nvim: Add LSP support

Though we had removed this earlier bring it back. It saves the hassle of
having different plugin, packages or bindings for different languages.

Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>

nvim/.config/nvim/init.vim

@@ -61,7 +61,6 @@ Plug 'LnL7/vim-nix', { 'for': 'nix' }
 Plug 'Shougo/deoplete.nvim', { 'do': ':UpdateRemotePlugins' }
 Plug 'deoplete-plugins/deoplete-tag'
 " For Python
-Plug 'davidhalter/jedi-vim', { 'for': 'python' }
 Plug 'zchee/deoplete-jedi', { 'for': 'python' }
 Plug 'numirias/semshi', { 'for': 'python', 'do': ':UpdateRemotePlugins' }
 " Autocomplete for Rust
@@ -92,6 +91,7 @@ Plug 'tpope/vim-sleuth'
 Plug 'tpope/vim-vinegar'
 Plug 'wellle/targets.vim'
 Plug 'Yggdroot/indentLine'
+Plug 'autozimu/LanguageClient-neovim', { 'branch': 'next', 'do': 'bash install.sh' }
 " Miscellaneous
 Plug 'editorconfig/editorconfig-vim'
 Plug 'igankevich/mesonic'
@@ -144,6 +144,7 @@ set noswapfile          " no swap files
 set foldmethod=syntax   " Create folds based on files syntax
 set nofoldenable        " Open folds by default
 set undofile            " Enable undo persistence across sessions
+set hidden              " Required by LC
 
 " Wild menu
 set wildmenu
@@ -420,11 +421,6 @@ augroup END
 
 augroup rust_maps
 	au!
-	au FileType rust nmap <buffer> gd <plug>DeopleteRustGoToDefinitionDefault
-	au FileType rust nmap <buffer> K  <plug>DeopleteRustShowDocumentation
-	au FileType rust nmap <buffer> gv <plug>DeopleteRustGoToDefinitionVSplit
-	au FileType rust nmap <buffer> g- <plug>DeopleteRustGoToDefinitionSplit
-	au FileType rust nmap <buffer> gt <plug>DeopleteRustGoToDefinitionTab
 	" Taken from http://seenaburns.com/vim-setup-for-rust/
 	" Neomake
 	" Gross hack to stop Neomake running when exitting because it creates a zombie cargo check process
@@ -490,6 +486,11 @@ augroup END
 " Automatically resize the window
 autocmd VimResized * wincmd =
 
+augroup LSP
+    au!
+    autocmd FileType haskell,rust,python :call SetLspKeybindings()
+augroup END
+
 " --------------------------- Plugin settings --------------------------------
 let g:haskell_enable_quantification = 1   " to enable highlighting of `forall`
 let g:haskell_enable_recursivedo = 1      " to enable highlighting of `mdo` and `rec`
@@ -531,8 +532,9 @@ call deoplete#custom#source('_',
             \ 'disabled_syntaxes', ['Comment', 'String'])
 call deoplete#custom#option('sources', {
 			\ '_' : ['buffer', 'tag', 'around', 'file', 'member'],
-			\ 'haskell': ['buffer', 'tag'],
-			\ 'rust': ['racer', 'buffer', 'tag'],
+			\ 'haskell': ['LanguageClient', 'buffer', 'tag'],
+			\ 'rust': ['LanguageClient', 'buffer'],
+			\ 'python': ['LanguageClient', 'buffer'],
 			\ 'purescript': ['buffer', 'omni'],
 			\})
 call deoplete#custom#source('omni', 'functions', {
@@ -547,8 +549,6 @@ call deoplete#custom#option({
 			\ 'smart_case': v:true,
 			\ })
 let g:deoplete#sources#rust#disable_keymap = 1
-let g:deoplete#sources#rust#racer_binary=expand('$HOME/.cargo/bin/racer')
-let g:deoplete#sources#rust#rust_source_path=expand('$HOME/GitSources/rust/src')
 let g:rustfmt_autosave = 1
 
 " Use airline
@@ -629,26 +629,6 @@ let g:cpp_class_decl_highlight = 1
 let g:cpp_posix_standard = 1
 let g:cpp_concepts_highlight = 1
 
-let g:jedi#goto_command = "gt"
-let g:jedi#goto_assignments_command = "ga"
-let g:jedi#goto_definitions_command = "gd"
-let g:jedi#documentation_command = "K"
-let g:jedi#usages_command = "gu"
-let g:jedi#completions_command = "<Tab>"
-let g:jedi#rename_command = "gr"
-
-let g:jedi#auto_initialization = 1
-let g:jedi#auto_vim_configuration = 0
-let g:jedi#use_tabs_not_buffers = 1
-let g:jedi#popup_on_dot = 1
-let g:jedi#popup_select_first = 0
-let g:jedi#smart_auto_mappings = 0
-let g:jedi#show_call_signatures = "2"
-let g:jedi#show_call_signatures_delay = 0
-let g:jedi#show_call_signatures_modes = 'i'
-let g:jedi#enable_speed_debugging = 0
-let g:jedi#completions_enabled = 0
-
 " For SLIMV
 let g:lisp_rainbow=1
 " For Purescript
@@ -662,6 +642,16 @@ let g:fzf_layout = { 'window': 'call CreateCentredFloatingWindow()' }
 " Quickr
 let g:quickr_cscope_keymaps = 0
 
+" LSP
+let g:LanguageClient_autoStart = 0
+let g:LanguageClient_loggingFile = expand('$HOME/.cache/LC.log')
+let g:LanguageClient_selectionUI = "quickfix"
+let g:LanguageClient_serverCommands = {
+            \ 'haskell': ['ghcide', '--lsp'],
+            \ 'rust': ['ra_lsp_server'],
+            \ 'python': ['pyls'],
+            \ }
+
 " ----------------------------- Functions ------------------------------------
 function! NvimGdbNoTKeymaps()
   tnoremap <silent> <buffer> <Esc> <C-\><C-n>
@@ -700,3 +690,23 @@ function! s:incsearch_config(...) abort
 				\   'is_expr': 0
 				\ }), get(a:, 1, {}))
 endfunction
+
+function! SetLspKeybindings()
+	nnoremap gd :call LanguageClient#textDocument_definition()<CR>
+	nnoremap gr :call LanguageClient#textDocument_rename()<CR>
+	nnoremap gx :call LanguageClient#textDocument_references()<CR>
+	nnoremap K  :call LanguageClient#textDocument_hover()<CR>
+
+    nnoremap lcs :LanguageClientStart<CR>
+    nnoremap lch :LanguageClientStop<CR>
+	nnoremap lcm :call LanguageClient_contextMenu()<CR>
+	nnoremap ltd :call LanguageClient#textDocument_typeDefinition()<CR>
+	nnoremap ldi :call LanguageClient#textDocument_implementation()<CR>
+	nnoremap lcl :call LanguageClient#textDocument_codeLens()<CR>
+	nnoremap lca :call LanguageClient#textDocument_codeAction()<CR>
+	nnoremap lrf :call LanguageClient#textDocument_rangeFormatting()<CR>
+	nnoremap lf  :call LanguageClient#textDocument_formatting()<CR>
+	nnoremap la  :call LanguageClient_workspace_applyEdit()<CR>
+	nnoremap lc  :call LanguageClient#textDocument_completion()<CR>
+	nnoremap ls  :call LanguageClient_textDocument_documentSymbol()<CR>
+endfunction