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use rustc_errors::{DiagnosticBuilder, LintDiagnosticBuilder};
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
use rustc_session::lint::builtin::CONST_ITEM_MUTATION;
use rustc_span::def_id::DefId;
use crate::MirLint;
pub struct CheckConstItemMutation;
impl<'tcx> MirLint<'tcx> for CheckConstItemMutation {
fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
let mut checker = ConstMutationChecker { body, tcx, target_local: None };
checker.visit_body(&body);
}
}
struct ConstMutationChecker<'a, 'tcx> {
body: &'a Body<'tcx>,
tcx: TyCtxt<'tcx>,
target_local: Option<Local>,
}
impl<'tcx> ConstMutationChecker<'_, 'tcx> {
fn is_const_item(&self, local: Local) -> Option<DefId> {
if let Some(box LocalInfo::ConstRef { def_id }) = self.body.local_decls[local].local_info {
Some(def_id)
} else {
None
}
}
fn is_const_item_without_destructor(&self, local: Local) -> Option<DefId> {
let def_id = self.is_const_item(local)?;
match self.tcx.calculate_dtor(def_id, |_, _| Ok(())) {
Some(_) => None,
None => Some(def_id),
}
}
fn lint_const_item_usage(
&self,
place: &Place<'tcx>,
const_item: DefId,
location: Location,
decorate: impl for<'b> FnOnce(LintDiagnosticBuilder<'b, ()>) -> DiagnosticBuilder<'b, ()>,
) {
if !place.projection.iter().any(|p| matches!(p, PlaceElem::Deref)) {
let source_info = self.body.source_info(location);
let lint_root = self.body.source_scopes[source_info.scope]
.local_data
.as_ref()
.assert_crate_local()
.lint_root;
self.tcx.struct_span_lint_hir(
CONST_ITEM_MUTATION,
lint_root,
source_info.span,
|lint| {
decorate(lint)
.span_note(self.tcx.def_span(const_item), "`const` item defined here")
.emit();
},
);
}
}
}
impl<'tcx> Visitor<'tcx> for ConstMutationChecker<'_, 'tcx> {
fn visit_statement(&mut self, stmt: &Statement<'tcx>, loc: Location) {
if let StatementKind::Assign(box (lhs, _)) = &stmt.kind {
if !lhs.projection.is_empty() {
if let Some(def_id) = self.is_const_item_without_destructor(lhs.local) {
self.lint_const_item_usage(&lhs, def_id, loc, |lint| {
let mut lint = lint.build("attempting to modify a `const` item");
lint.note("each usage of a `const` item creates a new temporary; the original `const` item will not be modified");
lint
})
}
}
self.target_local = lhs.as_local();
}
self.super_statement(stmt, loc);
self.target_local = None;
}
fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, loc: Location) {
if let Rvalue::Ref(_, BorrowKind::Mut { .. }, place) = rvalue {
let local = place.local;
if let Some(def_id) = self.is_const_item(local) {
let method_did = self.target_local.and_then(|target_local| {
crate::util::find_self_call(self.tcx, &self.body, target_local, loc.block)
});
let lint_loc =
if method_did.is_some() { self.body.terminator_loc(loc.block) } else { loc };
self.lint_const_item_usage(place, def_id, lint_loc, |lint| {
let mut lint = lint.build("taking a mutable reference to a `const` item");
lint
.note("each usage of a `const` item creates a new temporary")
.note("the mutable reference will refer to this temporary, not the original `const` item");
if let Some((method_did, _substs)) = method_did {
lint.span_note(self.tcx.def_span(method_did), "mutable reference created due to call to this method");
}
lint
});
}
}
self.super_rvalue(rvalue, loc);
}
}