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|
use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
use if_chain::if_chain;
use rustc_hir::def_id::DefId;
use rustc_hir::{Closure, Expr, ExprKind, StmtKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_middle::ty::{Clause, GenericPredicates, PredicateKind, ProjectionPredicate, TraitPredicate};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::{sym, BytePos, Span};
declare_clippy_lint! {
/// ### What it does
/// Checks for functions that expect closures of type
/// Fn(...) -> Ord where the implemented closure returns the unit type.
/// The lint also suggests to remove the semi-colon at the end of the statement if present.
///
/// ### Why is this bad?
/// Likely, returning the unit type is unintentional, and
/// could simply be caused by an extra semi-colon. Since () implements Ord
/// it doesn't cause a compilation error.
/// This is the same reasoning behind the unit_cmp lint.
///
/// ### Known problems
/// If returning unit is intentional, then there is no
/// way of specifying this without triggering needless_return lint
///
/// ### Example
/// ```rust
/// let mut twins = vec!((1, 1), (2, 2));
/// twins.sort_by_key(|x| { x.1; });
/// ```
#[clippy::version = "1.47.0"]
pub UNIT_RETURN_EXPECTING_ORD,
correctness,
"fn arguments of type Fn(...) -> Ord returning the unit type ()."
}
declare_lint_pass!(UnitReturnExpectingOrd => [UNIT_RETURN_EXPECTING_ORD]);
fn get_trait_predicates_for_trait_id<'tcx>(
cx: &LateContext<'tcx>,
generics: GenericPredicates<'tcx>,
trait_id: Option<DefId>,
) -> Vec<TraitPredicate<'tcx>> {
let mut preds = Vec::new();
for (pred, _) in generics.predicates {
if_chain! {
if let PredicateKind::Clause(Clause::Trait(poly_trait_pred)) = pred.kind().skip_binder();
let trait_pred = cx.tcx.erase_late_bound_regions(pred.kind().rebind(poly_trait_pred));
if let Some(trait_def_id) = trait_id;
if trait_def_id == trait_pred.trait_ref.def_id;
then {
preds.push(trait_pred);
}
}
}
preds
}
fn get_projection_pred<'tcx>(
cx: &LateContext<'tcx>,
generics: GenericPredicates<'tcx>,
trait_pred: TraitPredicate<'tcx>,
) -> Option<ProjectionPredicate<'tcx>> {
generics.predicates.iter().find_map(|(proj_pred, _)| {
if let ty::PredicateKind::Clause(Clause::Projection(pred)) = proj_pred.kind().skip_binder() {
let projection_pred = cx.tcx.erase_late_bound_regions(proj_pred.kind().rebind(pred));
if projection_pred.projection_ty.substs == trait_pred.trait_ref.substs {
return Some(projection_pred);
}
}
None
})
}
fn get_args_to_check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Vec<(usize, String)> {
let mut args_to_check = Vec::new();
if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) {
let fn_sig = cx.tcx.fn_sig(def_id);
let generics = cx.tcx.predicates_of(def_id);
let fn_mut_preds = get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().fn_mut_trait());
let ord_preds = get_trait_predicates_for_trait_id(cx, generics, cx.tcx.get_diagnostic_item(sym::Ord));
let partial_ord_preds =
get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().partial_ord_trait());
// Trying to call erase_late_bound_regions on fn_sig.inputs() gives the following error
// The trait `rustc::ty::TypeFoldable<'_>` is not implemented for
// `&[rustc_middle::ty::Ty<'_>]`
let inputs_output = cx.tcx.erase_late_bound_regions(fn_sig.inputs_and_output());
inputs_output
.iter()
.rev()
.skip(1)
.rev()
.enumerate()
.for_each(|(i, inp)| {
for trait_pred in &fn_mut_preds {
if_chain! {
if trait_pred.self_ty() == inp;
if let Some(return_ty_pred) = get_projection_pred(cx, generics, *trait_pred);
then {
if ord_preds
.iter()
.any(|ord| Some(ord.self_ty()) == return_ty_pred.term.ty())
{
args_to_check.push((i, "Ord".to_string()));
} else if partial_ord_preds
.iter()
.any(|pord| pord.self_ty() == return_ty_pred.term.ty().unwrap())
{
args_to_check.push((i, "PartialOrd".to_string()));
}
}
}
}
});
}
args_to_check
}
fn check_arg<'tcx>(cx: &LateContext<'tcx>, arg: &'tcx Expr<'tcx>) -> Option<(Span, Option<Span>)> {
if_chain! {
if let ExprKind::Closure(&Closure { body, fn_decl_span, .. }) = arg.kind;
if let ty::Closure(_def_id, substs) = &cx.typeck_results().node_type(arg.hir_id).kind();
let ret_ty = substs.as_closure().sig().output();
let ty = cx.tcx.erase_late_bound_regions(ret_ty);
if ty.is_unit();
then {
let body = cx.tcx.hir().body(body);
if_chain! {
if let ExprKind::Block(block, _) = body.value.kind;
if block.expr.is_none();
if let Some(stmt) = block.stmts.last();
if let StmtKind::Semi(_) = stmt.kind;
then {
let data = stmt.span.data();
// Make a span out of the semicolon for the help message
Some((fn_decl_span, Some(data.with_lo(data.hi-BytePos(1)))))
} else {
Some((fn_decl_span, None))
}
}
} else {
None
}
}
}
impl<'tcx> LateLintPass<'tcx> for UnitReturnExpectingOrd {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
if let ExprKind::MethodCall(_, receiver, args, _) = expr.kind {
let arg_indices = get_args_to_check(cx, expr);
let args = std::iter::once(receiver).chain(args.iter()).collect::<Vec<_>>();
for (i, trait_name) in arg_indices {
if i < args.len() {
match check_arg(cx, args[i]) {
Some((span, None)) => {
span_lint(
cx,
UNIT_RETURN_EXPECTING_ORD,
span,
&format!(
"this closure returns \
the unit type which also implements {trait_name}"
),
);
},
Some((span, Some(last_semi))) => {
span_lint_and_help(
cx,
UNIT_RETURN_EXPECTING_ORD,
span,
&format!(
"this closure returns \
the unit type which also implements {trait_name}"
),
Some(last_semi),
"probably caused by this trailing semicolon",
);
},
None => {},
}
}
}
}
}
}
|
