fix: prevent panic when formatting complex generics#6630
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avrabe wants to merge 1 commit intorust-lang:mainfrom
Open
fix: prevent panic when formatting complex generics#6630avrabe wants to merge 1 commit intorust-lang:mainfrom
avrabe wants to merge 1 commit intorust-lang:mainfrom
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Handle cases where rewrite_generics fails due to long generic constraints by implementing a fallback to infinite width and preserving original formatting when necessary.
Contributor
|
Hi, I just came across your PR. Would it be alright if I try it out to see if #6396 fixes the unwrap error in that test case? (This seems orthogonal to the mentioned PR though, so just to verify whether the issue is duplicate or not) |
Author
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@ding-young Sure, would be good to see. https://github.com/pulseengine/wrt is where my problem originate from. My patch makes this repository format again. Otherwise it actually stripped away code. |
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TheLostLambda
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Sep 30, 2025
This is now a different, newer PR that supports the 2024 edition: rust-lang/rustfmt#6630
mobiusklein
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Oct 1, 2025
#31) * style: run (patched) rustfmt I was originally perplexed as to why the crate wasn't already formatted, but quickly found out why... Though the PR seems to have languished for some time, I've run a patched version of rustfmt that completes without crashing: rust-lang/rustfmt#6396 * style: fix `mismatched_lifetime_syntaxes` lint * style: remove unnecessary macro imports This is a strange case — I had to look this up myself! Because you have a `#[macro_use]` above the `params` module in `lib.rs`, all of the macros in `params.rs` are automatically made available crate-wide. This import of the macro in `scan_properties.rs` is therefore redundant! The same logic applies to `impl_param_described`. https://lukaswirth.dev/tlborm/decl-macros/minutiae/scoping.html * style: fix clippy `derivable_impls` For `enum`s, you can add a tag and `#[derive(Default)]` instead of manually implementing the same code: https://doc.rust-lang.org/std/default/trait.Default.html#enums * style: fix clippy `single_match` * style: fix clippy `redundant_closure` * style: clippy fix `unnecessary_unwrap` * style: clippy fix `manual_is_multiple_of` NOTE: This method was added in a recent version of Rust (1.87.0), so changing to this code means that our minimum supported Rust version would become that! If you'd rather keep compatibility with older-than-stable versions of Rust, we should leave this unchanged! * chore(edition): run `cargo update` * style(edition): run `cargo --fix edition` Performs some automatic migration to the 2024 edition of Rust. Will be followed by a cleanup commit. * style(edition): bump to Rust 2024 * style(edition): reformat using (patched) rustfmt This is now a different, newer PR that supports the 2024 edition: rust-lang/rustfmt#6630 * style(edition): `expr_2021` -> `expr` in macros The 2024 edition changed `expr`s to accept `const` and `_` expressions, but because no macros in `mzdata` included any `const` or `_` keywords in their syntax, no change needs to be made. * style(edition): `match` back to `if let` None of the migrated code seemed to depend on any exact `Drop` timing, so the overly-cautious `if let` -> `match` migration was unnecessary. * style(edition): change `gen` to `this_generation` In the 2024 edition, `gen` became a reserved Rust keyword. Using `r#gen` is still possible, but probably not best practice, so I've renamed the old `gen` variables. * style: fix clippy `let_and_return` * style: fix clippy `collapsible_if`
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Fixes #6571
Problem
rustfmt panics with
Option::unwrap() on a None valuewhen formatting enums with very long generic type constraints. This occurs when the generic constraints exceed the available width budget (~80-100 characters), causingrewrite_genericsto fail andformat_genericsto returnNone, which is then unwrapped.Solution
This PR implements a three-tier fallback strategy in
format_generics:shape.infinite_width()Changes
format_genericsfunction insrc/items.rsto handle width budget exhaustion gracefullyissue-6571.rsto prevent future regressionsTesting
This fix ensures rustfmt can process files with complex generic constraints without crashing, while maintaining proper formatting where possible.