Handle flow extra errors (#946)

Show more information for Flow errors with :ALEDetail

ale_linters/javascript/flow.vim

@@ -1,6 +1,9 @@
 " Author: Zach Perrault -- @zperrault
 " Description: FlowType checking for JavaScript files
 
+" Flow extra errors
+" Author: Florian Beeres <yuuki@protonmail.com>
+
 call ale#Set('javascript_flow_executable', 'flow')
 call ale#Set('javascript_flow_use_global', 0)
 
@@ -53,6 +56,44 @@ function! s:GetJSONLines(lines) abort
     return a:lines[l:start_index :]
 endfunction
 
+function! s:ExtraErrorMsg(current, new) abort
+    let l:newMsg = ''
+
+    if a:current is# ''
+        " extra messages appear to already have a :
+        let l:newMsg = a:new
+    else
+        let l:newMsg = a:current . ' ' . a:new
+    endif
+
+    return l:newMsg
+endfunction
+
+
+function! s:GetDetails(error) abort
+    let l:detail = ''
+
+    for l:extra_error in a:error.extra
+
+        if has_key(l:extra_error, 'message')
+            for l:extra_message in l:extra_error.message
+                let l:detail = s:ExtraErrorMsg(l:detail, l:extra_message.descr)
+            endfor
+        endif
+
+        if has_key(l:extra_error, 'children')
+            for l:child in l:extra_error.children
+                for l:child_message in l:child.message
+                    let l:detail = l:detail . ' ' . l:child_message.descr
+                endfor
+            endfor
+        endif
+
+    endfor
+
+    return l:detail
+endfunction
+
 function! ale_linters#javascript#flow#Handle(buffer, lines) abort
     let l:str = join(s:GetJSONLines(a:lines), '')
 
@@ -91,12 +132,19 @@ function! ale_linters#javascript#flow#Handle(buffer, lines) abort
             let l:text = l:text . ' See also: ' . l:error.operation.descr
         endif
 
-        call add(l:output, {
+        let l:errorToAdd = {
         \   'lnum': l:line,
         \   'col': l:col,
         \   'text': l:text,
-        \   'type': l:error.level is# 'error' ? 'E' : 'W',
-        \})
+        \   'type': has_key(l:error, 'level') && l:error.level is# 'error' ? 'E' : 'W',
+        \}
+
+        if has_key(l:error, 'extra')
+            let l:errorToAdd.detail = s:GetDetails(l:error)
+        endif
+
+        call add(l:output, l:errorToAdd)
+
     endfor
 
     return l:output