From 50b936cd58723a86e121a5ec26561c438c4949eb Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Fri, 24 Apr 2026 01:17:20 +0300
Subject: [PATCH] checker: fix Compiler doesn't catch type mismatch with `int`
 and `time.Duration` (fixes #18873)

---
 vlib/v/checker/struct.v                       | 21 +++++++++++++++++++
 .../tests/time_duration_assign_to_int_err.out | 14 +++++++++++++
 .../tests/time_duration_assign_to_int_err.vv  | 20 ++++++++++++++++++
 3 files changed, 55 insertions(+)
 create mode 100644 vlib/v/checker/tests/time_duration_assign_to_int_err.out
 create mode 100644 vlib/v/checker/tests/time_duration_assign_to_int_err.vv

diff --git a/vlib/v/checker/struct.v b/vlib/v/checker/struct.v
index b10acfa14..1c9dce493 100644
--- a/vlib/v/checker/struct.v
+++ b/vlib/v/checker/struct.v
@@ -1099,6 +1099,11 @@ or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
 							pos:     init_field.expr.pos()
 						}
 						init_field.typ = exp_type
+					} else if c.has_direct_numeric_alias_struct_init_mismatch(init_field.expr,
+						got_type, exp_type)
+					{
+						c.error('cannot assign to field `${field_info.name}`: ${c.expected_msg(got_type,
+							exp_type)}', init_field.pos)
 					} else {
 						c.check_expected(c.unwrap_generic(got_type), c.unwrap_generic(exp_type)) or {
 							// For generic types, the same concrete type may have been
@@ -1313,6 +1318,22 @@ or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
 	return node.typ
 }
 
+fn (c &Checker) has_direct_numeric_alias_struct_init_mismatch(expr ast.Expr, got ast.Type, expected ast.Type) bool {
+	if expr.remove_par() !is ast.Ident && expr.remove_par() !is ast.SelectorExpr {
+		return false
+	}
+	got_sym := c.table.sym(got)
+	if got_sym.kind != .alias || got_sym.info !is ast.Alias {
+		return false
+	}
+	got_num_type := c.table.unalias_num_type(got).clear_flags()
+	expected_num_type := c.table.unalias_num_type(expected).clear_flags()
+	if !got_num_type.is_number() || !expected_num_type.is_number() {
+		return false
+	}
+	return c.promote_num(expected_num_type, got_num_type) != expected_num_type
+}
+
 // Check uninitialized refs/sum types
 // The variable `fields` contains two parts, the first part is the same as info.fields,
 // and the second part is all fields embedded in the structure
diff --git a/vlib/v/checker/tests/time_duration_assign_to_int_err.out b/vlib/v/checker/tests/time_duration_assign_to_int_err.out
new file mode 100644
index 000000000..e1090c2b6
--- /dev/null
+++ b/vlib/v/checker/tests/time_duration_assign_to_int_err.out
@@ -0,0 +1,14 @@
+vlib/v/checker/tests/time_duration_assign_to_int_err.vv:10:3: error: cannot assign to field `x`: expected `int`, not `time.Duration`
+    8 |     d := time.second
+    9 |     _ := Foo{
+   10 |         x: d
+      |         ~~~~
+   11 |     }
+   12 | }
+vlib/v/checker/tests/time_duration_assign_to_int_err.vv:16:3: error: cannot assign to field `x`: expected `int`, not `time.Duration`
+   14 | fn bad_struct_init_direct() {
+   15 |     _ := Foo{
+   16 |         x: time.second
+      |         ~~~~~~~~~~~~~~
+   17 |     }
+   18 | }
diff --git a/vlib/v/checker/tests/time_duration_assign_to_int_err.vv b/vlib/v/checker/tests/time_duration_assign_to_int_err.vv
new file mode 100644
index 000000000..dd11b858c
--- /dev/null
+++ b/vlib/v/checker/tests/time_duration_assign_to_int_err.vv
@@ -0,0 +1,20 @@
+import time
+
+struct Foo {
+	x int
+}
+
+fn bad_struct_init() {
+	d := time.second
+	_ := Foo{
+		x: d
+	}
+}
+
+fn bad_struct_init_direct() {
+	_ := Foo{
+		x: time.second
+	}
+}
+
+fn main() {}
-- 
2.39.5