From 7cec516ef9a60aec740725ca35050b5345d95818 Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@joshtriplett.org>
Date: Sat, 18 Aug 2018 16:20:25 -0700
Subject: [PATCH] Don't emit "unused extern crate" warnings for `extern crate
foo as _;`
When importing a crate and renaming it to an underscore-prefixed name,
suppress "unused extern crate" warnings (but not idiom lints).
---
src/librustc_typeck/check_unused.rs | 33 +++++++++++--------
.../ui/rfc-2166-underscore-imports/basic.rs | 2 +-
.../rfc-2166-underscore-imports/basic.stderr | 12 -------
3 files changed, 21 insertions(+), 26 deletions(-)
diff --git a/src/librustc_typeck/check_unused.rs b/src/librustc_typeck/check_unused.rs
index d7aec1d62cdd6..fa152b386a825 100644
--- a/src/librustc_typeck/check_unused.rs
+++ b/src/librustc_typeck/check_unused.rs
@@ -133,19 +133,21 @@ fn unused_crates_lint<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>) {
// If the crate is fully unused, we suggest removing it altogether.
// We do this in any edition.
- if let Some(&span) = unused_extern_crates.get(&extern_crate.def_id) {
- assert_eq!(extern_crate.def_id.krate, LOCAL_CRATE);
- let hir_id = tcx.hir.definitions().def_index_to_hir_id(extern_crate.def_id.index);
- let id = tcx.hir.hir_to_node_id(hir_id);
- let msg = "unused extern crate";
- tcx.struct_span_lint_node(lint, id, span, msg)
- .span_suggestion_short_with_applicability(
- span,
- "remove it",
- String::new(),
- Applicability::MachineApplicable)
- .emit();
- continue;
+ if extern_crate.warn_if_unused {
+ if let Some(&span) = unused_extern_crates.get(&extern_crate.def_id) {
+ assert_eq!(extern_crate.def_id.krate, LOCAL_CRATE);
+ let hir_id = tcx.hir.definitions().def_index_to_hir_id(extern_crate.def_id.index);
+ let id = tcx.hir.hir_to_node_id(hir_id);
+ let msg = "unused extern crate";
+ tcx.struct_span_lint_node(lint, id, span, msg)
+ .span_suggestion_short_with_applicability(
+ span,
+ "remove it",
+ String::new(),
+ Applicability::MachineApplicable)
+ .emit();
+ continue;
+ }
}
// If we are not in Rust 2018 edition, then we don't make any further
@@ -202,6 +204,10 @@ struct ExternCrateToLint {
/// crate_name`), and -- perhaps surprisingly -- this stores the
/// *original* name (`item.name` will contain the new name)
orig_name: Option<ast::Name>,
+
+ /// if `false`, the original name started with `_`, so we shouldn't lint
+ /// about it going unused (but we should still emit idiom lints).
+ warn_if_unused: bool,
}
impl<'a, 'tcx, 'v> ItemLikeVisitor<'v> for CollectExternCrateVisitor<'a, 'tcx> {
@@ -213,6 +219,7 @@ impl<'a, 'tcx, 'v> ItemLikeVisitor<'v> for CollectExternCrateVisitor<'a, 'tcx> {
def_id: extern_crate_def_id,
span: item.span,
orig_name,
+ warn_if_unused: !item.name.as_str().starts_with('_'),
}
);
}
diff --git a/src/test/ui/rfc-2166-underscore-imports/basic.rs b/src/test/ui/rfc-2166-underscore-imports/basic.rs
index 89771be7bc84f..104bd9e166c79 100644
--- a/src/test/ui/rfc-2166-underscore-imports/basic.rs
+++ b/src/test/ui/rfc-2166-underscore-imports/basic.rs
@@ -30,7 +30,7 @@ mod m {
mod unused {
use m::Tr1 as _; //~ WARN unused import
use S as _; //~ WARN unused import
- extern crate core as _; //~ WARN unused extern crate
+ extern crate core as _; // OK
}
mod outer {
diff --git a/src/test/ui/rfc-2166-underscore-imports/basic.stderr b/src/test/ui/rfc-2166-underscore-imports/basic.stderr
index c12c74b50e264..2be0317019d3c 100644
--- a/src/test/ui/rfc-2166-underscore-imports/basic.stderr
+++ b/src/test/ui/rfc-2166-underscore-imports/basic.stderr
@@ -16,15 +16,3 @@ warning: unused import: `S as _`
LL | use S as _; //~ WARN unused import
| ^^^^^^
-warning: unused extern crate
- --> $DIR/basic.rs:33:5
- |
-LL | extern crate core as _; //~ WARN unused extern crate
- | ^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
- |
-note: lint level defined here
- --> $DIR/basic.rs:14:25
- |
-LL | #![warn(unused_imports, unused_extern_crates)]
- | ^^^^^^^^^^^^^^^^^^^^
-