Add print_stdout and print_stderr lints (#17446) (#18233)

# Objective

- Prevent usage of `println!`, `eprintln!` and the like because they
require `std`
- Fixes #17446

## Solution

- Enable the `print_stdout` and `print_stderr` clippy lints
- Replace all `println!` and `eprintln!` occurrences with `log::*` where
applicable or alternatively ignore the warnings

## Testing

- Run `cargo clippy --workspace` to ensure that there are no warnings
relating to printing to `stdout` or `stderr`

Author: sirius94

Cargo.toml

@@ -51,6 +51,8 @@ unwrap_or_default = "warn"
 needless_lifetimes = "allow"
 too_many_arguments = "allow"
 nonstandard_macro_braces = "warn"
+print_stdout = "warn"
+print_stderr = "warn"
 
 ptr_as_ptr = "warn"
 ptr_cast_constness = "warn"

crates/bevy_asset/src/asset_changed.rs

@@ -281,6 +281,7 @@ unsafe impl<A: AsAssetId> QueryFilter for AssetChanged<A> {
 }
 
 #[cfg(test)]
+#[expect(clippy::print_stdout, reason = "Allowed in tests.")]
 mod tests {
     use crate::{AssetEvents, AssetPlugin, Handle};
     use alloc::{vec, vec::Vec};

crates/bevy_ecs/examples/change_detection.rs

@@ -8,6 +8,7 @@
 
 #![expect(
     clippy::std_instead_of_core,
+    clippy::print_stdout,
     reason = "Examples should not follow this lint"
 )]
 

crates/bevy_ecs/examples/events.rs

@@ -1,6 +1,8 @@
 //! In this example a system sends a custom event with a 50/50 chance during any frame.
 //! If an event was send, it will be printed by the console in a receiving system.
 
+#![expect(clippy::print_stdout, reason = "Allowed in examples.")]
+
 use bevy_ecs::{event::EventRegistry, prelude::*};
 
 fn main() {

crates/bevy_ecs/examples/resources.rs

@@ -3,6 +3,7 @@
 
 #![expect(
     clippy::std_instead_of_core,
+    clippy::print_stdout,
     reason = "Examples should not follow this lint"
 )]
 

crates/bevy_ecs/src/error/bevy_error.rs

@@ -139,6 +139,7 @@ std::thread_local! {
 
 /// When called, this will skip the currently configured panic hook when a [`BevyError`] backtrace has already been printed.
 #[cfg(feature = "backtrace")]
+#[expect(clippy::print_stdout, reason = "Allowed behind `std` feature gate.")]
 pub fn bevy_error_panic_hook(
     current_hook: impl Fn(&std::panic::PanicHookInfo),
 ) -> impl Fn(&std::panic::PanicHookInfo) {

crates/bevy_ecs/src/query/iter.rs

@@ -2585,6 +2585,7 @@ impl<T> Ord for NeutralOrd<T> {
 }
 
 #[cfg(test)]
+#[expect(clippy::print_stdout, reason = "Allowed in tests.")]
 mod tests {
     use alloc::vec::Vec;
     use std::println;

crates/bevy_ecs/src/query/mod.rs

@@ -102,6 +102,7 @@ impl<T> DebugCheckedUnwrap for Option<T> {
 }
 
 #[cfg(test)]
+#[expect(clippy::print_stdout, reason = "Allowed in tests.")]
 mod tests {
     use crate::{
         archetype::Archetype,

crates/bevy_ecs/src/schedule/executor/multi_threaded.rs

@@ -5,10 +5,9 @@ use bevy_utils::{default, syncunsafecell::SyncUnsafeCell};
 use concurrent_queue::ConcurrentQueue;
 use core::{any::Any, panic::AssertUnwindSafe};
 use fixedbitset::FixedBitSet;
-use std::{
-    eprintln,
-    sync::{Mutex, MutexGuard},
-};
+#[cfg(feature = "std")]
+use std::eprintln;
+use std::sync::{Mutex, MutexGuard};
 
 #[cfg(feature = "trace")]
 use tracing::{info_span, Span};
@@ -283,7 +282,11 @@ impl<'scope, 'env: 'scope, 'sys> Context<'scope, 'env, 'sys> {
             .push(SystemResult { system_index })
             .unwrap_or_else(|error| unreachable!("{}", error));
         if let Err(payload) = res {
-            eprintln!("Encountered a panic in system `{}`!", &*system.name());
+            #[cfg(feature = "std")]
+            #[expect(clippy::print_stderr, reason = "Allowed behind `std` feature gate.")]
+            {
+                eprintln!("Encountered a panic in system `{}`!", &*system.name());
+            }
             // set the payload to propagate the error
             {
                 let mut panic_payload = self.environment.executor.panic_payload.lock().unwrap();
@@ -741,10 +744,14 @@ fn apply_deferred(
             system.apply_deferred(world);
         }));
         if let Err(payload) = res {
-            eprintln!(
-                "Encountered a panic when applying buffers for system `{}`!",
-                &*system.name()
-            );
+            #[cfg(feature = "std")]
+            #[expect(clippy::print_stderr, reason = "Allowed behind `std` feature gate.")]
+            {
+                eprintln!(
+                    "Encountered a panic when applying buffers for system `{}`!",
+                    &*system.name()
+                );
+            }
             return Err(payload);
         }
     }

crates/bevy_ecs/src/schedule/executor/simple.rs

@@ -118,6 +118,7 @@ impl SystemExecutor for SimpleExecutor {
             });
 
             #[cfg(feature = "std")]
+            #[expect(clippy::print_stderr, reason = "Allowed behind `std` feature gate.")]
             {
                 if let Err(payload) = std::panic::catch_unwind(f) {
                     eprintln!("Encountered a panic in system `{}`!", &*system.name());