CocAction('codeLens') => Source id of codelens not found

[MaskRay]

Describe the bug
:call CocAction('codeLens') displays an error message [coc.nvim] Source id of codelens not found"

To Reproduce
~/.config/nvim/coc-settings.json:

{
  "languageserver": {
    "ccls": {
      "command": "ccls",
      "filetypes": ["c", "cpp", "objc", "objcpp"]
    }
  }
}

1. cd /tmp/d; git init
2. echo 'int a;' > a.cc
3. nvim a.cc
4. Execute :call CocAction('codeLens')

Expected behavior
textDocument/codeLen result is rendered somewhere

Additional context

sysdig -As9999 --unbuffered -p '%evt.buffer' "proc.exe contains ccls and fd.type=unix":

Content-Length: 113

{"jsonrpc":"2.0","id":16,"method":"textDocument/codeLens","params":{"textDocument":{"uri":"file:///tmp/d/a.cc"}}}

Content-Length: 239

{"jsonrpc":"2.0","id":16,"result":[{"range":{"start":{"line":0,"character":4},"end":{"line":0,"character":5}},"command":{"title":"0 ref","command":"ccls.xref","arguments":["{\"usr\":16721564935990383768,\"kind\":4,\"field\":\"uses\"}"]}}]}

Note it encodes a JSON string as the only element of "arguments" (to make VSCode happy):

"arguments":["{\"usr\":16721564935990383768,\"kind\":4,\"field\":\"uses\"}"]

/tmp/coc-nvim.log log entry:

2018-11-23T21:19:51.601 ERROR (pid:17076) [codelens] - Cannot read property 'command' of null

[chemzqm]

The command not exists, an extension could help to regist custom command.

[MaskRay]

Does it make sense to postpone the error reporting to when the user actually clicks the button (tricks the command)?

My supposed interaction is:

• User invokes textDocument/codeLens
• Server returns:

{"jsonrpc":"2.0","id":16,"result":[{"range":{"start":{"line":0,"character":4},"end":{"line":0,"character":5}},"command":{"title":"0 ref","command":"ccls.xref","arguments":["{\"usr\":16721564935990383768,\"kind\":4,\"field\":\"uses\"}"]}}]}

• range and command.title are rendered even if the server does not know the actual command. In this particular case, "title": "0 ref" means the declaration has 0 references. The title is more important than whether the command is rendered as a clickable button.
• User clicks the 0 refs button (code lens). As there is no extension to handle the command ccls.xref, coc.nvim can bail out and print an error message in this step, instead of sending

{"title":"0 ref","command":"ccls.xref","arguments":["{\"usr\":16721564935990383768,\"kind\":4,\"field\":\"uses\"}"]}

Here is how CodeLens is rendered in vscode-ccls. These "* refs" are clickable buttons, but whether they are clickable does not matter too much. coc.nvim can print an error message as the command is not supported by an extension.

I feel it is distracting as it takes too much vertical space. emacs-ccls puts all lenses at the line end by default.

[chemzqm]

Coc will use set_virtual_text of neovim for codeLenes feature.