provider: decide status by g:loaded_xx_provider

runtime/autoload/provider/clipboard.vim

@@ -1,6 +1,16 @@
 " The clipboard provider uses shell commands to communicate with the clipboard.
 " The provider function will only be registered if a supported command is
 " available.
+
+if exists('g:loaded_clipboard_provider')
+  finish
+endif
+" Default to FALSE.  Set by provider#clipboard#Executable() later.
+" To force a reload:
+"   :unlet g:loaded_clipboard_provider
+"   :runtime autoload/provider/clipboard.vim
+let g:loaded_clipboard_provider = 0
+
 let s:copy = {}
 let s:paste = {}
 let s:clipboard = {}
@@ -48,9 +58,6 @@ endfunction
 let s:cache_enabled = 1
 let s:err = ''
 
-" eval_has_provider checks the variable to verify provider status
-let g:provider#clipboard#enabled = 0
-
 function! provider#clipboard#Error() abort
   return s:err
 endfunction
@@ -123,12 +130,6 @@ function! provider#clipboard#Executable() abort
   return ''
 endfunction
 
-" Call this to setup/reload the provider
-function! provider#clipboard#Reload()
-  " #enabled is used by eval_has_provider()
-  let g:provider#clipboard#enabled = !empty(provider#clipboard#Executable())
-endfunction
-
 function! s:clipboard.get(reg) abort
   if type(s:paste[a:reg]) == v:t_func
     return s:paste[a:reg]()
@@ -195,4 +196,5 @@ function! provider#clipboard#Call(method, args) abort
   endtry
 endfunction
 
-call provider#clipboard#Reload()
+" eval_has_provider() decides based on this variable.
+let g:loaded_clipboard_provider = !empty(provider#clipboard#Executable())

runtime/autoload/provider/node.vim

@@ -1,8 +1,7 @@
 if exists('g:loaded_node_provider')
   finish
 endif
-let g:loaded_node_provider = 1
-let g:provider#node#enabled = 0
+let g:loaded_node_provider = 0
 
 function! s:is_minimum_version(version, min_major, min_minor) abort
   if empty(a:version)
@@ -141,12 +140,10 @@ endfunction
 
 let s:err = ''
 let s:prog = provider#node#Detect()
+let g:loaded_node_provider = !empty(s:prog)
 
-if empty(s:prog)
+if !g:loaded_node_provider
   let s:err = 'Cannot find the "neovim" node package. Try :checkhealth'
-else
-  let g:provider#node#enabled = 1
 endif
 
 call remote#host#RegisterPlugin('node-provider', 'node', [])
-

runtime/autoload/provider/python.vim

@@ -7,10 +7,8 @@
 if exists('g:loaded_python_provider')
   finish
 endif
-let g:loaded_python_provider = 1
-
 let [s:prog, s:err] = provider#pythonx#Detect(2)
-let g:provider#python#enabled = !empty(s:prog)
+let g:loaded_python_provider = !empty(s:prog)
 
 function! provider#python#Prog() abort
   return s:prog

runtime/autoload/provider/python3.vim

@@ -7,10 +7,8 @@
 if exists('g:loaded_python3_provider')
   finish
 endif
-let g:loaded_python3_provider = 1
-
 let [s:prog, s:err] = provider#pythonx#Detect(3)
-let g:provider#python3#enabled = !empty(s:prog)
+let g:loaded_python3_provider = !empty(s:prog)
 
 function! provider#python3#Prog() abort
   return s:prog

runtime/autoload/provider/ruby.vim

@@ -2,12 +2,11 @@
 if exists('g:loaded_ruby_provider')
   finish
 endif
-let g:loaded_ruby_provider = 1
+let g:loaded_ruby_provider = 0
 
 function! provider#ruby#Detect() abort
   return s:prog
 endfunction
-let g:provider#ruby#enabled = 0
 
 function! provider#ruby#Prog() abort
   return s:prog
@@ -63,11 +62,10 @@ endfunction
 let s:err = ''
 let s:prog = s:detect()
 let s:plugin_path = expand('<sfile>:p:h') . '/script_host.rb'
+let g:loaded_ruby_provider = !empty(s:prog)
 
-if empty(s:prog)
+if !g:loaded_ruby_provider
   let s:err = 'Cannot find the neovim RubyGem. Try :checkhealth'
-else
-  let g:provider#ruby#enabled = 1
 endif
 
 call remote#host#RegisterClone('legacy-ruby-provider', 'ruby')

runtime/doc/develop.txt

@@ -84,12 +84,11 @@ Developer guidelines				        *dev-guidelines*
 
 PROVIDERS 						*dev-provider*
 
-A goal of Nvim is to allow extension of the editor without special knowledge
-in the core. But some Vim components are too tightly coupled; in those cases
-a "provider" hook is exposed.
+A primary goal of Nvim is to allow extension of the editor without special
+knowledge in the core.  Some core functions are delegated to "providers"
+implemented as external scripts.
 
-Consider two examples of integration with external systems that are
-implemented in Vim and are now decoupled from Nvim core as providers:
+Examples:
 
 1. In the Vim source code, clipboard logic accounts for more than 1k lines of
    C source code (ui.c), to perform two tasks that are now accomplished with
@@ -101,29 +100,28 @@ implemented in Vim and are now decoupled from Nvim core as providers:
    scripting is performed by an external host process implemented in ~2k lines
    of Python.
 
-Ideally we could implement Python and clipboard integration in pure vimscript
-and without touching the C code. But this is infeasible without compromising
-backwards compatibility with Vim; that's where providers help.
+The provider framework invokes VimL from C.  It is composed of two functions
+in eval.c:
 
-The provider framework helps call vimscript from C. It is composed of two
-functions in eval.c:
-
-- eval_call_provider(name, method, arguments): calls provider#(name)#Call
+- eval_call_provider(name, method, arguments): calls provider#{name}#Call
   with the method and arguments.
-- eval_has_provider(name): Checks if a provider is implemented. Returns true
-  if the provider#(name)#enabled variable is not 0. Called by |has()|
-  (vimscript) to check if features are available.
-
-The provider#(name)#Call function implements integration with an external
-system, because shell commands and |RPC| clients are easier to work with in
-vimscript.
+- eval_has_provider(name): Checks the `g:loaded_{name}_provider` variable
+  which must be set by the provider script to indicate whether it is enabled
+  and working. Called by |has()| to check if features are available.
 
 For example, the Python provider is implemented by the
-autoload/provider/python.vim script; the variable provider#python#enabled is only
-1 if a valid external Python host is found. That works well with the
-`has('python')` expression (normally used by Python plugins) because if the
-Python host isn't installed then the plugin will "think" it is running in
-a Vim compiled without the "+python" feature.
+"autoload/provider/python.vim" script, which sets `g:loaded_python_provider`
+to TRUE only if a valid external Python host is found.  Then `has("python")`
+reflects whether Python support is working.
+
+							*provider-reload*
+Sometimes a GUI or other application may want to force a provider to
+"reload".  To reload a provider, undefine its "loaded" flag, then use
+|:runtime| to reload it: >
+
+    :unlet g:loaded_clipboard_provider
+    :runtime autoload/provider/clipboard.vim
+
 
 DOCUMENTATION						*dev-doc*
 

src/nvim/eval.c

@@ -23968,27 +23968,35 @@ typval_T eval_call_provider(char *provider, char *method, list_T *arguments)
   return rettv;
 }
 
-/// Check if a named provider is enabled
+/// Checks if a named provider is enabled.
 bool eval_has_provider(const char *provider)
 {
-  char enabled_varname[256];
-  int enabled_varname_len = snprintf(enabled_varname, sizeof(enabled_varname),
-                                     "provider#%s#enabled", provider);
-
+  char buf[256];
+  int len;
   typval_T tv;
-  if (get_var_tv(enabled_varname, enabled_varname_len, &tv,
-                 NULL, false, false) == FAIL) {
-    char call_varname[256];
-    snprintf(call_varname, sizeof(call_varname), "provider#%s#Call", provider);
-    int has_call = !!find_func((char_u *)call_varname);
 
-    if (has_call && p_lpl) {
-      emsgf("Provider '%s' failed to set %s", provider, enabled_varname);
+  // Get the g:loaded_xx_provider variable.
+  len = snprintf(buf, sizeof(buf), "g:loaded_%s_provider", provider);
+  if (get_var_tv(buf, len, &tv, NULL, false, true) == FAIL) {
+    // Trigger autoload once.
+    len = snprintf(buf, sizeof(buf), "provider#%s#bogus", provider);
+    script_autoload(buf, len, false);
+
+    // Retry the (non-autoload-style) variable.
+    len = snprintf(buf, sizeof(buf), "g:loaded_%s_provider", provider);
+    if (get_var_tv(buf, len, &tv, NULL, false, true) == FAIL) {
+      // Show a hint if Call() is defined but g:loaded_xx_provider is missing.
+      snprintf(buf, sizeof(buf), "provider#%s#Call", provider);
+      bool has_call = !!find_func((char_u *)buf);
+      if (has_call && p_lpl) {
+        emsgf("provider: %s: missing required variable g:loaded_%s_provider",
+              provider, provider);
+      }
+      return false;
     }
-    return false;
   }
 
-  return (tv.v_type == VAR_NUMBER) ? tv.vval.v_number != 0: true;
+  return (tv.v_type == VAR_NUMBER) ? !!tv.vval.v_number : false;
 }
 
 /// Writes "<sourcing_name>:<sourcing_lnum>" to `buf[bufsize]`.

test/functional/fixtures/autoload/provider/brokencall.vim

@@ -1,2 +1,2 @@
 " A dummy test provider
-let g:provider#brokencall#enabled = 1
+let g:loaded_brokencall_provider = 1

test/functional/fixtures/autoload/provider/brokenenabled.vim

@@ -1,5 +1,5 @@
-" Dummy test provider, missing
-" let g:provider#brokenenabled#enabled = 0
+" Dummy test provider, missing this required variable:
+"   let g:loaded_brokenenabled_provider = 0
 
 function! provider#brokenenabled#Call(method, args)
   return 42

test/functional/fixtures/autoload/provider/clipboard.vim

@@ -1,3 +1,5 @@
+let g:loaded_clipboard_provider = 1
+
 let g:test_clip = { '+': [''], '*': [''], }
 
 let s:methods = {}
@@ -35,8 +37,6 @@ function! s:methods.set(lines, regtype, reg)
   let g:test_clip[a:reg] = [a:lines, a:regtype]
 endfunction
 
-let provider#clipboard#enabled = 1
-
 function! provider#clipboard#Call(method, args)
   return call(s:methods[a:method],a:args,s:methods)
 endfunction

test/functional/provider/provider_spec.lua

@@ -1,19 +1,21 @@
 
 local helpers = require('test.functional.helpers')(after_each)
-local clear, eq, feed_command, eval = helpers.clear, helpers.eq, helpers.feed_command, helpers.eval
+local clear, eq, eval = helpers.clear, helpers.eq, helpers.eval
+local command = helpers.command
+local expect_err = helpers.expect_err
 
-describe('Providers', function()
+describe('providers', function()
   before_each(function()
     clear('--cmd', 'let &rtp = "test/functional/fixtures,".&rtp')
   end)
 
-  it('must set the enabled variable or fail', function()
-    eq(42, eval("provider#brokenenabled#Call('dosomething', [])"))
-	feed_command("call has('brokenenabled')")
-    eq(0, eval("has('brokenenabled')"))
+  it('must define g:loaded_xx_provider', function()
+    command('set loadplugins')
+    expect_err('Vim:provider: brokenenabled: missing required variable g:loaded_brokenenabled_provider',
+      eval, "has('brokenenabled')")
   end)
 
-  it('without Call() are enabled', function()
+  it('without Call() but with g:loaded_xx_provider', function()
     eq(1, eval("has('brokencall')"))
   end)
 end)