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improve diagnostic for literals in lint attributes #164486

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Merged
rust-bors merged 7 commits into from
Oct 18, 2026
+165 −66
Merged

improve diagnostic for literals in lint attributes #164486

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c7ea602
add test for literals in lint attributes
annieversary Oct 17, 2026
7142f9a
improve diagnostic for literals in lint attributes
annieversary Oct 17, 2026
1cb7727
rename sub to kind in attribute diagnostics
annieversary Oct 17, 2026
4245f27
change label in BadAttributeLit to be more descriptive
annieversary Oct 18, 2026
1c9a4b7
change t/u/l/lint-attribute-literals to not deduplicate-diagnostics
annieversary Oct 18, 2026
f9d044c
simplify BadAttributeLit diagnostic message
annieversary Oct 18, 2026
31b27ab
add test for the BadAttributeLitHelp::Other case
annieversary Oct 18, 2026
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114 changes: 63 additions & 51 deletions compiler/rustc_attr_parsing/src/attributes/lint.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ use thin_vec::ThinVec;

use crate::attributes::{AcceptMapping, AttributeParser, AttributeStability};
use crate::context::{AcceptContext, ExpectStringLiteral, FinalizeContext};
use crate::parser::ArgParser;
use crate::parser::{ArgParser, MetaItemOrLitParser};
use crate::target_checking::AllowedTargets;
use crate::target_checking::Policy::{Allow, Warn};
use crate::{AttributeTemplate, diagnostics, template};
Expand Down Expand Up @@ -37,7 +37,7 @@ impl LintParser {
if !p.path().word_is(sym::reason) {
cx.emit_err(diagnostics::MalformedAttribute {
span: p.span(),
sub: diagnostics::MalformedAttributeSub::BadAttributeArgument(p.span()),
kind: diagnostics::MalformedAttributeKind::BadAttributeArgument(p.span()),
});
} else {
parsers = &parsers[..(parsers.len() - 1)];
Expand All @@ -48,58 +48,70 @@ impl LintParser {
};

for item in parsers {
if let Some(p) = item.meta_item() {
match p.args() {
ArgParser::NoArgs => {
let (tool, lint_name, rest) = match &*p.path().0.segments {
[] => unreachable!(),
[lint_name] => (None, lint_name.ident.name, None),
[tool, lint_name] => (Some(tool.ident), lint_name.ident.name, None),
[tool, lint_name, rest @ ..] => {
let rest = rest
.iter()
.map(|s| s.ident.name)
.collect::<Vec<_>>()
.into();
(Some(tool.ident), lint_name.ident.name, Some(rest))
}
};
match item {
MetaItemOrLitParser::MetaItemParser(p) => {
match p.args() {
ArgParser::NoArgs => {
let (tool, lint_name, rest) = match &*p.path().0.segments {
[] => unreachable!(),
[lint_name] => (None, lint_name.ident.name, None),
[tool, lint_name] => {
(Some(tool.ident), lint_name.ident.name, None)
}
[tool, lint_name, rest @ ..] => {
let rest = rest
.iter()
.map(|s| s.ident.name)
.collect::<Vec<_>>()
.into();
(Some(tool.ident), lint_name.ident.name, Some(rest))
}
};

self.lints.push(LintCheck {
tool,
lint_name,
lint_span: p.span(),
kind,
attr_id,
reason,
attr_span,
rest,
})
}
// We're found a `reason = "reason"` but we're not the last element.
ArgParser::NameValue(nv) if p.path().word_is(sym::reason) => {
cx.emit_err(diagnostics::MalformedAttribute {
span: p.span(),
sub: diagnostics::MalformedAttributeSub::ReasonMustComeLast(
item.span(),
),
});
nv.expect_string_literal(cx);
}
ArgParser::NameValue(_) | ArgParser::List(_) => {
cx.emit_err(diagnostics::MalformedAttribute {
span: p.span(),
sub: diagnostics::MalformedAttributeSub::BadAttributeArgument(
item.span(),
),
});
self.lints.push(LintCheck {
tool,
lint_name,
lint_span: p.span(),
kind,
attr_id,
reason,
attr_span,
rest,
})
}
// We've found a `reason = "reason"` but we're not the last element.
ArgParser::NameValue(nv) if p.path().word_is(sym::reason) => {
cx.emit_err(diagnostics::MalformedAttribute {
span: p.span(),
kind: diagnostics::MalformedAttributeKind::ReasonMustComeLast(
item.span(),
),
});
nv.expect_string_literal(cx);
}
ArgParser::NameValue(_) | ArgParser::List(_) => {
cx.emit_err(diagnostics::MalformedAttribute {
span: p.span(),
kind: diagnostics::MalformedAttributeKind::BadAttributeArgument(
item.span(),
),
});
}
}
}
} else {
cx.emit_err(diagnostics::MalformedAttribute {
span: item.span(),
sub: diagnostics::MalformedAttributeSub::BadAttributeArgument(item.span()),
});
MetaItemOrLitParser::Lit(lit) => {
cx.emit_err(diagnostics::BadAttributeLit {
span: item.span(),
help: if lit.kind.is_str() {
diagnostics::BadAttributeLitHelp::StrLit {
sym: lit.symbol,
kind: kind.sym(),
}
} else {
diagnostics::BadAttributeLitHelp::Other { kind: kind.sym() }
},
});
}
}
}
if parsers.is_empty() {
Expand Down
22 changes: 20 additions & 2 deletions compiler/rustc_attr_parsing/src/diagnostics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2139,17 +2139,35 @@ pub(crate) struct MalformedAttribute {
#[primary_span]
pub span: Span,
#[subdiagnostic]
pub sub: MalformedAttributeSub,
pub kind: MalformedAttributeKind,
}

#[derive(Subdiagnostic)]
pub(crate) enum MalformedAttributeSub {
pub(crate) enum MalformedAttributeKind {
#[label("bad attribute argument")]
BadAttributeArgument(#[primary_span] Span),
#[label("reason in lint attribute must come last")]
ReasonMustComeLast(#[primary_span] Span),
}

#[derive(Diagnostic)]
#[diag("expected path to a lint, found literal")]
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Outdated
pub(crate) struct BadAttributeLit {
#[primary_span]
#[label("not the name of a lint")]
pub span: Span,
#[subdiagnostic]
pub help: BadAttributeLitHelp,
}

#[derive(Subdiagnostic)]
pub(crate) enum BadAttributeLitHelp {
#[help("try using `#[{$kind}({$sym})]`")]
StrLit { sym: Symbol, kind: Symbol },
#[help("for example, write `#[{$kind}(dead_code)]` for `dead_code`")]
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Other { kind: Symbol },
}

#[derive(Subdiagnostic)]
pub(crate) enum UnusedNote {
#[note("attribute `{$name}` with an empty list has no effect")]
Expand Down
7 changes: 4 additions & 3 deletions tests/ui/diagnostic-flags/deduplicate-diagnostics.deduplicate.stderr
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Original file line number Diff line number Diff line change
@@ -1,8 +1,10 @@
error[E0452]: malformed lint attribute input
error: expected path to a lint, found literal
--> $DIR/deduplicate-diagnostics.rs:10:8
|
LL | #[deny("literal")]
| ^^^^^^^^^ bad attribute argument
| ^^^^^^^^^ not the name of a lint
|
= help: try using `#[deny(literal)]`

error: cannot find derive macro `Unresolved` in this scope
--> $DIR/deduplicate-diagnostics.rs:6:10
Expand All @@ -12,4 +14,3 @@ LL | #[derive(Unresolved)]

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0452`.
17 changes: 10 additions & 7 deletions tests/ui/diagnostic-flags/deduplicate-diagnostics.duplicate.stderr
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Original file line number Diff line number Diff line change
@@ -1,8 +1,10 @@
error[E0452]: malformed lint attribute input
error: expected path to a lint, found literal
--> $DIR/deduplicate-diagnostics.rs:10:8
|
LL | #[deny("literal")]
| ^^^^^^^^^ bad attribute argument
| ^^^^^^^^^ not the name of a lint
|
= help: try using `#[deny(literal)]`

error: cannot find derive macro `Unresolved` in this scope
--> $DIR/deduplicate-diagnostics.rs:6:10
Expand All @@ -18,22 +20,23 @@ LL | #[derive(Unresolved)]
|
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0452]: malformed lint attribute input
error: expected path to a lint, found literal
--> $DIR/deduplicate-diagnostics.rs:10:8
|
LL | #[deny("literal")]
| ^^^^^^^^^ bad attribute argument
| ^^^^^^^^^ not the name of a lint
|
= help: try using `#[deny(literal)]`
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0452]: malformed lint attribute input
error: expected path to a lint, found literal
--> $DIR/deduplicate-diagnostics.rs:10:8
|
LL | #[deny("literal")]
| ^^^^^^^^^ bad attribute argument
| ^^^^^^^^^ not the name of a lint
|
= help: try using `#[deny(literal)]`
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error: aborting due to 5 previous errors

For more information about this error, try `rustc --explain E0452`.
6 changes: 3 additions & 3 deletions tests/ui/diagnostic-flags/deduplicate-diagnostics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@
//[duplicate]~| ERROR cannot find derive macro `Unresolved` in this scope
struct S;

#[deny("literal")] //~ ERROR malformed lint attribute input
//[duplicate]~| ERROR malformed lint attribute input
//[duplicate]~| ERROR malformed lint attribute input
#[deny("literal")] //~ ERROR expected path to a lint, found literal
//[duplicate]~| ERROR expected path to a lint, found literal
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//[duplicate]~| ERROR expected path to a lint, found literal
fn main() {}
7 changes: 7 additions & 0 deletions tests/ui/lint/lint-attribute-literals.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
// Checks that lint attributes with literals have an explanatory error

#[allow("literal")]
//~^ ERROR expected path to a lint, found literal
//~| ERROR expected path to a lint, found literal
//~| ERROR expected path to a lint, found literal
fn main() {}
28 changes: 28 additions & 0 deletions tests/ui/lint/lint-attribute-literals.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
error: expected path to a lint, found literal
--> $DIR/lint-attribute-literals.rs:3:9
|
LL | #[allow("literal")]
| ^^^^^^^^^ not the name of a lint
|
= help: try using `#[allow(literal)]`

error: expected path to a lint, found literal
--> $DIR/lint-attribute-literals.rs:3:9
|
LL | #[allow("literal")]
| ^^^^^^^^^ not the name of a lint
|
= help: try using `#[allow(literal)]`
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error: expected path to a lint, found literal
--> $DIR/lint-attribute-literals.rs:3:9
|
LL | #[allow("literal")]
| ^^^^^^^^^ not the name of a lint
|
= help: try using `#[allow(literal)]`
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error: aborting due to 3 previous errors

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