checker: check fn return type mismatch (#14081)

vlib/v/checker/return.v

@@ -32,7 +32,8 @@ pub fn (mut c Checker) return_stmt(mut node ast.Return) {
 		}
 	}
 	mut got_types := []ast.Type{}
-	for expr in node.exprs {
+	mut expr_idxs := []int{}
+	for i, expr in node.exprs {
 		typ := c.expr(expr)
 		if typ == ast.void_type {
 			c.error('`$expr` used as value', node.pos)
@@ -42,9 +43,11 @@ pub fn (mut c Checker) return_stmt(mut node ast.Return) {
 		if sym.kind == .multi_return {
 			for t in sym.mr_info().types {
 				got_types << t
+				expr_idxs << i
 			}
 		} else {
 			got_types << typ
+			expr_idxs << i
 		}
 	}
 	node.types = got_types
@@ -82,7 +85,7 @@ pub fn (mut c Checker) return_stmt(mut node ast.Return) {
 		got_typ := c.unwrap_generic(got_types[i])
 		if got_typ.has_flag(.optional) && (!exp_type.has_flag(.optional)
 			|| c.table.type_to_str(got_typ) != c.table.type_to_str(exp_type)) {
-			pos := node.exprs[i].pos()
+			pos := node.exprs[expr_idxs[i]].pos()
 			c.error('cannot use `${c.table.type_to_str(got_typ)}` as type `${c.table.type_to_str(exp_type)}` in return argument',
 				pos)
 		}
@@ -93,19 +96,19 @@ pub fn (mut c Checker) return_stmt(mut node ast.Return) {
 				if c.type_implements(got_typ, exp_type, node.pos) {
 					if !got_typ.is_ptr() && !got_typ.is_pointer() && got_typ_sym.kind != .interface_
 						&& !c.inside_unsafe {
-						c.mark_as_referenced(mut &node.exprs[i], true)
+						c.mark_as_referenced(mut &node.exprs[expr_idxs[i]], true)
 					}
 				}
 				continue
 			}
-			pos := node.exprs[i].pos()
+			pos := node.exprs[expr_idxs[i]].pos()
 			c.error('cannot use `$got_typ_sym.name` as type `${c.table.type_to_str(exp_type)}` in return argument',
 				pos)
 		}
 		if (got_typ.is_ptr() || got_typ.is_pointer())
 			&& (!exp_type.is_ptr() && !exp_type.is_pointer()) {
-			pos := node.exprs[i].pos()
-			if node.exprs[i].is_auto_deref_var() {
+			pos := node.exprs[expr_idxs[i]].pos()
+			if node.exprs[expr_idxs[i]].is_auto_deref_var() {
 				continue
 			}
 			c.error('fn `$c.table.cur_fn.name` expects you to return a non reference type `${c.table.type_to_str(exp_type)}`, but you are returning `${c.table.type_to_str(got_typ)}` instead',
@@ -114,8 +117,8 @@ pub fn (mut c Checker) return_stmt(mut node ast.Return) {
 		if (exp_type.is_ptr() || exp_type.is_pointer())
 			&& (!got_typ.is_ptr() && !got_typ.is_pointer()) && got_typ != ast.int_literal_type
 			&& !c.pref.translated && !c.file.is_translated {
-			pos := node.exprs[i].pos()
-			if node.exprs[i].is_auto_deref_var() {
+			pos := node.exprs[expr_idxs[i]].pos()
+			if node.exprs[expr_idxs[i]].is_auto_deref_var() {
 				continue
 			}
 			c.error('fn `$c.table.cur_fn.name` expects you to return a reference type `${c.table.type_to_str(exp_type)}`, but you are returning `${c.table.type_to_str(got_typ)}` instead',

vlib/v/checker/tests/fn_return_type_mismatch.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/fn_return_type_mismatch.vv:6:9: error: cannot use `i64` as type `int` in return argument
+    4 |
+    5 | fn func2() (int, int) {
+    6 |     return func1()
+      |            ~~~~~~~
+    7 | }
+    8 |

vlib/v/checker/tests/fn_return_type_mismatch.vv

@@ -0,0 +1,9 @@
+fn func1() (i64, i64) {
+	return i64(1), i64(2)
+}
+
+fn func2() (int, int) {
+	return func1()
+}
+
+fn main() {}