How to search within a vimscript function

FWIW, this looks a lot like a job for the built-in :help definition-search but, for some reason, the default ftplugin for Ruby doesn't set :help 'define', which is crucial for this feature to work.

Let's fix that by creating after/ftplugin/ruby.vim and populating it with the following line:

setlocal define=\^\\s\*\\(class\\\|def\\\|module\\) 

which essentially tells Vim to look for lines that start with either class, def, or module as cues when searching for "definitions".

Once that is done, we can simply leverage the built-in :help :djump:

:dj Annotation 

or even:

:dj annotation 

if :help 'ignorecase' is on.

And, if you really want a mapping (though :dj compares quite well to your <leader>gtoc), you can go with a very simple:

nnoremap <key> :djump<Space> 

Bonus: you also get [D and friends.

Let's start by removing those useless colons:

function! GotoClass(className) normal! 1G normal! /class\s\+ . a:className<CR> endfunction nnoremap <key> :call GotoClass(input('Class name: '))<CR> 

Now, the most obvious issue is that :help :normal can't do concatenation.

The following line literally searches for class, followed by one or more whitespace characters, followed by a space, followed by any character except \n, followed by a space, followed by a:className<CR>:

normal! /class\s\+ . a:className<CR> 

which is unlikely to find any match, which explains why your function only moves the cursor to the top of the buffer. Also, the <CR> is useless in this context.

A simple fix would be to use :help :execute, which does concatenation:

function! GotoClass(className) normal! 1G execute "normal! /class\s\+" . a:className endfunction nnoremap <key> :call GotoClass(input('Class name: '))<CR> 

But we can do better. Instead of abusing :normal, which doesn't really add any value here, let's use :help :/ to replace these two lines:

normal! 1G execute "normal! /class\s\+" . a:className 

with a single line:

function! GotoClass(className) execute "1/class\s\+" . a:className endfunction nnoremap <key> :call GotoClass(input('Class name: '))<CR> 

Let's not stop there! Is that custom function really necessary? We could use :help search() and get rid of it:

nnoremap <key> <Cmd>1call search('class\s\+' . input('Class name: '))<CR> 

At this point I wanted to go even further with :help searchdecl(), which would have allowed me to get rid of concatenation, but it proved to be a lot less reliable than I expected so I'm afraid I reached the end of the line.