bevy_lint/lints/suspicious/
iter_current_update_events.rs

1//! Checks for calls to `Events::<T>::iter_current_update_events()`.
2//!
3//! # Motivation
4//!
5//! `Events::<T>::iter_current_update_events()` lets you read all of the current events since
6//! `Events::<T>::update()` was last called, similar to `EventReader<T>`. Unlike `EventReader<T>`,
7//! `iter_current_update_events()` does not track which events have already been read. As such,
8//! `iter_current_update_events()` is highly discouraged because it may skip events or yield them
9//! multiple times.
10//!
11//! # Example
12//!
13//! ```
14//! # use bevy::prelude::*;
15//! #
16//! #[derive(Event)]
17//! struct MyEvent;
18//!
19//! fn my_system(events: Res<Events<MyEvent>>) {
20//!     for event in events.iter_current_update_events() {
21//!         // ...
22//!     }
23//! }
24//! ```
25//!
26//! Use instead:
27//!
28//! ```
29//! # use bevy::prelude::*;
30//! #
31//! #[derive(Event)]
32//! struct MyEvent;
33//!
34//! fn my_system(mut events: EventReader<MyEvent>) {
35//!     for event in events.read() {
36//!         // ...
37//!     }
38//! }
39//! ```
40
41use clippy_utils::{diagnostics::span_lint_and_help, ty::match_type};
42use rustc_hir::Expr;
43use rustc_lint::{LateContext, LateLintPass};
44use rustc_span::Symbol;
45
46use crate::{declare_bevy_lint, declare_bevy_lint_pass, utils::hir_parse::MethodCall};
47
48declare_bevy_lint! {
49    pub ITER_CURRENT_UPDATE_EVENTS,
50    super::SUSPICIOUS,
51    "called `Events::<T>::iter_current_update_events()`",
52}
53
54declare_bevy_lint_pass! {
55    pub IterCurrentUpdateEvents => [ITER_CURRENT_UPDATE_EVENTS.lint],
56
57    @default = {
58        iter_current_update_events: Symbol = Symbol::intern("iter_current_update_events"),
59    },
60}
61
62impl<'tcx> LateLintPass<'tcx> for IterCurrentUpdateEvents {
63    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
64        // If this expression was generated by an external macro, don't lint it.
65        if expr.span.in_external_macro(cx.tcx.sess.source_map()) {
66            return;
67        }
68
69        if let Some(method_call) = MethodCall::try_from(cx, expr) {
70            // Find the adjusted type of the receiver. Type adjustment does things like
71            // auto-dereference and type coercion. In this example, we use the adjusted type so
72            // that we can also handle `Res<Events<T>>`.
73            //
74            // ```
75            // fn plain(events: Events<T>) {
76            //     // Original type is `Events<T>`, adjusted type is `Events<T>`.
77            //     let _ = events.iter_current_update_events();
78            // }
79            //
80            // fn res(events: Res<Events<T>>) {
81            //     // Original type is `Res<Events<T>>`, adjusted type is `Events<T>`.
82            //     let _ = events.iter_current_update_events();
83            // }
84            // ```
85            let src_ty = cx
86                .typeck_results()
87                .expr_ty_adjusted(method_call.receiver)
88                .peel_refs();
89
90            if !match_type(cx, src_ty, &crate::paths::EVENTS) {
91                return;
92            }
93
94            if method_call.method_path.ident.name == self.iter_current_update_events {
95                span_lint_and_help(
96                    cx,
97                    ITER_CURRENT_UPDATE_EVENTS.lint,
98                    method_call.span,
99                    ITER_CURRENT_UPDATE_EVENTS.lint.desc,
100                    None,
101                    "`iter_current_update_events()` does not track which events have already been seen, consider using `EventReader<T>` instead",
102                );
103            }
104        }
105    }
106}
bevy_lint/lints/suspicious/iter_current_update_events.rs

bevy_lint/lints/suspicious/
iter_current_update_events.rs
