From 06825006b3ea89b43c2c5e12179b4abb01b993bb Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Mon, 1 Jul 2024 15:00:26 -0300
Subject: [PATCH] cgen: fix array fixed empty struct code generated on clang
 (fix #21761) (#21764)

---
 vlib/v/ast/types.v                           | 10 ++++++++++
 vlib/v/gen/c/cgen.v                          | 12 ++++++++++--
 vlib/v/gen/c/dumpexpr.v                      |  9 +++++++--
 vlib/v/tests/array_fixed_empty_struct_test.v | 16 ++++++++++++++++
 4 files changed, 43 insertions(+), 4 deletions(-)
 create mode 100644 vlib/v/tests/array_fixed_empty_struct_test.v

diff --git a/vlib/v/ast/types.v b/vlib/v/ast/types.v
index 9130e9995faf96..1bb6d8cd354098 100644
--- a/vlib/v/ast/types.v
+++ b/vlib/v/ast/types.v
@@ -925,6 +925,16 @@ pub fn (t &ArrayFixed) is_compatible(t2 ArrayFixed) bool {
 	return t.size == t2.size && t.elem_type == t2.elem_type
 }
 
+pub fn (t &TypeSymbol) is_empty_struct_array() bool {
+	if t.info is ArrayFixed {
+		elem_sym := global_table.final_sym(t.info.elem_type)
+		if elem_sym.info is Struct {
+			return elem_sym.info.fields.len == 0
+		}
+	}
+	return false
+}
+
 pub fn (t &TypeSymbol) is_array_fixed() bool {
 	if t.info is ArrayFixed {
 		return true
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 0948a4f211d3fc..c789dc2dc9bb00 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -4295,7 +4295,7 @@ fn (mut g Gen) debugger_stmt(node ast.DebuggerStmt) {
 fn (mut g Gen) enum_decl(node ast.EnumDecl) {
 	enum_name := util.no_dots(node.name)
 	is_flag := node.is_flag
-	if g.pref.ccompiler == 'msvc' {
+	if g.is_cc_msvc {
 		mut last_value := '0'
 		enum_typ_name := g.table.get_type_name(node.typ)
 		g.enum_typedefs.writeln('')
@@ -6278,6 +6278,8 @@ fn (mut g Gen) global_decl(node ast.GlobalDecl) {
 			default_initializer := g.type_default(field.typ)
 			if default_initializer == '{0}' && should_init {
 				def_builder.write_string(' = {0}')
+			} else if default_initializer == '{EMPTY_STRUCT_INITIALIZATION}' && should_init {
+				init = '\tmemcpy(${field.name}, (${styp}){${g.type_default(field.typ)}}, sizeof(${styp})); // global'
 			} else {
 				if field.name !in ['as_cast_type_indexes', 'g_memory_block', 'global_allocator'] {
 					init = '\t${field.name} = *(${styp}*)&((${styp}[]){${g.type_default(field.typ)}}[0]); // global'
@@ -7161,7 +7163,13 @@ fn (mut g Gen) type_default(typ_ ast.Type) string {
 		.string {
 			return '(string){.str=(byteptr)"", .is_lit=1}'
 		}
-		.interface_, .sum_type, .array_fixed, .multi_return, .thread {
+		.array_fixed {
+			if sym.is_empty_struct_array() {
+				return '{EMPTY_STRUCT_INITIALIZATION}'
+			}
+			return '{0}'
+		}
+		.interface_, .sum_type, .multi_return, .thread {
 			return '{0}'
 		}
 		.alias {
diff --git a/vlib/v/gen/c/dumpexpr.v b/vlib/v/gen/c/dumpexpr.v
index f18af667226d42..8d629c0f87c6b6 100644
--- a/vlib/v/gen/c/dumpexpr.v
+++ b/vlib/v/gen/c/dumpexpr.v
@@ -227,11 +227,16 @@ fn (mut g Gen) dump_expr_definitions() {
 		surrounder.builder_write_afters(mut dump_fns)
 		if is_fixed_arr_ret {
 			tmp_var := g.new_tmp_var()
+			init_str := if dump_sym.is_empty_struct_array() {
+				'{EMPTY_STRUCT_INITIALIZATION}'
+			} else {
+				'{0}'
+			}
 			if typ.is_ptr() {
-				dump_fns.writeln('\t${str_dumparg_ret_type} ${tmp_var} = HEAP(${g.typ(typ.set_nr_muls(0))}, {0});')
+				dump_fns.writeln('\t${str_dumparg_ret_type} ${tmp_var} = HEAP(${g.typ(typ.set_nr_muls(0))}, ${init_str});')
 				dump_fns.writeln('\tmemcpy(${tmp_var}->ret_arr, dump_arg, sizeof(${str_dumparg_type}));')
 			} else {
-				dump_fns.writeln('\t${str_dumparg_ret_type} ${tmp_var} = {0};')
+				dump_fns.writeln('\t${str_dumparg_ret_type} ${tmp_var} = ${init_str};')
 				dump_fns.writeln('\tmemcpy(${tmp_var}.ret_arr, dump_arg, sizeof(${str_dumparg_type}));')
 			}
 			dump_fns.writeln('\treturn ${tmp_var};')
diff --git a/vlib/v/tests/array_fixed_empty_struct_test.v b/vlib/v/tests/array_fixed_empty_struct_test.v
new file mode 100644
index 00000000000000..7e33aa26db3319
--- /dev/null
+++ b/vlib/v/tests/array_fixed_empty_struct_test.v
@@ -0,0 +1,16 @@
+@[has_globals]
+module main
+
+const num_elements = 10
+
+struct DummyStruct {
+}
+
+__global (
+	d [num_elements]DummyStruct
+)
+
+fn test_main() {
+	a := dump(d)
+	assert a.len == num_elements
+}