From bd49980909575c71b5e47286e695cd57c6d1b954 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 11 Mar 2026 12:36:12 +0300
Subject: [PATCH] cgen: compiling issue (fixes #16832)

---
 vlib/v/gen/c/auto_str_methods.v               | 25 ++++++++++------
 .../cstruct_opaque_typedef_auto_str_test.c.v  | 30 +++++++++++++++++++
 vlib/v/tests/c_structs/opaque_pgconn.h        |  1 +
 3 files changed, 47 insertions(+), 9 deletions(-)
 create mode 100644 vlib/v/tests/c_structs/cstruct_opaque_typedef_auto_str_test.c.v
 create mode 100644 vlib/v/tests/c_structs/opaque_pgconn.h

diff --git a/vlib/v/gen/c/auto_str_methods.v b/vlib/v/gen/c/auto_str_methods.v
index ea5b84984..16b8025ab 100644
--- a/vlib/v/gen/c/auto_str_methods.v
+++ b/vlib/v/gen/c/auto_str_methods.v
@@ -204,6 +204,7 @@ fn (mut g Gen) gen_str_for_option(typ ast.Type, styp string, str_fn_name string,
 	sym := g.table.sym(parent_type)
 	sym_has_str_method, expects_ptr, _ := sym.str_method_info()
 	parent_str_fn_name := g.get_str_fn(parent_type)
+	parent_cast_type := g.auto_str_storage_cast_type(parent_type)
 
 	g.definitions.writeln('string ${str_fn_name}(${styp} it);')
 	g.auto_str_funcs.writeln('string ${str_fn_name}(${styp} it) { return indent_${str_fn_name}(it, 0); }')
@@ -217,17 +218,17 @@ fn (mut g Gen) gen_str_for_option(typ ast.Type, styp string, str_fn_name string,
 		} else {
 			'*'.repeat(typ.nr_muls() + 1)
 		}
-		'${dot}(${sym.cname}**)&'
+		'${dot}(${parent_cast_type}**)&'
 	} else if typ.has_flag(.option_mut_param_t) {
-		'*(${sym.cname}*)'
+		'*(${parent_cast_type}*)'
 	} else if expects_ptr {
-		'(${sym.cname}*)'
+		'(${parent_cast_type}*)'
 	} else {
-		'*(${sym.cname}*)'
+		'*(${parent_cast_type}*)'
 	}
 	if sym.kind == .string {
 		if typ.nr_muls() > 1 {
-			g.auto_str_funcs.writeln('\t\tres = builtin__ptr_str(*(${sym.cname}**)&it.data);')
+			g.auto_str_funcs.writeln('\t\tres = builtin__ptr_str(*(${parent_cast_type}**)&it.data);')
 		} else {
 			tmp_res := '${parent_str_fn_name}(${deref}it.data)'
 			g.auto_str_funcs.writeln('\t\tres = ${str_intp_sq(tmp_res)};')
@@ -238,7 +239,7 @@ fn (mut g Gen) gen_str_for_option(typ ast.Type, styp string, str_fn_name string,
 		g.auto_str_funcs.writeln('\t\tres = ${parent_str_fn_name}();')
 	} else {
 		if typ.nr_muls() > 1 {
-			g.auto_str_funcs.writeln('\t\tres = builtin__ptr_str(*(${sym.cname}**)&it.data);')
+			g.auto_str_funcs.writeln('\t\tres = builtin__ptr_str(*(${parent_cast_type}**)&it.data);')
 		} else {
 			g.auto_str_funcs.writeln('\t\tres = ${parent_str_fn_name}(${deref}it.data);')
 		}
@@ -257,6 +258,7 @@ fn (mut g Gen) gen_str_for_result(typ ast.Type, styp string, str_fn_name string)
 	sym := g.table.sym(parent_type)
 	sym_has_str_method, _, _ := sym.str_method_info()
 	parent_str_fn_name := g.get_str_fn(parent_type)
+	parent_cast_type := g.auto_str_storage_cast_type(parent_type)
 
 	g.definitions.writeln('string ${str_fn_name}(${styp} it);')
 	g.auto_str_funcs.writeln('string ${str_fn_name}(${styp} it) { return indent_${str_fn_name}(it, 0); }')
@@ -265,12 +267,12 @@ fn (mut g Gen) gen_str_for_result(typ ast.Type, styp string, str_fn_name string)
 	g.auto_str_funcs.writeln('\tstring res;')
 	g.auto_str_funcs.writeln('\tif (!it.is_error) {')
 	if sym.kind == .string {
-		tmp_res := '${parent_str_fn_name}(*(${sym.cname}*)it.data)'
+		tmp_res := '${parent_str_fn_name}(*(${parent_cast_type}*)it.data)'
 		g.auto_str_funcs.writeln('\t\tres = ${str_intp_sq(tmp_res)};')
 	} else if should_use_indent_func(sym.kind) && !sym_has_str_method {
-		g.auto_str_funcs.writeln('\t\tres = indent_${parent_str_fn_name}(*(${sym.cname}*)it.data, indent_count);')
+		g.auto_str_funcs.writeln('\t\tres = indent_${parent_str_fn_name}(*(${parent_cast_type}*)it.data, indent_count);')
 	} else {
-		g.auto_str_funcs.writeln('\t\tres = ${parent_str_fn_name}(*(${sym.cname}*)it.data);')
+		g.auto_str_funcs.writeln('\t\tres = ${parent_str_fn_name}(*(${parent_cast_type}*)it.data);')
 	}
 	g.auto_str_funcs.writeln('\t} else {')
 
@@ -282,6 +284,11 @@ fn (mut g Gen) gen_str_for_result(typ ast.Type, styp string, str_fn_name string)
 	g.auto_str_funcs.writeln('}')
 }
 
+@[inline]
+fn (mut g Gen) auto_str_storage_cast_type(typ ast.Type) string {
+	return g.base_type(typ).trim('*')
+}
+
 fn (mut g Gen) gen_str_for_alias(info ast.Alias, styp string, str_fn_name string) {
 	parent_str_fn_name := g.get_str_fn(info.parent_type)
 	parent_sym := g.table.sym(info.parent_type)
diff --git a/vlib/v/tests/c_structs/cstruct_opaque_typedef_auto_str_test.c.v b/vlib/v/tests/c_structs/cstruct_opaque_typedef_auto_str_test.c.v
new file mode 100644
index 000000000..ebda17a23
--- /dev/null
+++ b/vlib/v/tests/c_structs/cstruct_opaque_typedef_auto_str_test.c.v
@@ -0,0 +1,30 @@
+#include "@VMODROOT/opaque_pgconn.h"
+
+@[typedef]
+struct C.PGconn {}
+
+struct DB {
+	conn &C.PGconn = unsafe { nil }
+}
+
+struct OptionalDB {
+	conn ?&C.PGconn
+}
+
+fn test_auto_str_for_opaque_c_typedef_ptr_field() {
+	db := DB{
+		conn: unsafe { &C.PGconn(malloc(1)) }
+	}
+	assert dump('${db}') == 'DB{
+    conn: &C.PGconn{}
+}'
+}
+
+fn test_auto_str_for_optional_opaque_c_typedef_ptr_field() {
+	db := OptionalDB{
+		conn: unsafe { &C.PGconn(malloc(1)) }
+	}
+	assert dump('${db}') == 'OptionalDB{
+    conn: &Option(C.PGconn{})
+}'
+}
diff --git a/vlib/v/tests/c_structs/opaque_pgconn.h b/vlib/v/tests/c_structs/opaque_pgconn.h
new file mode 100644
index 000000000..f610251cc
--- /dev/null
+++ b/vlib/v/tests/c_structs/opaque_pgconn.h
@@ -0,0 +1 @@
+typedef struct pg_conn PGconn;
-- 
2.39.5