From 92a2ba8fd56c8d476e229695e7dcf324e9e44ceb Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 21 Apr 2026 14:52:06 +0300
Subject: [PATCH] cgen: fix segfault or error c code when shared variable
 initialized (fixes #26379)

---
 vlib/v/gen/c/assign.v                         |  5 ++
 vlib/v/gen/c/cgen.v                           |  6 +-
 vlib/v/tests/concurrency/shared_assign_test.v | 62 +++++++++++++++++++
 3 files changed, 70 insertions(+), 3 deletions(-)

diff --git a/vlib/v/gen/c/assign.v b/vlib/v/gen/c/assign.v
index 60c974ccf..7a1b15084 100644
--- a/vlib/v/gen/c/assign.v
+++ b/vlib/v/gen/c/assign.v
@@ -83,6 +83,11 @@ fn (mut g Gen) expr_in_value_context(expr ast.Expr, value_type ast.Type, expecte
 		else {}
 	}
 
+	if expected_type.has_flag(.shared_f) && !value_type.has_flag(.shared_f) && value_type.is_ptr()
+		&& !expected_type.has_option_or_result() {
+		g.expr_with_cast(expr_copy, value_type, expected_type)
+		return
+	}
 	g.expr(expr_copy)
 }
 
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 710a1ecb9..4d12ffd64 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -4691,9 +4691,6 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 	if expected_type.has_flag(.shared_f) && !got_type_raw.has_flag(.shared_f)
 		&& !expected_type.has_option_or_result() {
 		shared_styp := exp_styp[0..exp_styp.len - 1] // `shared` implies ptr, so eat one `*`
-		if got_type_raw.is_ptr() {
-			g.error('cannot convert reference to `shared`', expr.pos())
-		}
 		if exp_sym.kind == .array {
 			g.writeln('(${shared_styp}*)__dup_shared_array(&(${shared_styp}){.mtx = {0}, .val =')
 		} else if exp_sym.kind == .map {
@@ -4703,6 +4700,9 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 		}
 		old_is_shared := g.is_shared
 		g.is_shared = false
+		if got_type_raw.is_ptr() {
+			g.write('*'.repeat(got_type_raw.nr_muls()))
+		}
 		g.expr(expr)
 		g.is_shared = old_is_shared
 		g.writeln('}, sizeof(${shared_styp}))')
diff --git a/vlib/v/tests/concurrency/shared_assign_test.v b/vlib/v/tests/concurrency/shared_assign_test.v
index 8382d2030..7026d4e8f 100644
--- a/vlib/v/tests/concurrency/shared_assign_test.v
+++ b/vlib/v/tests/concurrency/shared_assign_test.v
@@ -1,3 +1,8 @@
+import os
+import rand
+
+const vexe = @VEXE
+
 struct Foo {
 mut:
 	a int
@@ -107,3 +112,60 @@ fn test_re_assign_map() {
 		assert m[0] == 1
 	}
 }
+
+struct SharedAssignStructA {
+	commands []string
+}
+
+struct SharedAssignStructB {
+	s SharedAssignStructA
+}
+
+fn test_assign_from_pointer_ident_with_nested_struct() {
+	mut src := &SharedAssignStructB{}
+	shared shared_copy := src
+	shared spread_copy := SharedAssignStructB{
+		...src
+	}
+	rlock shared_copy, spread_copy {
+		assert shared_copy.s.commands == []string{}
+		assert spread_copy.s.commands == []string{}
+	}
+}
+
+fn test_assign_from_pointer_ident_emits_shared_copy_in_c_output() {
+	tmp_dir := os.join_path(os.vtmp_dir(), 'shared_assign_cgen_${rand.ulid()}')
+	os.mkdir_all(tmp_dir) or { panic(err) }
+	defer {
+		os.rmdir_all(tmp_dir) or {}
+	}
+	source_path := os.join_path(tmp_dir, 'main.v')
+	c_path := os.join_path(tmp_dir, 'main.c')
+	source := [
+		'module main',
+		'',
+		'struct StructA {',
+		'\tcommands []string',
+		'}',
+		'',
+		'struct StructB {',
+		'\ts StructA',
+		'}',
+		'',
+		'fn main() {',
+		'\tmut src := &StructB{}',
+		'\tshared copy := src',
+		'\trlock copy {',
+		'\t\tprintln(copy.s)',
+		'\t}',
+		'}',
+	].join_lines()
+	os.write_file(source_path, source) or { panic(err) }
+	res :=
+		os.execute('${os.quoted_path(vexe)} -o ${os.quoted_path(c_path)} ${os.quoted_path(source_path)}')
+	assert res.exit_code == 0, res.output
+	csrc := os.read_file(c_path) or { panic(err) }
+	assert csrc.contains('__shared__main__StructB* copy = (__shared__main__StructB*)__dup__shared__main__StructB')
+	assert csrc.contains('*src}, sizeof(__shared__main__StructB))')
+	assert !csrc.contains('__shared__main__StructB* copy = src;')
+}
-- 
2.39.5