mirror of https://github.com/rust-lang/rust.git
new lint: Returning unit from closures expecting Ord
This lint catches cases where the last statement of a closure expecting an instance of Ord has a trailing semi-colon. It compiles since the closure ends up return () which also implements Ord but causes unexpected results in cases such as sort_by_key. Fixes #5080 reprise: rebase, update and address all concerns
This commit is contained in:
Matthias Krüger
Paris DOUADY
parent
2ca58e7dda
commit
126790999a
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@ -1679,6 +1679,7 @@ Released 2018-09-13
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[`uninit_assumed_init`]: https://rust-lang.github.io/rust-clippy/master/index.html#uninit_assumed_init
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[`unit_arg`]: https://rust-lang.github.io/rust-clippy/master/index.html#unit_arg
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[`unit_cmp`]: https://rust-lang.github.io/rust-clippy/master/index.html#unit_cmp
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[`unit_return_expecting_ord`]: https://rust-lang.github.io/rust-clippy/master/index.html#unit_return_expecting_ord
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[`unknown_clippy_lints`]: https://rust-lang.github.io/rust-clippy/master/index.html#unknown_clippy_lints
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[`unnecessary_cast`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
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[`unnecessary_filter_map`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_filter_map
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@ -300,6 +300,7 @@ mod trivially_copy_pass_by_ref;
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mod try_err;
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mod types;
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mod unicode;
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mod unit_return_expecting_ord;
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mod unnamed_address;
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mod unnecessary_sort_by;
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mod unnested_or_patterns;
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@ -826,6 +827,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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&unicode::NON_ASCII_LITERAL,
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&unicode::UNICODE_NOT_NFC,
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&unicode::ZERO_WIDTH_SPACE,
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&unit_return_expecting_ord::UNIT_RETURN_EXPECTING_ORD,
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&unnamed_address::FN_ADDRESS_COMPARISONS,
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&unnamed_address::VTABLE_ADDRESS_COMPARISONS,
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&unnecessary_sort_by::UNNECESSARY_SORT_BY,
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@ -891,6 +893,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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store.register_late_pass(|| box attrs::Attributes);
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store.register_late_pass(|| box blocks_in_if_conditions::BlocksInIfConditions);
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store.register_late_pass(|| box unicode::Unicode);
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store.register_late_pass(|| box unit_return_expecting_ord::UnitReturnExpectingOrd);
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store.register_late_pass(|| box strings::StringAdd);
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store.register_late_pass(|| box implicit_return::ImplicitReturn);
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store.register_late_pass(|| box implicit_saturating_sub::ImplicitSaturatingSub);
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@ -1436,6 +1439,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&types::UNNECESSARY_CAST),
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LintId::of(&types::VEC_BOX),
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LintId::of(&unicode::ZERO_WIDTH_SPACE),
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LintId::of(&unit_return_expecting_ord::UNIT_RETURN_EXPECTING_ORD),
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LintId::of(&unnamed_address::FN_ADDRESS_COMPARISONS),
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LintId::of(&unnamed_address::VTABLE_ADDRESS_COMPARISONS),
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LintId::of(&unnecessary_sort_by::UNNECESSARY_SORT_BY),
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@ -1692,6 +1696,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&types::CAST_REF_TO_MUT),
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LintId::of(&types::UNIT_CMP),
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LintId::of(&unicode::ZERO_WIDTH_SPACE),
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LintId::of(&unit_return_expecting_ord::UNIT_RETURN_EXPECTING_ORD),
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LintId::of(&unnamed_address::FN_ADDRESS_COMPARISONS),
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LintId::of(&unnamed_address::VTABLE_ADDRESS_COMPARISONS),
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LintId::of(&unused_io_amount::UNUSED_IO_AMOUNT),
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@ -0,0 +1,177 @@
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use crate::utils::{get_trait_def_id, paths, span_lint, span_lint_and_help};
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use if_chain::if_chain;
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use rustc_hir::def_id::DefId;
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use rustc_hir::{Expr, ExprKind, StmtKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_middle::ty::{GenericPredicates, PredicateKind, ProjectionPredicate, TraitPredicate};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::{BytePos, Span};
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declare_clippy_lint! {
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/// **What it does:** Checks for functions that expect closures of type
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/// Fn(...) -> Ord where the implemented closure returns the unit type.
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/// The lint also suggests to remove the semi-colon at the end of the statement if present.
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///
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/// **Why is this bad?** Likely, returning the unit type is unintentional, and
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/// could simply be caused by an extra semi-colon. Since () implements Ord
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/// it doesn't cause a compilation error.
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/// This is the same reasoning behind the unit_cmp lint.
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///
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/// **Known problems:** If returning unit is intentional, then there is no
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/// way of specifying this without triggering needless_return lint
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///
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/// **Example:**
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///
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/// ```rust
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/// let mut twins = vec!((1,1), (2,2));
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/// twins.sort_by_key(|x| { x.1; });
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/// ```
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pub UNIT_RETURN_EXPECTING_ORD,
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correctness,
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"fn arguments of type Fn(...) -> Ord returning the unit type ()."
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}
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declare_lint_pass!(UnitReturnExpectingOrd => [UNIT_RETURN_EXPECTING_ORD]);
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fn get_trait_predicates_for_trait_id<'tcx>(
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cx: &LateContext<'tcx>,
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generics: GenericPredicates<'tcx>,
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trait_id: Option<DefId>,
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) -> Vec<TraitPredicate<'tcx>> {
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let mut preds = Vec::new();
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for (pred, _) in generics.predicates {
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if_chain! {
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if let PredicateKind::Trait(poly_trait_pred, _) = pred.kind();
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let trait_pred = cx.tcx.erase_late_bound_regions(&poly_trait_pred);
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if let Some(trait_def_id) = trait_id;
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if trait_def_id == trait_pred.trait_ref.def_id;
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then {
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preds.push(trait_pred);
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}
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}
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}
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preds
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}
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fn get_projection_pred<'tcx>(
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cx: &LateContext<'tcx>,
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generics: GenericPredicates<'tcx>,
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pred: TraitPredicate<'tcx>,
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) -> Option<ProjectionPredicate<'tcx>> {
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generics.predicates.iter().find_map(|(proj_pred, _)| {
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if let PredicateKind::Projection(proj_pred) = proj_pred.kind() {
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let projection_pred = cx.tcx.erase_late_bound_regions(proj_pred);
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if projection_pred.projection_ty.substs == pred.trait_ref.substs {
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return Some(projection_pred);
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}
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}
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None
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})
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}
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fn get_args_to_check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Vec<(usize, String)> {
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let mut args_to_check = Vec::new();
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if let Some(def_id) = cx.tables().type_dependent_def_id(expr.hir_id) {
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let fn_sig = cx.tcx.fn_sig(def_id);
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let generics = cx.tcx.predicates_of(def_id);
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let fn_mut_preds = get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().fn_mut_trait());
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let ord_preds = get_trait_predicates_for_trait_id(cx, generics, get_trait_def_id(cx, &paths::ORD));
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let partial_ord_preds =
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get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().partial_ord_trait());
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// Trying to call erase_late_bound_regions on fn_sig.inputs() gives the following error
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// The trait `rustc::ty::TypeFoldable<'_>` is not implemented for `&[&rustc::ty::TyS<'_>]`
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let inputs_output = cx.tcx.erase_late_bound_regions(&fn_sig.inputs_and_output());
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inputs_output
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.iter()
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.rev()
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.skip(1)
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.rev()
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.enumerate()
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.for_each(|(i, inp)| {
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for trait_pred in &fn_mut_preds {
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if_chain! {
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if trait_pred.self_ty() == inp;
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if let Some(return_ty_pred) = get_projection_pred(cx, generics, *trait_pred);
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then {
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if ord_preds.iter().any(|ord| ord.self_ty() == return_ty_pred.ty) {
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args_to_check.push((i, "Ord".to_string()));
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} else if partial_ord_preds.iter().any(|pord| pord.self_ty() == return_ty_pred.ty) {
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args_to_check.push((i, "PartialOrd".to_string()));
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}
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}
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}
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}
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});
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}
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args_to_check
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}
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fn check_arg<'tcx>(cx: &LateContext<'tcx>, arg: &'tcx Expr<'tcx>) -> Option<(Span, Option<Span>)> {
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if_chain! {
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if let ExprKind::Closure(_, _fn_decl, body_id, span, _) = arg.kind;
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if let ty::Closure(_def_id, substs) = &cx.tables().node_type(arg.hir_id).kind;
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let ret_ty = substs.as_closure().sig().output();
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let ty = cx.tcx.erase_late_bound_regions(&ret_ty);
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if ty.is_unit();
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then {
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if_chain! {
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let body = cx.tcx.hir().body(body_id);
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if let ExprKind::Block(block, _) = body.value.kind;
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if block.expr.is_none();
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if let Some(stmt) = block.stmts.last();
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if let StmtKind::Semi(_) = stmt.kind;
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then {
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let data = stmt.span.data();
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// Make a span out of the semicolon for the help message
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Some((span, Some(Span::new(data.hi-BytePos(1), data.hi, data.ctxt))))
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} else {
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Some((span, None))
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}
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}
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} else {
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None
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}
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}
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}
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impl<'tcx> LateLintPass<'tcx> for UnitReturnExpectingOrd {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
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if let ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
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let arg_indices = get_args_to_check(cx, expr);
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for (i, trait_name) in arg_indices {
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if i < args.len() {
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match check_arg(cx, &args[i]) {
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Some((span, None)) => {
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span_lint(
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cx,
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UNIT_RETURN_EXPECTING_ORD,
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span,
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&format!(
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"this closure returns \
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the unit type which also implements {}",
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trait_name
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),
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);
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},
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Some((span, Some(last_semi))) => {
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span_lint_and_help(
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cx,
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UNIT_RETURN_EXPECTING_ORD,
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span,
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&format!(
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"this closure returns \
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the unit type which also implements {}",
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trait_name
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),
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Some(last_semi),
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&"probably caused by this trailing semicolon".to_string(),
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);
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},
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None => {},
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}
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}
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}
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}
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}
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}
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@ -2292,6 +2292,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
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deprecation: None,
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module: "types",
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},
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Lint {
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name: "unit_return_expecting_ord",
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group: "correctness",
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desc: "fn arguments of type Fn(...) -> Ord returning the unit type ().",
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deprecation: None,
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module: "unit_return_expecting_ord",
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},
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Lint {
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name: "unknown_clippy_lints",
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group: "style",
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@ -0,0 +1,36 @@
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#![warn(clippy::unit_return_expecting_ord)]
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#![allow(clippy::needless_return)]
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#![allow(clippy::unused_unit)]
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#![feature(is_sorted)]
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struct Struct {
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field: isize,
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}
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fn double(i: isize) -> isize {
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i * 2
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}
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fn unit(_i: isize) {}
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fn main() {
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let mut structs = vec![Struct { field: 2 }, Struct { field: 1 }];
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structs.sort_by_key(|s| {
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double(s.field);
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});
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structs.sort_by_key(|s| double(s.field));
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structs.is_sorted_by_key(|s| {
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double(s.field);
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});
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structs.is_sorted_by_key(|s| {
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if s.field > 0 {
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()
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} else {
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return ();
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}
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});
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structs.sort_by_key(|s| {
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return double(s.field);
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});
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structs.sort_by_key(|s| unit(s.field));
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}
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@ -0,0 +1,39 @@
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error: this closure returns the unit type which also implements Ord
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--> $DIR/unit_return_expecting_ord.rs:18:25
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LL | structs.sort_by_key(|s| {
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| ^^^
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= note: `-D clippy::unit-return-expecting-ord` implied by `-D warnings`
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help: probably caused by this trailing semicolon
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--> $DIR/unit_return_expecting_ord.rs:19:24
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LL | double(s.field);
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| ^
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error: this closure returns the unit type which also implements PartialOrd
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--> $DIR/unit_return_expecting_ord.rs:22:30
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LL | structs.is_sorted_by_key(|s| {
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| ^^^
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help: probably caused by this trailing semicolon
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--> $DIR/unit_return_expecting_ord.rs:23:24
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LL | double(s.field);
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| ^
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error: this closure returns the unit type which also implements PartialOrd
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--> $DIR/unit_return_expecting_ord.rs:25:30
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LL | structs.is_sorted_by_key(|s| {
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| ^^^
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error: this closure returns the unit type which also implements Ord
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--> $DIR/unit_return_expecting_ord.rs:35:25
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LL | structs.sort_by_key(|s| unit(s.field));
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| ^^^
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error: aborting due to 4 previous errors
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