rustc_lint/
interior_mutable_consts.rs

1use rustc_hir::attrs::AttributeKind;
2use rustc_hir::def::{DefKind, Res};
3use rustc_hir::{Expr, ExprKind, ItemKind, Node, find_attr};
4use rustc_session::{declare_lint, declare_lint_pass};
5
6use crate::lints::{ConstItemInteriorMutationsDiag, ConstItemInteriorMutationsSuggestionStatic};
7use crate::{LateContext, LateLintPass, LintContext};
8
9declare_lint! {
10    /// The `const_item_interior_mutations` lint checks for calls which
11    /// mutates an interior mutable const-item.
12    ///
13    /// ### Example
14    ///
15    /// ```rust
16    /// use std::sync::Once;
17    ///
18    /// const INIT: Once = Once::new(); // using `INIT` will always create a temporary and
19    ///                                 // never modify it-self on use, should be a `static`
20    ///                                 // instead for shared use
21    ///
22    /// fn init() {
23    ///     INIT.call_once(|| {
24    ///         println!("Once::call_once first call");
25    ///     });
26    ///     INIT.call_once(|| {                          // this second will also print
27    ///         println!("Once::call_once second call"); // as each call to `INIT` creates
28    ///     });                                          // new temporary
29    /// }
30    /// ```
31    ///
32    /// {{produces}}
33    ///
34    /// ### Explanation
35    ///
36    /// Calling a method which mutates an interior mutable type has no effect as const-item
37    /// are essentially inlined wherever they are used, meaning that they are copied
38    /// directly into the relevant context when used rendering modification through
39    /// interior mutability ineffective across usage of that const-item.
40    ///
41    /// The current implementation of this lint only warns on significant `std` and
42    /// `core` interior mutable types, like `Once`, `AtomicI32`, ... this is done out
43    /// of prudence to avoid false-positive and may be extended in the future.
44    pub CONST_ITEM_INTERIOR_MUTATIONS,
45    Warn,
46    "checks for calls which mutates a interior mutable const-item"
47}
48
49declare_lint_pass!(InteriorMutableConsts => [CONST_ITEM_INTERIOR_MUTATIONS]);
50
51impl<'tcx> LateLintPass<'tcx> for InteriorMutableConsts {
52    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
53        let typeck = cx.typeck_results();
54
55        let (method_did, receiver) = match expr.kind {
56            // matching on `<receiver>.method(..)`
57            ExprKind::MethodCall(_, receiver, _, _) => {
58                (typeck.type_dependent_def_id(expr.hir_id), receiver)
59            }
60            // matching on `function(&<receiver>, ...)`
61            ExprKind::Call(path, [receiver, ..]) => match receiver.kind {
62                ExprKind::AddrOf(_, _, receiver) => match path.kind {
63                    ExprKind::Path(ref qpath) => {
64                        (cx.qpath_res(qpath, path.hir_id).opt_def_id(), receiver)
65                    }
66                    _ => return,
67                },
68                _ => return,
69            },
70            _ => return,
71        };
72
73        let Some(method_did) = method_did else {
74            return;
75        };
76
77        if let ExprKind::Path(qpath) = &receiver.kind
78            && let Res::Def(DefKind::Const | DefKind::AssocConst, const_did) =
79                typeck.qpath_res(qpath, receiver.hir_id)
80            // Let's do the attribute check after the other checks for perf reasons
81            && find_attr!(
82                cx.tcx.get_all_attrs(method_did),
83                AttributeKind::RustcShouldNotBeCalledOnConstItems(_)
84            )
85            && let Some(method_name) = cx.tcx.opt_item_ident(method_did)
86            && let Some(const_name) = cx.tcx.opt_item_ident(const_did)
87            && let Some(const_ty) = typeck.node_type_opt(receiver.hir_id)
88        {
89            // Find the local `const`-item and create the suggestion to use `static` instead
90            let sugg_static = if let Some(Node::Item(const_item)) =
91                cx.tcx.hir_get_if_local(const_did)
92                && let ItemKind::Const(ident, _generics, _ty, _body_id) = const_item.kind
93            {
94                if let Some(vis_span) = const_item.vis_span.find_ancestor_inside(const_item.span)
95                    && const_item.span.can_be_used_for_suggestions()
96                    && vis_span.can_be_used_for_suggestions()
97                {
98                    Some(ConstItemInteriorMutationsSuggestionStatic::Spanful {
99                        const_: const_item.vis_span.between(ident.span),
100                        before: if !vis_span.is_empty() { " " } else { "" },
101                    })
102                } else {
103                    Some(ConstItemInteriorMutationsSuggestionStatic::Spanless)
104                }
105            } else {
106                None
107            };
108
109            cx.emit_span_lint(
110                CONST_ITEM_INTERIOR_MUTATIONS,
111                expr.span,
112                ConstItemInteriorMutationsDiag {
113                    method_name,
114                    const_name,
115                    const_ty,
116                    receiver_span: receiver.span,
117                    sugg_static,
118                },
119            );
120        }
121    }
122}
rustc_lint/interior_mutable_consts.rs

rustc_lint/
interior_mutable_consts.rs
