Inserting strings with `<plug>` inside `<cmd>`

Question

When using <cmd>...<cr>, there are some special keys such as <plug> or <cmd> that are not allowed to be contained inside the block. Trying to execute the command will result in:

E5521: <Cmd> mapping must end with <CR> before second <Cmd>

E5522: <Cmd> mapping must not include <Plug> key

However, sometimes these special keys may appear in the mapping, not to be executed, but inside strings. A practical example is vim-repeat. If you want to set it up by calling repeat#set, there'll most likely be a <plug> key in the string passed to the function:

<cmd>call repeat#set("\<Plug>MyWonderfulMap", v:count)<cr>

The "\<Plug>" should not part of the execution, but simply part of the string. However, the above will still fail, since <Plug> is still between <cmd> and <cr>. We are forced to use the : alternative:

:call repeat#set("\<Plug>MyWonderfulMap", v:count)<cr>

This is sub-optimal however, since it does not work for insert and visual modes.

So knowing that, is there a way to pass the key <plug> inside a function, without it being caught by the <cmd>...<cr> block?

Answer 1

It is possible if you manage escaping rules very carefully. For example,

nnoremap x <cmd>echo "<bslash><lt>Plug>MyWonderfulMap" v:count<cr>

Then :map x prints:

n  x           * <Cmd>echo "\<Plug>MyWonderfulMap" v:count<CR>

And typing 3x echos, as expected,

<80><fd>SMyWonderfulMap 3

Breaking what is happening here down by interpolation step:

1. nnoremap substitutes all the <> escape codes, <bslash> becomes \ and <lt> becomes <.

2. when the map is executed, normal double quotes rules substitutes \<Plug> with the sequence <80><fd>S which is vim's way of denoting plug maps.