fix(toml): deprecate hyphen lint names and error on duplicates by raushan728 · Pull Request #17051 · rust-lang/cargo

raushan728 · 2026-05-30T11:09:15Z

Lint names in [lints] accepted both - and _ as separators. This meant unexpected_cfgs and unexpected-cfgs were treated as distinct keys by the TOML parser, causing ambiguous behavior when both appeared in the same block.

Changes:

Deprecation warning when a lint name uses - instead of _, will not work in a future edition
Error when two lint names conflict after normalization
Normalize lint names to _ before passing them to rustc

rustbot · 2026-05-30T11:09:20Z

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Owners of files modified in this PR: @ehuss, @epage, @weihanglo
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epage · 2026-05-30T11:44:38Z

+                ));
+            }
+            if let Some(existing) = seen_normalized.get(&normalized) {
+                anyhow::bail!(


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

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?

If it is edition gated then it shouldn't affect 2024 edition.

Note: if we edition-gate an error, we need a hand-written migration in cargo fix

Right, gating against 2024 was the bug since that's already shipped.
Which edition should the error land on, since 2024 is taken?

epage · 2026-05-30T11:45:18Z

        for (name, config) in lints {
+            let normalized = name.replace('-', "_");
+            if name.contains('-') {
+                warnings.push(format!(


The issue said we were suppose to error in the next edition.

View changes since the review

Why was this resolved when that error is not present and no reason is given for why it was resolved?

That was resolved too early without addressing your point. Will
restore the edition-gated error once we settle on the edition.

epage · 2026-05-30T11:46:55Z

+                ));
+            }
+            if let Some(existing) = seen_normalized.get(&normalized) {
+                anyhow::bail!(


Should we generate an error or push an error?

View changes since the review

rustbot · 2026-06-01T05:44:56Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

epage · 2026-06-16T17:29:52Z

+                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}")


Why does this commit exist?

View changes since the review

rustc already accepts both forms in flags, so this isn't a bug fix, just consistency. Can drop it if you'd rather keep the diff minimal.

epage · 2026-06-16T17:30:24Z

+[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`


Something isn't working right with this

View changes since the review

epage · 2026-06-16T17:30:56Z

+[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`


This lint should likely be changed to this_lint_does_not_exist in a separate commit

View changes since the review

These use hyphens incidentally to test something unrelated. Will add a prep commit renaming them to underscore first.

epage · 2026-06-16T17:32:23Z


    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


In a separate commit, we should change this to confusable_idents

View changes since the review

Same here, will fold into the prep commit.

epage · 2026-06-16T17:32:52Z

-                unexpected-cfgs = "warn"
+                unexpected-cfgs = "allow"


Why is this change made?

View changes since the review

Leftover from a removed test case. Reverting to warn.

rustbot assigned epage May 30, 2026

rustbot added A-manifest Area: Cargo.toml issues S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 30, 2026

epage reviewed May 30, 2026

View reviewed changes

raushan728 force-pushed the fix/lint-hyphen-deprecation-and-duplicate-detection branch 2 times, most recently from fae8f97 to 5cf81cd Compare May 31, 2026 06:56

raushan728 requested a review from epage May 31, 2026 07:21

raushan728 commented May 31, 2026

View reviewed changes

Comment thread tests/testsuite/lints_table.rs Outdated

raushan728 added 4 commits June 1, 2026 05:15

test(toml): add baseline tests for hyphenated and duplicate lint names

88a8dab

fix(toml): warn on hyphen lint names

38527bb

fix(toml): error on duplicate normalized lint names

4bb4f1b

refactor(toml): normalize lint names before passing to rustc flags

0f44606

raushan728 force-pushed the fix/lint-hyphen-deprecation-and-duplicate-detection branch from 5cf81cd to 0f44606 Compare June 1, 2026 05:44

epage reviewed Jun 16, 2026

View reviewed changes

		[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`

		[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`

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