]>
Commit | Line | Data |
---|---|---|
1b1a35ee XL |
1 | use rustc_errors::DiagnosticBuilder; |
2 | use rustc_middle::lint::LintDiagnosticBuilder; | |
3 | use rustc_middle::mir::visit::Visitor; | |
4 | use rustc_middle::mir::*; | |
5 | use rustc_middle::ty::TyCtxt; | |
6 | use rustc_session::lint::builtin::CONST_ITEM_MUTATION; | |
7 | use rustc_span::def_id::DefId; | |
8 | ||
9 | use crate::transform::{MirPass, MirSource}; | |
10 | ||
11 | pub struct CheckConstItemMutation; | |
12 | ||
13 | impl<'tcx> MirPass<'tcx> for CheckConstItemMutation { | |
14 | fn run_pass(&self, tcx: TyCtxt<'tcx>, _src: MirSource<'tcx>, body: &mut Body<'tcx>) { | |
15 | let mut checker = ConstMutationChecker { body, tcx, target_local: None }; | |
16 | checker.visit_body(&body); | |
17 | } | |
18 | } | |
19 | ||
20 | struct ConstMutationChecker<'a, 'tcx> { | |
21 | body: &'a Body<'tcx>, | |
22 | tcx: TyCtxt<'tcx>, | |
23 | target_local: Option<Local>, | |
24 | } | |
25 | ||
26 | impl<'a, 'tcx> ConstMutationChecker<'a, 'tcx> { | |
27 | fn is_const_item(&self, local: Local) -> Option<DefId> { | |
28 | if let Some(box LocalInfo::ConstRef { def_id }) = self.body.local_decls[local].local_info { | |
29 | Some(def_id) | |
30 | } else { | |
31 | None | |
32 | } | |
33 | } | |
34 | ||
35 | fn is_const_item_without_destructor(&self, local: Local) -> Option<DefId> { | |
36 | let def_id = self.is_const_item(local)?; | |
37 | let mut any_dtor = |_tcx, _def_id| Ok(()); | |
38 | ||
39 | // We avoid linting mutation of a const item if the const's type has a | |
40 | // Drop impl. The Drop logic observes the mutation which was performed. | |
41 | // | |
42 | // pub struct Log { msg: &'static str } | |
43 | // pub const LOG: Log = Log { msg: "" }; | |
44 | // impl Drop for Log { | |
45 | // fn drop(&mut self) { println!("{}", self.msg); } | |
46 | // } | |
47 | // | |
48 | // LOG.msg = "wow"; // prints "wow" | |
49 | // | |
50 | // FIXME(https://github.com/rust-lang/rust/issues/77425): | |
51 | // Drop this exception once there is a stable attribute to suppress the | |
52 | // const item mutation lint for a single specific const only. Something | |
53 | // equivalent to: | |
54 | // | |
55 | // #[const_mutation_allowed] | |
56 | // pub const LOG: Log = Log { msg: "" }; | |
57 | match self.tcx.calculate_dtor(def_id, &mut any_dtor) { | |
58 | Some(_) => None, | |
59 | None => Some(def_id), | |
60 | } | |
61 | } | |
62 | ||
63 | fn lint_const_item_usage( | |
64 | &self, | |
65 | const_item: DefId, | |
66 | location: Location, | |
67 | decorate: impl for<'b> FnOnce(LintDiagnosticBuilder<'b>) -> DiagnosticBuilder<'b>, | |
68 | ) { | |
69 | let source_info = self.body.source_info(location); | |
70 | let lint_root = self.body.source_scopes[source_info.scope] | |
71 | .local_data | |
72 | .as_ref() | |
73 | .assert_crate_local() | |
74 | .lint_root; | |
75 | ||
76 | self.tcx.struct_span_lint_hir(CONST_ITEM_MUTATION, lint_root, source_info.span, |lint| { | |
77 | decorate(lint) | |
78 | .span_note(self.tcx.def_span(const_item), "`const` item defined here") | |
79 | .emit() | |
80 | }); | |
81 | } | |
82 | } | |
83 | ||
84 | impl<'a, 'tcx> Visitor<'tcx> for ConstMutationChecker<'a, 'tcx> { | |
85 | fn visit_statement(&mut self, stmt: &Statement<'tcx>, loc: Location) { | |
86 | if let StatementKind::Assign(box (lhs, _)) = &stmt.kind { | |
87 | // Check for assignment to fields of a constant | |
88 | // Assigning directly to a constant (e.g. `FOO = true;`) is a hard error, | |
89 | // so emitting a lint would be redundant. | |
90 | if !lhs.projection.is_empty() { | |
91 | if let Some(def_id) = self.is_const_item_without_destructor(lhs.local) { | |
92 | // Don't lint on writes through a pointer | |
93 | // (e.g. `unsafe { *FOO = 0; *BAR.field = 1; }`) | |
94 | if !matches!(lhs.projection.last(), Some(PlaceElem::Deref)) { | |
95 | self.lint_const_item_usage(def_id, loc, |lint| { | |
96 | let mut lint = lint.build("attempting to modify a `const` item"); | |
97 | lint.note("each usage of a `const` item creates a new temporary - the original `const` item will not be modified"); | |
98 | lint | |
99 | }) | |
100 | } | |
101 | } | |
102 | } | |
103 | // We are looking for MIR of the form: | |
104 | // | |
105 | // ``` | |
106 | // _1 = const FOO; | |
107 | // _2 = &mut _1; | |
108 | // method_call(_2, ..) | |
109 | // ``` | |
110 | // | |
111 | // Record our current LHS, so that we can detect this | |
112 | // pattern in `visit_rvalue` | |
113 | self.target_local = lhs.as_local(); | |
114 | } | |
115 | self.super_statement(stmt, loc); | |
116 | self.target_local = None; | |
117 | } | |
118 | fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, loc: Location) { | |
119 | if let Rvalue::Ref(_, BorrowKind::Mut { .. }, place) = rvalue { | |
120 | let local = place.local; | |
121 | if let Some(def_id) = self.is_const_item(local) { | |
122 | // If this Rvalue is being used as the right-hand side of a | |
123 | // `StatementKind::Assign`, see if it ends up getting used as | |
124 | // the `self` parameter of a method call (as the terminator of our current | |
125 | // BasicBlock). If so, we emit a more specific lint. | |
126 | let method_did = self.target_local.and_then(|target_local| { | |
127 | crate::util::find_self_call(self.tcx, &self.body, target_local, loc.block) | |
128 | }); | |
129 | let lint_loc = | |
130 | if method_did.is_some() { self.body.terminator_loc(loc.block) } else { loc }; | |
131 | self.lint_const_item_usage(def_id, lint_loc, |lint| { | |
132 | let mut lint = lint.build("taking a mutable reference to a `const` item"); | |
133 | lint | |
134 | .note("each usage of a `const` item creates a new temporary") | |
135 | .note("the mutable reference will refer to this temporary, not the original `const` item"); | |
136 | ||
137 | if let Some((method_did, _substs)) = method_did { | |
138 | lint.span_note(self.tcx.def_span(method_did), "mutable reference created due to call to this method"); | |
139 | } | |
140 | ||
141 | lint | |
142 | }); | |
143 | } | |
144 | } | |
145 | self.super_rvalue(rvalue, loc); | |
146 | } | |
147 | } |