checker, cgen: fix if expr with result (#15709)

vlib/v/checker/if.v

@@ -188,7 +188,7 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 					}
 				}
 				c.expected_type = former_expected_type
-				if c.expected_type.has_flag(.optional) {
+				if c.expected_type.has_flag(.optional) || c.expected_type.has_flag(.result) {
 					if node.typ == ast.void_type {
 						node.is_expr = true
 						node.typ = c.expected_type

vlib/v/gen/c/if.v

@@ -7,7 +7,7 @@ import v.ast
 
 fn (mut g Gen) need_tmp_var_in_if(node ast.IfExpr) bool {
 	if node.is_expr && g.inside_ternary == 0 {
-		if g.is_autofree || node.typ.has_flag(.optional) {
+		if g.is_autofree || node.typ.has_flag(.optional) || node.typ.has_flag(.result) {
 			return true
 		}
 		for branch in node.branches {
@@ -142,6 +142,8 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 	if needs_tmp_var {
 		if node.typ.has_flag(.optional) {
 			g.inside_if_optional = true
+		} else if node.typ.has_flag(.result) {
+			g.inside_if_result = true
 		}
 		styp := g.typ(node.typ)
 		cur_line = g.go_before_stmt(0)
@@ -325,5 +327,7 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 	}
 	if node.typ.has_flag(.optional) {
 		g.inside_if_optional = false
+	} else if node.typ.has_flag(.result) {
+		g.inside_if_result = false
 	}
 }

vlib/v/tests/if_expr_with_result_test.v

@@ -0,0 +1,17 @@
+fn foo(i int) ?bool {
+	return if i == 0 { true } else { none }
+}
+
+fn bar(i int) !bool {
+	return if i == 0 { true } else { error('') }
+}
+
+fn test_if_expr_with_result() {
+	r1 := foo(0) or { false }
+	println(r1)
+	assert r1
+
+	r2 := bar(0) or { false }
+	println(r2)
+	assert r2
+}