Parse lets as if they were items for diagnostics. #159044
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cc @rust-lang/rustfmt The parser was modified, potentially altering the grammar of (stable) Rust cc @fmease |
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r? @fee1-dead rustbot has assigned @fee1-dead. Use Why was this reviewer chosen?The reviewer was selected based on:
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kpreid
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Jul 9, 2026
| .parse_item( | ||
| ForceCollect::Yes, | ||
| AllowConstBlockItems::Yes, | ||
| StmtWouldBeAllowed::NoOrUnknown, |
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I don’t like that I had to add a new parameter to parse_item everywhere, but I don’t know what would be better. Probably a new distinct entry point function.
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Tidy doesn’t like how long this file is now. Should I split it in this PR? Put up a separate PR? Ignore?
| let error = match allow_suggest_stmt { | ||
| StmtWouldBeAllowed::Yes => { | ||
| // We are in a function, `const` block, or other context in which a `let` | ||
| // *would* be allowed, except that we must have parsed some item-modifier |
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Is there an established term for these keywords like pub and final that appear before the item-kind keyword? I picked “modifier” arbitrarily.
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| }; | ||
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| // FIXME: Ideally, we would have a `ItemKind::Err` that optionally defines a name but |
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I could try to add this new item kind to this PR if desired.
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This change provides a precise diagnostic in all cases of `let` appearing in a context where items but not statements are permitted, and `let` appearing after an item modifier keyword (`pub` or `final`). It provides a suggestion for replacing `let` with `const` (which should be usable interactively in rust-analyzer). It provides advice when the user might have thought `final` meant what it means in Java (immutable variable declaration). It also consolidates two existing, less powerful `let` diagnostics into the new code: one for module bodies, and one for `trait`/`impl` bodies. In order to be able to determine whether a `let` *would* parse if written properly, it adds a new parameter, `StmtWouldBeAllowed`. This is a bit intrusive and not ideal, but I couldn’t think of a better solution, other than extending `FnContext` to mean more than it currently does, which seems not necessarily wise.
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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. |
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Partially addresses #92615.
Fixes #101622.
This change provides a precise diagnostic in all cases of
letappearing in a context where items but not statements are permitted, andletappearing after an item modifier keyword (puborfinal).It provides a suggestion for replacing
letwithconst(which should be usable interactively in rust-analyzer). It provides advice when the user might have thoughtfinalmeant what it means in Java (immutable variable declaration).It also consolidates two existing, less powerful
letdiagnostics into the new code: one for module bodies, and one fortrait/implbodies.In order to be able to determine whether a
letwould parse if written properly, it adds a new parameter to the parsing functions,StmtWouldBeAllowed. This is a bit intrusive and not ideal, but I couldn’t think of a better solution, other than extendingFnContextto mean more than it currently does, which seems not necessarily wise.