fix(toml): show required rust-version in unstable edition error by yash-kumarx · Pull Request #16653 · rust-lang/cargo

yash-kumarx · 2026-02-18T18:10:17Z

What does this PR try to resolve?

Fixes the unhelpful error when a package declares an unstable edition on a
stable Cargo toolchain. Previously the error told the user to "try a newer
version of Cargo" but gave no indication of which version, forcing them to
dig through docs.

This PR adds a help: line that names the required toolchain version,
derived from the package's rust-version field (or from
Edition::first_version() once that is set at unstable time).

Before:

Consider trying a newer version of Cargo (this may require the nightly release).
See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#unstable-editions

After:

Consider trying a newer version of Cargo (this may require the nightly release).
help: mypackage@0.1.0 requires rustc 1.90
See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#unstable-editions

Also fixes a latent bug in edition_unstable_gated: it expected
feature 'edition{next}' but current code emits feature 'unstable-editions'.
The test was silently skipping because Edition::LATEST_UNSTABLE is None.

Fixes #15305

rustbot · 2026-02-18T18:10:21Z

r? @ehuss

rustbot has assigned @ehuss.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: @ehuss, @epage, @weihanglo
@ehuss, @epage, @weihanglo expanded to ehuss, epage, weihanglo
Random selection from ehuss, epage, weihanglo

weihanglo

Also fixes a latent bug in edition_unstable_gated: it expected
feature 'edition{next}' but current code emits feature 'unstable-editions'.
The test was silently skipping because Edition::LATEST_UNSTABLE is None.

Not having time reviewing the diff, though with that "and" I would assume this PR has at least two commits but I only saw commit. We recommend atomic commits for Git history management.

View changes since this review

yash-kumarx · 2026-02-18T19:33:33Z

Also fixes a latent bug in edition_unstable_gated: it expected
feature 'edition{next}' but current code emits feature 'unstable-editions'.
The test was silently skipping because Edition::LATEST_UNSTABLE is None.

Not having time reviewing the diff, though with that "and" I would assume this PR has at least two commits but I only saw commit. We recommend atomic commits for Git history management.

View changes since this review

@weihanglo Done, Split into two atomic commits:

fix(test): corrects the edition_unstable_gated test which was expecting the wrong feature name and silently skipping
fix(toml): the actual fix — adds the help: hint derived from rust-version

Thank you for your feedback

epage · 2026-02-23T14:16:27Z

tests/testsuite/edition.rs


 Caused by:
-  feature `edition{next}` is required
+  feature `unstable-editions` is required


How did you verify this output with the test still being skipped?

FYI this question is still outstanding

Truly sorry @epage,
Since LATEST_UNSTABLE is None right now, the test always returns early so runtime verification is not possible. I verified it by reading the source: unstable_editions is defined in features.rs and require() applies .replace("_", "-") to the name, which gives unstable-editions. The docs URL fragment is also hardcoded in the same feature definition. Both are constants so I'm fairly confident the expected output is right, but if you say I can revert this change and leave the test untouched if you would prefer to revisit it when LATEST_UNSTABLE gets set again.

As an old coworker said "if it isn't tested, then it is broken". That is going to a bit of an extreme imo but I think it applies here. You found that the output is incorrect for your reading of the code but the same kind of inspection is the only way to check if the new version of the code is correct. I would lean towards not changing it. On top of that, this doesn't seem to be related to this PR.

tests/testsuite/edition.rs

epage · 2026-02-23T14:18:59Z

FYI I believe this is addressing #15305. Please link out to relevant issues in the PR description. If you say Fixes #15305 on its own line, github will automatically close it on merge.

src/cargo/util/toml/mod.rs

yash-kumarx · 2026-02-24T15:18:51Z

@rustbot ready

tests/testsuite/edition.rs

yash-kumarx · 2026-02-24T19:44:05Z

@rustbot ready

Add a test `future_edition_with_rust_version_hint` that exercises the case where a package uses an unstable edition (`future`) and also sets `rust-version`. This records the current behavior before the fix -- the error message does not yet include a hint about the required Rust toolchain version.

When a package specifies an unstable edition (e.g. `edition = "future"`) and also declares a `rust-version`, the feature-gate error now appends a `help:` line of the form: help: <name>@<version> requires rust <msrv> This mirrors the style used elsewhere in Cargo (e.g. dependency MSRV conflicts) and gives the user an actionable pointer to the toolchain they need. Implementation: add `Features::require_with_hint` that takes an optional help string and emits it after the documentation link; call it from the unstable-edition check in `toml/mod.rs`, passing a hint built from the package name, version, and `rust-version` field. Closes rust-lang#15305

yash-kumarx · 2026-02-25T09:59:44Z

@rustbot ready

epage

Thanks!

View changes since this review

## What does this PR try to resolve? Fixes the unhelpful error when a package declares an unstable edition on a stable Cargo toolchain. Previously the error told the user to "try a newer version of Cargo" but gave no indication of *which* version, forcing them to dig through docs. This PR adds a `help:` line that names the required toolchain version, derived from the package's `rust-version` field (or from `Edition::first_version()` once that is set at unstable time). Before: ``` Consider trying a newer version of Cargo (this may require the nightly release). See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#unstable-editions ``` After: ``` Consider trying a newer version of Cargo (this may require the nightly release). help: mypackage@0.1.0 requires rustc 1.90 See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#unstable-editions ``` Also fixes a latent bug in `edition_unstable_gated`: it expected `feature 'edition{next}'` but current code emits `feature 'unstable-editions'`. The test was silently skipping because `Edition::LATEST_UNSTABLE` is `None`. Fixes #15305

rustbot assigned ehuss Feb 18, 2026

rustbot added A-manifest Area: Cargo.toml issues A-unstable Area: nightly unstable support S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 18, 2026

weihanglo reviewed Feb 18, 2026

View reviewed changes

yash-kumarx force-pushed the fix-edition-version-hint branch from 6a5139b to 824fed0 Compare February 18, 2026 19:28