Deprecate implicit vim-scripts expansion

vim-scripts.org is no longer maintained.

Close #625

plug.vim

@@ -579,7 +579,7 @@ function! s:infer_properties(name, repo)
       let uri = repo
     else
       if repo !~ '/'
-        let repo = 'vim-scripts/'. repo
+        throw printf('Invalid argument: %s (implicit `vim-scripts'' expansion is deprecated)', repo)
       endif
       let fmt = get(g:, 'plug_url_format', 'https://git::@github.com/%s.git')
       let uri = printf(fmt, repo)

test/regressions.vader

@@ -230,7 +230,7 @@ Execute (#159: shell=/bin/tcsh):
 **********************************************************************
 Execute (#154: Spaces in &rtp should not be escaped):
   call plug#begin('/tmp/vim-plug-test/plug it')
-  Plug 'seoul256 vim'
+  Plug 'foo/seoul256 vim'
   call plug#end()
   Log &rtp
   Assert stridx(&rtp, 'plug it/seoul256 vim') >= 0
@@ -238,12 +238,12 @@ Execute (#154: Spaces in &rtp should not be escaped):
 **********************************************************************
 Execute (#184: Duplicate entries in &rtp):
   call plug#begin('/tmp/vim-plug-test/plugged')
-  Plug 'plugin1'
-    \| Plug 'plugin0'
+  Plug 'foo/plugin1'
+    \| Plug 'foo/plugin0'
 
-  Plug 'plugin2'
-    \| Plug 'plugin0'
-    \| Plug 'plugin1'
+  Plug 'foo/plugin2'
+    \| Plug 'foo/plugin0'
+    \| Plug 'foo/plugin1'
   call plug#end()
 
   Log &rtp
@@ -311,7 +311,7 @@ Execute (#474: Load ftdetect files in filetypedetect augroup):
 **********************************************************************
 Execute (#489/#587 On-demand loading with 'on' option should trigger BufRead autocmd w/o nomodeline):
   call plug#begin('$PLUG_FIXTURES')
-  Plug 'ftplugin-msg', { 'on': 'XXX' }
+  Plug 'foo/ftplugin-msg', { 'on': 'XXX' }
   call plug#end()
 
   tabnew a.java

test/workflow.vader

@@ -57,12 +57,17 @@ Execute (Test Plug command):
   AssertEqual join([g:temp_plugged, 'vim-emoji/'], '/'), g:plugs['vim-emoji'].dir
 
   " vim-scripts/
-  Plug 'beauty256'
+  Plug 'vim-scripts/beauty256'
   AssertEqual 'file:///tmp/vim-plug-test/vim-scripts/beauty256', g:plugs.beauty256.uri
   AssertEqual 'master', g:plugs.beauty256.branch
 
   AssertEqual 4, len(g:plugs)
 
+  redir => out
+  Plug 'beauty256'
+  redir END
+  Assert out =~ 'Invalid argument: beauty256'
+
 Execute (Plug command with dictionary option):
   Log string(g:plugs)
   Plug 'junegunn/seoul256.vim', { 'branch': 'no-t_co', 'rtp': '././' }
@@ -1230,7 +1235,7 @@ Execute (Using g:plug_url_format):
   let g:plug_url_format = 'git@bitbucket.org:%s.git'
   Plug 'junegunn/seoul256.vim'
   let g:plug_url_format = 'git@bitsocket.org:%s.git'
-  Plug 'beauty256'
+  Plug 'vim-scripts/beauty256'
   AssertEqual 'git@bitbucket.org:junegunn/seoul256.vim.git', g:plugs['seoul256.vim'].uri
   AssertEqual 'git@bitsocket.org:vim-scripts/beauty256.git', g:plugs['beauty256'].uri
   let g:plug_url_format = prev_plug_url_format