Fix bug in sqlfluff implementation & implement fixer support (#4365)

* Account for no sqlfluff output

Avoid crashes when there isn't any output from sqlfluff.

* Add supplort for sqlfluff as a fixer

ale_linters/sql/sqlfluff.vim

@@ -37,7 +37,13 @@ endfunction
 
 function! ale_linters#sql#sqlfluff#Handle(buffer, lines) abort
     let l:output = []
-    let l:json = ale#util#FuzzyJSONDecode(a:lines, {})[0]
+    let l:json_lines = ale#util#FuzzyJSONDecode(a:lines, [])
+
+    if empty(l:json_lines)
+        return l:output
+    endif
+
+    let l:json = l:json_lines[0]
 
     " if there's no warning, 'result' is `null`.
     if empty(get(l:json, 'violations'))

autoload/ale/fix/registry.vim

@@ -386,6 +386,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['sh'],
 \       'description': 'Fix sh files with shfmt.',
 \   },
+\   'sqlfluff': {
+\       'function': 'ale#fixers#sqlfluff#Fix',
+\       'suggested_filetypes': ['sql'],
+\       'description': 'Fix SQL files with sqlfluff.',
+\   },
 \   'sqlfmt': {
 \       'function': 'ale#fixers#sqlfmt#Fix',
 \       'suggested_filetypes': ['sql'],

autoload/ale/fixers/sqlfluff.vim

@@ -0,0 +1,25 @@
+" Author: Carl Smedstad <carl.smedstad at protonmail dot com>
+" Description: Fixing SQL files with sqlfluff
+
+call ale#Set('sql_sqlfluff_executable', 'sqlfluff')
+
+function! ale#fixers#sqlfluff#Fix(buffer) abort
+    let l:executable = ale#Var(a:buffer, 'sql_sqlfluff_executable')
+
+    let l:cmd =
+    \    ale#Escape(l:executable)
+    \    . ' fix --force'
+
+    let l:config_file = ale#path#FindNearestFile(a:buffer, '.sqlfluff')
+
+    if !empty(l:config_file)
+        let l:cmd .= ' --config ' . ale#Escape(l:config_file)
+    else
+        let l:cmd .= ' --dialect ansi'
+    endif
+
+    return {
+    \   'command': l:cmd . ' %t > /dev/null',
+    \   'read_temporary_file': 1,
+    \}
+endfunction