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fix(toml): deprecate hyphen lint names and error on duplicates #17051

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fix(toml): deprecate hyphen lint names and error on duplicates #17051

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88a8dab
test(toml): add baseline tests for hyphenated and duplicate lint names
raushan728 May 30, 2026
38527bb
fix(toml): warn on hyphen lint names
raushan728 May 31, 2026
4bb4f1b
fix(toml): error on duplicate normalized lint names
raushan728 May 31, 2026
0f44606
refactor(toml): normalize lint names before passing to rustc flags
raushan728 May 30, 2026
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21 changes: 19 additions & 2 deletions src/cargo/util/toml/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2690,7 +2690,23 @@ supported tools: {}",
if tool == "cargo" && !gctx.cli_unstable().cargo_lints {
warn_for_cargo_lint_feature(gctx, warnings);
}
let mut seen_normalized: HashMap<String, String> = HashMap::new();
for (name, config) in lints {
let normalized = name.replace('-', "_");
if name.contains('-') {
warnings.push(format!(
"`lints.{tool}.{name}` is deprecated in favor of \
`lints.{tool}.{normalized}` and will not work in a \
future edition"
));
}
if let Some(existing) = seen_normalized.get(&normalized) {
anyhow::bail!(

@epage epage May 30, 2026 •
edited by rustbot
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When a commit has "and" in it, it is a good sign it isn't atomic. This is a separate change.

This is also a breaking change. We either need to start as a future incompat warning or deprecate and error in the next edition.

View changes since the review

@raushan728 raushan728 May 31, 2026 •
edited
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Initially had edition-gated error for both but it broke existing crates on 2024 edition.Changed hyphen names to warnings.push only. For duplicates, kept bail! should this follow the same pattern as hyphen names warnings.push for now, error in future edition?

@epage epage May 30, 2026 •
edited by rustbot
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Should we generate an error or push an error?

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"duplicate lint `{existing}` in `[lints.{tool}]`, \
conflicts with `{name}`"
);
}
seen_normalized.insert(normalized.clone(), name.to_string());
if let Some((prefix, suffix)) = name.split_once("::") {
if tool == prefix {
anyhow::bail!(
Expand Down Expand Up @@ -2772,10 +2788,11 @@ fn lints_to_rustflags(lints: &manifest::TomlLints) -> CargoResult<Vec<String>> {
manifest::TomlLintLevel::Allow => "--allow",
};

let normalized_name = name.replace('-', "_");
let option = if tool == "rust" {
format!("{flag}={name}")
format!("{flag}={normalized_name}")
} else {
format!("{flag}={tool}::{name}")
format!("{flag}={tool}::{normalized_name}")
};
(
config.priority(),
Expand Down
3 changes: 2 additions & 1 deletion tests/testsuite/lints/mod.rs
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Expand Up @@ -47,6 +47,7 @@ im-a-teapot = "warn"
foo.cargo("fetch -Zcargo-lints")
.masquerade_as_nightly_cargo(&["cargo-lints", "test-dummy-unstable"])
.with_stderr_data(str![[r#"
[WARNING] Cargo.toml: `lints.cargo.im-a-teapot` is deprecated in favor of `lints.cargo.im_a_teapot` and will not work in a future edition
[WARNING] unknown lint: `im-a-teapot`
--> Cargo.toml:12:1
|
Expand All @@ -55,7 +56,7 @@ im-a-teapot = "warn"
|
= [NOTE] `cargo::unknown_lints` is set to `warn` by default
= [HELP] there is a lint with a similar name: `im_a_teapot`
[WARNING] `foo` (manifest) generated 1 warning
[WARNING] `foo` (manifest) generated 2 warnings

"#]])
.run();
Expand Down
11 changes: 8 additions & 3 deletions tests/testsuite/lints/unknown_lints.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,14 +26,15 @@ this-lint-does-not-exist = "warn"
p.cargo("fetch -Zcargo-lints")
.masquerade_as_nightly_cargo(&["cargo-lints"])
.with_stderr_data(str![[r#"
[WARNING] Cargo.toml: `lints.cargo.this-lint-does-not-exist` is deprecated in favor of `lints.cargo.this_lint_does_not_exist` and will not work in a future edition
[WARNING] unknown lint: `this-lint-does-not-exist`
--> Cargo.toml:11:1
|
11 | this-lint-does-not-exist = "warn"
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
= [NOTE] `cargo::unknown_lints` is set to `warn` in `[lints]`
[WARNING] `foo` (manifest) generated 1 warning
[WARNING] `foo` (manifest) generated 2 warnings

"#]])
.run();
Expand Down Expand Up @@ -73,14 +74,17 @@ workspace = true
p.cargo("fetch -Zcargo-lints")
.masquerade_as_nightly_cargo(&["cargo-lints"])
.with_stderr_data(str![[r#"
[WARNING] Cargo.toml: `lints.cargo.this-lint-does-not-exist` is deprecated in favor of `lints.cargo.this_lint_does_not_exist` and will not work in a future edition
[WARNING] unknown lint: `this-lint-does-not-exist`
--> Cargo.toml:8:1
|
8 | this-lint-does-not-exist = "warn"
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
= [NOTE] `cargo::unknown_lints` is set to `warn` in `[lints]`
[WARNING] workspace (manifest) generated 1 warning
[WARNING] workspace (manifest) generated 2 warnings
[WARNING] foo/Cargo.toml: `lints.cargo.this-lint-does-not-exist` is deprecated in favor of `lints.cargo.this_lint_does_not_exist` and will not work in a future edition
[WARNING] `foo` (manifest) generated 1 warning

"#]])
.run();
Expand Down Expand Up @@ -117,14 +121,15 @@ authors = []
p.cargo("fetch -Zcargo-lints")
.masquerade_as_nightly_cargo(&["cargo-lints"])
.with_stderr_data(str![[r#"
[WARNING] Cargo.toml: `lints.cargo.this-lint-does-not-exist` is deprecated in favor of `lints.cargo.this_lint_does_not_exist` and will not work in a future edition
[WARNING] unknown lint: `this-lint-does-not-exist`
--> Cargo.toml:8:1
|
8 | this-lint-does-not-exist = "warn"
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
= [NOTE] `cargo::unknown_lints` is set to `warn` in `[lints]`
[WARNING] workspace (manifest) generated 1 warning
[WARNING] workspace (manifest) generated 2 warnings
[WARNING] missing `[lints]` to inherit `[workspace.lints]`
--> foo/Cargo.toml
= [NOTE] `cargo::missing_lints_inheritance` is set to `warn` by default
Expand Down
68 changes: 67 additions & 1 deletion tests/testsuite/lints_table.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -166,9 +166,11 @@ fn warn_on_unused_key() {

foo.cargo("check")
.with_stderr_data(str![[r#"
[WARNING] Cargo.toml: `lints.rust.rust-2018-idioms` is deprecated in favor of `lints.rust.rust_2018_idioms` and will not work in a future edition
[WARNING] Cargo.toml: unused manifest key: `lints.rust.rust-2018-idioms.unused`
[WARNING] Cargo.toml: `lints.rust.rust-2018-idioms` is deprecated in favor of `lints.rust.rust_2018_idioms` and will not work in a future edition
[WARNING] Cargo.toml: unused manifest key: `lints.rust.rust-2018-idioms.unused`
[WARNING] `foo` (manifest) generated 2 warnings
[WARNING] `foo` (manifest) generated 4 warnings
[CHECKING] foo v0.0.1 ([ROOT]/foo)
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s

Expand Down Expand Up @@ -720,6 +722,8 @@ pub const Ĕ: i32 = 2;

foo.cargo("check")
.with_stderr_data(str![[r#"
[WARNING] Cargo.toml: `lints.rust.confusable-idents` is deprecated in favor of `lints.rust.confusable_idents` and will not work in a future edition
[WARNING] `foo` (manifest) generated 1 warning
[CHECKING] foo v0.0.1 ([ROOT]/foo)
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s

Expand All @@ -728,6 +732,8 @@ pub const Ĕ: i32 = 2;

foo.cargo("test --doc")
.with_stderr_data(str![[r#"
[WARNING] Cargo.toml: `lints.rust.confusable-idents` is deprecated in favor of `lints.rust.confusable_idents` and will not work in a future edition
[WARNING] `foo` (manifest) generated 1 warning
[COMPILING] foo v0.0.1 ([ROOT]/foo)
[FINISHED] `test` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
[DOCTEST] foo
Expand Down Expand Up @@ -843,3 +849,63 @@ im_a_teapot = "warn"
"#]])
.run();
}

#[cargo_test]
fn hyphen_in_lint_name() {
let foo = project()
.file(
"Cargo.toml",
r#"
[package]
name = "foo"
version = "0.0.1"
edition = "2015"

[lints.rust]
unexpected-cfgs = "allow"
"#,
)
.file("src/lib.rs", "")
.build();

foo.cargo("check")
.with_stderr_data(str![[r#"
[WARNING] Cargo.toml: `lints.rust.unexpected-cfgs` is deprecated in favor of `lints.rust.unexpected_cfgs` and will not work in a future edition
[WARNING] `foo` (manifest) generated 1 warning
[CHECKING] foo v0.0.1 ([ROOT]/foo)
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s

"#]])
.run();
}

#[cargo_test]
fn duplicate_lint_name_hyphen_and_underscore() {
let foo = project()
.file(
"Cargo.toml",
r#"
[package]
name = "foo"
version = "0.0.1"
edition = "2015"

[lints.rust]
unexpected_cfgs = "warn"
unexpected-cfgs = "allow"
"#,
)
.file("src/lib.rs", "")
.build();

foo.cargo("check")
.with_status(101)
.with_stderr_data(str![[r#"
[ERROR] failed to parse manifest at `[ROOT]/foo/Cargo.toml`

Caused by:
duplicate lint `unexpected-cfgs` in `[lints.rust]`, conflicts with `unexpected_cfgs`

"#]])
.run();
}
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