From 7af8fafc18db21c6995b776ed2404a9febe09c52 Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sun, 22 Dec 2024 09:06:55 -0300
Subject: [PATCH] ast,parser,checker: fix identification of abstract vs real
 interface methods (interface with a str() method) (fix #23006) (#23238)

---
 vlib/v/ast/types.v                            |  6 ++---
 vlib/v/checker/fn.v                           |  2 +-
 vlib/v/parser/struct.v                        |  1 +
 .../interfaces/interface_arr_auto_str_test.v  | 25 +++++++++++++++++++
 4 files changed, 30 insertions(+), 4 deletions(-)
 create mode 100644 vlib/v/tests/interfaces/interface_arr_auto_str_test.v

diff --git a/vlib/v/ast/types.v b/vlib/v/ast/types.v
index 832521cb1..36ddfab49 100644
--- a/vlib/v/ast/types.v
+++ b/vlib/v/ast/types.v
@@ -1722,8 +1722,8 @@ pub fn (t &TypeSymbol) has_method(name string) bool {
 }
 
 pub fn (t &TypeSymbol) has_method_with_generic_parent(name string) bool {
-	t.find_method_with_generic_parent(name) or { return false }
-	return true
+	m := t.find_method_with_generic_parent(name) or { return false }
+	return t.kind != .interface || !m.no_body
 }
 
 pub fn (t &TypeSymbol) find_method(name string) ?Fn {
@@ -1813,7 +1813,7 @@ pub fn (t &TypeSymbol) str_method_info() (bool, bool, int) {
 	mut expects_ptr := false
 	mut nr_args := 0
 	if sym_str_method := t.find_method_with_generic_parent('str') {
-		has_str_method = true
+		has_str_method = t.kind != .interface || !sym_str_method.no_body
 		nr_args = sym_str_method.params.len
 		if nr_args > 0 {
 			expects_ptr = sym_str_method.params[0].typ.is_ptr()
diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 353610cd3..572557835 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -2544,7 +2544,7 @@ fn (mut c Checker) method_call(mut node ast.CallExpr, mut continue_check &bool)
 		c.fail_if_unreadable(node.left, left_type, 'receiver')
 	}
 	if left_sym.language != .js && (!left_sym.is_builtin() && method.mod != 'builtin')
-		&& method.language == .v && method.no_body {
+		&& method.language == .v && final_left_sym.kind != .interface && method.no_body {
 		c.error('cannot call a method that does not have a body', node.pos)
 	}
 	if node.concrete_types.len > 0 && method.generic_names.len > 0
diff --git a/vlib/v/parser/struct.v b/vlib/v/parser/struct.v
index b2d8a4017..ff88f1dc2 100644
--- a/vlib/v/parser/struct.v
+++ b/vlib/v/parser/struct.v
@@ -738,6 +738,7 @@ fn (mut p Parser) interface_decl() ast.InterfaceDecl {
 				is_pub:        true
 				is_method:     true
 				receiver_type: typ
+				no_body:       true
 			}
 			ts.register_method(tmethod)
 			info.methods << tmethod
diff --git a/vlib/v/tests/interfaces/interface_arr_auto_str_test.v b/vlib/v/tests/interfaces/interface_arr_auto_str_test.v
new file mode 100644
index 000000000..1d0b79746
--- /dev/null
+++ b/vlib/v/tests/interfaces/interface_arr_auto_str_test.v
@@ -0,0 +1,25 @@
+interface Interface {
+	str() string
+}
+
+struct Result[T] {
+	data []T
+}
+
+struct Foobar {
+}
+
+fn (f Foobar) str() string {
+	return 'foobar'
+}
+
+fn test_main() {
+	assert Result[Interface]{}.str() == 'Result[Interface]{
+    data: []
+}'
+	assert Result[Foobar]{
+		data: [Foobar{}]
+	}.str() == 'Result[Foobar]{
+    data: [foobar]
+}'
+}
-- 
2.39.5