Bump syn from 1.0.109 to 2.0.3 in /lang/rust

[dependabot]

Bumps syn from 1.0.109 to 2.0.3.

Release notes

Sourced from syn's releases.

2.0.2

• Documentation improvements

2.0.1

• Add methods on syn::Meta for reporting error on an incorrect kind of attribute (#1409)

2.0.0

This release contains a batch of syntax tree improvements to incorporate ongoing Rust language development from the past 3.5 years since syn 1.

It never seems like an ideal time to finalize a syntax tree design, considering the frankly alarming number of syntax-disrupting language features currently in flight: keyword generics, restrictions, capabilities and contexts, conditional constness, new varieties of literals, dyn revamp such as explicitly dyn-safe traits and dyn-star, expression syntax in various phases of being added or being torn out (const blocks, try blocks, raw references), auto traits and negative impls, generalizations to higher rank trait bounds, async closures and static async trait methods, postfix keywords, pattern types, return type notation, unsafe attributes, …

The plan continues to be the same as laid out originally in the 1.0.0 release announcement:

Be aware that the underlying Rust language will continue to evolve. Syn is able to accommodate most kinds of Rust grammar changes via the nonexhaustive enums and Verbatim variants in the syntax tree, but we will plan to put out new major versions on a 12 to 24 month cadence to incorporate ongoing language changes as needed.

If anything, the takeaway from the 3.5 year longevity of syn 1 is that this period was tamer from a language development perspective than anticipated, but that is unlikely to last and I think around 24 months is still the correct cadence to expect between releases going forward.

Breaking changes

• Minimum required Rust version is raised from rustc 1.31 to 1.56.

Expressions

• Support for box expr syntax has been deleted, as it has been deleted recently from rustc.

• Support for type ascription syntax expr: Type in expression position has been deleted.

• Support for unstable &raw const expr raw-pointer reference syntax has been deleted.

• The representation of generic arguments has been unified between method calls and non-method paths into a single GenericArgument type, which supersedes the previous GenericMethodArgument and MethodTurbofish.

• Generic arguments now distinguish between associated types (AssocType) and associated constant values (AssocConst). Previously these would be parsed ambiguously as Binding.

• The binary assignment operators in BinOp have been renamed to align with the naming used by the standard library's core::ops module's traits. For example BinOp::AddEq is now called BinOp::AddAssign.

• Expr::Struct struct construction expressions now support structs which are a variant of an enum associated type of a trait, as in <Type as Trait>::Assoc::Variant { ... }, which has recently been added to Rust.

• Expr::Range now follows the start and end naming used by the standard library's RangeBounds trait, rather than from/to or lo/hi.

• Expr::AssignOp has been merged into Expr::Binary, which now represents both non-assignment and assignment binary operators.

• Stricter parsing of ranges. None of the following are valid expressions, but were previously accepted by syn: ..=, lo..=, ..., ...hi, lo..., lo...hi.

• Expr::Closure now includes a representation for for<...> lifetimes.

Statements

... (truncated)

Commits

• 25def51 Release 2.0.3
• 4f3803d Merge pull request #1412 from dtolnay/exprgroup
• 516a5b5 Provide Expr::Group even with features="full" off
• cac5cc6 Release 2.0.2
• 8f826ef Touch up spacing in example for parse_multi_with_leading_vert
• fc58fcf Fix typo in Stmt::Macro documentation
• e298152 Release 2.0.1
• b87a0a1 Merge pull request #1409 from dtolnay/requiremeta
• 59dd7cc Add methods on Meta for error reporting an incorrect kind of attribute
• 11c0b6c Build attribute parse errors using std::fmt system
• Additional commits viewable in compare view

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