From cd1c0d2dc00420adf0a8e2a60e5386e3ef190198 Mon Sep 17 00:00:00 2001
From: Hennadii Chernyshchyk <genaloner@gmail.com>
Date: Wed, 8 Feb 2023 23:24:36 +0000
Subject: [PATCH] Add condition negation (#7559)

# Objective

Closes #7202

## Solution

~~Introduce a `not` helper to pipe conditions. Opened mostly for discussion. Maybe create an extension trait with `not` method? Please, advice.~~
Introduce `not(condition)` condition that inverses the result of the passed.

---

## Changelog

### Added

- `not` condition.
---
 crates/bevy_ecs/src/schedule/condition.rs | 40 +++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/crates/bevy_ecs/src/schedule/condition.rs b/crates/bevy_ecs/src/schedule/condition.rs
index 541ed202957b6c..763d88d8e09015 100644
--- a/crates/bevy_ecs/src/schedule/condition.rs
+++ b/crates/bevy_ecs/src/schedule/condition.rs
@@ -24,8 +24,11 @@ mod sealed {
 }
 
 pub mod common_conditions {
-    use crate::schedule::{State, States};
-    use crate::system::{Res, Resource};
+    use super::Condition;
+    use crate::{
+        schedule::{State, States},
+        system::{In, IntoPipeSystem, ReadOnlySystem, Res, Resource},
+    };
 
     /// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
     /// if the first time the condition is run and false every time after
@@ -105,4 +108,37 @@ pub mod common_conditions {
             None => false,
         }
     }
+
+    /// Generates a  [`Condition`](super::Condition) that inverses the result of passed one.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bevy_ecs::prelude::*;
+    /// // Building a new schedule/app...
+    /// let mut sched = Schedule::default();
+    /// sched.add_system(
+    ///         // This system will never run.
+    ///         my_system.run_if(not(always_true))
+    ///     )
+    ///     // ...
+    /// #   ;
+    /// # let mut world = World::new();
+    /// # sched.run(&mut world);
+    ///
+    /// // A condition that always returns true.
+    /// fn always_true() -> bool {
+    ///    true
+    /// }
+    /// #
+    /// # fn my_system() { unreachable!() }
+    /// ```
+    pub fn not<Params, C: Condition<Params>>(
+        condition: C,
+    ) -> impl ReadOnlySystem<In = (), Out = bool>
+    where
+        C::System: ReadOnlySystem,
+    {
+        condition.pipe(|In(val): In<bool>| !val)
+    }
 }