--- /dev/null
+use crate::utils::{get_trait_def_id, paths, span_lint, span_lint_and_help};
+use if_chain::if_chain;
+use rustc_hir::def_id::DefId;
+use rustc_hir::{Expr, ExprKind, StmtKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty;
+use rustc_middle::ty::{GenericPredicates, PredicateKind, ProjectionPredicate, TraitPredicate};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::{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; });
+ /// ```
+ 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::Trait(poly_trait_pred, _) = pred.kind().skip_binder();
+ let trait_pred = cx.tcx.erase_late_bound_regions(ty::Binder::bind(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>,
+ pred: TraitPredicate<'tcx>,
+) -> Option<ProjectionPredicate<'tcx>> {
+ generics.predicates.iter().find_map(|(proj_pred, _)| {
+ if let ty::PredicateKind::Projection(proj_pred) = proj_pred.kind().skip_binder() {
+ let projection_pred = cx.tcx.erase_late_bound_regions(ty::Binder::bind(proj_pred));
+ if projection_pred.projection_ty.substs == 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, get_trait_def_id(cx, &paths::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::ty::TyS<'_>]`
+ 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| ord.self_ty() == return_ty_pred.ty) {
+ args_to_check.push((i, "Ord".to_string()));
+ } else if partial_ord_preds.iter().any(|pord| pord.self_ty() == return_ty_pred.ty) {
+ 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(_, _fn_decl, body_id, 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 {
+ if_chain! {
+ let body = cx.tcx.hir().body(body_id);
+ 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((span, Some(Span::new(data.hi-BytePos(1), data.hi, data.ctxt))))
+ } else {
+ Some((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(_, _, ref args, _) = expr.kind {
+ let arg_indices = get_args_to_check(cx, expr);
+ 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".to_string(),
+ );
+ },
+ None => {},
+ }
+ }
+ }
+ }
+ }
+}
projects / rustc.git / blobdiff