provider: skip non-provider has() feature-names

We don't want to retry autoload sourcing (slow) for every random has()
query that finds it way to eval_call_provider().

src/nvim/eval.c

@@ -23969,28 +23969,37 @@ typval_T eval_call_provider(char *provider, char *method, list_T *arguments)
 }
 
 /// Checks if a named provider is enabled.
-bool eval_has_provider(const char *provider)
+bool eval_has_provider(const char *name)
 {
+  if (!strequal(name, "clipboard")
+      && !strequal(name, "python")
+      && !strequal(name, "python3")
+      && !strequal(name, "ruby")
+      && !strequal(name, "node")) {
+    // Avoid autoload for non-provider has() features.
+    return false;
+  }
+
   char buf[256];
   int len;
   typval_T tv;
 
   // Get the g:loaded_xx_provider variable.
-  len = snprintf(buf, sizeof(buf), "g:loaded_%s_provider", provider);
+  len = snprintf(buf, sizeof(buf), "g:loaded_%s_provider", name);
   if (get_var_tv(buf, len, &tv, NULL, false, true) == FAIL) {
     // Trigger autoload once.
-    len = snprintf(buf, sizeof(buf), "provider#%s#bogus", provider);
+    len = snprintf(buf, sizeof(buf), "provider#%s#bogus", name);
     script_autoload(buf, len, false);
 
     // Retry the (non-autoload-style) variable.
-    len = snprintf(buf, sizeof(buf), "g:loaded_%s_provider", provider);
+    len = snprintf(buf, sizeof(buf), "g:loaded_%s_provider", name);
     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);
+      snprintf(buf, sizeof(buf), "provider#%s#Call", name);
       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);
+              name, name);
       }
       return false;
     }

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

@@ -1,2 +0,0 @@
-" A dummy test provider
-let g:loaded_brokencall_provider = 2

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

@@ -1,6 +1,6 @@
 " Dummy test provider, missing this required variable:
 "   let g:loaded_brokenenabled_provider = 0
 
-function! provider#brokenenabled#Call(method, args)
+function! provider#python#Call(method, args)
   return 42
 endfunction

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

@@ -0,0 +1,2 @@
+" A dummy test provider
+let g:loaded_ruby_provider = 2

test/functional/provider/provider_spec.lua

@@ -11,11 +11,15 @@ describe('providers', function()
 
   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')")
+    -- Using test-fixture with broken impl:
+    -- test/functional/fixtures/autoload/provider/python.vim
+    expect_err('Vim:provider: python: missing required variable g:loaded_python_provider',
+      eval, "has('python')")
   end)
 
   it('without Call() but with g:loaded_xx_provider', function()
-    eq(1, eval("has('brokencall')"))
+    -- Using test-fixture with broken impl:
+    -- test/functional/fixtures/autoload/provider/ruby.vim
+    eq(1, eval("has('ruby')"))
   end)
 end)