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Disallow cfg attribute (maybe others) on generic parameters #51279
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cc #48848
Context of why it should be disallowed: https://botbot.me/mozilla/rust-lang/2018-06-01/?msg=100694737&page=1
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on Jun 20, 2026
As of 1.27, it is legal to put attributes on generic parameters. E.g.
fn foo<#[allow(dead_code)] T>(_t: T){}, although none of the current attributes do anything. This includes attributes we may want to use in the future, such ascfg. To avoid doing the warning song and dance we did with#[must_use]on functions, we should disallow them before the feature actually stabilizes.