Add ccls support for C/C++/ObjC

ale_linters/cpp/ccls.vim

@@ -0,0 +1,30 @@
+" Author: Ye Jingchen <ye.jingchen@gmail.com>, Ben Falconer <ben@falconers.me.uk>, jtalowell <jtalowell@protonmail.com>
+" Description: A language server for C++
+
+call ale#Set('cpp_ccls_executable', 'ccls')
+call ale#Set('cpp_ccls_init_options', {})
+
+function! ale_linters#cpp#ccls#GetProjectRoot(buffer) abort
+    let l:project_root = ale#path#FindNearestFile(a:buffer, '.ccls-root')
+
+    if empty(l:project_root)
+        let l:project_root = ale#path#FindNearestFile(a:buffer, 'compile_commands.json')
+    elseif empty(l:project_root)
+        let l:project_root = ale#path#FindNearestFile(a:buffer, '.ccls')
+    endif
+
+    return !empty(l:project_root) ? fnamemodify(l:project_root, ':h') : ''
+endfunction
+
+function! ale_linters#cpp#ccls#GetInitializationOptions(buffer) abort
+    return ale#Var(a:buffer, 'cpp_ccls_init_options')
+endfunction
+
+call ale#linter#Define('cpp', {
+\   'name': 'ccls',
+\   'lsp': 'stdio',
+\   'executable_callback': ale#VarFunc('cpp_ccls_executable'),
+\   'command': '%e',
+\   'project_root_callback': 'ale_linters#cpp#ccls#GetProjectRoot',
+\   'initialization_options_callback': 'ale_linters#cpp#ccls#GetInitializationOptions',
+\})