checker: reject void type condition (#8737)

vlib/builtin/cfns.c.v

@@ -213,7 +213,7 @@ fn C.RemoveDirectory() int
 fn C.GetStdHandle(u32) voidptr
 
 // fn C.SetConsoleMode()
-fn C.SetConsoleMode(voidptr, u32)
+fn C.SetConsoleMode(voidptr, u32) int
 
 // fn C.GetConsoleMode() int
 fn C.GetConsoleMode(voidptr, &u32) int

vlib/v/checker/checker.v

@@ -4755,10 +4755,7 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) table.Type {
 				// check condition type is boolean
 				c.expected_type = table.bool_type
 				cond_typ := c.expr(branch.cond)
-				if cond_typ.idx() !in [table.bool_type_idx, table.void_type_idx]
-					&& !c.pref.translated {
-					// void types are skipped, because they mean the var was initialized incorrectly
-					// (via missing function etc)
+				if cond_typ.idx() != table.bool_type_idx && !c.pref.translated {
 					typ_sym := c.table.get_type_symbol(cond_typ)
 					c.error('non-bool type `$typ_sym.name` used as if condition', branch.pos)
 				}

vlib/v/checker/tests/if_non_bool_cond.out

@@ -0,0 +1,20 @@
+vlib/v/checker/tests/if_non_bool_cond.vv:2:2: error: non-bool type `string` used as if condition
+    1 | fn main() {
+    2 |     if '10' {
+      |     ~~~~~~~
+    3 |         println('10')
+    4 |     }
+vlib/v/checker/tests/if_non_bool_cond.vv:6:2: error: non-bool type `int literal` used as if condition
+    4 |     }
+    5 | 
+    6 |     if 5 {
+      |     ~~~~
+    7 |         println(5)
+    8 |     }
+vlib/v/checker/tests/if_non_bool_cond.vv:10:2: error: non-bool type `void` used as if condition
+    8 |     }
+    9 | 
+   10 |     if println('v') {
+      |     ~~~~~~~~~~~~~~~
+   11 |         println('println')
+   12 |     }

vlib/v/checker/tests/if_non_bool_cond.vv

@@ -0,0 +1,13 @@
+fn main() {
+	if '10' {
+		println('10')
+	}
+
+	if 5 {
+		println(5)
+	}
+
+	if println('v') {
+		println('println')
+	}
+}