patch 9.1.1863: Cannot test for working "+" register

Problem:  Cannot test for working "+" register
Solution: Add a few more feature tests (Foxe Chen)

closes: #18541

Signed-off-by: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/clipboard.c

@@ -3573,7 +3573,6 @@ get_clipmethod(char_u *str, bool *plus UNUSED, bool *star)
 #endif
 		*star = star_avail == 1;
 	    }
-
 	    else if (
 #ifndef ONE_CLIPBOARD
 		    plus_avail == -1 ||
@@ -3585,7 +3584,6 @@ get_clipmethod(char_u *str, bool *plus UNUSED, bool *star)
 		goto exit;
 	    }
 	}
-
 	// Keep on going in order to catch errors
 	if (method != CLIPMETHOD_NONE && ret == CLIPMETHOD_FAIL)
 	    ret = method;

src/evalfunc.c

@@ -7929,8 +7929,22 @@ f_has(typval_T *argvars, typval_T *rettv)
 	else if (STRICMP(name, "clipboard_working") == 0)
 	{
 	    x = TRUE;
+#ifdef FEAT_CLIPBOARD
+	    n = clip_star.available || clip_plus.available;
+#endif
+	}
+	else if (STRICMP(name, "clipboard_star_avail") == 0)
+	{
+	    x = TRUE;
 #ifdef FEAT_CLIPBOARD
 	    n = clip_star.available;
+#endif
+	}
+	else if (STRICMP(name, "clipboard_plus_avail") == 0)
+	{
+	    x = TRUE;
+#ifdef FEAT_CLIPBOARD
+	    n = clip_plus.available && &clip_star != &clip_plus;
 #endif
 	}
     }

src/testdir/test_eval_stuff.vim

@@ -727,4 +727,48 @@ func Test_eval_string_in_special_key()
   silent! echo 0{1-$"\<S--{>n|nö%
 endfunc
 
+func AvailableTest()
+  return g:vim_test_plus .. g:vim_test_star
+endfunc
+
+func Test_clipboard_runtime_features()
+  " Use clipboard provider because we can change if a register is available or
+  " not.
+  CheckFeature clipboard_provider
+  CheckFeature clipboard
+
+    let g:vim_test_plus = ''
+    let g:vim_test_star = ''
+
+  let v:clipproviders["evaltest"] = {
+        \ "available": function("AvailableTest")
+        \ }
+
+  set clipmethod=evaltest
+
+  if has('win32') || has('macunix')
+    let g:vim_test_plus = '+'
+    let g:vim_test_star = '*'
+    clipreset
+
+    " plus register should be disabled on windows or macos
+    call assert_equal(0, has('clipboard_plus_avail'))
+    call assert_equal(1, has('clipboard_star_avail'))
+  else
+    let g:vim_test_plus = '+'
+    let g:vim_test_star = '*'
+    clipreset
+
+    call assert_equal(1, has('clipboard_plus_avail'))
+    call assert_equal(1, has('clipboard_star_avail'))
+
+    let g:vim_test_plus = ""
+    clipreset
+
+    call assert_equal(0, has('clipboard_plus_avail'))
+  endif
+
+  set clipmethod&
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1863,
 /**/
     1862,
 /**/