cgen: fix alloc empty struct array error (#14007)

vlib/arrays/arrays_test.v

@@ -300,3 +300,15 @@ fn test_alias_string_contains() {
 	names := [Str('')]
 	assert (Str('') in names) == true
 }
+
+struct XYZ {}
+
+fn test_array_append_empty_struct() {
+	mut names := []XYZ{cap: 2}
+	names << XYZ{}
+	assert (XYZ{} in names) == true
+
+	// test fixed array
+	array := [XYZ{}]
+	assert (XYZ{} in names) == true
+}

vlib/v/gen/c/array.v

@@ -151,7 +151,7 @@ fn (mut g Gen) array_init(node ast.ArrayInit) {
 			} else {
 				g.write('0, ')
 			}
-			if elem_type.unaliased_sym.kind == .function {
+			if elem_type.unaliased_sym.kind == .function || g.is_empty_struct(elem_type) {
 				g.write('sizeof(voidptr), ')
 			} else {
 				g.write('sizeof($elem_styp), ')
@@ -217,7 +217,7 @@ fn (mut g Gen) array_init(node ast.ArrayInit) {
 		} else {
 			g.write('0, ')
 		}
-		if elem_type.unaliased_sym.kind == .function {
+		if elem_type.unaliased_sym.kind == .function || g.is_empty_struct(elem_type) {
 			g.write('sizeof(voidptr), ')
 		} else {
 			g.write('sizeof($elem_styp), ')
@@ -251,6 +251,8 @@ fn (mut g Gen) array_init(node ast.ArrayInit) {
 	len := node.exprs.len
 	if elem_type.unaliased_sym.kind == .function {
 		g.write('new_array_from_c_array($len, $len, sizeof(voidptr), _MOV((voidptr[$len]){')
+	} else if g.is_empty_struct(elem_type) {
+		g.write('new_array_from_c_array${noscan}($len, $len, sizeof(voidptr), _MOV(($elem_styp[$len]){')
 	} else {
 		g.write('new_array_from_c_array${noscan}($len, $len, sizeof($elem_styp), _MOV(($elem_styp[$len]){')
 	}

vlib/v/gen/c/struct.v

@@ -305,3 +305,18 @@ fn (mut g Gen) zero_struct_field(field ast.StructField) bool {
 	}
 	return true
 }
+
+fn (mut g Gen) is_empty_struct(t Type) bool {
+	sym := t.unaliased_sym
+	match sym.info {
+		ast.Struct {
+			if sym.info.fields.len > 0 || sym.info.embeds.len > 0 {
+				return false
+			}
+			return true
+		}
+		else {
+			return false
+		}
+	}
+}