Vim stops treating "<Plug>" as a keyword to call functions in insert mode

Question

I have the following configuration in my vimrc file.

inoremap <C-A> <Plug>InsertComment

And somewhere in my vim folder I defined

inoremap <silent> <Plug>InsertComment <ESC>:call INSERT_MY_COMMENT

The mapping worked really well after I configured it. But somehow recently it stopped functioning. And whenever I can to use the Key-bind in the insert mode, instead calling the function that I mapped, vim will just paste the entire <Plug>InsertComment thing to my buffer.

I tried to debug and found out that if I map

inoremap <C-A> <ESC>:call INSERT_MY_COMMENT

it still works as desired, which means there must be something wrong with the <Plug> part.

But I really have no clue on why <Plug> would stop being interpreted by vim as a handle to call other plugins.

I also tried to manually copy and paste

inoremap <silent> <Plug>InsertComment <ESC>:call INSERT_MY_COMMENT
inoremap <C-A> <Plug>InsertComment

in to vim's command line, just to make sure the configurations have not accidentally been unset. But still, vim wouldn't accept that as a function, but rather copy the plain text to buffer.

Answer 1

If you use a nore mapping to tie a sequence of keys to <plug>something, even if there is a mapping behind that <plug>something, it'll be ignored. In the documentation, nore is said to prevent recursion. That's what is happening here.

That means that: the <plug>something mapping shall indeed be defined with noremap, but the actual keybinding chosen shall not.

IOW, the correct definitions become

" in a plugin: 
inoremap <silent> <Plug>InsertComment <c-o>:call INSERT_MY_COMMENT()<cr>

" in your .vimrc
imap <C-A> <Plug>InsertComment

Answer 2

Your problem is that you are using

inoremap <C-A> <Plug>InsertComment

That basically means, that recursive resolution of your mapped keys is prevented which is usually not what you want. Therefore change your mapping to

imap <C-A> <Plug>InsertComment

See also the extensive help

(Start reading from the paragraph that starts with MAPPING)