Signature help (#479)

* Add signatureHelp

* Use <buffer>

* Check lsp_use_trigger_characters_for_signature_help

* Rename to lsp_signature_help_enabled

* Use InsertCharPre

* Add abort

* Check documentation exists

Author: mattn

autoload/lsp.vim

@@ -659,6 +659,9 @@ function! s:handle_initialize(server_name, data) abort
     for l:Init_callback in l:init_callbacks
         call l:Init_callback(a:data)
     endfor
+    if g:lsp_signature_help_enabled
+        call lsp#ui#vim#signature_help#setup()
+    endif
 
     doautocmd User lsp_server_init
 endfunction

autoload/lsp/capabilities.vim

@@ -103,3 +103,23 @@ function! lsp#capabilities#get_text_document_change_sync_kind(server_name) abort
     endif
     return 1
 endfunction
+
+function! lsp#capabilities#has_signature_help_provider(server_name) abort
+    let l:capabilities = lsp#get_server_capabilities(a:server_name)
+    if !empty(l:capabilities) && has_key(l:capabilities, 'signatureHelpProvider')
+        return 1
+    endif
+    return 0
+endfunction
+
+function! lsp#capabilities#get_signature_help_trigger_characters(server_name) abort
+    let l:capabilities = lsp#get_server_capabilities(a:server_name)
+    if !empty(l:capabilities) && has_key(l:capabilities, 'signatureHelpProvider')
+        if type(l:capabilities['signatureHelpProvider']) == type({})
+            if  has_key(l:capabilities['signatureHelpProvider'], 'triggerCharacters')
+                return l:capabilities['signatureHelpProvider']['triggerCharacters']
+            endif
+        endif
+    endif
+    return []
+endfunction

autoload/lsp/ui/vim/signature_help.vim

@@ -0,0 +1,71 @@
+function! s:not_supported(what) abort
+    return lsp#utils#error(a:what.' not supported for '.&filetype)
+endfunction
+
+function! lsp#ui#vim#signature_help#get_signature_help_under_cursor() abort
+    let l:servers = filter(lsp#get_whitelisted_servers(), 'lsp#capabilities#has_signature_help_provider(v:val)')
+
+    if len(l:servers) == 0
+        call s:not_supported('Retrieving signature help')
+        return
+    endif
+
+    let l:position = lsp#get_position()
+    let l:position.character += 1
+    for l:server in l:servers
+        call lsp#send_request(l:server, {
+            \ 'method': 'textDocument/signatureHelp',
+            \ 'params': {
+            \   'textDocument': lsp#get_text_document_identifier(),
+            \   'position': position,
+            \ },
+            \ 'on_notification': function('s:handle_signature_help', [l:server]),
+            \ })
+    endfor
+
+    echo 'Retrieving signature help ...'
+    return
+endfunction
+
+function! s:handle_signature_help(server, data) abort
+    if lsp#client#is_error(a:data['response'])
+        call lsp#utils#error('Failed to retrieve signature help information for ' . a:server)
+        return
+    endif
+
+    if !has_key(a:data['response'], 'result')
+        return
+    endif
+
+    if !empty(a:data['response']['result']) && !empty(a:data['response']['result']['signatures'])
+        let l:signature = a:data['response']['result']['signatures'][0]
+        let l:contents = [l:signature['label']]
+        if has_key(l:signature, 'documentation')
+            call add(l:contents, l:signature['documentation'])
+        endif
+        call lsp#ui#vim#output#preview(l:contents, {'statusline': ' LSP SignatureHelp'})
+        return
+    else
+        " signature help is used while inserting. So this must be graceful.
+        "call lsp#utils#error('No signature help information found')
+    endif
+endfunction
+
+function! s:insert_char_pre() abort
+    let l:buf = bufnr('%')
+    for l:server_name in lsp#get_whitelisted_servers(l:buf)
+        let l:keys = lsp#capabilities#get_signature_help_trigger_characters(l:server_name)
+        for l:key in l:keys
+            if l:key ==# v:char
+                call timer_start(0, {_-> lsp#ui#vim#signature_help#get_signature_help_under_cursor() })
+            endif
+        endfor
+    endfor
+endfunction
+
+function! lsp#ui#vim#signature_help#setup() abort
+    augroup _lsp_signature_help_
+        autocmd!
+        autocmd InsertCharPre <buffer> call s:insert_char_pre()
+    augroup END
+endfunction

doc/vim-lsp.txt

@@ -31,6 +31,7 @@ CONTENTS                                                  *vim-lsp-contents*
       g:lsp_peek_alignment                  |g:lsp_peek_alignment|
       g:lsp_preview_max_width               |g:lsp_preview_max_width|
       g:lsp_preview_max_height		    |g:lsp_preview_max_height|
+      g:lsp_signature_help_enabled          |g:lsp_signature_help_enabled|
     Functions                             |vim-lsp-functions|
       enable                                |vim-lsp-enable|
       disable                               |vim-lsp-disable|
@@ -454,6 +455,17 @@ g:lsp_preview_max_height                         *g:lsp_preview_max_height*
     If positive, determines the maximum height of the preview window in
     characters. Use a value of `-1` to disable setting a maximum height.
 
+g:lsp_signature_help_enabled                *g:lsp_signature_help_enabled*
+    Type: |Number|
+    Default: `1`
+
+    Enable support for signature help. Set to `0` to disable.
+
+    Example:
+>
+	let g:lsp_signature_help_enabled = 1
+	let g:lsp_signature_help_enabled = 0
+
 ===============================================================================
 FUNCTIONS	                                        *vim-lsp-functions*
 

plugin/lsp.vim

@@ -32,6 +32,7 @@ let g:lsp_preview_doubletap = get(g:, 'lsp_preview_doubletap', [function('lsp#ui
 let g:lsp_peek_alignment = get(g:, 'lsp_peek_alignment', 'center')
 let g:lsp_preview_max_width = get(g:, 'lsp_preview_max_width', -1)
 let g:lsp_preview_max_height = get(g:, 'lsp_preview_max_height', -1)
+let g:lsp_signature_help_enabled = get(g:, 'lsp_signature_help_enabled', 1)
 
 let g:lsp_get_vim_completion_item = get(g:, 'lsp_get_vim_completion_item', [function('lsp#omni#default_get_vim_completion_item')])
 let g:lsp_get_supported_capabilities = get(g:, 'lsp_get_supported_capabilities', [function('lsp#default_get_supported_capabilities')])
@@ -68,6 +69,7 @@ command! LspTypeDefinition call lsp#ui#vim#type_definition()
 command! -nargs=0 LspStatus echo lsp#get_server_status()
 command! LspNextReference call lsp#ui#vim#references#jump(+1)
 command! LspPreviousReference call lsp#ui#vim#references#jump(-1)
+command! -nargs=? -complete=customlist,lsp#utils#empty_complete LspSignatureHelp call lsp#ui#vim#signature_help#get_signature_help_under_cursor()
 
 nnoremap <plug>(lsp-code-action) :<c-u>call lsp#ui#vim#code_action()<cr>
 nnoremap <plug>(lsp-declaration) :<c-u>call lsp#ui#vim#declaration(0)<cr>
@@ -93,3 +95,4 @@ nnoremap <plug>(lsp-peek-implementation) :<c-u>call lsp#ui#vim#implementation(1)
 nnoremap <plug>(lsp-status) :<c-u>echo lsp#get_server_status()<cr>
 nnoremap <plug>(lsp-next-reference) :<c-u>call lsp#ui#vim#references#jump(+1)<cr>
 nnoremap <plug>(lsp-previous-reference) :<c-u>call lsp#ui#vim#references#jump(-1)<cr>
+nnoremap <plug>(lsp-signature-help) :<c-u>call lsp#ui#vim#signature_help#get_signature_help_under_cursor()<cr>