builtin,checker: remove @[markused] from fn isnil(), set c.table.used_features.auto_str_ptr = true instead (#23464)

Author: kbkpbot

vlib/builtin/builtin.v

@@ -5,7 +5,7 @@
 module builtin
 
 // isnil returns true if an object is nil (only for C objects).
-@[inline; markused]
+@[inline]
 pub fn isnil(v voidptr) bool {
 	return v == 0
 }

vlib/v/checker/str.v

@@ -56,12 +56,12 @@ fn (mut c Checker) string_inter_lit(mut node ast.StringInterLiteral) ast.Type {
 		if c.pref.skip_unused && !c.is_builtin_mod {
 			if !c.table.sym(ftyp).has_method('str') {
 				c.table.used_features.auto_str = true
-				if ftyp.is_ptr() {
-					c.table.used_features.auto_str_ptr = true
-				}
 			} else {
 				c.table.used_features.print_types[ftyp.idx()] = true
 			}
+			if ftyp.is_ptr() {
+				c.table.used_features.auto_str_ptr = true
+			}
 			c.table.used_features.interpolation = true
 		}
 		c.fail_if_unreadable(expr, ftyp, 'interpolation object')

vlib/v/tests/skip_unused/auto_string.run.out

@@ -0,0 +1,3 @@
+Hello Tom
+C->&Tom
+&1.24

vlib/v/tests/skip_unused/auto_string.skip_unused.run.out

@@ -0,0 +1,3 @@
+Hello Tom
+C->&Tom
+&1.24

vlib/v/tests/skip_unused/auto_string.vv

@@ -0,0 +1,9 @@
+a := 'Tom'
+b := 'Hello ${a}'
+c := &a
+println(b)
+println('C->${c}')
+
+f := 1.24
+f_p := &f
+println('${f_p}')