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Use span of ignored impls for explanatory note
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@FabianWolff
FabianWolff committed Jan 15, 2022
1 parent bd1f09d commit 8b459dd
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Showing 4 changed files with 52 additions and 39 deletions.
46 changes: 27 additions & 19 deletions compiler/rustc_passes/src/dead.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ use rustc_middle::middle::privacy;
use rustc_middle::ty::{self, DefIdTree, TyCtxt};
use rustc_session::lint;
use rustc_span::symbol::{sym, Symbol};
use rustc_span::Span;
use std::mem;

// Any local node that may call something in its body block should be
Expand Down Expand Up @@ -49,7 +50,9 @@ struct MarkSymbolVisitor<'tcx> {
// maps from tuple struct constructors to tuple struct items
struct_constructors: FxHashMap<LocalDefId, LocalDefId>,
// maps from ADTs to ignored derived traits (e.g. Debug and Clone)
ignored_derived_traits: FxHashMap<DefId, Vec<DefId>>,
// and the span of their respective impl (i.e., part of the derive
// macro)
ignored_derived_traits: FxHashMap<DefId, Vec<(Span, DefId)>>,
}

impl<'tcx> MarkSymbolVisitor<'tcx> {
Expand Down Expand Up @@ -255,10 +258,12 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
if self.tcx.has_attr(trait_of, sym::rustc_trivial_field_reads) {
let trait_ref = self.tcx.impl_trait_ref(impl_of).unwrap();
if let ty::Adt(adt_def, _) = trait_ref.self_ty().kind() {
let impl_span = self.tcx.def_span(impl_of);
if let Some(v) = self.ignored_derived_traits.get_mut(&adt_def.did) {
v.push(trait_of);
v.push((impl_span, trait_of));
} else {
self.ignored_derived_traits.insert(adt_def.did, vec![trait_of]);
self.ignored_derived_traits
.insert(adt_def.did, vec![(impl_span, trait_of)]);
}
}
return true;
Expand Down Expand Up @@ -588,7 +593,7 @@ fn create_and_seed_worklist<'tcx>(
fn find_live<'tcx>(
tcx: TyCtxt<'tcx>,
access_levels: &privacy::AccessLevels,
) -> (FxHashSet<LocalDefId>, FxHashMap<DefId, Vec<DefId>>) {
) -> (FxHashSet<LocalDefId>, FxHashMap<DefId, Vec<(Span, DefId)>>) {
let (worklist, struct_constructors) = create_and_seed_worklist(tcx, access_levels);
let mut symbol_visitor = MarkSymbolVisitor {
worklist,
Expand All @@ -610,7 +615,7 @@ fn find_live<'tcx>(
struct DeadVisitor<'tcx> {
tcx: TyCtxt<'tcx>,
live_symbols: FxHashSet<LocalDefId>,
ignored_derived_traits: FxHashMap<DefId, Vec<DefId>>,
ignored_derived_traits: FxHashMap<DefId, Vec<(Span, DefId)>>,
}

impl<'tcx> DeadVisitor<'tcx> {
Expand Down Expand Up @@ -683,26 +688,29 @@ impl<'tcx> DeadVisitor<'tcx> {
let hir = self.tcx.hir();
if let Some(encl_scope) = hir.get_enclosing_scope(id) {
if let Some(encl_def_id) = hir.opt_local_def_id(encl_scope) {
if let Some(ign_traits) = self.ignored_derived_traits.get(&encl_def_id.to_def_id()) {
if let Some(ign_traits) =
self.ignored_derived_traits.get(&encl_def_id.to_def_id())
{
let traits_str = ign_traits
.iter()
.map(|t| format!("`{}`", self.tcx.item_name(*t))).collect::<Vec<_>>()
.map(|(_, t)| format!("`{}`", self.tcx.item_name(*t)))
.collect::<Vec<_>>()
.join(" and ");
let plural_s = pluralize!(ign_traits.len());
let article = if ign_traits.len() > 1 { "" } else { "a " };
let is_are = if ign_traits.len() > 1 { "these are" } else { "this is" };
let msg = format!("`{}` has {}derived impl{} for the trait{} {}, but {} ignored during dead code analysis",
self.tcx.item_name(encl_def_id.to_def_id()),
article,
plural_s,
plural_s,
traits_str,
is_are);
if let Some(span) = self.tcx.def_ident_span(encl_def_id) {
err.span_note(span, &msg);
} else {
err.note(&msg);
}
let msg = format!(
"`{}` has {}derived impl{} for the trait{} {}, but {} \
intentionally ignored during dead code analysis",
self.tcx.item_name(encl_def_id.to_def_id()),
article,
plural_s,
plural_s,
traits_str,
is_are
);
let multispan = ign_traits.iter().map(|(s, _)| *s).collect::<Vec<_>>();
err.span_note(multispan, &msg);
}
}
}
Expand Down
9 changes: 5 additions & 4 deletions src/test/ui/derive-uninhabited-enum-38885.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -5,11 +5,12 @@ LL | Void(Void),
| ^^^^^^^^^^
|
= note: `-W dead-code` implied by `-W unused`
note: `Foo` has a derived impl for the trait `Debug`, but this is ignored during dead code analysis
--> $DIR/derive-uninhabited-enum-38885.rs:11:6
note: `Foo` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis
--> $DIR/derive-uninhabited-enum-38885.rs:10:10
|
LL | enum Foo {
| ^^^
LL | #[derive(Debug)]
| ^^^^^
= note: this warning originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)

warning: 1 warning emitted

27 changes: 15 additions & 12 deletions src/test/ui/derives/clone-debug-dead-code.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -16,35 +16,38 @@ error: field is never read: `f`
LL | struct B { f: () }
| ^^^^^
|
note: `B` has a derived impl for the trait `Clone`, but this is ignored during dead code analysis
--> $DIR/clone-debug-dead-code.rs:10:8
note: `B` has a derived impl for the trait `Clone`, but this is intentionally ignored during dead code analysis
--> $DIR/clone-debug-dead-code.rs:9:10
|
LL | struct B { f: () }
| ^
LL | #[derive(Clone)]
| ^^^^^
= note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)

error: field is never read: `f`
--> $DIR/clone-debug-dead-code.rs:14:12
|
LL | struct C { f: () }
| ^^^^^
|
note: `C` has a derived impl for the trait `Debug`, but this is ignored during dead code analysis
--> $DIR/clone-debug-dead-code.rs:14:8
note: `C` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis
--> $DIR/clone-debug-dead-code.rs:13:10
|
LL | struct C { f: () }
| ^
LL | #[derive(Debug)]
| ^^^^^
= note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)

error: field is never read: `f`
--> $DIR/clone-debug-dead-code.rs:18:12
|
LL | struct D { f: () }
| ^^^^^
|
note: `D` has derived impls for the traits `Clone` and `Debug`, but these are ignored during dead code analysis
--> $DIR/clone-debug-dead-code.rs:18:8
note: `D` has derived impls for the traits `Clone` and `Debug`, but these are intentionally ignored during dead code analysis
--> $DIR/clone-debug-dead-code.rs:17:10
|
LL | struct D { f: () }
| ^
LL | #[derive(Debug,Clone)]
| ^^^^^ ^^^^^
= note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)

error: field is never read: `f`
--> $DIR/clone-debug-dead-code.rs:21:12
Expand Down
9 changes: 5 additions & 4 deletions src/test/ui/lint/dead-code/unused-variant.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -9,11 +9,12 @@ note: the lint level is defined here
|
LL | #![deny(dead_code)]
| ^^^^^^^^^
note: `Enum` has a derived impl for the trait `Clone`, but this is ignored during dead code analysis
--> $DIR/unused-variant.rs:4:6
note: `Enum` has a derived impl for the trait `Clone`, but this is intentionally ignored during dead code analysis
--> $DIR/unused-variant.rs:3:10
|
LL | enum Enum {
| ^^^^
LL | #[derive(Clone)]
| ^^^^^
= note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to previous error

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