chore: bump syn from 2.0.114 to 3.0.4

[dependabot]

Bumps syn from 2.0.114 to 3.0.4.

Release notes

Sourced from syn's releases.

3.0.4

• Allow safe fn in impl Parse for ForeignItemFn (#2078)

3.0.3

• Documentation improvements

3.0.2

• Add Error::new_range(start..end, "msg") (#2068, #2070)
• Add Cursor::prev_span

3.0.1

• Parse const traits (#2056, #2057, #2058, #2063, #2064)
• Parse unsafe binder types (#2065)
• Parse impl restrictions (#2066)

3.0.0

This release contains adjustments to the syntax tree to account for ongoing Rust language development from the 3 years since syn 2.0.0 and to anticipate some in-flight Rust language RFCs.

These include: default values in fields, pinned type sugar, raw lifetimes, generator blocks and functions, unnamed enum variants, attributes in tuple types and tuple patterns, named arguments in parenthesized generic argument lists, lightweight clones, const traits, const function pointers, mutability restricted fields, supertrait auto implementation, final associated functions, trait implementability restrictions, const blocks in path arguments, item-level const blocks, return type notation, never patterns, function delegation, mutable by-reference bindings, in-place initialization, field projections, explicitly dyn-compatible traits, view types, file-level frontmatter, generic const arguments, guard patterns, lazy type aliases, explicitly safe foreign items, super let, unsafe fields, pattern types, heterogeneous try-blocks, function contracts, async function trait bounds, static closure coroutine syntax, unsafe binder types, move expressions, for-await loops, and postfix keywords.

Breaking changes

Modifiers

To reserve more room for language evolution, there are 10 new non-exhaustive structs in the syntax tree having the following commonality:

• Name ending in Modifiers. {BlockModifiers, ClosureModifiers, ConstModifiers, FieldModifiers, FnModifiers, ImplModifiers, LocalModifiers, TraitBoundModifiers, TraitModifiers, TypeModifiers}

• Each implements Default. The default value is guaranteed to comprise no tokens.

• Non-exhaustive. Can only be instantiated by Syn's parser or by creating and then mutating ▁▁Modifiers::default().

• Does not implement Parse. When parsing, they are parsed by the enclosing syntax tree node.

• Does not implement ToTokens. In some cases the syntax that these nodes might hold in the future is not necessarily contiguous tokens.

• Provides .require_empty() -> Result<()> which returns a meaningfully spanned error if the modifiers are different from the empty default. This enables a caller to reject syntax it does not recognize without knowing what that syntax may be.

Types

• Type::BareFn has been renamed to Type::FnPtr to mirror the compiler's terminology. Together with this, BareVariadic is renamed to FnPtrVariadic.

• The mutually exclusive const_token and mutability fields of Type::Ptr have been unified into an enum of type PointerMutability, which was already previously used by Expr::RawAddr.

• Every Type variant now holds attributes, which can represent the attributes of element types inside a tuple type, or attributes for a function return type.

... (truncated)

Commits

• b5d62a6 Release 3.0.4
• abf019c Merge pull request #2078 from dtolnay/foreginitemfn
• d454333 Allow safe fn in impl Parse for ForeignItemFn
• 8011b1c Update test suite to nightly-2026-08-18
• 56a8d83 Raise rayon thread size for tests
• f2c5c50 Ignore assert_is_empty pedantic clippy lint
• 0eba76d Update test suite to nightly-2026-08-05
• baaebce Update test suite to nightly-2026-07-25
• b886a38 Update test suite to nightly-2026-07-24
• 3c41416 Update test suite to nightly-2026-07-23
• Additional commits viewable in compare view