From db550eba8fa1ade3cc5bb876a6143d6fa3c35792 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 11 Mar 2026 12:29:52 +0300
Subject: [PATCH] checker: C compilation error with shared struct (fixes
 #25160)

---
 vlib/v/ast/table.v                            | 26 ++++++++++++++++++-
 .../shared_receiver_mut_interface_err.out     |  8 ++++++
 .../shared_receiver_mut_interface_err.vv      | 17 ++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/shared_receiver_mut_interface_err.out
 create mode 100644 vlib/v/checker/tests/shared_receiver_mut_interface_err.vv

diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index a43a3fb95..1dd70f9ef 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -252,13 +252,18 @@ pub fn (t &Table) is_same_method(f &Fn, func &Fn) string {
 		if lsym.language == .js && rsym.language == .js {
 			return ''
 		}
+		has_unexpected_sharetype := f.params[i].is_shared != func.params[i].is_shared
+			|| f.params[i].is_atomic != func.params[i].is_atomic
 		has_unexpected_mutability := !f.params[i].is_mut && func.params[i].is_mut
 
-		if has_unexpected_type || has_unexpected_mutability {
+		if has_unexpected_type || has_unexpected_sharetype || has_unexpected_mutability {
 			exps := t.type_to_str(f.params[i].typ)
 			gots := t.type_to_str(func.params[i].typ)
 			if has_unexpected_type {
 				return 'expected `${exps}`, not `${gots}` for parameter ${i}'
+			} else if has_unexpected_sharetype {
+				return 'expected `${t.param_type_with_specifier(f.params[i], i == 0)}`, not `${t.param_type_with_specifier(func.params[i],
+					i == 0)}` for parameter ${i}'
 			} else {
 				return 'expected `${exps}` which is immutable, not `mut ${gots}`'
 			}
@@ -267,6 +272,25 @@ pub fn (t &Table) is_same_method(f &Fn, func &Fn) string {
 	return ''
 }
 
+fn (t &Table) param_type_with_specifier(p Param, is_receiver bool) string {
+	mut parts := []string{}
+	if p.is_mut {
+		parts << 'mut'
+	}
+	if p.is_shared {
+		parts << 'shared'
+	}
+	if p.is_atomic {
+		parts << 'atomic'
+	}
+	mut ptyp := p.typ.clear_flags(.shared_f, .atomic_f)
+	if is_receiver && ptyp.is_ptr() {
+		ptyp = ptyp.deref()
+	}
+	parts << t.type_to_str(ptyp)
+	return parts.join(' ')
+}
+
 pub fn (t &Table) find_fn(name string) ?Fn {
 	if f := t.fns[name] {
 		return f
diff --git a/vlib/v/checker/tests/shared_receiver_mut_interface_err.out b/vlib/v/checker/tests/shared_receiver_mut_interface_err.out
new file mode 100644
index 000000000..2d6584693
--- /dev/null
+++ b/vlib/v/checker/tests/shared_receiver_mut_interface_err.out
@@ -0,0 +1,8 @@
+vlib/v/checker/tests/shared_receiver_mut_interface_err.vv:16:19: error: `Input` incorrectly implements method `event` of interface `Handler`: expected `mut Handler`, not `mut shared Input` for parameter 0
+   14 | fn main() {
+   15 |     mut input := Input{}
+   16 |     take_handler(mut input)
+      |                      ~~~~~
+   17 | }
+Details: main.Handler has `fn event(mut x main.Handler)`
+         main.Input has `fn event(mut input shared main.Input)`
diff --git a/vlib/v/checker/tests/shared_receiver_mut_interface_err.vv b/vlib/v/checker/tests/shared_receiver_mut_interface_err.vv
new file mode 100644
index 000000000..9fe388e3b
--- /dev/null
+++ b/vlib/v/checker/tests/shared_receiver_mut_interface_err.vv
@@ -0,0 +1,17 @@
+module main
+
+interface Handler {
+mut:
+	event()
+}
+
+struct Input {}
+
+fn (shared input Input) event() {}
+
+fn take_handler(mut _ Handler) {}
+
+fn main() {
+	mut input := Input{}
+	take_handler(mut input)
+}
-- 
2.39.5