cgen: fix or-block with fixed array constants with GCC 15.2 (fix #26442) (#26443)

Author: Jesus Alvarez

vlib/v/gen/c/cgen.v

@@ -7404,7 +7404,19 @@ fn (mut g Gen) gen_or_block_stmts(cvar_name string, cast_typ string, stmts []ast
 						g.write('${cvar_name} = ')
 					}
 					if is_array_fixed {
-						g.write('memcpy(${cvar_name}${tmp_op}data, (${cast_typ})')
+						// For fixed arrays, we need memcpy. Use compound literal cast only for
+						// expressions that generate brace-enclosed initializers (which need
+						// to become compound literals), not for constants/variables where
+						// casting to array type is invalid C.
+						is_array_init := expr_stmt.expr is ast.ArrayInit
+							|| expr_stmt.expr is ast.StructInit
+							|| (expr_stmt.expr is ast.CastExpr
+							&& (expr_stmt.expr as ast.CastExpr).expr is ast.ArrayInit)
+						if is_array_init {
+							g.write('memcpy(${cvar_name}${tmp_op}data, (${cast_typ})')
+						} else {
+							g.write('memcpy(${cvar_name}${tmp_op}data, ')
+						}
 					}
 					// return expr or { fn_returns_option() }
 					if is_option && g.inside_return && expr_stmt.expr is ast.CallExpr

vlib/v/tests/options/option_fixed_arr_const_test.v

@@ -0,0 +1,20 @@
+// Test for or-block returning a fixed array constant.
+// Regression test for issue where cgen generated invalid C cast to array type.
+const default_arr = [f32(1.0), 2.0, 3.0, 4.0]!
+
+fn get_arr(key string) ?[4]f32 {
+	if key == 'valid' {
+		return [f32(0.1), 0.2, 0.3, 0.4]!
+	}
+	return none
+}
+
+fn test_or_block_with_fixed_array_const() {
+	result := get_arr('invalid') or { default_arr }
+	assert result == default_arr
+}
+
+fn test_or_block_with_valid_key() {
+	result := get_arr('valid') or { default_arr }
+	assert result == [f32(0.1), 0.2, 0.3, 0.4]!
+}