaaa',
+  \   'gawk: something.awk:5:       ^ unterminated string',
+  \   "gawk: something.awk:10: warning: escape sequence `\u' treated as plain `u'",
+  \ ])