patch 8.2.0188: Check commands don't work well with Vim9 script

Problem:    Check commands don't work well with Vim9 script.
Solution:   Improve constant expression handling.

src/testdir/check.vim

@@ -1,10 +1,12 @@
 source shared.vim
 
+command -nargs=1 MissingFeature throw 'Skipped: ' .. <args> .. ' feature missing'
+
 " Command to check for the presence of a feature.
 command -nargs=1 CheckFeature call CheckFeature(<f-args>)
 func CheckFeature(name)
   if !has(a:name)
-    throw 'Skipped: ' .. a:name .. ' feature missing'
+    MissingFeature a:name
   endif
 endfunc
 

src/testdir/test_vim9_expr.vim

@@ -31,7 +31,9 @@ def Test_expr1()
 
   assert_equal('two', false ? 'one' : 'two')
   assert_equal('two', 0 ? 'one' : 'two')
+  if has('float')
     assert_equal('two', 0.0 ? 'one' : 'two')
+  endif
   assert_equal('two', '' ? 'one' : 'two')
 "  assert_equal('one', 0z ? 'one' : 'two')
   assert_equal('two', [] ? 'one' : 'two')
@@ -420,7 +422,9 @@ def Test_expr5()
 enddef
 
 def Test_expr5_float()
-  CheckFeature float
+  if !has('float')
+    MissingFeature 'float'
+  else
     assert_equal(66.0, 60.0 + 6.0)
     assert_equal(66.0, 60.0 + 6)
     assert_equal(66.0, 60 + 6.0)
@@ -436,6 +440,7 @@ def Test_expr5_float()
     assert_equal(7.9, 8 - g:afloat)
     assert_equal(9.9, g:anint - g:afloat)
     assert_equal(-9.9, g:afloat - g:anint)
+  endif
 enddef
 
 func Test_expr5_fails()
@@ -476,8 +481,9 @@ def Test_expr6()
 enddef
 
 def Test_expr6_float()
-  CheckFeature float
+  if !has('float')
-
+    MissingFeature 'float'
+  else
     assert_equal(36.0, 6.0 * 6)
     assert_equal(36.0, 6 * 6.0)
     assert_equal(36.0, 6.0 * 6.0)
@@ -497,6 +503,7 @@ def Test_expr6_float()
     assert_equal(4.0, 6.0 * 4.0 / 6.0)
 
     assert_equal(4.0, 6.0 * 4.0 / 6.0)
+  endif
 enddef
 
 func Test_expr6_fails()
@@ -581,7 +588,9 @@ enddef
 
 def Test_expr7_float()
   " float constant
-  if has('float')
+  if !has('float')
+    MissingFeature 'float'
+  else
     assert_equal(g:float_zero, .0)
     assert_equal(g:float_zero, 0.0)
     assert_equal(g:float_neg, -9.8)

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    188,
 /**/
     187,
 /**/

src/vim9compile.c

@@ -3460,14 +3460,31 @@ new_scope(cctx_T *cctx, scopetype_T type)
 }
 
 /*
- * Evaluate an expression that is a constant: has(arg)
+ * Evaluate an expression that is a constant:
+ *  has(arg)
+ *
+ * Also handle:
+ *  ! in front		logical NOT
+ *
  * Return FAIL if the expression is not a constant.
  */
     static int
-evaluate_const_expr4(char_u **arg, cctx_T *cctx UNUSED, typval_T *tv)
+evaluate_const_expr7(char_u **arg, cctx_T *cctx UNUSED, typval_T *tv)
 {
     typval_T	argvars[2];
+    char_u	*start_leader, *end_leader;
 
+    /*
+     * Skip '!' characters.  They are handled later.
+     */
+    start_leader = *arg;
+    while (**arg == '!')
+	*arg = skipwhite(*arg + 1);
+    end_leader = *arg;
+
+    /*
+     * Recognize only has() for now.
+     */
     if (STRNCMP("has(", *arg, 4) != 0)
 	return FAIL;
     *arg = skipwhite(*arg + 4);
@@ -3497,6 +3514,13 @@ evaluate_const_expr4(char_u **arg, cctx_T *cctx UNUSED, typval_T *tv)
     f_has(argvars, tv);
     clear_tv(&argvars[0]);
 
+    while (start_leader < end_leader)
+    {
+	if (*start_leader == '!')
+	    tv->vval.v_number = !tv->vval.v_number;
+	++start_leader;
+    }
+
     return OK;
 }
 
@@ -3529,7 +3553,7 @@ evaluate_const_and_or(char_u **arg, cctx_T *cctx, char *op, typval_T *tv)
 	    *arg = skipwhite(p + 2);
 	    tv2.v_type = VAR_UNKNOWN;
 	    if ((opchar == '|' ? evaluate_const_expr3(arg, cctx, &tv2)
-			       : evaluate_const_expr4(arg, cctx, &tv2)) == FAIL)
+			       : evaluate_const_expr7(arg, cctx, &tv2)) == FAIL)
 	    {
 		clear_tv(&tv2);
 		return FAIL;
@@ -3558,7 +3582,7 @@ evaluate_const_and_or(char_u **arg, cctx_T *cctx, char *op, typval_T *tv)
 evaluate_const_expr3(char_u **arg, cctx_T *cctx, typval_T *tv)
 {
     // evaluate the first expression
-    if (evaluate_const_expr4(arg, cctx, tv) == FAIL)
+    if (evaluate_const_expr7(arg, cctx, tv) == FAIL)
 	return FAIL;
 
     // || and && work almost the same