dein package manager not installing plugins

Question

I'm very confused by the documentation in dein. It says:

dein#add({repo}[, {options}])
        Initialize a plugin.
        {repo} is the repository URI or local repository directory
        path.  If {repo} starts with github user name (ex:
        "Shougo/dein.vim"), dein will install github plugins.
        See |dein-options| for what to set in {options}.
        Note: You must call it in |dein#begin()| block.

So it sounds to me like I can just drop in call dein#add('dense-analysis/ale') and the plugin will be installed.

But the dense-analysis/ale plugin I want to use never gets installed and downloaded. I have the following in my .vimrc:

if dein#load_state('~/git_repos/dein')
  call dein#begin('~/git_repos/dein')

  " load plugins
    call dein#add('~/git_repos/dein/repos/github.com/Shougo/dein.vim')
    call dein#add('dense-analysis/ale')
    if !has('nvim')
      call dein#add('roxma/nvim-yarp')
      call dein#add('roxma/vim-hug-neovim-rpc')
    endif

  call dein#end()
  call dein#save_state()
endif

Answer 1

You need to call the "install" function after you open Vim with the vimrc including the dein configuration:

:call dein#install()

See step 3 in the "Quick Start" part of dein's README:

3. Open vim and install dein

:call dein#install()