Add support for Julia Language Server (#1894)

ale_linters/julia/languageserver.vim

@@ -0,0 +1,21 @@
+" Author: Bartolomeo Stellato <bartolomeo.stellato@gmail.com>
+" Description: A language server for Julia
+
+" Set julia executable variable
+call ale#Set('julia_executable', 'julia')
+
+function! ale_linters#julia#languageserver#GetCommand(buffer) abort
+    let l:julia_executable = ale#Var(a:buffer, 'julia_executable')
+    let l:cmd_string = 'using LanguageServer; server = LanguageServer.LanguageServerInstance(STDIN, STDOUT, false); server.runlinter = true; run(server);'
+
+    return ale#Escape(l:julia_executable) . ' --startup-file=no --history-file=no -e ' . ale#Escape(l:cmd_string)
+endfunction
+
+call ale#linter#Define('julia', {
+\   'name': 'languageserver',
+\   'lsp': 'stdio',
+\   'executable_callback': ale#VarFunc('julia_executable'),
+\   'command_callback': 'ale_linters#julia#languageserver#GetCommand',
+\   'language': 'julia',
+\   'project_root_callback': 'ale#julia#FindProjectRoot',
+\})