checker: fix if branch type nr_muls mismatch (fix #25556) (fix #25555) (#25571)

Author: felipensp

vlib/v/checker/if.v

@@ -396,6 +396,12 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 						c.error('mismatched types `${c.table.type_to_str(node.typ)}` and `${c.table.type_to_str(stmt.typ)}`',
 							node.pos)
 					} else {
+						if !node.typ.has_option_or_result() && !node.typ.has_flag(.shared_f)
+							&& stmt.typ != ast.voidptr_type
+							&& stmt.typ.nr_muls() != node.typ.nr_muls() {
+							c.error('mismatched types `${c.table.type_to_str(node.typ)}` and `${c.table.type_to_str(stmt.typ)}`',
+								node.pos)
+						}
 						if node.is_expr == false && c.type_resolver.is_generic_param_var(stmt.expr) {
 							// generic variable no yet type bounded
 							node.is_expr = true

vlib/v/checker/tests/if_mismatch_muls_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/if_mismatch_muls_err.vv:17:11: error: mismatched types `&&Dum` and `&Dum`
+   15 | 
+   16 | fn main() {
+   17 |     dummy := if false {
+      |              ~~
+   18 |         res := &Dum{
+   19 |             v: 2

vlib/v/checker/tests/if_mismatch_muls_err.vv

@@ -0,0 +1,28 @@
+module main
+
+struct Dummy {
+	v int
+}
+
+fn get_dummy() &Dum {
+	d := Dum{
+		v: 1
+	}
+	return &d
+}
+
+type Dum = Dummy
+
+fn main() {
+	dummy := if false {
+		res := &Dum{
+			v: 2
+		}
+		&res
+	} else {
+		r := get_dummy()
+		r
+	}
+
+	println(dummy)
+}