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Allow forbidden target features to be hard errors#152821

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wesleywiser wants to merge 1 commit intorust-lang:mainfrom
wesleywiser:add_forbidden_ctarget_feature_hard_error_option
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Allow forbidden target features to be hard errors#152821
wesleywiser wants to merge 1 commit intorust-lang:mainfrom
wesleywiser:add_forbidden_ctarget_feature_hard_error_option

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@wesleywiser wesleywiser commented Feb 18, 2026 •
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Sometimes when adding a new target features to the list of known target features, we want to completely forbid them from being used because they are ABI affecting and should be target modifiers instead. As such, we want to issue an error rather than a warning since there are no future compatibility concerns .

r? @workingjubilee since you're familiar with the motivating case in #136597

If I rebase that PR on top of this locally, then we get the following error messages when trying to activate the SLS target feature (note that they are errors not warnings and we've omitted the usual note about future compatibility):

error: target feature `harden-sls-ijmp` cannot be enabled with `-Ctarget-feature`: use `harden-sls` compiler flag instead

error: target feature `harden-sls-ret` cannot be enabled with `-Ctarget-feature`: use `harden-sls` compiler flag instead

error: aborting due to 2 previous errors

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 18, 2026
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rustbot commented Feb 18, 2026

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@wesleywiser wesleywiser force-pushed the add_forbidden_ctarget_feature_hard_error_option branch from a882953 to 31a3497 Compare February 18, 2026 20:40
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workingjubilee commented Feb 19, 2026

Thanks! This has indeed come up a few times (e.g. if nothing else, in features that we have never really had people rely on and thus a FCW makes no sense).

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rust-bors Bot commented Feb 23, 2026

☔ The latest upstream changes (presumably #153000) made this pull request unmergeable. Please resolve the merge conflicts.

@wesleywiser wesleywiser force-pushed the add_forbidden_ctarget_feature_hard_error_option branch from 31a3497 to 291765f Compare March 12, 2026 01:39
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rustbot commented Mar 12, 2026

This PR was rebased onto a different main 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.

@tomassedovic tomassedovic mentioned this pull request Mar 16, 2026
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wesleywiser commented Apr 8, 2026

Rolling a new reviewer since I know Jubilee has a lot on their plate and this isn't super niche 🙂

r? rust-lang/compiler

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rust-bors Bot commented May 5, 2026

☔ The latest upstream changes (presumably #156166) made this pull request unmergeable. Please resolve the merge conflicts.

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