cgen: fix optional in if expr (#15411)

vlib/v/gen/c/if.v

@@ -17,23 +17,9 @@ 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 true
-					}
-					if stmt.expr is ast.CallExpr {
-						if stmt.expr.is_method {
-							left_sym := g.table.sym(stmt.expr.receiver_type)
-							if left_sym.kind in [.array, .array_fixed, .map] {
-								return true
-							}
-						}
-						if stmt.expr.or_block.kind != .absent {
-							return true
-						}
-					}
 				}
 			}
 		}
@@ -41,6 +27,33 @@ fn (mut g Gen) need_tmp_var_in_if(node ast.IfExpr) bool {
 	return false
 }
 
+fn (mut g Gen) need_tmp_var_in_expr(expr ast.Expr) bool {
+	if is_noreturn_callexpr(expr) {
+		return true
+	}
+	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 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
+}
+
 fn (mut g Gen) if_expr(node ast.IfExpr) {
 	if node.is_comptime {
 		g.comptime_if(node)

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)
+	})
+}