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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.
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.
BareFnArg is renamed to NamedArg and is used in ParenthesizedGenericArguments, in addition to the existing use in Type::FnPtr.
Expressions
In Expr::Closure, the fields or1_token and or2_token have been renamed to inputs_begin and inputs_end to indicate the beginning and ending | token of the closure inputs.
Statements
Attributes are now preserved on all expression kinds in statement position. Previously, parsing would silently lose attributes on some expression statements without a dedicated Expr variant, such as tail-call expressions.
Patterns
The guard field of Arm is replaced by a new Pat::Guard variant held in the arm's pat.
Items
The unsafety field of Signature, which represented the presence or absence of unsafe, is replaced by a 3-way Safety enum which may be safe, unsafe, or default. ForeignItem::Static also gets a Safety.
Some of the fields of Receiver have been split to a non-exhaustive ReceiverKind enum to create room for proposed new kinds of method receivers, such as pinned.
Type aliases now hold a WhereClausePlacement to distinguish between early placement (which is the default for item-level type aliases and is deprecated in associated type aliases) and late placement (which is the default for associated type aliases and is unstable in item-level type aliases). Parsing and printing a syntax tree will now preserve the where-clause placement rather than rewriting it to the default placement for the item kind.
Generics
WherePredicate::Lifetime and WherePredicate::Type have a new field holding the attributes on the where-predicates.
GenericParam::Type and GenericParam::Const now match the rest of the syntax tree in holding their optional default using a single Option of tuple, rather than a pair of Option.
Literals
The Parse implementation of Lifetime no longer permits keyword lifetimes, matching a change in Rust 1.81 to deny such lifetimes pre-expansion. Lifetime::parse_any may be used to parse lifetimes permissive of keywords.
LitInt and LitFloat no longer implement From<proc_macro2::Literal>. Use Lit::new(literal) and then match Lit::Int or Lit::Float.
The StrStyle enum was unused and has been deleted.
More
File contains a new Option<Frontmatter>, but does not yet parse frontmatter in syn::parse_file until that language feature progresses closer to stabilization.
Some enums no longer provide From impls. Construct the variant by name instead, such as Expr::Array(e) in place of e.into().
The pop method of Punctuated<T, P> now returns Option<T> discarding the trailing punctuation if any, rather than Option<Pair<T, P>>. A new method pop_pair provides the old behavior.
Syntax tree traversal (visit, visit_mut, fold) no longer provides a method for processing Span. This was already incompletely supported and never walked most of the spans in a syntax tree.
The Speculative and AnyDelimiter traits have been sealed and cannot be implemented for types outside of Syn's ParseStream.
Configuration
📅 Schedule: (UTC)
Branch creation
At any time (no schedule defined)
Automerge
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🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.
♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.
🔕 Ignore: Close this PR and you won't be reminded about this update again.
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System calls cannot be simulated consistently and are left out of the measure. The reported value understates the real cost. Switch to the Walltime instrument to measure them.
⚠️6 benchmarks with a significant change ran on different hardware
Their base and head results were measured on machines with a different CPU, core count or memory, so the changes might not come from the code. Run base and head on the same runner type.
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This PR contains the following updates:
2.0→3.0Release Notes
dtolnay/syn (syn)
v3.0.9Compare Source
v3.0.8Compare Source
<-and->tokens in expressions (#2086, #2087)v3.0.7Compare Source
v3.0.6Compare Source
v3.0.5Compare Source
LitStr::parse_with(#2080, thanks @sunshowers)v3.0.4Compare Source
safe fninimpl Parse for ForeignItemFn(#2078)v3.0.3Compare Source
v3.0.2Compare Source
Error::new_range(start..end, "msg")(#2068, #2070)Cursor::prev_spanv3.0.1Compare Source
v3.0.0Compare Source
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.
[API documentation for 3.0]
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::BareFnhas been renamed toType::FnPtrto mirror the compiler's terminology. Together with this,BareVariadicis renamed toFnPtrVariadic.The mutually exclusive
const_tokenandmutabilityfields ofType::Ptrhave been unified into an enum of typePointerMutability, which was already previously used byExpr::RawAddr.Every
Typevariant now holds attributes, which can represent the attributes of element types inside a tuple type, or attributes for a function return type.BareFnArgis renamed toNamedArgand is used inParenthesizedGenericArguments, in addition to the existing use inType::FnPtr.Expressions
Expr::Closure, the fieldsor1_tokenandor2_tokenhave been renamed toinputs_beginandinputs_endto indicate the beginning and ending|token of the closure inputs.Statements
Patterns
guardfield ofArmis replaced by a newPat::Guardvariant held in the arm'spat.Items
The
unsafetyfield ofSignature, which represented the presence or absence ofunsafe, is replaced by a 3-waySafetyenum which may be safe, unsafe, or default.ForeignItem::Staticalso gets aSafety.Some of the fields of
Receiverhave been split to a non-exhaustiveReceiverKindenum to create room for proposed new kinds of method receivers, such as pinned.Type aliases now hold a
WhereClausePlacementto distinguish between early placement (which is the default for item-level type aliases and is deprecated in associated type aliases) and late placement (which is the default for associated type aliases and is unstable in item-level type aliases). Parsing and printing a syntax tree will now preserve the where-clause placement rather than rewriting it to the default placement for the item kind.Generics
WherePredicate::LifetimeandWherePredicate::Typehave a new field holding the attributes on the where-predicates.GenericParam::TypeandGenericParam::Constnow match the rest of the syntax tree in holding their optional default using a single Option of tuple, rather than a pair of Option.Literals
The
Parseimplementation ofLifetimeno longer permits keyword lifetimes, matching a change in Rust 1.81 to deny such lifetimes pre-expansion.Lifetime::parse_anymay be used to parse lifetimes permissive of keywords.LitIntandLitFloatno longer implementFrom<proc_macro2::Literal>. UseLit::new(literal)and then matchLit::IntorLit::Float.The
StrStyleenum was unused and has been deleted.More
Filecontains a newOption<Frontmatter>, but does not yet parse frontmatter insyn::parse_fileuntil that language feature progresses closer to stabilization.Some enums no longer provide
Fromimpls. Construct the variant by name instead, such asExpr::Array(e)in place ofe.into().The
popmethod ofPunctuated<T, P>now returnsOption<T>discarding the trailing punctuation if any, rather thanOption<Pair<T, P>>. A new methodpop_pairprovides the old behavior.Syntax tree traversal (
visit,visit_mut,fold) no longer provides a method for processingSpan. This was already incompletely supported and never walked most of the spans in a syntax tree.The
SpeculativeandAnyDelimitertraits have been sealed and cannot be implemented for types outside of Syn'sParseStream.Configuration
📅 Schedule: (UTC)
🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.
♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.
🔕 Ignore: Close this PR and you won't be reminded about this update again.
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