Language client: corrected diagnostic underline for some cases, and updated language server setup docs for rust

docs/language_servers.md

@@ -45,7 +45,7 @@ ln -s `which pyls` /usr/local/bin/python-language-server
 Install language server, and create symbolic link to enable server in juCi++:
 ```sh
 rustup update
-rustup component add rls-preview rust-analysis rust-src
+rustup component add rls rust-analysis rust-src
 
 ln -s `rustc --print sysroot`/bin/rls /usr/local/bin/rust-language-server
 ```

src/source_language_protocol.cc

@@ -949,10 +949,11 @@ void Source::LanguageProtocolView::update_diagnostics(std::vector<LanguageProtoc
       auto end = get_iter_at_line_pos(diagnostic.range.end.line, diagnostic.range.end.character);
 
       if(start == end) {
-        if(!end.is_end())
+        if(!end.ends_line())
           end.forward_char();
         else
-          start.backward_char();
+          while(start.ends_line() && start.backward_char()) { // Move start so that diagnostic underline is visible
+          }
       }
 
       bool error = false;