structured suggestions for single-use lifetime lint on fns and methods
It would be nice to demonstrate the shining correctness here with more run-rustfix tests than this, but unfortunately, that doesn't work with multipart suggestions yet (#53934). While we're here, reword the zero-use lifetime suggestion to "elide the unused lifetime" instead of "remove it". (It's classier.)
This commit is contained in:
Zack M. Davis
parent
1982f1887a
commit
fd28753e83
14 changed files with 169 additions and 37 deletions
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@ -1443,23 +1443,101 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
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/// helper method to determine the span to remove when suggesting the
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/// deletion of a lifetime
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fn lifetime_deletion_span(&self, name: ast::Ident, generics: &hir::Generics) -> Option<Span> {
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if generics.params.len() == 1 {
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// if sole lifetime, remove the `<>` brackets
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Some(generics.span)
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} else {
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generics.params.iter().enumerate().find_map(|(i, param)| {
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if param.name.ident() == name {
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// We also want to delete a leading or trailing comma
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// as appropriate
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if i >= generics.params.len() - 1 {
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Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
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} else {
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Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
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generics.params.iter().enumerate().find_map(|(i, param)| {
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if param.name.ident() == name {
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let mut in_band = false;
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if let hir::GenericParamKind::Lifetime { kind } = param.kind {
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if let hir::LifetimeParamKind::InBand = kind {
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in_band = true;
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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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if in_band {
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Some(param.span)
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} else {
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if generics.params.len() == 1 {
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// if sole lifetime, remove the entire `<>` brackets
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Some(generics.span)
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} else {
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// if removing within `<>` brackets, we also want to
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// delete a leading or trailing comma as appropriate
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if i >= generics.params.len() - 1 {
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Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
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} else {
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Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
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}
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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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// helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
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fn suggest_eliding_single_use_lifetime(
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&self, err: &mut DiagnosticBuilder<'_>, def_id: DefId, lifetime: &hir::Lifetime
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) {
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// FIXME: future work: also suggest `impl Foo<'_>` for `impl<'a> Foo<'a>`
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let name = lifetime.name.ident();
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let mut remove_decl = None;
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if let Some(parent_def_id) = self.tcx.parent(def_id) {
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if let Some(generics) = self.tcx.hir.get_generics(parent_def_id) {
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remove_decl = self.lifetime_deletion_span(name, generics);
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}
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}
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let mut remove_use = None;
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let mut find_arg_use_span = |inputs: &hir::HirVec<hir::Ty>| {
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for input in inputs {
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if let hir::TyKind::Rptr(lt, _) = input.node {
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if lt.name.ident() == name {
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// include the trailing whitespace between the ampersand and the type name
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let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
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remove_use = Some(
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self.tcx.sess.source_map()
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.span_until_non_whitespace(lt_through_ty_span)
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);
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break;
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}
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}
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}
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};
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if let Node::Lifetime(hir_lifetime) = self.tcx.hir.get(lifetime.id) {
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if let Some(parent) = self.tcx.hir.find(self.tcx.hir.get_parent(hir_lifetime.id)) {
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match parent {
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Node::Item(item) => {
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if let hir::ItemKind::Fn(decl, _, _, _) = &item.node {
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find_arg_use_span(&decl.inputs);
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}
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},
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Node::ImplItem(impl_item) => {
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if let hir::ImplItemKind::Method(sig, _) = &impl_item.node {
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find_arg_use_span(&sig.decl.inputs);
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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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if let (Some(decl_span), Some(use_span)) = (remove_decl, remove_use) {
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// if both declaration and use deletion spans start at the same
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// place ("start at" because the latter includes trailing
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// whitespace), then this is an in-band lifetime
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if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
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err.span_suggestion_with_applicability(
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use_span,
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"elide the single-use lifetime",
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String::new(),
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Applicability::MachineApplicable,
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);
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} else {
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err.multipart_suggestion_with_applicability(
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"elide the single-use lifetime",
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vec![(decl_span, String::new()), (use_span, String::new())],
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Applicability::MachineApplicable,
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);
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}
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}
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}
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@ -1521,8 +1599,15 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
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span,
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&format!("lifetime parameter `{}` only used once", name),
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);
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err.span_label(span, "this lifetime...");
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err.span_label(lifetime.span, "...is used only here");
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if span == lifetime.span {
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// spans are the same for in-band lifetime declarations
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err.span_label(span, "this lifetime is only used here");
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} else {
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err.span_label(span, "this lifetime...");
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err.span_label(lifetime.span, "...is used only here");
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}
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self.suggest_eliding_single_use_lifetime(&mut err, def_id, lifetime);
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err.emit();
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}
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}
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@ -1555,7 +1640,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
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if let Some(span) = unused_lt_span {
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err.span_suggestion_with_applicability(
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span,
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"remove it",
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"elide the unused lifetime",
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String::new(),
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Applicability::MachineApplicable,
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);
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@ -0,0 +1,28 @@
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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// run-rustfix
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#![feature(in_band_lifetimes)]
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#![deny(single_use_lifetimes)]
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#![allow(dead_code)]
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#![allow(unused_variables)]
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// Test that we DO warn when lifetime name is used only
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// once in a fn argument, even with in band lifetimes.
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fn a(x: &u32, y: &u32) {
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//~^ ERROR `'a` only used once
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//~| ERROR `'b` only used once
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//~| HELP elide the single-use lifetime
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//~| HELP elide the single-use lifetime
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}
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fn main() { }
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@ -8,6 +8,8 @@
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// run-rustfix
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#![feature(in_band_lifetimes)]
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#![deny(single_use_lifetimes)]
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#![allow(dead_code)]
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@ -19,6 +21,8 @@
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fn a(x: &'a u32, y: &'b u32) {
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//~^ ERROR `'a` only used once
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//~| ERROR `'b` only used once
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//~| HELP elide the single-use lifetime
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//~| HELP elide the single-use lifetime
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}
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fn main() { }
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@ -1,26 +1,26 @@
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error: lifetime parameter `'a` only used once
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--> $DIR/one-use-in-fn-argument-in-band.rs:19:10
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--> $DIR/one-use-in-fn-argument-in-band.rs:21:10
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LL | fn a(x: &'a u32, y: &'b u32) {
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| ^^
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| ^^-
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| |
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| this lifetime...
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| ...is used only here
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| this lifetime is only used here
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| help: elide the single-use lifetime
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note: lint level defined here
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--> $DIR/one-use-in-fn-argument-in-band.rs:12:9
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--> $DIR/one-use-in-fn-argument-in-band.rs:14:9
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LL | #![deny(single_use_lifetimes)]
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| ^^^^^^^^^^^^^^^^^^^^
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error: lifetime parameter `'b` only used once
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--> $DIR/one-use-in-fn-argument-in-band.rs:19:22
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--> $DIR/one-use-in-fn-argument-in-band.rs:21:22
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LL | fn a(x: &'a u32, y: &'b u32) {
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| ^^
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| ^^-
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| |
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| this lifetime...
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| ...is used only here
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| this lifetime is only used here
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| help: elide the single-use lifetime
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error: aborting due to 2 previous errors
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@ -16,6 +16,7 @@
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// once in a fn argument.
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fn a<'a>(x: &'a u32) { //~ ERROR `'a` only used once
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//~^ HELP elide the single-use lifetime
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}
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fn main() { }
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@ -11,6 +11,10 @@ note: lint level defined here
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LL | #![deny(single_use_lifetimes)]
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| ^^^^^^^^^^^^^^^^^^^^
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help: elide the single-use lifetime
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LL | fn a(x: &u32) { //~ ERROR `'a` only used once
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| -- --
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error: aborting due to previous error
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@ -20,6 +20,7 @@ struct Foo<'f> {
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impl<'f> Foo<'f> { //~ ERROR `'f` only used once
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fn inherent_a<'a>(&self, data: &'a u32) { //~ ERROR `'a` only used once
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//~^ HELP elide the single-use lifetime
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}
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}
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@ -11,6 +11,10 @@ note: lint level defined here
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LL | #![deny(single_use_lifetimes)]
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| ^^^^^^^^^^^^^^^^^^^^
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help: elide the single-use lifetime
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LL | fn inherent_a(&self, data: &u32) { //~ ERROR `'a` only used once
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| -- --
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error: lifetime parameter `'f` only used once
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--> $DIR/one-use-in-inherent-method-argument.rs:21:6
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@ -23,6 +23,7 @@ impl<'f> Iterator for Foo<'f> {
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type Item = &'f u32;
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fn next<'g>(&'g mut self) -> Option<Self::Item> { //~ ERROR `'g` only used once
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//~^ HELP elide the single-use lifetime
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None
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}
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}
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@ -11,6 +11,10 @@ note: lint level defined here
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LL | #![deny(single_use_lifetimes)]
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| ^^^^^^^^^^^^^^^^^^^^
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help: elide the single-use lifetime
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LL | fn next(&mut self) -> Option<Self::Item> { //~ ERROR `'g` only used once
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| ----
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error: aborting due to previous error
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@ -7,17 +7,17 @@
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fn september() {}
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//~^ ERROR lifetime parameter `'a` never used
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//~| HELP remove it
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//~| HELP elide the unused lifetime
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fn october<'b, T>(s: &'b T) -> &'b T {
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//~^ ERROR lifetime parameter `'a` never used
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//~| HELP remove it
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//~| HELP elide the unused lifetime
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s
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}
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fn november<'a>(s: &'a str) -> (&'a str) {
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//~^ ERROR lifetime parameter `'b` never used
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//~| HELP remove it
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//~| HELP elide the unused lifetime
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s
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}
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@ -7,17 +7,17 @@
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fn september<'a>() {}
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//~^ ERROR lifetime parameter `'a` never used
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//~| HELP remove it
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//~| HELP elide the unused lifetime
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fn october<'a, 'b, T>(s: &'b T) -> &'b T {
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//~^ ERROR lifetime parameter `'a` never used
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//~| HELP remove it
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//~| HELP elide the unused lifetime
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s
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}
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fn november<'a, 'b>(s: &'a str) -> (&'a str) {
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//~^ ERROR lifetime parameter `'b` never used
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//~| HELP remove it
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//~| HELP elide the unused lifetime
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s
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}
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@ -2,7 +2,7 @@ error: lifetime parameter `'a` never used
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--> $DIR/zero-uses-in-fn.rs:8:14
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LL | fn september<'a>() {}
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| -^^- help: remove it
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| -^^- help: elide the unused lifetime
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note: lint level defined here
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--> $DIR/zero-uses-in-fn.rs:5:9
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@ -16,7 +16,7 @@ error: lifetime parameter `'a` never used
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LL | fn october<'a, 'b, T>(s: &'b T) -> &'b T {
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| ^^--
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| |
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| help: remove it
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| help: elide the unused lifetime
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error: lifetime parameter `'b` never used
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--> $DIR/zero-uses-in-fn.rs:18:17
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@ -24,7 +24,7 @@ error: lifetime parameter `'b` never used
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LL | fn november<'a, 'b>(s: &'a str) -> (&'a str) {
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| --^^
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| |
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| help: remove it
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| help: elide the unused lifetime
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error: aborting due to 3 previous errors
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@ -2,7 +2,7 @@ error: lifetime parameter `'a` never used
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--> $DIR/zero-uses-in-impl.rs:8:6
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LL | impl<'a> Foo {} //~ ERROR `'a` never used
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| -^^- help: remove it
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| -^^- help: elide the unused lifetime
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note: lint level defined here
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--> $DIR/zero-uses-in-impl.rs:3:9
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