Allow storing format_args!() in variable or const #139135
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One day, clippy will not break when I make any change to format_args!(). That day is not today. |
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I've opened a separate issue for the panic discussion: #139621 |
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☔ The latest upstream changes (presumably #139632) made this pull request unmergeable. Please resolve the merge conflicts. |
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This makes it posisble to do:
let f = format_args!("Hello, {name}!");
We can now just make new_v1_formatted an unsafe fn.
These tests rely on internal implementation details of format_args!(), which have changed now.
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☔ The latest upstream changes (presumably #139983) made this pull request unmergeable. Please resolve the merge conflicts. |
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Closing this in favor of a slightly improved implementation without the |
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Allow storing format_args!() in variable Fixes rust-lang#92698 Tracking issue for super let: rust-lang#139076 This change allows: ```rust let name = "world"; let f = format_args!("hello {name}!"); println!("{f}"); ``` This will need an FCP. This implementation makes use of `super let`, which is unstable and might not exist in the future in its current form. However, it is entirely reasonable to assume future Rust will always have _a_ way of expressing temporary lifetimes like this, since the (stable) `pin!()` macro needs this. (This was also the motivation for merging rust-lang#139114.) > [!NOTE] > This PR causes many subtle changes in diagnostics output. Most of those are good. Some of those are bad. I've collected all the bad ones in the last commit. Those still need fixing. Marking this PR as draft. (This is a second version of rust-lang#139135)
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Fixes #92698
Tracking issue for super let: #139076
This change allows:
This will need an FCP.
This accidentally 'fixes' a bunch of tests/ui/codegen/equal-pointers-unequal/* tests. Those tests seem very fragile and should probably not depend on formatting implementation details.
This accidentally 'fixes' tests/ui/consts/const-eval/format.rs: it now allows anypanic!()in a const fn. This might be expected. But we should then work on a better error when such a panic!() is const evaluated. (Now it reaches unreachable_unchecked().)