cgen: fix return with option on orexpr (#20728)

vlib/v/gen/c/cgen.v

@@ -6624,19 +6624,30 @@ fn (mut g Gen) gen_or_block_stmts(cvar_name string, cast_typ string, stmts []ast
 						is_array_fixed = expr_stmt.expr is ast.ArrayInit
 							&& g.table.final_sym(return_type).kind == .array_fixed
 						if !is_array_fixed {
-							g.write('*(${cast_typ}*) ${cvar_name}.data = ')
+							if g.inside_return && !g.inside_struct_init
+								&& expr_stmt.expr is ast.CallExpr
+								&& return_type.has_option_or_result() {
+								g.write('${cvar_name} = ')
+							} else {
+								g.write('*(${cast_typ}*) ${cvar_name}.data = ')
+							}
 						}
 					} else {
 						g.write('${cvar_name} = ')
 					}
-
 					if is_array_fixed {
 						g.write('memcpy(${cvar_name}.data, (${cast_typ})')
 					}
-					old_inside_opt_data := g.inside_opt_data
-					g.inside_opt_data = true
-					g.expr_with_cast(expr_stmt.expr, expr_stmt.typ, return_type.clear_option_and_result())
-					g.inside_opt_data = old_inside_opt_data
+					// return expr or { fn_returns_option() }
+					if is_option && g.inside_return && expr_stmt.expr is ast.CallExpr
+						&& return_type.has_option_or_result() {
+						g.expr_with_cast(expr_stmt.expr, expr_stmt.typ, return_type)
+					} else {
+						old_inside_opt_data := g.inside_opt_data
+						g.inside_opt_data = true
+						g.expr_with_cast(expr_stmt.expr, expr_stmt.typ, return_type.clear_option_and_result())
+						g.inside_opt_data = old_inside_opt_data
+					}
 					if is_array_fixed {
 						g.write(', sizeof(${cast_typ}))')
 					}

vlib/v/tests/option_call_on_orexpr_test.v

@@ -0,0 +1,20 @@
+fn find_startswith_string(a []string, search string) ?string {
+	for s in a {
+		if s.starts_with(search) {
+			return s
+		}
+	}
+	return none
+}
+
+fn find_any_startswith_string(a []string, b []string, search string) ?string {
+	// cannot convert 'struct _option_string' to 'struct string'
+	// V wants the or {} block to return a string, but find_startswith_string returns ?string
+	return find_startswith_string(a, search) or { find_startswith_string(b, search) }
+}
+
+fn test_main() {
+	deadbeef := find_any_startswith_string(['foobar', 'barfoo'], ['deadbeef', 'beefdead'],
+		'dead')
+	assert deadbeef or { panic('unreachable') } == 'deadbeef'
+}