Fix and expose signatureHelp.

Close #274.

Author: Junfeng Li

plugin/LanguageClient.vim

@@ -589,6 +589,24 @@ function! LanguageClient#complete(findstart, base) abort
     endif
 endfunction
 
+function! LanguageClient_textDocument_signatureHelp(...) abort
+    if &buftype !=# '' || &filetype ==# ''
+        return
+    endif
+
+    let l:params = {
+                \ 'buftype': &buftype,
+                \ 'languageId': &filetype,
+                \ 'filename': s:Expand('%:p'),
+                \ 'line': line('.') - 1,
+                \ 'character': col('.') - 1,
+                \ 'handle': v:true,
+                \ }
+    call extend(l:params, a:0 >= 1 ? a:1 : {})
+    let callback = a:0 >= 2 ? a:2 : v:null
+    return LanguageClient#Call('textDocument/signatureHelp', l:params, l:callback)
+endfunction
+
 function! LanguageClient_workspace_applyEdit(...) abort
     if &buftype !=# '' || &filetype ==# ''
         return

src/languageclient.rs

@@ -2249,12 +2249,16 @@ impl ILanguageClient for Arc<Mutex<State>> {
                 .label
                 .split(&active_parameter.label)
                 .collect();
-            for chunk in chunks {
-                cmd += &format!(" | echon {}", chunk);
+            if chunks.len() == 2 {
+                let begin = chunks.get(0).cloned().unwrap_or_default();
+                let end = chunks.get(1).cloned().unwrap_or_default();
                 cmd += &format!(
-                    " | echohl Bold | echon {} | echohl None",
-                    active_parameter.label
+                    " | echon '{}' | echohl WarningMsg | echon '{}' | echohl None | echon '{}'",
+                    begin, active_parameter.label, end
                 );
+            } else {
+                // Active parameter is not part of signature.
+                cmd += &format!(" | echo '{}'", active_signature.label);
             }
             self.command(&cmd)?;
         } else {