Execution of nnoremap takes significant time

Question

I am developing a vim plugin and I have set a default mapping this way.

if !hasmapto('<Plug>DumpDebugString')
    nmap <unique> <Leader>ds  <Plug>DumpDebugString
    nmap <unique> <Leader>dS  <Plug>DumpDebugStringExpr
endif

...

nnoremap <silent> <Plug>DumpDebugString :<C-U> :call <SID>debugFunctionWrapper(0)<CR>
nnoremap <silent> <Plug>DumpDebugStringExpr :<C-U> :call <SID>debugFunctionWrapper(1)<CR>

When I try invoking ds the DumpDebugString method runs correctly but takes some time actually get called in the first place. It is run instantly only if I map it like this:

nmap <leader>ds <Plug>DumpDebugString<CR>

But the extra <CR> shouldn't be needed since it already included in the nnoremap call.

• I don't think it has anything to do with the actual mapping characters or with the use of <Plug>.
• Substituting :call <SID>debugFunctionWrapper(0)<CR> with something like :call str2nr("1")<CR> doesn't seem to solve the problem
• Adding <nowait> doesn't do anything.

For the story, here's the plugin: https://github.com/bergercookie/vim-debugstring

Answer 1

When you press Leader d s, Vim expands the keysequence into <plug>DumpDebugString. However, it doesn't expand the latter immediately, because it waits for you to maybe press Expr afterwards. This is due to the other <plug> mapping:

nmap <nowait> <unique> <Leader>dS  <Plug>DumpDebugStringExpr
                                                        ^^^^
                                                        Vim waits `&ttimeout` ms for these keys to be typed

One solution is to surround all your <plug> mappings with parentheses:

nmap <unique> <Leader>ds  <Plug>(DumpDebugString)
nmap <unique> <Leader>dS  <Plug>(DumpDebugStringExpr)

Now, when you press Leader d s, and it gets expanded into <plug>(DumpDebugString), there's no ambiguity anymore. Vim doesn't wait for Expr to be typed because there's no <plug>(DumpDebugString)Expr mapping.