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More detail for format! width bigger than u16::MAX #147283

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@estebank estebank commented Oct 2, 2025

Formatting the width of a numeric value is limited to a u16, but the macros accept any usize and can panic at runtime. Previously the panic didn't provide any additional information about the failure, other than "too big".

Noticed in https://internals.rust-lang.org/t/diagnostic-for-136932-width-limit/23589

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More detail for format! width bigger than u16::MAX
4bbe532 
Formatting the width of a numeric value is limited to a `u16`, but the macros accept any `usize` and can panic at runtime. Previously the panic didn't provide any additional information about the failure, other than "too big".
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rustbot commented Oct 2, 2025

Some changes occurred in library/core/src/fmt/rt.rs

cc @m-ou-se

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 2, 2025
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rustbot commented Oct 2, 2025

r? @Mark-Simulacrum

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rust-log-analyzer commented Oct 2, 2025

The job aarch64-gnu-llvm-20-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot) 
error[E0015]: cannot call non-const formatting macro in constant functions
    |
   ::: library/core/src/fmt/rt.rs:153:13
    |
153 |               panic!("Formatting argument out of range: `{x}` is bigger than `u16::MAX`");
    |               ---------------------------------------------------------------------------
    |               |
    |               in this macro invocation (#1)
    |               in this macro invocation (#2)
   --> library/core/src/panic.rs:62:38

@estebank estebank closed this Oct 2, 2025
@rustbot rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 2, 2025
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