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Replace cfg_attr in AST with rustc-cfg-placeholder for accurate span tracking
Previously, when evaluating a `#[cfg_attr(..)]` to false, the entire attribute was removed from the AST. Afterwards, we insert in its place a `#[rustc-cfg-placeholder]` attribute so that checks for attributes can still know about their placement. This is particularly relevant when we suggest removing items with `cfg_attr`s (fix #56328). We use `rustc-cfg-placeholder` as it is an ident that can't be written by the end user to begin with. We tweak the wording of the existing "unused `extern crate`" lint. ``` warning: unused `extern crate` --> $DIR/removing-extern-crate.rs:9:1 | LL | extern crate removing_extern_crate as foo; | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unused | note: the lint level is defined here --> $DIR/removing-extern-crate.rs:6:9 | LL | #![warn(rust_2018_idioms)] | ^^^^^^^^^^^^^^^^ = note: `#[warn(unused_extern_crates)]` implied by `#[warn(rust_2018_idioms)]` help: remove the unused `extern crate` | LL - #[cfg_attr(test, macro_use)] LL - extern crate removing_extern_crate as foo; LL + | ```
1 parent f7b4354 commit c560da8

34 files changed

+210
-77
lines changed

‎compiler/rustc_ast/src/ast.rs

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3143,6 +3143,10 @@ impl AttrItem {
31433143
|| self.path == sym::allow
31443144
|| self.path == sym::deny
31453145
}
3146+
3147+
pub fn is_cfg_placeholder(&self) -> bool {
3148+
self.path == sym::rustc_cfg_placeholder
3149+
}
31463150
}
31473151

31483152
/// `TraitRef`s appear in impls.

‎compiler/rustc_ast/src/attr/mod.rs

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -233,6 +233,7 @@ impl Attribute {
233233

234234
pub fn token_trees(&self) -> Vec<TokenTree> {
235235
match self.kind {
236+
AttrKind::Normal(ref normal) if normal.item.is_cfg_placeholder() => vec![],
236237
AttrKind::Normal(ref normal) => normal
237238
.tokens
238239
.as_ref()

‎compiler/rustc_ast_passes/src/ast_validation.rs

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -339,6 +339,10 @@ impl<'a> AstValidator<'a> {
339339
sym::deny,
340340
sym::expect,
341341
sym::forbid,
342+
// `cfg` and `cfg_attr` get replaced with an inert `rustc_cfg_placeholder` to
343+
// keep the attribute "spot" in the AST. This allows suggestions to remove an
344+
// item to provide a correct suggestion when `#[cfg_attr]`s are present.
345+
sym::rustc_cfg_placeholder,
342346
sym::warn,
343347
];
344348
!arr.contains(&attr.name_or_empty()) && rustc_attr_parsing::is_builtin_attr(*attr)

‎compiler/rustc_expand/src/config.rs

Lines changed: 19 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -292,7 +292,25 @@ impl<'a> StripUnconfigured<'a> {
292292
}
293293

294294
if !attr::cfg_matches(&cfg_predicate, &self.sess, self.lint_node_id, self.features) {
295-
return vec![];
295+
// `cfg` and `cfg_attr` gets replaced with an inert `rustc_cfg_placeholder` to keep the
296+
// attribute "spot" in the AST. This allows suggestions to remove an item to provide a
297+
// correct suggestion when `#[cfg_attr]`s are present.
298+
let item = ast::AttrItem {
299+
unsafety: ast::Safety::Default,
300+
path: ast::Path::from_ident(rustc_span::symbol::Ident::with_dummy_span(
301+
sym::rustc_cfg_placeholder,
302+
)),
303+
args: ast::AttrArgs::Empty,
304+
tokens: None,
305+
};
306+
let kind = ast::AttrKind::Normal(P(ast::NormalAttr { item, tokens: None }));
307+
let attr: ast::Attribute = ast::Attribute {
308+
kind,
309+
id: self.sess.psess.attr_id_generator.mk_attr_id(),
310+
style: ast::AttrStyle::Outer,
311+
span: cfg_attr.span,
312+
};
313+
return vec![attr];
296314
}
297315

298316
if recursive {

‎compiler/rustc_feature/src/builtin_attrs.rs

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -752,6 +752,12 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
752752
template!(Word, List: r#""...""#), DuplicatesOk,
753753
EncodeCrossCrate::Yes, INTERNAL_UNSTABLE
754754
),
755+
// placeholder that replaces `cfg_attr` in the item's attribute list
756+
ungated!(
757+
rustc_cfg_placeholder, Normal, template!(Word /* irrelevant */), DuplicatesOk,
758+
EncodeCrossCrate::No
759+
),
760+
755761

756762
// ==========================================================================
757763
// Internal attributes, Diagnostics related:

‎compiler/rustc_lint/messages.ftl

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -945,8 +945,9 @@ lint_unused_doc_comment = unused doc comment
945945
.label = rustdoc does not generate documentation for macro invocations
946946
.help = to document an item produced by a macro, the macro must produce the documentation as part of its expansion
947947
948-
lint_unused_extern_crate = unused extern crate
949-
.suggestion = remove it
948+
lint_unused_extern_crate = unused `extern crate`
949+
.label = unused
950+
.suggestion = remove the unused `extern crate`
950951
951952
lint_unused_import_braces = braces around {$node} is unnecessary
952953

‎compiler/rustc_lint/src/early/diagnostics.rs

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -292,8 +292,8 @@ pub(super) fn decorate_lint(
292292
BuiltinLintDiag::ByteSliceInPackedStructWithDerive { ty } => {
293293
lints::ByteSliceInPackedStructWithDerive { ty }.decorate_lint(diag);
294294
}
295-
BuiltinLintDiag::UnusedExternCrate { removal_span } => {
296-
lints::UnusedExternCrate { removal_span }.decorate_lint(diag);
295+
BuiltinLintDiag::UnusedExternCrate { span, removal_span } => {
296+
lints::UnusedExternCrate { span, removal_span }.decorate_lint(diag);
297297
}
298298
BuiltinLintDiag::ExternCrateNotIdiomatic { vis_span, ident_span } => {
299299
let suggestion_span = vis_span.between(ident_span);

‎compiler/rustc_lint/src/lints.rs

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3001,7 +3001,9 @@ pub(crate) struct ByteSliceInPackedStructWithDerive {
30013001
#[derive(LintDiagnostic)]
30023002
#[diag(lint_unused_extern_crate)]
30033003
pub(crate) struct UnusedExternCrate {
3004-
#[suggestion(code = "", applicability = "machine-applicable")]
3004+
#[label]
3005+
pub span: Span,
3006+
#[suggestion(code = "", applicability = "machine-applicable", style = "verbose")]
30053007
pub removal_span: Span,
30063008
}
30073009

‎compiler/rustc_lint_defs/src/lib.rs

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Original file line numberDiff line numberDiff line change
@@ -735,6 +735,7 @@ pub enum BuiltinLintDiag {
735735
ty: String,
736736
},
737737
UnusedExternCrate {
738+
span: Span,
738739
removal_span: Span,
739740
},
740741
ExternCrateNotIdiomatic {

‎compiler/rustc_passes/src/check_attr.rs

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -286,6 +286,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
286286
| sym::prelude_import
287287
| sym::panic_handler
288288
| sym::allow_internal_unsafe
289+
| sym::rustc_cfg_placeholder // Inert, it's a placeholder in the AST.
289290
| sym::fundamental
290291
| sym::lang
291292
| sym::needs_allocator
@@ -575,6 +576,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
575576
// conditional compilation
576577
sym::cfg,
577578
sym::cfg_attr,
579+
sym::rustc_cfg_placeholder,
578580
// testing (allowed here so better errors can be generated in `rustc_builtin_macros::test`)
579581
sym::test,
580582
sym::ignore,
@@ -2641,7 +2643,7 @@ impl<'tcx> Visitor<'tcx> for CheckAttrVisitor<'tcx> {
26412643
// only `#[cfg]` and `#[cfg_attr]` are allowed, but it should be removed
26422644
// if we allow more attributes (e.g., tool attributes and `allow/deny/warn`)
26432645
// in where clauses. After that, only `self.check_attributes` should be enough.
2644-
const ATTRS_ALLOWED: &[Symbol] = &[sym::cfg, sym::cfg_attr];
2646+
const ATTRS_ALLOWED: &[Symbol] = &[sym::cfg, sym::cfg_attr, sym::rustc_cfg_placeholder];
26452647
let spans = self
26462648
.tcx
26472649
.hir_attrs(where_predicate.hir_id)

‎compiler/rustc_resolve/src/check_unused.rs

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -154,6 +154,7 @@ impl<'a, 'ra, 'tcx> UnusedImportCheckVisitor<'a, 'ra, 'tcx> {
154154
extern_crate.id,
155155
span,
156156
BuiltinLintDiag::UnusedExternCrate {
157+
span: extern_crate.span,
157158
removal_span: extern_crate.span_with_attributes,
158159
},
159160
);

‎compiler/rustc_span/src/symbol.rs

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Original file line numberDiff line numberDiff line change
@@ -1745,6 +1745,8 @@ symbols! {
17451745
rustc_autodiff,
17461746
rustc_builtin_macro,
17471747
rustc_capture_analysis,
1748+
// We ensure that the attribute can't be written by end users by adding `-` to the name.
1749+
rustc_cfg_placeholder: "rustc-cfg-placeholder",
17481750
rustc_clean,
17491751
rustc_coherence_is_core,
17501752
rustc_coinductive,

‎tests/ui/editions/edition-extern-crate-allowed.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -5,6 +5,6 @@
55
#![warn(rust_2018_idioms)]
66

77
extern crate edition_extern_crate_allowed;
8-
//~^ WARNING unused extern crate
8+
//~^ WARNING unused `extern crate`
99

1010
fn main() {}

‎tests/ui/editions/edition-extern-crate-allowed.stderr

Lines changed: 6 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,15 +1,19 @@
1-
warning: unused extern crate
1+
warning: unused `extern crate`
22
--> $DIR/edition-extern-crate-allowed.rs:7:1
33
|
44
LL | extern crate edition_extern_crate_allowed;
5-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
5+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unused
66
|
77
note: the lint level is defined here
88
--> $DIR/edition-extern-crate-allowed.rs:5:9
99
|
1010
LL | #![warn(rust_2018_idioms)]
1111
| ^^^^^^^^^^^^^^^^
1212
= note: `#[warn(unused_extern_crates)]` implied by `#[warn(rust_2018_idioms)]`
13+
help: remove the unused `extern crate`
14+
|
15+
LL - extern crate edition_extern_crate_allowed;
16+
|
1317

1418
warning: 1 warning emitted
1519

‎tests/ui/imports/extern-crate-used.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -15,7 +15,7 @@ extern crate core as iso3;
1515
extern crate core as iso4;
1616

1717
// Doesn't introduce its extern prelude entry, so it's still considered unused.
18-
extern crate core; //~ ERROR unused extern crate
18+
extern crate core; //~ ERROR unused `extern crate`
1919

2020
mod m {
2121
use iso1::any as are_you_okay1;

‎tests/ui/imports/extern-crate-used.stderr

Lines changed: 7 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,19 @@
1-
error: unused extern crate
1+
error: unused `extern crate`
22
--> $DIR/extern-crate-used.rs:18:1
33
|
44
LL | extern crate core;
5-
| ^^^^^^^^^^^^^^^^^^ help: remove it
5+
| ^^^^^^^^^^^^^^^^^^ unused
66
|
77
note: the lint level is defined here
88
--> $DIR/extern-crate-used.rs:6:9
99
|
1010
LL | #![deny(unused_extern_crates)]
1111
| ^^^^^^^^^^^^^^^^^^^^
12+
help: remove the unused `extern crate`
13+
|
14+
LL - extern crate core;
15+
LL +
16+
|
1217

1318
error: aborting due to 1 previous error
1419

‎tests/ui/lint/unnecessary-extern-crate.rs

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -4,10 +4,10 @@
44
#![feature(test)]
55

66
extern crate core;
7-
//~^ ERROR unused extern crate
7+
//~^ ERROR unused `extern crate`
88
//~| HELP remove
99
extern crate core as x;
10-
//~^ ERROR unused extern crate
10+
//~^ ERROR unused `extern crate`
1111
//~| HELP remove
1212

1313
extern crate proc_macro;
@@ -29,11 +29,11 @@ mod foo {
2929
pub(super) extern crate alloc as d;
3030

3131
extern crate core;
32-
//~^ ERROR unused extern crate
32+
//~^ ERROR unused `extern crate`
3333
//~| HELP remove
3434

3535
extern crate core as x;
36-
//~^ ERROR unused extern crate
36+
//~^ ERROR unused `extern crate`
3737
//~| HELP remove
3838

3939
pub extern crate test;
@@ -42,11 +42,11 @@ mod foo {
4242

4343
mod bar {
4444
extern crate core;
45-
//~^ ERROR unused extern crate
45+
//~^ ERROR unused `extern crate`
4646
//~| HELP remove
4747

4848
extern crate core as x;
49-
//~^ ERROR unused extern crate
49+
//~^ ERROR unused `extern crate`
5050
//~| HELP remove
5151

5252
pub(in crate::foo::bar) extern crate alloc as e;

‎tests/ui/lint/unnecessary-extern-crate.stderr

Lines changed: 41 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -1,44 +1,73 @@
1-
error: unused extern crate
1+
error: unused `extern crate`
22
--> $DIR/unnecessary-extern-crate.rs:6:1
33
|
44
LL | extern crate core;
5-
| ^^^^^^^^^^^^^^^^^^ help: remove it
5+
| ^^^^^^^^^^^^^^^^^^ unused
66
|
77
note: the lint level is defined here
88
--> $DIR/unnecessary-extern-crate.rs:3:9
99
|
1010
LL | #![deny(unused_extern_crates)]
1111
| ^^^^^^^^^^^^^^^^^^^^
12+
help: remove the unused `extern crate`
13+
|
14+
LL - extern crate core;
15+
|
1216

13-
error: unused extern crate
17+
error: unused `extern crate`
1418
--> $DIR/unnecessary-extern-crate.rs:9:1
1519
|
1620
LL | extern crate core as x;
17-
| ^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
21+
| ^^^^^^^^^^^^^^^^^^^^^^^ unused
22+
|
23+
help: remove the unused `extern crate`
24+
|
25+
LL - extern crate core as x;
26+
|
1827

19-
error: unused extern crate
28+
error: unused `extern crate`
2029
--> $DIR/unnecessary-extern-crate.rs:31:5
2130
|
2231
LL | extern crate core;
23-
| ^^^^^^^^^^^^^^^^^^ help: remove it
32+
| ^^^^^^^^^^^^^^^^^^ unused
33+
|
34+
help: remove the unused `extern crate`
35+
|
36+
LL - extern crate core;
37+
|
2438

25-
error: unused extern crate
39+
error: unused `extern crate`
2640
--> $DIR/unnecessary-extern-crate.rs:35:5
2741
|
2842
LL | extern crate core as x;
29-
| ^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
43+
| ^^^^^^^^^^^^^^^^^^^^^^^ unused
44+
|
45+
help: remove the unused `extern crate`
46+
|
47+
LL - extern crate core as x;
48+
|
3049

31-
error: unused extern crate
50+
error: unused `extern crate`
3251
--> $DIR/unnecessary-extern-crate.rs:44:9
3352
|
3453
LL | extern crate core;
35-
| ^^^^^^^^^^^^^^^^^^ help: remove it
54+
| ^^^^^^^^^^^^^^^^^^ unused
55+
|
56+
help: remove the unused `extern crate`
57+
|
58+
LL - extern crate core;
59+
|
3660

37-
error: unused extern crate
61+
error: unused `extern crate`
3862
--> $DIR/unnecessary-extern-crate.rs:48:9
3963
|
4064
LL | extern crate core as x;
41-
| ^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
65+
| ^^^^^^^^^^^^^^^^^^^^^^^ unused
66+
|
67+
help: remove the unused `extern crate`
68+
|
69+
LL - extern crate core as x;
70+
|
4271

4372
error: aborting due to 6 previous errors
4473

‎tests/ui/lint/unused/lint-unused-extern-crate.rs

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
#![allow(unused_variables)]
99
#![allow(deprecated)]
1010

11-
extern crate lint_unused_extern_crate5; //~ ERROR: unused extern crate
11+
extern crate lint_unused_extern_crate5; //~ ERROR: unused `extern crate`
1212

1313
pub extern crate lint_unused_extern_crate4; // no error, it is re-exported
1414

@@ -26,7 +26,7 @@ use other::*;
2626

2727
mod foo {
2828
// Test that this is unused even though an earlier `extern crate` is used.
29-
extern crate lint_unused_extern_crate2; //~ ERROR unused extern crate
29+
extern crate lint_unused_extern_crate2; //~ ERROR unused `extern crate`
3030
}
3131

3232
fn main() {

‎tests/ui/lint/unused/lint-unused-extern-crate.stderr

Lines changed: 15 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1,20 +1,31 @@
1-
error: unused extern crate
1+
error: unused `extern crate`
22
--> $DIR/lint-unused-extern-crate.rs:11:1
33
|
44
LL | extern crate lint_unused_extern_crate5;
5-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
5+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unused
66
|
77
note: the lint level is defined here
88
--> $DIR/lint-unused-extern-crate.rs:7:9
99
|
1010
LL | #![deny(unused_extern_crates)]
1111
| ^^^^^^^^^^^^^^^^^^^^
12+
help: remove the unused `extern crate`
13+
|
14+
LL - extern crate lint_unused_extern_crate5;
15+
LL +
16+
|
1217

13-
error: unused extern crate
18+
error: unused `extern crate`
1419
--> $DIR/lint-unused-extern-crate.rs:29:5
1520
|
1621
LL | extern crate lint_unused_extern_crate2;
17-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
22+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unused
23+
|
24+
help: remove the unused `extern crate`
25+
|
26+
LL - extern crate lint_unused_extern_crate2;
27+
LL +
28+
|
1829

1930
error: aborting due to 2 previous errors
2031

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