patch 8.2.1528: Vim9: :endif not found after "if false"

Problem:    Vim9: :endif not found after "if false".
Solution:   When skipping still check for a following command. (closes #6797)

Author: brammool

src/testdir/test_vim9_script.vim

@@ -2122,6 +2122,14 @@ def Test_if_const_expr()
     res = true
   endif
   assert_equal(false, res)
+
+  # with constant "false" expression may be invalid so long as the syntax is OK
+  if false | eval 0 | endif
+  if false | eval burp + 234 | endif
+  if false | echo burp 234 'asd' | endif
+  if false
+    burp
+  endif
 enddef
 
 def Test_if_const_expr_fails()

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1528,
 /**/
     1527,
 /**/

src/vim9compile.c

@@ -4014,6 +4014,13 @@ compile_expr1(char_u **arg,  cctx_T *cctx, ppconst_T *ppconst)
     int		ppconst_used = ppconst->pp_used;
     char_u	*next;
 
+    // Ignore all kinds of errors when not producing code.
+    if (cctx->ctx_skip == SKIP_YES)
+    {
+	skip_expr(arg);
+	return OK;
+    }
+
     // Evaluate the first expression.
     if (compile_expr2(arg, cctx, ppconst) == FAIL)
 	return FAIL;
@@ -6724,17 +6731,8 @@ compile_def_function(ufunc_T *ufunc, int set_return_type, cctx_T *outer_cctx)
 
 	p = skipwhite(p);
 
-	if (cctx.ctx_skip == SKIP_YES
-		&& ea.cmdidx != CMD_if
+	if (cctx.ctx_had_return
 		&& ea.cmdidx != CMD_elseif
-		&& ea.cmdidx != CMD_else
-		&& ea.cmdidx != CMD_endif)
-	{
-	    line = (char_u *)"";
-	    continue;
-	}
-
-	if (ea.cmdidx != CMD_elseif
 		&& ea.cmdidx != CMD_else
 		&& ea.cmdidx != CMD_endif
 		&& ea.cmdidx != CMD_endfor
@@ -6743,11 +6741,8 @@ compile_def_function(ufunc_T *ufunc, int set_return_type, cctx_T *outer_cctx)
 		&& ea.cmdidx != CMD_finally
 		&& ea.cmdidx != CMD_endtry)
 	{
-	    if (cctx.ctx_had_return)
-	    {
-		emsg(_(e_unreachable_code_after_return));
-		goto erret;
-	    }
+	    emsg(_(e_unreachable_code_after_return));
+	    goto erret;
 	}
 
 	switch (ea.cmdidx)
@@ -6845,7 +6840,7 @@ compile_def_function(ufunc_T *ufunc, int set_return_type, cctx_T *outer_cctx)
 		    if (compile_expr0(&p, &cctx) == FAIL)
 			goto erret;
 
-		    // drop the return value
+		    // drop the result
 		    generate_instr_drop(&cctx, ISN_DROP, 1);
 
 		    line = skipwhite(p);
@@ -6859,7 +6854,7 @@ compile_def_function(ufunc_T *ufunc, int set_return_type, cctx_T *outer_cctx)
 		    line = compile_mult_expr(p, ea.cmdidx, &cctx);
 		    break;
 
-	    // TODO: other commands with an expression argument
+	    // TODO: any other commands with an expression argument?
 
 	    case CMD_append:
 	    case CMD_change:
@@ -6870,8 +6865,14 @@ compile_def_function(ufunc_T *ufunc, int set_return_type, cctx_T *outer_cctx)
 		    goto erret;
 
 	    case CMD_SIZE:
-		    semsg(_(e_invalid_command_str), ea.cmd);
-		    goto erret;
+		    if (cctx.ctx_skip != SKIP_YES)
+		    {
+			semsg(_(e_invalid_command_str), ea.cmd);
+			goto erret;
+		    }
+		    // We don't check for a next command here.
+		    line = (char_u *)"";
+		    break;
 
 	    default:
 		    // Not recognized, execute with do_cmdline_cmd().