From 5716ea7682c2af84a94472770e5b14dc3b1d585d Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 15 Apr 2026 02:15:20 +0300
Subject: [PATCH] checker: fix .str() method inconsistent behavior (fixes
 #25825)

---
 vlib/v/ast/table.v                            | 19 +++++++++++++++----
 vlib/v/checker/checker.v                      | 11 ++++++++---
 .../tests/interface_implicit_str_char_err.out |  6 ++++++
 .../tests/interface_implicit_str_char_err.vv  | 11 +++++++++++
 .../interface_implicit_str_method_test.v      |  9 +++++++++
 5 files changed, 49 insertions(+), 7 deletions(-)
 create mode 100644 vlib/v/checker/tests/interface_implicit_str_char_err.out
 create mode 100644 vlib/v/checker/tests/interface_implicit_str_char_err.vv

diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index d5fc49cb9..7f79bd80d 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -319,19 +319,27 @@ pub fn (t &Table) type_has_implicit_str_method(typ Type, method &Fn) bool {
 	if typ.has_option_or_result() {
 		return false
 	}
-	if typ.is_any_kind_of_pointer() {
-		return false
-	}
 	sym := t.sym(typ.clear_flag(.variadic))
 	if sym.has_method_with_generic_parent('str') {
 		return false
 	}
+	if sym.kind == .char && typ.nr_muls() == 0 {
+		return false
+	}
+	if sym.kind == .function {
+		return false
+	}
+	if typ.is_any_kind_of_pointer() || typ in voidptr_types || typ in byteptr_types
+		|| typ in charptr_types || typ == nil_type {
+		return true
+	}
 	match sym.info {
 		Alias, Array, ArrayFixed, Enum, FnType, Struct, Map, MultiReturn, SumType, Chan, Thread {
 			return sym.name != 'nil'
 		}
 		else {
-			return false
+			return sym.kind in [.i8, .i16, .i32, .int, .i64, .isize, .u8, .u16, .u32, .u64, .usize,
+				.f32, .f64, .rune, .bool, .string, .generic_inst]
 		}
 	}
 }
@@ -2259,6 +2267,9 @@ pub fn (t &Table) does_type_implement_interface(typ Type, inter_typ Type) bool {
 		}
 		// verify methods
 		for imethod in inter_sym.info.methods {
+			if t.is_compatible_auto_str_method(imethod) && typ.nr_muls() == 0 && sym.kind == .char {
+				return false
+			}
 			if method := t.find_method_with_embeds(sym, imethod.name) {
 				msg := t.is_same_method(imethod, method)
 				if msg.len > 0 {
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index e30477f8d..f814bd19c 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2213,11 +2213,16 @@ fn (mut c Checker) type_implements_with_mut_receiver(typ ast.Type, interface_typ
 
 		// Verify methods
 		for imethod in imethods {
+			if c.table.is_compatible_auto_str_method(imethod) && utyp.nr_muls() == 0
+				&& typ_sym.kind == .char {
+				c.error("`${styp}` doesn't implement method `${imethod.name}` of interface `${inter_sym.name}`",
+					pos)
+				are_methods_implemented = false
+				continue
+			}
 			mut method := typ_sym.find_method_with_generic_parent(imethod.name) or {
 				c.table.find_method_with_embeds(typ_sym, imethod.name) or {
-					// `str() string` is auto-generated for all types during cgen
-					if imethod.name == 'str' && imethod.params.len == 1
-						&& imethod.return_type == ast.string_type {
+					if c.table.type_has_implicit_str_method(utyp, imethod) {
 						are_methods_implemented = true
 						continue
 					}
diff --git a/vlib/v/checker/tests/interface_implicit_str_char_err.out b/vlib/v/checker/tests/interface_implicit_str_char_err.out
new file mode 100644
index 000000000..326db99ca
--- /dev/null
+++ b/vlib/v/checker/tests/interface_implicit_str_char_err.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/interface_implicit_str_char_err.vv:10:7: error: `char` doesn't implement method `str` of interface `Stringy`
+    8 | 
+    9 | fn main() {
+   10 |     take(char(91))
+      |          ~~~~~~~~
+   11 | }
diff --git a/vlib/v/checker/tests/interface_implicit_str_char_err.vv b/vlib/v/checker/tests/interface_implicit_str_char_err.vv
new file mode 100644
index 000000000..433a46b1b
--- /dev/null
+++ b/vlib/v/checker/tests/interface_implicit_str_char_err.vv
@@ -0,0 +1,11 @@
+interface Stringy {
+	str() string
+}
+
+fn take(v Stringy) {
+	_ = v
+}
+
+fn main() {
+	take(char(91))
+}
diff --git a/vlib/v/tests/interfaces/interface_implicit_str_method_test.v b/vlib/v/tests/interfaces/interface_implicit_str_method_test.v
index 3e595c7c6..d6dcff111 100644
--- a/vlib/v/tests/interfaces/interface_implicit_str_method_test.v
+++ b/vlib/v/tests/interfaces/interface_implicit_str_method_test.v
@@ -12,6 +12,10 @@ fn join(values ...Stringy) string {
 	return values.map(it.str()).join(' ')
 }
 
+fn collect(values []Stringy) string {
+	return values.map(it.str()).join(' ')
+}
+
 fn test_interface_implicit_str_method() {
 	some_struct := SomeStruct{}
 	assert stringify('hi there') == 'hi there'
@@ -20,3 +24,8 @@ fn test_interface_implicit_str_method() {
 	assert stringify(some_struct) == 'SomeStruct{}'
 	assert join('hi', 42, false, some_struct) == 'hi 42 false SomeStruct{}'
 }
+
+fn test_interface_implicit_str_method_for_pointer_arrays() {
+	values := [&SomeStruct{}]
+	assert collect(values) == 'SomeStruct{}'
+}
-- 
2.39.5