LSP configuration via didChangeConfiguration (#1852)

* adding LSP configuration via workspace/didChangeConfiguration

autoload/ale/linter.vim

@@ -255,6 +255,14 @@ function! ale#linter#PreProcess(filetype, linter) abort
         elseif has_key(a:linter, 'initialization_options')
             let l:obj.initialization_options = a:linter.initialization_options
         endif
+
+        if has_key(a:linter, 'lsp_config')
+            if type(a:linter.lsp_config) isnot v:t_dict
+                throw '`lsp_config` must be a Dictionary'
+            endif
+
+            let l:obj.lsp_config = a:linter.lsp_config
+        endif
     endif
 
     let l:obj.output_stream = get(a:linter, 'output_stream', 'stdout')

autoload/ale/lsp/message.vim

@@ -138,3 +138,9 @@ function! ale#lsp#message#Hover(buffer, line, column) abort
     \   'position': {'line': a:line - 1, 'character': a:column},
     \}]
 endfunction
+
+function! ale#lsp#message#DidChangeConfiguration(buffer, config) abort
+    return [0, 'workspace/didChangeConfiguration', {
+    \   'settings': a:config,
+    \}]
+endfunction

autoload/ale/lsp_linter.vim

@@ -190,6 +190,12 @@ function! ale#lsp_linter#StartLSP(buffer, linter) abort
 
     let l:language_id = ale#util#GetFunction(a:linter.language_callback)(a:buffer)
 
+    if !empty(get(a:linter, 'lsp_config'))
+        " set LSP configuration options (workspace/didChangeConfiguration)
+        let l:config_message = ale#lsp#message#DidChangeConfiguration(a:buffer, a:linter.lsp_config)
+        call ale#lsp#Send(l:conn_id, l:config_message)
+    endif
+
     let l:details = {
     \   'buffer': a:buffer,
     \   'connection_id': l:conn_id,