From ee94af07e0e8a626fbf30d44b972ef93bc4da925 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 14 Apr 2026 12:45:27 +0300
Subject: [PATCH] checker: Compiler accepts &int as a key for map[int]int
 (fixes #23069)

---
 vlib/v/checker/checker.v         | 33 ++++++++++++++++++++++++++++++--
 vlib/v/checker/infix.v           |  6 +++---
 vlib/v/checker/tests/map_ops.out | 26 ++++++++++++++++++++-----
 vlib/v/checker/tests/map_ops.vv  |  5 +++++
 4 files changed, 60 insertions(+), 10 deletions(-)

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 4e4a301b1..5d61ebf59 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -7284,6 +7284,35 @@ fn (mut c Checker) check_index(typ_sym &ast.TypeSymbol, index ast.Expr, index_ty
 	}
 }
 
+fn (mut c Checker) check_map_key_type(got ast.Type, expected ast.Type) bool {
+	if c.map_key_pointer_mismatch(got, expected) {
+		return false
+	}
+	return c.check_types(got, expected)
+}
+
+fn (c &Checker) map_key_pointer_mismatch(got ast.Type, expected ast.Type) bool {
+	got_final_sym := c.table.final_sym(got)
+	expected_final_sym := c.table.final_sym(expected)
+	if got_final_sym.idx != expected_final_sym.idx {
+		return false
+	}
+	if got.is_any_kind_of_pointer() != expected.is_any_kind_of_pointer() {
+		return true
+	}
+	return got.is_ptr() && expected.is_ptr() && got.nr_muls() != expected.nr_muls()
+}
+
+fn (c &Checker) map_key_expected_msg(got ast.Type, expected ast.Type, key_expr ast.Expr,
+	container string) string {
+	mut msg := c.expected_msg(got, expected)
+	if container.len > 0 && c.map_key_pointer_mismatch(got, expected) && got.is_ptr()
+		&& !expected.is_any_kind_of_pointer() && got.nr_muls() == expected.nr_muls() + 1 {
+		msg += '; did you mean `${container}[*${key_expr}]`?'
+	}
+	return msg
+}
+
 fn (mut c Checker) index_expr(mut node ast.IndexExpr) ast.Type {
 	mut typ := c.expr(mut node.left)
 	if typ == 0 {
@@ -7420,8 +7449,8 @@ fn (mut c Checker) index_expr(mut node ast.IndexExpr) ast.Type {
 				got_typ_str, expected_typ_str := c.get_string_names_of(actual_index_type, key_type)
 				c.error('invalid key: cannot use `${got_typ_str}` as `${expected_typ_str}`, it must be unwrapped first',
 					node.index.pos())
-			} else if !c.check_types(index_type, key_type) {
-				err := c.expected_msg(index_type, key_type)
+			} else if !c.check_map_key_type(index_type, key_type) {
+				err := c.map_key_expected_msg(index_type, key_type, node.index, '${node.left}')
 				c.error('invalid key: ${err}', node.pos)
 			}
 			value_sym := c.table.sym(info.value_type)
diff --git a/vlib/v/checker/infix.v b/vlib/v/checker/infix.v
index b7d9cba40..0fdd1e992 100644
--- a/vlib/v/checker/infix.v
+++ b/vlib/v/checker/infix.v
@@ -415,9 +415,9 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 				}
 				.map {
 					map_info := right_final_sym.map_info()
-					c.check_expected(left_type, map_info.key_type) or {
-						c.error('left operand to `${node.op}` does not match the map key type: ${err.msg()}',
-							left_right_pos)
+					if !c.check_map_key_type(left_type, map_info.key_type) {
+						c.error('left operand to `${node.op}` does not match the map key type: ${c.map_key_expected_msg(left_type,
+							map_info.key_type, node.left, '')}', left_right_pos)
 					}
 					node.left_type = map_info.key_type
 				}
diff --git a/vlib/v/checker/tests/map_ops.out b/vlib/v/checker/tests/map_ops.out
index d88625153..af1093c2f 100644
--- a/vlib/v/checker/tests/map_ops.out
+++ b/vlib/v/checker/tests/map_ops.out
@@ -11,29 +11,45 @@ vlib/v/checker/tests/map_ops.vv:4:3: error: invalid key: expected `int`, not `st
     4 |     m['hi'] = 8
       |      ~~~~~~
     5 |     m[&m] += 4
-    6 | }
+    6 |     a := 10
 vlib/v/checker/tests/map_ops.vv:4:12: error: cannot assign to `m['hi']`: expected `string`, not `int literal`
     2 |     mut m := map[int]string{}
     3 |     _ = m[`!`]
     4 |     m['hi'] = 8
       |               ^
     5 |     m[&m] += 4
-    6 | }
+    6 |     a := 10
 vlib/v/checker/tests/map_ops.vv:5:3: error: invalid key: expected `int`, not `&map[int]string`
     3 |     _ = m[`!`]
     4 |     m['hi'] = 8
     5 |     m[&m] += 4
       |      ~~~~
-    6 | }
+    6 |     a := 10
+    7 |     ptr := &a
 vlib/v/checker/tests/map_ops.vv:5:11: error: invalid right operand: string += int literal
     3 |     _ = m[`!`]
     4 |     m['hi'] = 8
     5 |     m[&m] += 4
       |              ^
-    6 | }
+    6 |     a := 10
+    7 |     ptr := &a
 vlib/v/checker/tests/map_ops.vv:5:11: error: cannot assign to `m[&m]`: expected `string`, not `int literal`
     3 |     _ = m[`!`]
     4 |     m['hi'] = 8
     5 |     m[&m] += 4
       |              ^
-    6 | }
+    6 |     a := 10
+    7 |     ptr := &a
+vlib/v/checker/tests/map_ops.vv:9:3: error: invalid key: expected `int`, not `&int`; did you mean `n[*ptr]`?
+    7 |     ptr := &a
+    8 |     mut n := map[int]int{}
+    9 |     n[ptr] = 1
+      |      ~~~~~
+   10 |     _ = ptr in n
+   11 | }
+vlib/v/checker/tests/map_ops.vv:10:6: error: left operand to `in` does not match the map key type: expected `int`, not `&int`
+    8 |     mut n := map[int]int{}
+    9 |     n[ptr] = 1
+   10 |     _ = ptr in n
+      |         ~~~~~~~~
+   11 | }
diff --git a/vlib/v/checker/tests/map_ops.vv b/vlib/v/checker/tests/map_ops.vv
index 0522021b8..f5e161e35 100644
--- a/vlib/v/checker/tests/map_ops.vv
+++ b/vlib/v/checker/tests/map_ops.vv
@@ -3,4 +3,9 @@ fn test_map() {
 	_ = m[`!`]
 	m['hi'] = 8
 	m[&m] += 4
+	a := 10
+	ptr := &a
+	mut n := map[int]int{}
+	n[ptr] = 1
+	_ = ptr in n
 }
-- 
2.39.5