From 8e927daa77fab0f11d6f5280a5eff5c651e3e537 Mon Sep 17 00:00:00 2001
From: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Date: Fri, 12 Aug 2022 19:18:27 +0200
Subject: [PATCH] Add `defer` (#12013)
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* Add defer
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Convert to macro + review fixes
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Apply suggestions from code review
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
* Move into new file and add panic unwind tests
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Fix doc and Clippy
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
---
substrate/primitives/core/src/defer.rs | 140 +++++++++++++++++++++++++
substrate/primitives/core/src/lib.rs | 1 +
2 files changed, 141 insertions(+)
create mode 100644 substrate/primitives/core/src/defer.rs
diff --git a/substrate/primitives/core/src/defer.rs b/substrate/primitives/core/src/defer.rs
new file mode 100644
index 00000000000..d14b26d59e4
--- /dev/null
+++ b/substrate/primitives/core/src/defer.rs
@@ -0,0 +1,140 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2022 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Contains the [`crate::defer!`] macro for *deferring* the execution
+//! of code until the current scope is dropped.
+//! This helps with *always* executing cleanup code.
+
+/// Executes the wrapped closure on drop.
+///
+/// Should be used together with the [`crate::defer!`] macro.
+#[must_use]
+pub struct DeferGuard<F: FnOnce()>(pub Option<F>);
+
+impl<F: FnOnce()> Drop for DeferGuard<F> {
+ fn drop(&mut self) {
+ self.0.take().map(|f| f());
+ }
+}
+
+/// Executes the given code when the current scope is dropped.
+///
+/// Multiple calls to [`crate::defer!`] will execute the passed codes in reverse order.
+/// This also applies to panic stack unwinding.
+///
+/// # Example
+///
+/// ```rust
+/// use sp_core::defer;
+///
+/// let message = std::cell::RefCell::new("".to_string());
+/// {
+/// defer!(
+/// message.borrow_mut().push_str("world!");
+/// );
+/// defer!(
+/// message.borrow_mut().push_str("Hello ");
+/// );
+/// }
+/// assert_eq!(*message.borrow(), "Hello world!");
+/// ```
+#[macro_export]
+macro_rules! defer(
+ ( $( $code:tt )* ) => {
+ let _guard = $crate::defer::DeferGuard(Some(|| { $( $code )* }));
+ };
+);
+
+#[cfg(test)]
+mod test {
+ #[test]
+ fn defer_guard_works() {
+ let mut called = false;
+ {
+ defer!(
+ called = true;
+ );
+ }
+ assert!(called, "DeferGuard should have executed the closure");
+ }
+
+ #[test]
+ /// `defer` executes the code in reverse order of being called.
+ fn defer_guard_order_works() {
+ let called = std::cell::RefCell::new(1);
+
+ defer!(
+ assert_eq!(*called.borrow(), 3);
+ );
+ defer!(
+ assert_eq!(*called.borrow(), 2);
+ *called.borrow_mut() = 3;
+ );
+ defer!({
+ assert_eq!(*called.borrow(), 1);
+ *called.borrow_mut() = 2;
+ });
+ }
+
+ #[test]
+ #[allow(unused_braces)]
+ #[allow(clippy::unnecessary_operation)]
+ fn defer_guard_syntax_works() {
+ let called = std::cell::RefCell::new(0);
+ {
+ defer!(*called.borrow_mut() += 1);
+ defer!(*called.borrow_mut() += 1;); // With ;
+ defer!({ *called.borrow_mut() += 1 });
+ defer!({ *called.borrow_mut() += 1 };); // With ;
+ }
+ assert_eq!(*called.borrow(), 4);
+ }
+
+ #[test]
+ /// `defer` executes the code even in case of a panic.
+ fn defer_guard_panic_unwind_works() {
+ use std::panic::{catch_unwind, AssertUnwindSafe};
+ let mut called = false;
+
+ let should_panic = catch_unwind(AssertUnwindSafe(|| {
+ defer!(called = true);
+ panic!();
+ }));
+
+ assert!(should_panic.is_err(), "DeferGuard should have panicked");
+ assert!(called, "DeferGuard should have executed the closure");
+ }
+
+ #[test]
+ /// `defer` executes the code even in case another `defer` panics.
+ fn defer_guard_defer_panics_unwind_works() {
+ use std::panic::{catch_unwind, AssertUnwindSafe};
+ let counter = std::cell::RefCell::new(0);
+
+ let should_panic = catch_unwind(AssertUnwindSafe(|| {
+ defer!(*counter.borrow_mut() += 1);
+ defer!(
+ *counter.borrow_mut() += 1;
+ panic!();
+ );
+ defer!(*counter.borrow_mut() += 1);
+ }));
+
+ assert!(should_panic.is_err(), "DeferGuard should have panicked");
+ assert_eq!(*counter.borrow(), 3, "DeferGuard should have executed the closure");
+ }
+}
diff --git a/substrate/primitives/core/src/lib.rs b/substrate/primitives/core/src/lib.rs
index ab3334f9e4f..f48adc274f5 100644
--- a/substrate/primitives/core/src/lib.rs
+++ b/substrate/primitives/core/src/lib.rs
@@ -56,6 +56,7 @@ pub use hashing::{blake2_128, blake2_256, keccak_256, twox_128, twox_256, twox_6
pub mod crypto;
pub mod hexdisplay;
+pub mod defer;
pub mod ecdsa;
pub mod ed25519;
pub mod hash;
--
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