Can't detect the new plugin, if the plugin is put inside if branch

[dlintw]

Warning: I will close the issue without the minimal init.vim and the reproduce ways.

Problems summary

Expected

If I install /usr/bin/ag then 'dein' will install plugin ack.vim.
If there is no /usr/bin/ag then 'dein' will skip install plugin ack.vim.

Environment Information

• OS: Arch Linux
• Vim version: 8.0

Provide a minimal .vimrc with less than 50 lines (Required!)

" Your minimal .vimrc
set runtimepath^=~/path/to/dein.nvim/
call dein#begin(path)
call dein#begin('~/.vim/dein')                                                
call dein#add('~/.vim/dein/repos/github.com/Shougo/dein.vim') 
if executable('ag')                                                         
    call dein#add('mileszs/ack.vim') " :Ack <key> % search local                
endif                       
call dein#end()
call dein#save_state()                                                        
                                                                                
filetype plugin indent on                                                       
syntax enable                                                                   
                                                                                
if dein#check_install()                                                         
  call dein#save_state()                                                        
endif                                                                           
                                                                                
filetype plugin indent on                                                       
syntax enable                                                                   
                                                                                
if dein#check_install()                                                         
  call dein#install()                                                           
endif                                                                       

The reproduce ways from Vim starting (Required!)

1. vim

Screen shot (if possible)

Upload the log messages by :redir and :message

[Mephistophiles]

It's not possible.

[Shougo]

What is the problem?

Can't detect the new plugin, if the plugin is put inside if branch

This is the Vim feature.
The block is not executed.

[dlintw]

Is there any method to install plugin 'ack.vim' only when executable 'ag' exist?
What's the proper .vimrc should I rewrite?

[Shougo]

I think it works.

But the below is better.

    call dein#add('mileszs/ack.vim', {'if': executable('ag')}) " :Ack <key> % search local                

[Shougo]

You use dein cache feature.
The plugin data is already cached. So, the condition check executable('ag') is ignored.

[dlintw]

Thanks for your tip for simple one 'if' logic, but, could you explain a rewrite vimrc for the following logic?

if has("lua")
  call dein#add('Shougo/neocomplete.vim')
elseif has('python')
  call dein#add('Valloric/YouCompleteMe')
endif

[Shougo]

call dein#add('Shougo/neocomplete.vim', {'if': has('lua')})

if !dein#tap('neocomplete.vim')
  call dein#add('Valloric/YouCompleteMe', {'if': has('python')})
endif

[dlintw]

In your previous comment, you said:

You use dein cache feature.
The plugin data is already cached. So, the condition check executable('ag') is ignored.

Does the if !dein#tap should set outside the cache? I mean the .vimrc should be

" minimal .vimrc
set runtimepath^=~/path/to/dein.nvim/
call dein#begin(path)
call dein#begin('~/.vim/dein')                                                
  call dein#add('~/.vim/dein/repos/github.com/Shougo/dein.vim') 
  call dein#add('Shougo/neocomplete.vim', {'if':has('python')})
call dein#end()
call dein#save_state()
if !dein#tap('neocomplete.vim')
  call dein#add('Valloric/YouCompleteMe', {'if': has('python')})
endif
filetype plugin indent on                                                       
syntax enable                                                                   
if dein#check_install()                                                         
  call dein#save_state()                                                        
endif                                                                                                                                     
filetype plugin indent on                                                       
syntax enable                                                          
if dein#check_install()                                                         
  call dein#install()                                                           
endif     

[Shougo]

" minimal .vimrc
set runtimepath^=~/path/to/dein.nvim/
call dein#begin('~/.vim/dein')                                                
call dein#add('~/.vim/dein/repos/github.com/Shougo/dein.vim') 
call dein#add('Shougo/neocomplete.vim', {'if':has('python')})
if !dein#tap('neocomplete.vim')
  call dein#add('Valloric/YouCompleteMe', {'if': has('python')})
endif
call dein#end()
filetype plugin indent on                                                       
syntax enable                                                                   
                                                                                                                               
filetype plugin indent on                                                       
syntax enable                                                          
if dein#check_install()                                                         
  call dein#install()                                                           
endif

dein#tap() is OK after dein#end(), but dein#add() must be before dein#end().