cgen: fix optional in if expr (#15411)

vlib/v/gen/c/if.v

@@ -17,26 +17,39 @@ fn (mut g Gen) need_tmp_var_in_if(node ast.IfExpr) bool {
 			if branch.stmts.len == 1 {
 				if branch.stmts[0] is ast.ExprStmt {
 					stmt := branch.stmts[0] as ast.ExprStmt
-					if is_noreturn_callexpr(stmt.expr) {
+					if g.need_tmp_var_in_expr(stmt.expr) {
 						return true
 					}
-					if stmt.expr is ast.MatchExpr {
+				}
+			}
+		}
+	}
+	return false
+}
+
+fn (mut g Gen) need_tmp_var_in_expr(expr ast.Expr) bool {
+	if is_noreturn_callexpr(expr) {
 		return true
 	}
-					if stmt.expr is ast.CallExpr {
-						if stmt.expr.is_method {
-							left_sym := g.table.sym(stmt.expr.receiver_type)
+	if expr is ast.MatchExpr {
+		return true
+	}
+	if expr is ast.CallExpr {
+		if expr.is_method {
+			left_sym := g.table.sym(expr.receiver_type)
 			if left_sym.kind in [.array, .array_fixed, .map] {
 				return true
 			}
 		}
-						if stmt.expr.or_block.kind != .absent {
+		if expr.or_block.kind != .absent {
 			return true
 		}
 	}
+	if expr is ast.CastExpr {
+		return g.need_tmp_var_in_expr(expr.expr)
 	}
-			}
-		}
+	if expr is ast.ParExpr {
+		return g.need_tmp_var_in_expr(expr.expr)
 	}
 	return false
 }

vlib/v/tests/inout/printing_optional_in_if_expr.out

@@ -0,0 +1 @@
+1

vlib/v/tests/inout/printing_optional_in_if_expr.vv

@@ -0,0 +1,11 @@
+fn optional() ?int {
+	return 1
+}
+
+fn main() {
+	println(if true {
+		i32(optional() or { 2 })
+	} else {
+		i32(8)
+	})
+}