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Auto merge of rust-lang#82795 - m-ou-se:rollup-uzx0b92, r=m-ou-se
Rollup of 10 pull requests Successful merges: - rust-lang#80723 (Implement NOOP_METHOD_CALL lint) - rust-lang#80763 (resolve: Reduce scope of `pub_use_of_private_extern_crate` deprecation lint) - rust-lang#81136 (Improved IO Bytes Size Hint) - rust-lang#81939 (Add suggestion `.collect()` for iterators in iterators) - rust-lang#82289 (Fix underflow in specialized ZipImpl::size_hint) - rust-lang#82728 (Avoid unnecessary Vec construction in BufReader) - rust-lang#82764 (Add {BTreeMap,HashMap}::try_insert) - rust-lang#82770 (Add assert_matches macro.) - rust-lang#82773 (Add diagnostic item to `Default` trait) - rust-lang#82787 (Remove unused code from main.js) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,111 @@ | ||
| use crate::context::LintContext; | ||
| use crate::rustc_middle::ty::TypeFoldable; | ||
| use crate::LateContext; | ||
| use crate::LateLintPass; | ||
| use rustc_hir::def::DefKind; | ||
| use rustc_hir::{Expr, ExprKind}; | ||
| use rustc_middle::ty; | ||
| use rustc_span::symbol::sym; | ||
|
|
||
| declare_lint! { | ||
| /// The `noop_method_call` lint detects specific calls to noop methods | ||
| /// such as a calling `<&T as Clone>::clone` where `T: !Clone`. | ||
| /// | ||
| /// ### Example | ||
| /// | ||
| /// ```rust | ||
| /// # #![allow(unused)] | ||
| /// #![warn(noop_method_call)] | ||
| /// struct Foo; | ||
| /// let foo = &Foo; | ||
| /// let clone: &Foo = foo.clone(); | ||
| /// ``` | ||
| /// | ||
| /// {{produces}} | ||
| /// | ||
| /// ### Explanation | ||
| /// | ||
| /// Some method calls are noops meaning that they do nothing. Usually such methods | ||
| /// are the result of blanket implementations that happen to create some method invocations | ||
| /// that end up not doing anything. For instance, `Clone` is implemented on all `&T`, but | ||
| /// calling `clone` on a `&T` where `T` does not implement clone, actually doesn't do anything | ||
| /// as references are copy. This lint detects these calls and warns the user about them. | ||
| pub NOOP_METHOD_CALL, | ||
| Allow, | ||
| "detects the use of well-known noop methods" | ||
| } | ||
|
|
||
| declare_lint_pass!(NoopMethodCall => [NOOP_METHOD_CALL]); | ||
|
|
||
| impl<'tcx> LateLintPass<'tcx> for NoopMethodCall { | ||
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { | ||
| // We only care about method calls. | ||
| let (call, elements) = match expr.kind { | ||
| ExprKind::MethodCall(call, _, elements, _) => (call, elements), | ||
| _ => return, | ||
| }; | ||
| // We only care about method calls corresponding to the `Clone`, `Deref` and `Borrow` | ||
| // traits and ignore any other method call. | ||
| let (trait_id, did) = match cx.typeck_results().type_dependent_def(expr.hir_id) { | ||
| // Verify we are dealing with a method/associated function. | ||
| Some((DefKind::AssocFn, did)) => match cx.tcx.trait_of_item(did) { | ||
| // Check that we're dealing with a trait method for one of the traits we care about. | ||
| Some(trait_id) | ||
| if [sym::Clone, sym::Deref, sym::Borrow] | ||
| .iter() | ||
| .any(|s| cx.tcx.is_diagnostic_item(*s, trait_id)) => | ||
| { | ||
| (trait_id, did) | ||
| } | ||
| _ => return, | ||
| }, | ||
| _ => return, | ||
| }; | ||
| let substs = cx.typeck_results().node_substs(expr.hir_id); | ||
| if substs.needs_subst() { | ||
| // We can't resolve on types that require monomorphization, so we don't handle them if | ||
| // we need to perfom substitution. | ||
| return; | ||
| } | ||
| let param_env = cx.tcx.param_env(trait_id); | ||
| // Resolve the trait method instance. | ||
| let i = match ty::Instance::resolve(cx.tcx, param_env, did, substs) { | ||
| Ok(Some(i)) => i, | ||
| _ => return, | ||
| }; | ||
| // (Re)check that it implements the noop diagnostic. | ||
| for s in [sym::noop_method_clone, sym::noop_method_deref, sym::noop_method_borrow].iter() { | ||
| if cx.tcx.is_diagnostic_item(*s, i.def_id()) { | ||
| let method = &call.ident.name; | ||
| let receiver = &elements[0]; | ||
| let receiver_ty = cx.typeck_results().expr_ty(receiver); | ||
| let expr_ty = cx.typeck_results().expr_ty_adjusted(expr); | ||
| if receiver_ty != expr_ty { | ||
| // This lint will only trigger if the receiver type and resulting expression \ | ||
| // type are the same, implying that the method call is unnecessary. | ||
| return; | ||
| } | ||
| let expr_span = expr.span; | ||
| let note = format!( | ||
| "the type `{:?}` which `{}` is being called on is the same as \ | ||
| the type returned from `{}`, so the method call does not do \ | ||
| anything and can be removed", | ||
| receiver_ty, method, method, | ||
| ); | ||
|
|
||
| let span = expr_span.with_lo(receiver.span.hi()); | ||
| cx.struct_span_lint(NOOP_METHOD_CALL, span, |lint| { | ||
| let method = &call.ident.name; | ||
| let message = format!( | ||
| "call to `.{}()` on a reference in this situation does nothing", | ||
| &method, | ||
| ); | ||
| lint.build(&message) | ||
| .span_label(span, "unnecessary method call") | ||
| .note(¬e) | ||
| .emit() | ||
| }); | ||
| } | ||
| } | ||
| } | ||
| } |
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