pub struct Cursor<'a> { /* private fields */ }Available on crate feature
parsing only.Expand description
A cheaply copyable cursor into a TokenBuffer.
This cursor holds a shared reference into the immutable data which is used
internally to represent a TokenStream, and can be efficiently manipulated
and copied around.
An empty Cursor can be created directly, or one may create a TokenBuffer
object and get a cursor to its first token with begin().
Two cursors are equal if they have the same location in the same input stream, and have the same scope.
This type is available only if Syn is built with the "parsing" feature.
Implementations§
source§impl<'a> Cursor<'a>
impl<'a> Cursor<'a>
sourcepub fn eof(self) -> bool
pub fn eof(self) -> bool
Checks whether the cursor is currently pointing at the end of its valid scope.
Examples found in repository?
More examples
src/parse.rs (line 448)
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fn span_of_unexpected_ignoring_nones(mut cursor: Cursor) -> Option<Span> {
if cursor.eof() {
return None;
}
while let Some((inner, _span, rest)) = cursor.group(Delimiter::None) {
if let Some(unexpected) = span_of_unexpected_ignoring_nones(inner) {
return Some(unexpected);
}
cursor = rest;
}
if cursor.eof() {
None
} else {
Some(cursor.span())
}
}
impl<'a> ParseBuffer<'a> {
/// Parses a syntax tree node of type `T`, advancing the position of our
/// parse stream past it.
pub fn parse<T: Parse>(&self) -> Result<T> {
T::parse(self)
}
/// Calls the given parser function to parse a syntax tree node of type `T`
/// from this stream.
///
/// # Example
///
/// The parser below invokes [`Attribute::parse_outer`] to parse a vector of
/// zero or more outer attributes.
///
/// [`Attribute::parse_outer`]: crate::Attribute::parse_outer
///
/// ```
/// use syn::{Attribute, Ident, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses a unit struct with attributes.
/// //
/// // #[path = "s.tmpl"]
/// // struct S;
/// struct UnitStruct {
/// attrs: Vec<Attribute>,
/// struct_token: Token![struct],
/// name: Ident,
/// semi_token: Token![;],
/// }
///
/// impl Parse for UnitStruct {
/// fn parse(input: ParseStream) -> Result<Self> {
/// Ok(UnitStruct {
/// attrs: input.call(Attribute::parse_outer)?,
/// struct_token: input.parse()?,
/// name: input.parse()?,
/// semi_token: input.parse()?,
/// })
/// }
/// }
/// ```
pub fn call<T>(&self, function: fn(ParseStream) -> Result<T>) -> Result<T> {
function(self)
}
/// Looks at the next token in the parse stream to determine whether it
/// matches the requested type of token.
///
/// Does not advance the position of the parse stream.
///
/// # Syntax
///
/// Note that this method does not use turbofish syntax. Pass the peek type
/// inside of parentheses.
///
/// - `input.peek(Token![struct])`
/// - `input.peek(Token![==])`
/// - `input.peek(Ident)` *(does not accept keywords)*
/// - `input.peek(Ident::peek_any)`
/// - `input.peek(Lifetime)`
/// - `input.peek(token::Brace)`
///
/// # Example
///
/// In this example we finish parsing the list of supertraits when the next
/// token in the input is either `where` or an opening curly brace.
///
/// ```
/// use syn::{braced, token, Generics, Ident, Result, Token, TypeParamBound};
/// use syn::parse::{Parse, ParseStream};
/// use syn::punctuated::Punctuated;
///
/// // Parses a trait definition containing no associated items.
/// //
/// // trait Marker<'de, T>: A + B<'de> where Box<T>: Clone {}
/// struct MarkerTrait {
/// trait_token: Token![trait],
/// ident: Ident,
/// generics: Generics,
/// colon_token: Option<Token![:]>,
/// supertraits: Punctuated<TypeParamBound, Token![+]>,
/// brace_token: token::Brace,
/// }
///
/// impl Parse for MarkerTrait {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let trait_token: Token![trait] = input.parse()?;
/// let ident: Ident = input.parse()?;
/// let mut generics: Generics = input.parse()?;
/// let colon_token: Option<Token![:]> = input.parse()?;
///
/// let mut supertraits = Punctuated::new();
/// if colon_token.is_some() {
/// loop {
/// supertraits.push_value(input.parse()?);
/// if input.peek(Token![where]) || input.peek(token::Brace) {
/// break;
/// }
/// supertraits.push_punct(input.parse()?);
/// }
/// }
///
/// generics.where_clause = input.parse()?;
/// let content;
/// let empty_brace_token = braced!(content in input);
///
/// Ok(MarkerTrait {
/// trait_token,
/// ident,
/// generics,
/// colon_token,
/// supertraits,
/// brace_token: empty_brace_token,
/// })
/// }
/// }
/// ```
pub fn peek<T: Peek>(&self, token: T) -> bool {
let _ = token;
T::Token::peek(self.cursor())
}
/// Looks at the second-next token in the parse stream.
///
/// This is commonly useful as a way to implement contextual keywords.
///
/// # Example
///
/// This example needs to use `peek2` because the symbol `union` is not a
/// keyword in Rust. We can't use just `peek` and decide to parse a union if
/// the very next token is `union`, because someone is free to write a `mod
/// union` and a macro invocation that looks like `union::some_macro! { ...
/// }`. In other words `union` is a contextual keyword.
///
/// ```
/// use syn::{Ident, ItemUnion, Macro, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses either a union or a macro invocation.
/// enum UnionOrMacro {
/// // union MaybeUninit<T> { uninit: (), value: T }
/// Union(ItemUnion),
/// // lazy_static! { ... }
/// Macro(Macro),
/// }
///
/// impl Parse for UnionOrMacro {
/// fn parse(input: ParseStream) -> Result<Self> {
/// if input.peek(Token![union]) && input.peek2(Ident) {
/// input.parse().map(UnionOrMacro::Union)
/// } else {
/// input.parse().map(UnionOrMacro::Macro)
/// }
/// }
/// }
/// ```
pub fn peek2<T: Peek>(&self, token: T) -> bool {
fn peek2(buffer: &ParseBuffer, peek: fn(Cursor) -> bool) -> bool {
if let Some(group) = buffer.cursor().group(Delimiter::None) {
if group.0.skip().map_or(false, peek) {
return true;
}
}
buffer.cursor().skip().map_or(false, peek)
}
let _ = token;
peek2(self, T::Token::peek)
}
/// Looks at the third-next token in the parse stream.
pub fn peek3<T: Peek>(&self, token: T) -> bool {
fn peek3(buffer: &ParseBuffer, peek: fn(Cursor) -> bool) -> bool {
if let Some(group) = buffer.cursor().group(Delimiter::None) {
if group.0.skip().and_then(Cursor::skip).map_or(false, peek) {
return true;
}
}
buffer
.cursor()
.skip()
.and_then(Cursor::skip)
.map_or(false, peek)
}
let _ = token;
peek3(self, T::Token::peek)
}
/// Parses zero or more occurrences of `T` separated by punctuation of type
/// `P`, with optional trailing punctuation.
///
/// Parsing continues until the end of this parse stream. The entire content
/// of this parse stream must consist of `T` and `P`.
///
/// # Example
///
/// ```
/// # use quote::quote;
/// #
/// use syn::{parenthesized, token, Ident, Result, Token, Type};
/// use syn::parse::{Parse, ParseStream};
/// use syn::punctuated::Punctuated;
///
/// // Parse a simplified tuple struct syntax like:
/// //
/// // struct S(A, B);
/// struct TupleStruct {
/// struct_token: Token![struct],
/// ident: Ident,
/// paren_token: token::Paren,
/// fields: Punctuated<Type, Token![,]>,
/// semi_token: Token![;],
/// }
///
/// impl Parse for TupleStruct {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let content;
/// Ok(TupleStruct {
/// struct_token: input.parse()?,
/// ident: input.parse()?,
/// paren_token: parenthesized!(content in input),
/// fields: content.parse_terminated(Type::parse)?,
/// semi_token: input.parse()?,
/// })
/// }
/// }
/// #
/// # let input = quote! {
/// # struct S(A, B);
/// # };
/// # syn::parse2::<TupleStruct>(input).unwrap();
/// ```
pub fn parse_terminated<T, P: Parse>(
&self,
parser: fn(ParseStream) -> Result<T>,
) -> Result<Punctuated<T, P>> {
Punctuated::parse_terminated_with(self, parser)
}
/// Returns whether there are tokens remaining in this stream.
///
/// This method returns true at the end of the content of a set of
/// delimiters, as well as at the very end of the complete macro input.
///
/// # Example
///
/// ```
/// use syn::{braced, token, Ident, Item, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses a Rust `mod m { ... }` containing zero or more items.
/// struct Mod {
/// mod_token: Token![mod],
/// name: Ident,
/// brace_token: token::Brace,
/// items: Vec<Item>,
/// }
///
/// impl Parse for Mod {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let content;
/// Ok(Mod {
/// mod_token: input.parse()?,
/// name: input.parse()?,
/// brace_token: braced!(content in input),
/// items: {
/// let mut items = Vec::new();
/// while !content.is_empty() {
/// items.push(content.parse()?);
/// }
/// items
/// },
/// })
/// }
/// }
/// ```
pub fn is_empty(&self) -> bool {
self.cursor().eof()
}
/// Constructs a helper for peeking at the next token in this stream and
/// building an error message if it is not one of a set of expected tokens.
///
/// # Example
///
/// ```
/// use syn::{ConstParam, Ident, Lifetime, LifetimeDef, Result, Token, TypeParam};
/// use syn::parse::{Parse, ParseStream};
///
/// // A generic parameter, a single one of the comma-separated elements inside
/// // angle brackets in:
/// //
/// // fn f<T: Clone, 'a, 'b: 'a, const N: usize>() { ... }
/// //
/// // On invalid input, lookahead gives us a reasonable error message.
/// //
/// // error: expected one of: identifier, lifetime, `const`
/// // |
/// // 5 | fn f<!Sized>() {}
/// // | ^
/// enum GenericParam {
/// Type(TypeParam),
/// Lifetime(LifetimeDef),
/// Const(ConstParam),
/// }
///
/// impl Parse for GenericParam {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let lookahead = input.lookahead1();
/// if lookahead.peek(Ident) {
/// input.parse().map(GenericParam::Type)
/// } else if lookahead.peek(Lifetime) {
/// input.parse().map(GenericParam::Lifetime)
/// } else if lookahead.peek(Token![const]) {
/// input.parse().map(GenericParam::Const)
/// } else {
/// Err(lookahead.error())
/// }
/// }
/// }
/// ```
pub fn lookahead1(&self) -> Lookahead1<'a> {
lookahead::new(self.scope, self.cursor())
}
/// Forks a parse stream so that parsing tokens out of either the original
/// or the fork does not advance the position of the other.
///
/// # Performance
///
/// Forking a parse stream is a cheap fixed amount of work and does not
/// involve copying token buffers. Where you might hit performance problems
/// is if your macro ends up parsing a large amount of content more than
/// once.
///
/// ```
/// # use syn::{Expr, Result};
/// # use syn::parse::ParseStream;
/// #
/// # fn bad(input: ParseStream) -> Result<Expr> {
/// // Do not do this.
/// if input.fork().parse::<Expr>().is_ok() {
/// return input.parse::<Expr>();
/// }
/// # unimplemented!()
/// # }
/// ```
///
/// As a rule, avoid parsing an unbounded amount of tokens out of a forked
/// parse stream. Only use a fork when the amount of work performed against
/// the fork is small and bounded.
///
/// When complex speculative parsing against the forked stream is
/// unavoidable, use [`parse::discouraged::Speculative`] to advance the
/// original stream once the fork's parse is determined to have been
/// successful.
///
/// For a lower level way to perform speculative parsing at the token level,
/// consider using [`ParseStream::step`] instead.
///
/// [`parse::discouraged::Speculative`]: discouraged::Speculative
/// [`ParseStream::step`]: ParseBuffer::step
///
/// # Example
///
/// The parse implementation shown here parses possibly restricted `pub`
/// visibilities.
///
/// - `pub`
/// - `pub(crate)`
/// - `pub(self)`
/// - `pub(super)`
/// - `pub(in some::path)`
///
/// To handle the case of visibilities inside of tuple structs, the parser
/// needs to distinguish parentheses that specify visibility restrictions
/// from parentheses that form part of a tuple type.
///
/// ```
/// # struct A;
/// # struct B;
/// # struct C;
/// #
/// struct S(pub(crate) A, pub (B, C));
/// ```
///
/// In this example input the first tuple struct element of `S` has
/// `pub(crate)` visibility while the second tuple struct element has `pub`
/// visibility; the parentheses around `(B, C)` are part of the type rather
/// than part of a visibility restriction.
///
/// The parser uses a forked parse stream to check the first token inside of
/// parentheses after the `pub` keyword. This is a small bounded amount of
/// work performed against the forked parse stream.
///
/// ```
/// use syn::{parenthesized, token, Ident, Path, Result, Token};
/// use syn::ext::IdentExt;
/// use syn::parse::{Parse, ParseStream};
///
/// struct PubVisibility {
/// pub_token: Token![pub],
/// restricted: Option<Restricted>,
/// }
///
/// struct Restricted {
/// paren_token: token::Paren,
/// in_token: Option<Token![in]>,
/// path: Path,
/// }
///
/// impl Parse for PubVisibility {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let pub_token: Token![pub] = input.parse()?;
///
/// if input.peek(token::Paren) {
/// let ahead = input.fork();
/// let mut content;
/// parenthesized!(content in ahead);
///
/// if content.peek(Token![crate])
/// || content.peek(Token![self])
/// || content.peek(Token![super])
/// {
/// return Ok(PubVisibility {
/// pub_token,
/// restricted: Some(Restricted {
/// paren_token: parenthesized!(content in input),
/// in_token: None,
/// path: Path::from(content.call(Ident::parse_any)?),
/// }),
/// });
/// } else if content.peek(Token![in]) {
/// return Ok(PubVisibility {
/// pub_token,
/// restricted: Some(Restricted {
/// paren_token: parenthesized!(content in input),
/// in_token: Some(content.parse()?),
/// path: content.call(Path::parse_mod_style)?,
/// }),
/// });
/// }
/// }
///
/// Ok(PubVisibility {
/// pub_token,
/// restricted: None,
/// })
/// }
/// }
/// ```
pub fn fork(&self) -> Self {
ParseBuffer {
scope: self.scope,
cell: self.cell.clone(),
marker: PhantomData,
// Not the parent's unexpected. Nothing cares whether the clone
// parses all the way unless we `advance_to`.
unexpected: Cell::new(Some(Rc::new(Cell::new(Unexpected::None)))),
}
}
/// Triggers an error at the current position of the parse stream.
///
/// # Example
///
/// ```
/// use syn::{Expr, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Some kind of loop: `while` or `for` or `loop`.
/// struct Loop {
/// expr: Expr,
/// }
///
/// impl Parse for Loop {
/// fn parse(input: ParseStream) -> Result<Self> {
/// if input.peek(Token![while])
/// || input.peek(Token![for])
/// || input.peek(Token![loop])
/// {
/// Ok(Loop {
/// expr: input.parse()?,
/// })
/// } else {
/// Err(input.error("expected some kind of loop"))
/// }
/// }
/// }
/// ```
pub fn error<T: Display>(&self, message: T) -> Error {
error::new_at(self.scope, self.cursor(), message)
}
/// Speculatively parses tokens from this parse stream, advancing the
/// position of this stream only if parsing succeeds.
///
/// This is a powerful low-level API used for defining the `Parse` impls of
/// the basic built-in token types. It is not something that will be used
/// widely outside of the Syn codebase.
///
/// # Example
///
/// ```
/// use proc_macro2::TokenTree;
/// use syn::Result;
/// use syn::parse::ParseStream;
///
/// // This function advances the stream past the next occurrence of `@`. If
/// // no `@` is present in the stream, the stream position is unchanged and
/// // an error is returned.
/// fn skip_past_next_at(input: ParseStream) -> Result<()> {
/// input.step(|cursor| {
/// let mut rest = *cursor;
/// while let Some((tt, next)) = rest.token_tree() {
/// match &tt {
/// TokenTree::Punct(punct) if punct.as_char() == '@' => {
/// return Ok(((), next));
/// }
/// _ => rest = next,
/// }
/// }
/// Err(cursor.error("no `@` was found after this point"))
/// })
/// }
/// #
/// # fn remainder_after_skipping_past_next_at(
/// # input: ParseStream,
/// # ) -> Result<proc_macro2::TokenStream> {
/// # skip_past_next_at(input)?;
/// # input.parse()
/// # }
/// #
/// # use syn::parse::Parser;
/// # let remainder = remainder_after_skipping_past_next_at
/// # .parse_str("a @ b c")
/// # .unwrap();
/// # assert_eq!(remainder.to_string(), "b c");
/// ```
pub fn step<F, R>(&self, function: F) -> Result<R>
where
F: for<'c> FnOnce(StepCursor<'c, 'a>) -> Result<(R, Cursor<'c>)>,
{
// Since the user's function is required to work for any 'c, we know
// that the Cursor<'c> they return is either derived from the input
// StepCursor<'c, 'a> or from a Cursor<'static>.
//
// It would not be legal to write this function without the invariant
// lifetime 'c in StepCursor<'c, 'a>. If this function were written only
// in terms of 'a, the user could take our ParseBuffer<'a>, upcast it to
// a ParseBuffer<'short> which some shorter lifetime than 'a, invoke
// `step` on their ParseBuffer<'short> with a closure that returns
// Cursor<'short>, and we would wrongly write that Cursor<'short> into
// the Cell intended to hold Cursor<'a>.
//
// In some cases it may be necessary for R to contain a Cursor<'a>.
// Within Syn we solve this using `advance_step_cursor` which uses the
// existence of a StepCursor<'c, 'a> as proof that it is safe to cast
// from Cursor<'c> to Cursor<'a>. If needed outside of Syn, it would be
// safe to expose that API as a method on StepCursor.
let (node, rest) = function(StepCursor {
scope: self.scope,
cursor: self.cell.get(),
marker: PhantomData,
})?;
self.cell.set(rest);
Ok(node)
}
/// Returns the `Span` of the next token in the parse stream, or
/// `Span::call_site()` if this parse stream has completely exhausted its
/// input `TokenStream`.
pub fn span(&self) -> Span {
let cursor = self.cursor();
if cursor.eof() {
self.scope
} else {
crate::buffer::open_span_of_group(cursor)
}
}src/lookahead.rs (line 116)
112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136
pub fn error(self) -> Error {
let comparisons = self.comparisons.borrow();
match comparisons.len() {
0 => {
if self.cursor.eof() {
Error::new(self.scope, "unexpected end of input")
} else {
Error::new(self.cursor.span(), "unexpected token")
}
}
1 => {
let message = format!("expected {}", comparisons[0]);
error::new_at(self.scope, self.cursor, message)
}
2 => {
let message = format!("expected {} or {}", comparisons[0], comparisons[1]);
error::new_at(self.scope, self.cursor, message)
}
_ => {
let join = comparisons.join(", ");
let message = format!("expected one of: {}", join);
error::new_at(self.scope, self.cursor, message)
}
}
}sourcepub fn group(self, delim: Delimiter) -> Option<(Cursor<'a>, Span, Cursor<'a>)>
pub fn group(self, delim: Delimiter) -> Option<(Cursor<'a>, Span, Cursor<'a>)>
If the cursor is pointing at a Group with the given delimiter, returns
a cursor into that group and one pointing to the next TokenTree.
Examples found in repository?
More examples
src/parse.rs (line 451)
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fn span_of_unexpected_ignoring_nones(mut cursor: Cursor) -> Option<Span> {
if cursor.eof() {
return None;
}
while let Some((inner, _span, rest)) = cursor.group(Delimiter::None) {
if let Some(unexpected) = span_of_unexpected_ignoring_nones(inner) {
return Some(unexpected);
}
cursor = rest;
}
if cursor.eof() {
None
} else {
Some(cursor.span())
}
}
impl<'a> ParseBuffer<'a> {
/// Parses a syntax tree node of type `T`, advancing the position of our
/// parse stream past it.
pub fn parse<T: Parse>(&self) -> Result<T> {
T::parse(self)
}
/// Calls the given parser function to parse a syntax tree node of type `T`
/// from this stream.
///
/// # Example
///
/// The parser below invokes [`Attribute::parse_outer`] to parse a vector of
/// zero or more outer attributes.
///
/// [`Attribute::parse_outer`]: crate::Attribute::parse_outer
///
/// ```
/// use syn::{Attribute, Ident, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses a unit struct with attributes.
/// //
/// // #[path = "s.tmpl"]
/// // struct S;
/// struct UnitStruct {
/// attrs: Vec<Attribute>,
/// struct_token: Token![struct],
/// name: Ident,
/// semi_token: Token![;],
/// }
///
/// impl Parse for UnitStruct {
/// fn parse(input: ParseStream) -> Result<Self> {
/// Ok(UnitStruct {
/// attrs: input.call(Attribute::parse_outer)?,
/// struct_token: input.parse()?,
/// name: input.parse()?,
/// semi_token: input.parse()?,
/// })
/// }
/// }
/// ```
pub fn call<T>(&self, function: fn(ParseStream) -> Result<T>) -> Result<T> {
function(self)
}
/// Looks at the next token in the parse stream to determine whether it
/// matches the requested type of token.
///
/// Does not advance the position of the parse stream.
///
/// # Syntax
///
/// Note that this method does not use turbofish syntax. Pass the peek type
/// inside of parentheses.
///
/// - `input.peek(Token![struct])`
/// - `input.peek(Token![==])`
/// - `input.peek(Ident)` *(does not accept keywords)*
/// - `input.peek(Ident::peek_any)`
/// - `input.peek(Lifetime)`
/// - `input.peek(token::Brace)`
///
/// # Example
///
/// In this example we finish parsing the list of supertraits when the next
/// token in the input is either `where` or an opening curly brace.
///
/// ```
/// use syn::{braced, token, Generics, Ident, Result, Token, TypeParamBound};
/// use syn::parse::{Parse, ParseStream};
/// use syn::punctuated::Punctuated;
///
/// // Parses a trait definition containing no associated items.
/// //
/// // trait Marker<'de, T>: A + B<'de> where Box<T>: Clone {}
/// struct MarkerTrait {
/// trait_token: Token![trait],
/// ident: Ident,
/// generics: Generics,
/// colon_token: Option<Token![:]>,
/// supertraits: Punctuated<TypeParamBound, Token![+]>,
/// brace_token: token::Brace,
/// }
///
/// impl Parse for MarkerTrait {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let trait_token: Token![trait] = input.parse()?;
/// let ident: Ident = input.parse()?;
/// let mut generics: Generics = input.parse()?;
/// let colon_token: Option<Token![:]> = input.parse()?;
///
/// let mut supertraits = Punctuated::new();
/// if colon_token.is_some() {
/// loop {
/// supertraits.push_value(input.parse()?);
/// if input.peek(Token![where]) || input.peek(token::Brace) {
/// break;
/// }
/// supertraits.push_punct(input.parse()?);
/// }
/// }
///
/// generics.where_clause = input.parse()?;
/// let content;
/// let empty_brace_token = braced!(content in input);
///
/// Ok(MarkerTrait {
/// trait_token,
/// ident,
/// generics,
/// colon_token,
/// supertraits,
/// brace_token: empty_brace_token,
/// })
/// }
/// }
/// ```
pub fn peek<T: Peek>(&self, token: T) -> bool {
let _ = token;
T::Token::peek(self.cursor())
}
/// Looks at the second-next token in the parse stream.
///
/// This is commonly useful as a way to implement contextual keywords.
///
/// # Example
///
/// This example needs to use `peek2` because the symbol `union` is not a
/// keyword in Rust. We can't use just `peek` and decide to parse a union if
/// the very next token is `union`, because someone is free to write a `mod
/// union` and a macro invocation that looks like `union::some_macro! { ...
/// }`. In other words `union` is a contextual keyword.
///
/// ```
/// use syn::{Ident, ItemUnion, Macro, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses either a union or a macro invocation.
/// enum UnionOrMacro {
/// // union MaybeUninit<T> { uninit: (), value: T }
/// Union(ItemUnion),
/// // lazy_static! { ... }
/// Macro(Macro),
/// }
///
/// impl Parse for UnionOrMacro {
/// fn parse(input: ParseStream) -> Result<Self> {
/// if input.peek(Token![union]) && input.peek2(Ident) {
/// input.parse().map(UnionOrMacro::Union)
/// } else {
/// input.parse().map(UnionOrMacro::Macro)
/// }
/// }
/// }
/// ```
pub fn peek2<T: Peek>(&self, token: T) -> bool {
fn peek2(buffer: &ParseBuffer, peek: fn(Cursor) -> bool) -> bool {
if let Some(group) = buffer.cursor().group(Delimiter::None) {
if group.0.skip().map_or(false, peek) {
return true;
}
}
buffer.cursor().skip().map_or(false, peek)
}
let _ = token;
peek2(self, T::Token::peek)
}
/// Looks at the third-next token in the parse stream.
pub fn peek3<T: Peek>(&self, token: T) -> bool {
fn peek3(buffer: &ParseBuffer, peek: fn(Cursor) -> bool) -> bool {
if let Some(group) = buffer.cursor().group(Delimiter::None) {
if group.0.skip().and_then(Cursor::skip).map_or(false, peek) {
return true;
}
}
buffer
.cursor()
.skip()
.and_then(Cursor::skip)
.map_or(false, peek)
}
let _ = token;
peek3(self, T::Token::peek)
}
/// Parses zero or more occurrences of `T` separated by punctuation of type
/// `P`, with optional trailing punctuation.
///
/// Parsing continues until the end of this parse stream. The entire content
/// of this parse stream must consist of `T` and `P`.
///
/// # Example
///
/// ```
/// # use quote::quote;
/// #
/// use syn::{parenthesized, token, Ident, Result, Token, Type};
/// use syn::parse::{Parse, ParseStream};
/// use syn::punctuated::Punctuated;
///
/// // Parse a simplified tuple struct syntax like:
/// //
/// // struct S(A, B);
/// struct TupleStruct {
/// struct_token: Token![struct],
/// ident: Ident,
/// paren_token: token::Paren,
/// fields: Punctuated<Type, Token![,]>,
/// semi_token: Token![;],
/// }
///
/// impl Parse for TupleStruct {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let content;
/// Ok(TupleStruct {
/// struct_token: input.parse()?,
/// ident: input.parse()?,
/// paren_token: parenthesized!(content in input),
/// fields: content.parse_terminated(Type::parse)?,
/// semi_token: input.parse()?,
/// })
/// }
/// }
/// #
/// # let input = quote! {
/// # struct S(A, B);
/// # };
/// # syn::parse2::<TupleStruct>(input).unwrap();
/// ```
pub fn parse_terminated<T, P: Parse>(
&self,
parser: fn(ParseStream) -> Result<T>,
) -> Result<Punctuated<T, P>> {
Punctuated::parse_terminated_with(self, parser)
}
/// Returns whether there are tokens remaining in this stream.
///
/// This method returns true at the end of the content of a set of
/// delimiters, as well as at the very end of the complete macro input.
///
/// # Example
///
/// ```
/// use syn::{braced, token, Ident, Item, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses a Rust `mod m { ... }` containing zero or more items.
/// struct Mod {
/// mod_token: Token![mod],
/// name: Ident,
/// brace_token: token::Brace,
/// items: Vec<Item>,
/// }
///
/// impl Parse for Mod {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let content;
/// Ok(Mod {
/// mod_token: input.parse()?,
/// name: input.parse()?,
/// brace_token: braced!(content in input),
/// items: {
/// let mut items = Vec::new();
/// while !content.is_empty() {
/// items.push(content.parse()?);
/// }
/// items
/// },
/// })
/// }
/// }
/// ```
pub fn is_empty(&self) -> bool {
self.cursor().eof()
}
/// Constructs a helper for peeking at the next token in this stream and
/// building an error message if it is not one of a set of expected tokens.
///
/// # Example
///
/// ```
/// use syn::{ConstParam, Ident, Lifetime, LifetimeDef, Result, Token, TypeParam};
/// use syn::parse::{Parse, ParseStream};
///
/// // A generic parameter, a single one of the comma-separated elements inside
/// // angle brackets in:
/// //
/// // fn f<T: Clone, 'a, 'b: 'a, const N: usize>() { ... }
/// //
/// // On invalid input, lookahead gives us a reasonable error message.
/// //
/// // error: expected one of: identifier, lifetime, `const`
/// // |
/// // 5 | fn f<!Sized>() {}
/// // | ^
/// enum GenericParam {
/// Type(TypeParam),
/// Lifetime(LifetimeDef),
/// Const(ConstParam),
/// }
///
/// impl Parse for GenericParam {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let lookahead = input.lookahead1();
/// if lookahead.peek(Ident) {
/// input.parse().map(GenericParam::Type)
/// } else if lookahead.peek(Lifetime) {
/// input.parse().map(GenericParam::Lifetime)
/// } else if lookahead.peek(Token![const]) {
/// input.parse().map(GenericParam::Const)
/// } else {
/// Err(lookahead.error())
/// }
/// }
/// }
/// ```
pub fn lookahead1(&self) -> Lookahead1<'a> {
lookahead::new(self.scope, self.cursor())
}
/// Forks a parse stream so that parsing tokens out of either the original
/// or the fork does not advance the position of the other.
///
/// # Performance
///
/// Forking a parse stream is a cheap fixed amount of work and does not
/// involve copying token buffers. Where you might hit performance problems
/// is if your macro ends up parsing a large amount of content more than
/// once.
///
/// ```
/// # use syn::{Expr, Result};
/// # use syn::parse::ParseStream;
/// #
/// # fn bad(input: ParseStream) -> Result<Expr> {
/// // Do not do this.
/// if input.fork().parse::<Expr>().is_ok() {
/// return input.parse::<Expr>();
/// }
/// # unimplemented!()
/// # }
/// ```
///
/// As a rule, avoid parsing an unbounded amount of tokens out of a forked
/// parse stream. Only use a fork when the amount of work performed against
/// the fork is small and bounded.
///
/// When complex speculative parsing against the forked stream is
/// unavoidable, use [`parse::discouraged::Speculative`] to advance the
/// original stream once the fork's parse is determined to have been
/// successful.
///
/// For a lower level way to perform speculative parsing at the token level,
/// consider using [`ParseStream::step`] instead.
///
/// [`parse::discouraged::Speculative`]: discouraged::Speculative
/// [`ParseStream::step`]: ParseBuffer::step
///
/// # Example
///
/// The parse implementation shown here parses possibly restricted `pub`
/// visibilities.
///
/// - `pub`
/// - `pub(crate)`
/// - `pub(self)`
/// - `pub(super)`
/// - `pub(in some::path)`
///
/// To handle the case of visibilities inside of tuple structs, the parser
/// needs to distinguish parentheses that specify visibility restrictions
/// from parentheses that form part of a tuple type.
///
/// ```
/// # struct A;
/// # struct B;
/// # struct C;
/// #
/// struct S(pub(crate) A, pub (B, C));
/// ```
///
/// In this example input the first tuple struct element of `S` has
/// `pub(crate)` visibility while the second tuple struct element has `pub`
/// visibility; the parentheses around `(B, C)` are part of the type rather
/// than part of a visibility restriction.
///
/// The parser uses a forked parse stream to check the first token inside of
/// parentheses after the `pub` keyword. This is a small bounded amount of
/// work performed against the forked parse stream.
///
/// ```
/// use syn::{parenthesized, token, Ident, Path, Result, Token};
/// use syn::ext::IdentExt;
/// use syn::parse::{Parse, ParseStream};
///
/// struct PubVisibility {
/// pub_token: Token![pub],
/// restricted: Option<Restricted>,
/// }
///
/// struct Restricted {
/// paren_token: token::Paren,
/// in_token: Option<Token![in]>,
/// path: Path,
/// }
///
/// impl Parse for PubVisibility {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let pub_token: Token![pub] = input.parse()?;
///
/// if input.peek(token::Paren) {
/// let ahead = input.fork();
/// let mut content;
/// parenthesized!(content in ahead);
///
/// if content.peek(Token![crate])
/// || content.peek(Token![self])
/// || content.peek(Token![super])
/// {
/// return Ok(PubVisibility {
/// pub_token,
/// restricted: Some(Restricted {
/// paren_token: parenthesized!(content in input),
/// in_token: None,
/// path: Path::from(content.call(Ident::parse_any)?),
/// }),
/// });
/// } else if content.peek(Token![in]) {
/// return Ok(PubVisibility {
/// pub_token,
/// restricted: Some(Restricted {
/// paren_token: parenthesized!(content in input),
/// in_token: Some(content.parse()?),
/// path: content.call(Path::parse_mod_style)?,
/// }),
/// });
/// }
/// }
///
/// Ok(PubVisibility {
/// pub_token,
/// restricted: None,
/// })
/// }
/// }
/// ```
pub fn fork(&self) -> Self {
ParseBuffer {
scope: self.scope,
cell: self.cell.clone(),
marker: PhantomData,
// Not the parent's unexpected. Nothing cares whether the clone
// parses all the way unless we `advance_to`.
unexpected: Cell::new(Some(Rc::new(Cell::new(Unexpected::None)))),
}
}
/// Triggers an error at the current position of the parse stream.
///
/// # Example
///
/// ```
/// use syn::{Expr, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Some kind of loop: `while` or `for` or `loop`.
/// struct Loop {
/// expr: Expr,
/// }
///
/// impl Parse for Loop {
/// fn parse(input: ParseStream) -> Result<Self> {
/// if input.peek(Token![while])
/// || input.peek(Token![for])
/// || input.peek(Token![loop])
/// {
/// Ok(Loop {
/// expr: input.parse()?,
/// })
/// } else {
/// Err(input.error("expected some kind of loop"))
/// }
/// }
/// }
/// ```
pub fn error<T: Display>(&self, message: T) -> Error {
error::new_at(self.scope, self.cursor(), message)
}
/// Speculatively parses tokens from this parse stream, advancing the
/// position of this stream only if parsing succeeds.
///
/// This is a powerful low-level API used for defining the `Parse` impls of
/// the basic built-in token types. It is not something that will be used
/// widely outside of the Syn codebase.
///
/// # Example
///
/// ```
/// use proc_macro2::TokenTree;
/// use syn::Result;
/// use syn::parse::ParseStream;
///
/// // This function advances the stream past the next occurrence of `@`. If
/// // no `@` is present in the stream, the stream position is unchanged and
/// // an error is returned.
/// fn skip_past_next_at(input: ParseStream) -> Result<()> {
/// input.step(|cursor| {
/// let mut rest = *cursor;
/// while let Some((tt, next)) = rest.token_tree() {
/// match &tt {
/// TokenTree::Punct(punct) if punct.as_char() == '@' => {
/// return Ok(((), next));
/// }
/// _ => rest = next,
/// }
/// }
/// Err(cursor.error("no `@` was found after this point"))
/// })
/// }
/// #
/// # fn remainder_after_skipping_past_next_at(
/// # input: ParseStream,
/// # ) -> Result<proc_macro2::TokenStream> {
/// # skip_past_next_at(input)?;
/// # input.parse()
/// # }
/// #
/// # use syn::parse::Parser;
/// # let remainder = remainder_after_skipping_past_next_at
/// # .parse_str("a @ b c")
/// # .unwrap();
/// # assert_eq!(remainder.to_string(), "b c");
/// ```
pub fn step<F, R>(&self, function: F) -> Result<R>
where
F: for<'c> FnOnce(StepCursor<'c, 'a>) -> Result<(R, Cursor<'c>)>,
{
// Since the user's function is required to work for any 'c, we know
// that the Cursor<'c> they return is either derived from the input
// StepCursor<'c, 'a> or from a Cursor<'static>.
//
// It would not be legal to write this function without the invariant
// lifetime 'c in StepCursor<'c, 'a>. If this function were written only
// in terms of 'a, the user could take our ParseBuffer<'a>, upcast it to
// a ParseBuffer<'short> which some shorter lifetime than 'a, invoke
// `step` on their ParseBuffer<'short> with a closure that returns
// Cursor<'short>, and we would wrongly write that Cursor<'short> into
// the Cell intended to hold Cursor<'a>.
//
// In some cases it may be necessary for R to contain a Cursor<'a>.
// Within Syn we solve this using `advance_step_cursor` which uses the
// existence of a StepCursor<'c, 'a> as proof that it is safe to cast
// from Cursor<'c> to Cursor<'a>. If needed outside of Syn, it would be
// safe to expose that API as a method on StepCursor.
let (node, rest) = function(StepCursor {
scope: self.scope,
cursor: self.cell.get(),
marker: PhantomData,
})?;
self.cell.set(rest);
Ok(node)
}
/// Returns the `Span` of the next token in the parse stream, or
/// `Span::call_site()` if this parse stream has completely exhausted its
/// input `TokenStream`.
pub fn span(&self) -> Span {
let cursor = self.cursor();
if cursor.eof() {
self.scope
} else {
crate::buffer::open_span_of_group(cursor)
}
}
/// Provides low-level access to the token representation underlying this
/// parse stream.
///
/// Cursors are immutable so no operations you perform against the cursor
/// will affect the state of this parse stream.
pub fn cursor(&self) -> Cursor<'a> {
self.cell.get()
}
fn check_unexpected(&self) -> Result<()> {
match inner_unexpected(self).1 {
Some(span) => Err(Error::new(span, "unexpected token")),
None => Ok(()),
}
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl<T: Parse> Parse for Box<T> {
fn parse(input: ParseStream) -> Result<Self> {
input.parse().map(Box::new)
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl<T: Parse + Token> Parse for Option<T> {
fn parse(input: ParseStream) -> Result<Self> {
if T::peek(input.cursor()) {
Ok(Some(input.parse()?))
} else {
Ok(None)
}
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl Parse for TokenStream {
fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| Ok((cursor.token_stream(), Cursor::empty())))
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl Parse for TokenTree {
fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| match cursor.token_tree() {
Some((tt, rest)) => Ok((tt, rest)),
None => Err(cursor.error("expected token tree")),
})
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl Parse for Group {
fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
for delim in &[Delimiter::Parenthesis, Delimiter::Brace, Delimiter::Bracket] {
if let Some((inside, span, rest)) = cursor.group(*delim) {
let mut group = Group::new(*delim, inside.token_stream());
group.set_span(span);
return Ok((group, rest));
}
}
Err(cursor.error("expected group token"))
})
}src/group.rs (line 75)
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fn parse_delimited<'a>(
input: &ParseBuffer<'a>,
delimiter: Delimiter,
) -> Result<(Span, ParseBuffer<'a>)> {
input.step(|cursor| {
if let Some((content, span, rest)) = cursor.group(delimiter) {
let scope = crate::buffer::close_span_of_group(*cursor);
let nested = crate::parse::advance_step_cursor(cursor, content);
let unexpected = crate::parse::get_unexpected(input);
let content = crate::parse::new_parse_buffer(scope, nested, unexpected);
Ok(((span, content), rest))
} else {
let message = match delimiter {
Delimiter::Parenthesis => "expected parentheses",
Delimiter::Brace => "expected curly braces",
Delimiter::Bracket => "expected square brackets",
Delimiter::None => "expected invisible group",
};
Err(cursor.error(message))
}
})
}src/verbatim.rs (line 20)
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pub fn between<'a>(begin: ParseBuffer<'a>, end: ParseStream<'a>) -> TokenStream {
let end = end.cursor();
let mut cursor = begin.cursor();
assert!(crate::buffer::same_buffer(end, cursor));
let mut tokens = TokenStream::new();
while cursor != end {
let (tt, next) = cursor.token_tree().unwrap();
if crate::buffer::cmp_assuming_same_buffer(end, next) == Ordering::Less {
// A syntax node can cross the boundary of a None-delimited group
// due to such groups being transparent to the parser in most cases.
// Any time this occurs the group is known to be semantically
// irrelevant. https://github.com/dtolnay/syn/issues/1235
if let Some((inside, _span, after)) = cursor.group(Delimiter::None) {
assert!(next == after);
cursor = inside;
continue;
} else {
panic!("verbatim end must not be inside a delimited group");
}
}
tokens.extend(iter::once(tt));
cursor = next;
}
tokens
}sourcepub fn ident(self) -> Option<(Ident, Cursor<'a>)>
pub fn ident(self) -> Option<(Ident, Cursor<'a>)>
If the cursor is pointing at a Ident, returns it along with a cursor
pointing at the next TokenTree.
Examples found in repository?
src/ext.rs (line 91)
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fn parse_any(input: ParseStream) -> Result<Self> {
input.step(|cursor| match cursor.ident() {
Some((ident, rest)) => Ok((ident, rest)),
None => Err(cursor.error("expected ident")),
})
}
fn unraw(&self) -> Ident {
let string = self.to_string();
if string.starts_with("r#") {
Ident::new(&string[2..], self.span())
} else {
self.clone()
}
}
}
impl Peek for private::PeekFn {
type Token = private::IdentAny;
}
impl CustomToken for private::IdentAny {
fn peek(cursor: Cursor) -> bool {
cursor.ident().is_some()
}More examples
src/ident.rs (line 42)
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fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
if let Some((ident, rest)) = cursor.ident() {
if accept_as_ident(&ident) {
return Ok((ident, rest));
}
}
Err(cursor.error("expected identifier"))
})
}
}
#[cfg(feature = "parsing")]
impl Token for Ident {
fn peek(cursor: Cursor) -> bool {
if let Some((ident, _rest)) = cursor.ident() {
accept_as_ident(&ident)
} else {
false
}
}src/token.rs (line 573)
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fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
if let Some((ident, rest)) = cursor.ident() {
if ident == "_" {
return Ok((Underscore(ident.span()), rest));
}
}
if let Some((punct, rest)) = cursor.punct() {
if punct.as_char() == '_' {
return Ok((Underscore(punct.span()), rest));
}
}
Err(cursor.error("expected `_`"))
})
}
}
#[cfg(feature = "parsing")]
impl Token for Underscore {
fn peek(cursor: Cursor) -> bool {
if let Some((ident, _rest)) = cursor.ident() {
return ident == "_";
}
if let Some((punct, _rest)) = cursor.punct() {
return punct.as_char() == '_';
}
false
}
fn display() -> &'static str {
"`_`"
}
}
#[cfg(feature = "parsing")]
impl private::Sealed for Underscore {}
#[cfg(feature = "parsing")]
impl Token for Paren {
fn peek(cursor: Cursor) -> bool {
lookahead::is_delimiter(cursor, Delimiter::Parenthesis)
}
fn display() -> &'static str {
"parentheses"
}
}
#[cfg(feature = "parsing")]
impl Token for Brace {
fn peek(cursor: Cursor) -> bool {
lookahead::is_delimiter(cursor, Delimiter::Brace)
}
fn display() -> &'static str {
"curly braces"
}
}
#[cfg(feature = "parsing")]
impl Token for Bracket {
fn peek(cursor: Cursor) -> bool {
lookahead::is_delimiter(cursor, Delimiter::Bracket)
}
fn display() -> &'static str {
"square brackets"
}
}
#[cfg(feature = "parsing")]
impl Token for Group {
fn peek(cursor: Cursor) -> bool {
lookahead::is_delimiter(cursor, Delimiter::None)
}
fn display() -> &'static str {
"invisible group"
}
}
define_keywords! {
"abstract" pub struct Abstract /// `abstract`
"as" pub struct As /// `as`
"async" pub struct Async /// `async`
"auto" pub struct Auto /// `auto`
"await" pub struct Await /// `await`
"become" pub struct Become /// `become`
"box" pub struct Box /// `box`
"break" pub struct Break /// `break`
"const" pub struct Const /// `const`
"continue" pub struct Continue /// `continue`
"crate" pub struct Crate /// `crate`
"default" pub struct Default /// `default`
"do" pub struct Do /// `do`
"dyn" pub struct Dyn /// `dyn`
"else" pub struct Else /// `else`
"enum" pub struct Enum /// `enum`
"extern" pub struct Extern /// `extern`
"final" pub struct Final /// `final`
"fn" pub struct Fn /// `fn`
"for" pub struct For /// `for`
"if" pub struct If /// `if`
"impl" pub struct Impl /// `impl`
"in" pub struct In /// `in`
"let" pub struct Let /// `let`
"loop" pub struct Loop /// `loop`
"macro" pub struct Macro /// `macro`
"match" pub struct Match /// `match`
"mod" pub struct Mod /// `mod`
"move" pub struct Move /// `move`
"mut" pub struct Mut /// `mut`
"override" pub struct Override /// `override`
"priv" pub struct Priv /// `priv`
"pub" pub struct Pub /// `pub`
"ref" pub struct Ref /// `ref`
"return" pub struct Return /// `return`
"Self" pub struct SelfType /// `Self`
"self" pub struct SelfValue /// `self`
"static" pub struct Static /// `static`
"struct" pub struct Struct /// `struct`
"super" pub struct Super /// `super`
"trait" pub struct Trait /// `trait`
"try" pub struct Try /// `try`
"type" pub struct Type /// `type`
"typeof" pub struct Typeof /// `typeof`
"union" pub struct Union /// `union`
"unsafe" pub struct Unsafe /// `unsafe`
"unsized" pub struct Unsized /// `unsized`
"use" pub struct Use /// `use`
"virtual" pub struct Virtual /// `virtual`
"where" pub struct Where /// `where`
"while" pub struct While /// `while`
"yield" pub struct Yield /// `yield`
}
define_punctuation! {
"+" pub struct Add/1 /// `+`
"+=" pub struct AddEq/2 /// `+=`
"&" pub struct And/1 /// `&`
"&&" pub struct AndAnd/2 /// `&&`
"&=" pub struct AndEq/2 /// `&=`
"@" pub struct At/1 /// `@`
"!" pub struct Bang/1 /// `!`
"^" pub struct Caret/1 /// `^`
"^=" pub struct CaretEq/2 /// `^=`
":" pub struct Colon/1 /// `:`
"::" pub struct Colon2/2 /// `::`
"," pub struct Comma/1 /// `,`
"/" pub struct Div/1 /// `/`
"/=" pub struct DivEq/2 /// `/=`
"$" pub struct Dollar/1 /// `$`
"." pub struct Dot/1 /// `.`
".." pub struct Dot2/2 /// `..`
"..." pub struct Dot3/3 /// `...`
"..=" pub struct DotDotEq/3 /// `..=`
"=" pub struct Eq/1 /// `=`
"==" pub struct EqEq/2 /// `==`
">=" pub struct Ge/2 /// `>=`
">" pub struct Gt/1 /// `>`
"<=" pub struct Le/2 /// `<=`
"<" pub struct Lt/1 /// `<`
"*=" pub struct MulEq/2 /// `*=`
"!=" pub struct Ne/2 /// `!=`
"|" pub struct Or/1 /// `|`
"|=" pub struct OrEq/2 /// `|=`
"||" pub struct OrOr/2 /// `||`
"#" pub struct Pound/1 /// `#`
"?" pub struct Question/1 /// `?`
"->" pub struct RArrow/2 /// `->`
"<-" pub struct LArrow/2 /// `<-`
"%" pub struct Rem/1 /// `%`
"%=" pub struct RemEq/2 /// `%=`
"=>" pub struct FatArrow/2 /// `=>`
";" pub struct Semi/1 /// `;`
"<<" pub struct Shl/2 /// `<<`
"<<=" pub struct ShlEq/3 /// `<<=`
">>" pub struct Shr/2 /// `>>`
">>=" pub struct ShrEq/3 /// `>>=`
"*" pub struct Star/1 /// `*`
"-" pub struct Sub/1 /// `-`
"-=" pub struct SubEq/2 /// `-=`
"~" pub struct Tilde/1 /// `~`
}
define_delimiters! {
"{" pub struct Brace /// `{...}`
"[" pub struct Bracket /// `[...]`
"(" pub struct Paren /// `(...)`
" " pub struct Group /// None-delimited group
}
macro_rules! export_token_macro {
($($await_rule:tt)*) => {
/// A type-macro that expands to the name of the Rust type representation of a
/// given token.
///
/// See the [token module] documentation for details and examples.
///
/// [token module]: crate::token
// Unfortunate duplication due to a rustdoc bug.
// https://github.com/rust-lang/rust/issues/45939
#[macro_export]
macro_rules! Token {
[abstract] => { $crate::token::Abstract };
[as] => { $crate::token::As };
[async] => { $crate::token::Async };
[auto] => { $crate::token::Auto };
$($await_rule => { $crate::token::Await };)*
[become] => { $crate::token::Become };
[box] => { $crate::token::Box };
[break] => { $crate::token::Break };
[const] => { $crate::token::Const };
[continue] => { $crate::token::Continue };
[crate] => { $crate::token::Crate };
[default] => { $crate::token::Default };
[do] => { $crate::token::Do };
[dyn] => { $crate::token::Dyn };
[else] => { $crate::token::Else };
[enum] => { $crate::token::Enum };
[extern] => { $crate::token::Extern };
[final] => { $crate::token::Final };
[fn] => { $crate::token::Fn };
[for] => { $crate::token::For };
[if] => { $crate::token::If };
[impl] => { $crate::token::Impl };
[in] => { $crate::token::In };
[let] => { $crate::token::Let };
[loop] => { $crate::token::Loop };
[macro] => { $crate::token::Macro };
[match] => { $crate::token::Match };
[mod] => { $crate::token::Mod };
[move] => { $crate::token::Move };
[mut] => { $crate::token::Mut };
[override] => { $crate::token::Override };
[priv] => { $crate::token::Priv };
[pub] => { $crate::token::Pub };
[ref] => { $crate::token::Ref };
[return] => { $crate::token::Return };
[Self] => { $crate::token::SelfType };
[self] => { $crate::token::SelfValue };
[static] => { $crate::token::Static };
[struct] => { $crate::token::Struct };
[super] => { $crate::token::Super };
[trait] => { $crate::token::Trait };
[try] => { $crate::token::Try };
[type] => { $crate::token::Type };
[typeof] => { $crate::token::Typeof };
[union] => { $crate::token::Union };
[unsafe] => { $crate::token::Unsafe };
[unsized] => { $crate::token::Unsized };
[use] => { $crate::token::Use };
[virtual] => { $crate::token::Virtual };
[where] => { $crate::token::Where };
[while] => { $crate::token::While };
[yield] => { $crate::token::Yield };
[+] => { $crate::token::Add };
[+=] => { $crate::token::AddEq };
[&] => { $crate::token::And };
[&&] => { $crate::token::AndAnd };
[&=] => { $crate::token::AndEq };
[@] => { $crate::token::At };
[!] => { $crate::token::Bang };
[^] => { $crate::token::Caret };
[^=] => { $crate::token::CaretEq };
[:] => { $crate::token::Colon };
[::] => { $crate::token::Colon2 };
[,] => { $crate::token::Comma };
[/] => { $crate::token::Div };
[/=] => { $crate::token::DivEq };
[$] => { $crate::token::Dollar };
[.] => { $crate::token::Dot };
[..] => { $crate::token::Dot2 };
[...] => { $crate::token::Dot3 };
[..=] => { $crate::token::DotDotEq };
[=] => { $crate::token::Eq };
[==] => { $crate::token::EqEq };
[>=] => { $crate::token::Ge };
[>] => { $crate::token::Gt };
[<=] => { $crate::token::Le };
[<] => { $crate::token::Lt };
[*=] => { $crate::token::MulEq };
[!=] => { $crate::token::Ne };
[|] => { $crate::token::Or };
[|=] => { $crate::token::OrEq };
[||] => { $crate::token::OrOr };
[#] => { $crate::token::Pound };
[?] => { $crate::token::Question };
[->] => { $crate::token::RArrow };
[<-] => { $crate::token::LArrow };
[%] => { $crate::token::Rem };
[%=] => { $crate::token::RemEq };
[=>] => { $crate::token::FatArrow };
[;] => { $crate::token::Semi };
[<<] => { $crate::token::Shl };
[<<=] => { $crate::token::ShlEq };
[>>] => { $crate::token::Shr };
[>>=] => { $crate::token::ShrEq };
[*] => { $crate::token::Star };
[-] => { $crate::token::Sub };
[-=] => { $crate::token::SubEq };
[~] => { $crate::token::Tilde };
[_] => { $crate::token::Underscore };
}
};
}
// Old rustc does not permit `await` appearing anywhere in the source file.
// https://github.com/rust-lang/rust/issues/57919
// We put the Token![await] rule in a place that is not lexed by old rustc.
#[cfg(not(syn_omit_await_from_token_macro))]
include!("await.rs"); // export_token_macro! {[await]}
#[cfg(syn_omit_await_from_token_macro)]
export_token_macro! {}
// Not public API.
#[doc(hidden)]
#[cfg(feature = "parsing")]
pub mod parsing {
use crate::buffer::Cursor;
use crate::error::{Error, Result};
use crate::parse::ParseStream;
use crate::span::FromSpans;
use proc_macro2::{Spacing, Span};
pub fn keyword(input: ParseStream, token: &str) -> Result<Span> {
input.step(|cursor| {
if let Some((ident, rest)) = cursor.ident() {
if ident == token {
return Ok((ident.span(), rest));
}
}
Err(cursor.error(format!("expected `{}`", token)))
})
}
pub fn peek_keyword(cursor: Cursor, token: &str) -> bool {
if let Some((ident, _rest)) = cursor.ident() {
ident == token
} else {
false
}
}src/buffer.rs (line 261)
256 257 258 259 260 261 262 263 264 265 266 267 268 269 270
pub fn lifetime(mut self) -> Option<(Lifetime, Cursor<'a>)> {
self.ignore_none();
match self.entry() {
Entry::Punct(punct) if punct.as_char() == '\'' && punct.spacing() == Spacing::Joint => {
let next = unsafe { self.bump_ignore_group() };
let (ident, rest) = next.ident()?;
let lifetime = Lifetime {
apostrophe: punct.span(),
ident,
};
Some((lifetime, rest))
}
_ => None,
}
}src/lit.rs (line 752)
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fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
if let Some((lit, rest)) = cursor.literal() {
return Ok((Lit::new(lit), rest));
}
if let Some((ident, rest)) = cursor.ident() {
let value = ident == "true";
if value || ident == "false" {
let lit_bool = LitBool {
value,
span: ident.span(),
};
return Ok((Lit::Bool(lit_bool), rest));
}
}
if let Some((punct, rest)) = cursor.punct() {
if punct.as_char() == '-' {
if let Some((lit, rest)) = parse_negative_lit(punct, rest) {
return Ok((lit, rest));
}
}
}
Err(cursor.error("expected literal"))
})
}sourcepub fn punct(self) -> Option<(Punct, Cursor<'a>)>
pub fn punct(self) -> Option<(Punct, Cursor<'a>)>
If the cursor is pointing at a Punct, returns it along with a cursor
pointing at the next TokenTree.
Examples found in repository?
More examples
src/token.rs (line 578)
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fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
if let Some((ident, rest)) = cursor.ident() {
if ident == "_" {
return Ok((Underscore(ident.span()), rest));
}
}
if let Some((punct, rest)) = cursor.punct() {
if punct.as_char() == '_' {
return Ok((Underscore(punct.span()), rest));
}
}
Err(cursor.error("expected `_`"))
})
}
}
#[cfg(feature = "parsing")]
impl Token for Underscore {
fn peek(cursor: Cursor) -> bool {
if let Some((ident, _rest)) = cursor.ident() {
return ident == "_";
}
if let Some((punct, _rest)) = cursor.punct() {
return punct.as_char() == '_';
}
false
}
fn display() -> &'static str {
"`_`"
}
}
#[cfg(feature = "parsing")]
impl private::Sealed for Underscore {}
#[cfg(feature = "parsing")]
impl Token for Paren {
fn peek(cursor: Cursor) -> bool {
lookahead::is_delimiter(cursor, Delimiter::Parenthesis)
}
fn display() -> &'static str {
"parentheses"
}
}
#[cfg(feature = "parsing")]
impl Token for Brace {
fn peek(cursor: Cursor) -> bool {
lookahead::is_delimiter(cursor, Delimiter::Brace)
}
fn display() -> &'static str {
"curly braces"
}
}
#[cfg(feature = "parsing")]
impl Token for Bracket {
fn peek(cursor: Cursor) -> bool {
lookahead::is_delimiter(cursor, Delimiter::Bracket)
}
fn display() -> &'static str {
"square brackets"
}
}
#[cfg(feature = "parsing")]
impl Token for Group {
fn peek(cursor: Cursor) -> bool {
lookahead::is_delimiter(cursor, Delimiter::None)
}
fn display() -> &'static str {
"invisible group"
}
}
define_keywords! {
"abstract" pub struct Abstract /// `abstract`
"as" pub struct As /// `as`
"async" pub struct Async /// `async`
"auto" pub struct Auto /// `auto`
"await" pub struct Await /// `await`
"become" pub struct Become /// `become`
"box" pub struct Box /// `box`
"break" pub struct Break /// `break`
"const" pub struct Const /// `const`
"continue" pub struct Continue /// `continue`
"crate" pub struct Crate /// `crate`
"default" pub struct Default /// `default`
"do" pub struct Do /// `do`
"dyn" pub struct Dyn /// `dyn`
"else" pub struct Else /// `else`
"enum" pub struct Enum /// `enum`
"extern" pub struct Extern /// `extern`
"final" pub struct Final /// `final`
"fn" pub struct Fn /// `fn`
"for" pub struct For /// `for`
"if" pub struct If /// `if`
"impl" pub struct Impl /// `impl`
"in" pub struct In /// `in`
"let" pub struct Let /// `let`
"loop" pub struct Loop /// `loop`
"macro" pub struct Macro /// `macro`
"match" pub struct Match /// `match`
"mod" pub struct Mod /// `mod`
"move" pub struct Move /// `move`
"mut" pub struct Mut /// `mut`
"override" pub struct Override /// `override`
"priv" pub struct Priv /// `priv`
"pub" pub struct Pub /// `pub`
"ref" pub struct Ref /// `ref`
"return" pub struct Return /// `return`
"Self" pub struct SelfType /// `Self`
"self" pub struct SelfValue /// `self`
"static" pub struct Static /// `static`
"struct" pub struct Struct /// `struct`
"super" pub struct Super /// `super`
"trait" pub struct Trait /// `trait`
"try" pub struct Try /// `try`
"type" pub struct Type /// `type`
"typeof" pub struct Typeof /// `typeof`
"union" pub struct Union /// `union`
"unsafe" pub struct Unsafe /// `unsafe`
"unsized" pub struct Unsized /// `unsized`
"use" pub struct Use /// `use`
"virtual" pub struct Virtual /// `virtual`
"where" pub struct Where /// `where`
"while" pub struct While /// `while`
"yield" pub struct Yield /// `yield`
}
define_punctuation! {
"+" pub struct Add/1 /// `+`
"+=" pub struct AddEq/2 /// `+=`
"&" pub struct And/1 /// `&`
"&&" pub struct AndAnd/2 /// `&&`
"&=" pub struct AndEq/2 /// `&=`
"@" pub struct At/1 /// `@`
"!" pub struct Bang/1 /// `!`
"^" pub struct Caret/1 /// `^`
"^=" pub struct CaretEq/2 /// `^=`
":" pub struct Colon/1 /// `:`
"::" pub struct Colon2/2 /// `::`
"," pub struct Comma/1 /// `,`
"/" pub struct Div/1 /// `/`
"/=" pub struct DivEq/2 /// `/=`
"$" pub struct Dollar/1 /// `$`
"." pub struct Dot/1 /// `.`
".." pub struct Dot2/2 /// `..`
"..." pub struct Dot3/3 /// `...`
"..=" pub struct DotDotEq/3 /// `..=`
"=" pub struct Eq/1 /// `=`
"==" pub struct EqEq/2 /// `==`
">=" pub struct Ge/2 /// `>=`
">" pub struct Gt/1 /// `>`
"<=" pub struct Le/2 /// `<=`
"<" pub struct Lt/1 /// `<`
"*=" pub struct MulEq/2 /// `*=`
"!=" pub struct Ne/2 /// `!=`
"|" pub struct Or/1 /// `|`
"|=" pub struct OrEq/2 /// `|=`
"||" pub struct OrOr/2 /// `||`
"#" pub struct Pound/1 /// `#`
"?" pub struct Question/1 /// `?`
"->" pub struct RArrow/2 /// `->`
"<-" pub struct LArrow/2 /// `<-`
"%" pub struct Rem/1 /// `%`
"%=" pub struct RemEq/2 /// `%=`
"=>" pub struct FatArrow/2 /// `=>`
";" pub struct Semi/1 /// `;`
"<<" pub struct Shl/2 /// `<<`
"<<=" pub struct ShlEq/3 /// `<<=`
">>" pub struct Shr/2 /// `>>`
">>=" pub struct ShrEq/3 /// `>>=`
"*" pub struct Star/1 /// `*`
"-" pub struct Sub/1 /// `-`
"-=" pub struct SubEq/2 /// `-=`
"~" pub struct Tilde/1 /// `~`
}
define_delimiters! {
"{" pub struct Brace /// `{...}`
"[" pub struct Bracket /// `[...]`
"(" pub struct Paren /// `(...)`
" " pub struct Group /// None-delimited group
}
macro_rules! export_token_macro {
($($await_rule:tt)*) => {
/// A type-macro that expands to the name of the Rust type representation of a
/// given token.
///
/// See the [token module] documentation for details and examples.
///
/// [token module]: crate::token
// Unfortunate duplication due to a rustdoc bug.
// https://github.com/rust-lang/rust/issues/45939
#[macro_export]
macro_rules! Token {
[abstract] => { $crate::token::Abstract };
[as] => { $crate::token::As };
[async] => { $crate::token::Async };
[auto] => { $crate::token::Auto };
$($await_rule => { $crate::token::Await };)*
[become] => { $crate::token::Become };
[box] => { $crate::token::Box };
[break] => { $crate::token::Break };
[const] => { $crate::token::Const };
[continue] => { $crate::token::Continue };
[crate] => { $crate::token::Crate };
[default] => { $crate::token::Default };
[do] => { $crate::token::Do };
[dyn] => { $crate::token::Dyn };
[else] => { $crate::token::Else };
[enum] => { $crate::token::Enum };
[extern] => { $crate::token::Extern };
[final] => { $crate::token::Final };
[fn] => { $crate::token::Fn };
[for] => { $crate::token::For };
[if] => { $crate::token::If };
[impl] => { $crate::token::Impl };
[in] => { $crate::token::In };
[let] => { $crate::token::Let };
[loop] => { $crate::token::Loop };
[macro] => { $crate::token::Macro };
[match] => { $crate::token::Match };
[mod] => { $crate::token::Mod };
[move] => { $crate::token::Move };
[mut] => { $crate::token::Mut };
[override] => { $crate::token::Override };
[priv] => { $crate::token::Priv };
[pub] => { $crate::token::Pub };
[ref] => { $crate::token::Ref };
[return] => { $crate::token::Return };
[Self] => { $crate::token::SelfType };
[self] => { $crate::token::SelfValue };
[static] => { $crate::token::Static };
[struct] => { $crate::token::Struct };
[super] => { $crate::token::Super };
[trait] => { $crate::token::Trait };
[try] => { $crate::token::Try };
[type] => { $crate::token::Type };
[typeof] => { $crate::token::Typeof };
[union] => { $crate::token::Union };
[unsafe] => { $crate::token::Unsafe };
[unsized] => { $crate::token::Unsized };
[use] => { $crate::token::Use };
[virtual] => { $crate::token::Virtual };
[where] => { $crate::token::Where };
[while] => { $crate::token::While };
[yield] => { $crate::token::Yield };
[+] => { $crate::token::Add };
[+=] => { $crate::token::AddEq };
[&] => { $crate::token::And };
[&&] => { $crate::token::AndAnd };
[&=] => { $crate::token::AndEq };
[@] => { $crate::token::At };
[!] => { $crate::token::Bang };
[^] => { $crate::token::Caret };
[^=] => { $crate::token::CaretEq };
[:] => { $crate::token::Colon };
[::] => { $crate::token::Colon2 };
[,] => { $crate::token::Comma };
[/] => { $crate::token::Div };
[/=] => { $crate::token::DivEq };
[$] => { $crate::token::Dollar };
[.] => { $crate::token::Dot };
[..] => { $crate::token::Dot2 };
[...] => { $crate::token::Dot3 };
[..=] => { $crate::token::DotDotEq };
[=] => { $crate::token::Eq };
[==] => { $crate::token::EqEq };
[>=] => { $crate::token::Ge };
[>] => { $crate::token::Gt };
[<=] => { $crate::token::Le };
[<] => { $crate::token::Lt };
[*=] => { $crate::token::MulEq };
[!=] => { $crate::token::Ne };
[|] => { $crate::token::Or };
[|=] => { $crate::token::OrEq };
[||] => { $crate::token::OrOr };
[#] => { $crate::token::Pound };
[?] => { $crate::token::Question };
[->] => { $crate::token::RArrow };
[<-] => { $crate::token::LArrow };
[%] => { $crate::token::Rem };
[%=] => { $crate::token::RemEq };
[=>] => { $crate::token::FatArrow };
[;] => { $crate::token::Semi };
[<<] => { $crate::token::Shl };
[<<=] => { $crate::token::ShlEq };
[>>] => { $crate::token::Shr };
[>>=] => { $crate::token::ShrEq };
[*] => { $crate::token::Star };
[-] => { $crate::token::Sub };
[-=] => { $crate::token::SubEq };
[~] => { $crate::token::Tilde };
[_] => { $crate::token::Underscore };
}
};
}
// Old rustc does not permit `await` appearing anywhere in the source file.
// https://github.com/rust-lang/rust/issues/57919
// We put the Token![await] rule in a place that is not lexed by old rustc.
#[cfg(not(syn_omit_await_from_token_macro))]
include!("await.rs"); // export_token_macro! {[await]}
#[cfg(syn_omit_await_from_token_macro)]
export_token_macro! {}
// Not public API.
#[doc(hidden)]
#[cfg(feature = "parsing")]
pub mod parsing {
use crate::buffer::Cursor;
use crate::error::{Error, Result};
use crate::parse::ParseStream;
use crate::span::FromSpans;
use proc_macro2::{Spacing, Span};
pub fn keyword(input: ParseStream, token: &str) -> Result<Span> {
input.step(|cursor| {
if let Some((ident, rest)) = cursor.ident() {
if ident == token {
return Ok((ident.span(), rest));
}
}
Err(cursor.error(format!("expected `{}`", token)))
})
}
pub fn peek_keyword(cursor: Cursor, token: &str) -> bool {
if let Some((ident, _rest)) = cursor.ident() {
ident == token
} else {
false
}
}
pub fn punct<S: FromSpans>(input: ParseStream, token: &str) -> Result<S> {
let mut spans = [input.span(); 3];
punct_helper(input, token, &mut spans)?;
Ok(S::from_spans(&spans))
}
fn punct_helper(input: ParseStream, token: &str, spans: &mut [Span; 3]) -> Result<()> {
input.step(|cursor| {
let mut cursor = *cursor;
assert!(token.len() <= spans.len());
for (i, ch) in token.chars().enumerate() {
match cursor.punct() {
Some((punct, rest)) => {
spans[i] = punct.span();
if punct.as_char() != ch {
break;
} else if i == token.len() - 1 {
return Ok(((), rest));
} else if punct.spacing() != Spacing::Joint {
break;
}
cursor = rest;
}
None => break,
}
}
Err(Error::new(spans[0], format!("expected `{}`", token)))
})
}
pub fn peek_punct(mut cursor: Cursor, token: &str) -> bool {
for (i, ch) in token.chars().enumerate() {
match cursor.punct() {
Some((punct, rest)) => {
if punct.as_char() != ch {
break;
} else if i == token.len() - 1 {
return true;
} else if punct.spacing() != Spacing::Joint {
break;
}
cursor = rest;
}
None => break,
}
}
false
}src/lit.rs (line 763)
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fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
if let Some((lit, rest)) = cursor.literal() {
return Ok((Lit::new(lit), rest));
}
if let Some((ident, rest)) = cursor.ident() {
let value = ident == "true";
if value || ident == "false" {
let lit_bool = LitBool {
value,
span: ident.span(),
};
return Ok((Lit::Bool(lit_bool), rest));
}
}
if let Some((punct, rest)) = cursor.punct() {
if punct.as_char() == '-' {
if let Some((lit, rest)) = parse_negative_lit(punct, rest) {
return Ok((lit, rest));
}
}
}
Err(cursor.error("expected literal"))
})
}sourcepub fn literal(self) -> Option<(Literal, Cursor<'a>)>
pub fn literal(self) -> Option<(Literal, Cursor<'a>)>
If the cursor is pointing at a Literal, return it along with a cursor
pointing at the next TokenTree.
Examples found in repository?
More examples
src/lit.rs (line 748)
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fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
if let Some((lit, rest)) = cursor.literal() {
return Ok((Lit::new(lit), rest));
}
if let Some((ident, rest)) = cursor.ident() {
let value = ident == "true";
if value || ident == "false" {
let lit_bool = LitBool {
value,
span: ident.span(),
};
return Ok((Lit::Bool(lit_bool), rest));
}
}
if let Some((punct, rest)) = cursor.punct() {
if punct.as_char() == '-' {
if let Some((lit, rest)) = parse_negative_lit(punct, rest) {
return Ok((lit, rest));
}
}
}
Err(cursor.error("expected literal"))
})
}
}
fn parse_negative_lit(neg: Punct, cursor: Cursor) -> Option<(Lit, Cursor)> {
let (lit, rest) = cursor.literal()?;
let mut span = neg.span();
span = span.join(lit.span()).unwrap_or(span);
let mut repr = lit.to_string();
repr.insert(0, '-');
if let Some((digits, suffix)) = value::parse_lit_int(&repr) {
if let Some(mut token) = value::to_literal(&repr, &digits, &suffix) {
token.set_span(span);
return Some((
Lit::Int(LitInt {
repr: Box::new(LitIntRepr {
token,
digits,
suffix,
}),
}),
rest,
));
}
}
let (digits, suffix) = value::parse_lit_float(&repr)?;
let mut token = value::to_literal(&repr, &digits, &suffix)?;
token.set_span(span);
Some((
Lit::Float(LitFloat {
repr: Box::new(LitFloatRepr {
token,
digits,
suffix,
}),
}),
rest,
))
}sourcepub fn lifetime(self) -> Option<(Lifetime, Cursor<'a>)>
pub fn lifetime(self) -> Option<(Lifetime, Cursor<'a>)>
If the cursor is pointing at a Lifetime, returns it along with a
cursor pointing at the next TokenTree.
sourcepub fn token_stream(self) -> TokenStream
pub fn token_stream(self) -> TokenStream
Copies all remaining tokens visible from this cursor into a
TokenStream.
Examples found in repository?
src/parse.rs (line 283)
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Display::fmt(&self.cursor().token_stream(), f)
}
}
impl<'a> Debug for ParseBuffer<'a> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Debug::fmt(&self.cursor().token_stream(), f)
}
}
/// Cursor state associated with speculative parsing.
///
/// This type is the input of the closure provided to [`ParseStream::step`].
///
/// [`ParseStream::step`]: ParseBuffer::step
///
/// # Example
///
/// ```
/// use proc_macro2::TokenTree;
/// use syn::Result;
/// use syn::parse::ParseStream;
///
/// // This function advances the stream past the next occurrence of `@`. If
/// // no `@` is present in the stream, the stream position is unchanged and
/// // an error is returned.
/// fn skip_past_next_at(input: ParseStream) -> Result<()> {
/// input.step(|cursor| {
/// let mut rest = *cursor;
/// while let Some((tt, next)) = rest.token_tree() {
/// match &tt {
/// TokenTree::Punct(punct) if punct.as_char() == '@' => {
/// return Ok(((), next));
/// }
/// _ => rest = next,
/// }
/// }
/// Err(cursor.error("no `@` was found after this point"))
/// })
/// }
/// #
/// # fn remainder_after_skipping_past_next_at(
/// # input: ParseStream,
/// # ) -> Result<proc_macro2::TokenStream> {
/// # skip_past_next_at(input)?;
/// # input.parse()
/// # }
/// #
/// # use syn::parse::Parser;
/// # let remainder = remainder_after_skipping_past_next_at
/// # .parse_str("a @ b c")
/// # .unwrap();
/// # assert_eq!(remainder.to_string(), "b c");
/// ```
pub struct StepCursor<'c, 'a> {
scope: Span,
// This field is covariant in 'c.
cursor: Cursor<'c>,
// This field is contravariant in 'c. Together these make StepCursor
// invariant in 'c. Also covariant in 'a. The user cannot cast 'c to a
// different lifetime but can upcast into a StepCursor with a shorter
// lifetime 'a.
//
// As long as we only ever construct a StepCursor for which 'c outlives 'a,
// this means if ever a StepCursor<'c, 'a> exists we are guaranteed that 'c
// outlives 'a.
marker: PhantomData<fn(Cursor<'c>) -> Cursor<'a>>,
}
impl<'c, 'a> Deref for StepCursor<'c, 'a> {
type Target = Cursor<'c>;
fn deref(&self) -> &Self::Target {
&self.cursor
}
}
impl<'c, 'a> Copy for StepCursor<'c, 'a> {}
impl<'c, 'a> Clone for StepCursor<'c, 'a> {
fn clone(&self) -> Self {
*self
}
}
impl<'c, 'a> StepCursor<'c, 'a> {
/// Triggers an error at the current position of the parse stream.
///
/// The `ParseStream::step` invocation will return this same error without
/// advancing the stream state.
pub fn error<T: Display>(self, message: T) -> Error {
error::new_at(self.scope, self.cursor, message)
}
}
pub(crate) fn advance_step_cursor<'c, 'a>(proof: StepCursor<'c, 'a>, to: Cursor<'c>) -> Cursor<'a> {
// Refer to the comments within the StepCursor definition. We use the
// fact that a StepCursor<'c, 'a> exists as proof that 'c outlives 'a.
// Cursor is covariant in its lifetime parameter so we can cast a
// Cursor<'c> to one with the shorter lifetime Cursor<'a>.
let _ = proof;
unsafe { mem::transmute::<Cursor<'c>, Cursor<'a>>(to) }
}
pub(crate) fn new_parse_buffer(
scope: Span,
cursor: Cursor,
unexpected: Rc<Cell<Unexpected>>,
) -> ParseBuffer {
ParseBuffer {
scope,
// See comment on `cell` in the struct definition.
cell: Cell::new(unsafe { mem::transmute::<Cursor, Cursor<'static>>(cursor) }),
marker: PhantomData,
unexpected: Cell::new(Some(unexpected)),
}
}
pub(crate) enum Unexpected {
None,
Some(Span),
Chain(Rc<Cell<Unexpected>>),
}
impl Default for Unexpected {
fn default() -> Self {
Unexpected::None
}
}
impl Clone for Unexpected {
fn clone(&self) -> Self {
match self {
Unexpected::None => Unexpected::None,
Unexpected::Some(span) => Unexpected::Some(*span),
Unexpected::Chain(next) => Unexpected::Chain(next.clone()),
}
}
}
// We call this on Cell<Unexpected> and Cell<Option<T>> where temporarily
// swapping in a None is cheap.
fn cell_clone<T: Default + Clone>(cell: &Cell<T>) -> T {
let prev = cell.take();
let ret = prev.clone();
cell.set(prev);
ret
}
fn inner_unexpected(buffer: &ParseBuffer) -> (Rc<Cell<Unexpected>>, Option<Span>) {
let mut unexpected = get_unexpected(buffer);
loop {
match cell_clone(&unexpected) {
Unexpected::None => return (unexpected, None),
Unexpected::Some(span) => return (unexpected, Some(span)),
Unexpected::Chain(next) => unexpected = next,
}
}
}
pub(crate) fn get_unexpected(buffer: &ParseBuffer) -> Rc<Cell<Unexpected>> {
cell_clone(&buffer.unexpected).unwrap()
}
fn span_of_unexpected_ignoring_nones(mut cursor: Cursor) -> Option<Span> {
if cursor.eof() {
return None;
}
while let Some((inner, _span, rest)) = cursor.group(Delimiter::None) {
if let Some(unexpected) = span_of_unexpected_ignoring_nones(inner) {
return Some(unexpected);
}
cursor = rest;
}
if cursor.eof() {
None
} else {
Some(cursor.span())
}
}
impl<'a> ParseBuffer<'a> {
/// Parses a syntax tree node of type `T`, advancing the position of our
/// parse stream past it.
pub fn parse<T: Parse>(&self) -> Result<T> {
T::parse(self)
}
/// Calls the given parser function to parse a syntax tree node of type `T`
/// from this stream.
///
/// # Example
///
/// The parser below invokes [`Attribute::parse_outer`] to parse a vector of
/// zero or more outer attributes.
///
/// [`Attribute::parse_outer`]: crate::Attribute::parse_outer
///
/// ```
/// use syn::{Attribute, Ident, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses a unit struct with attributes.
/// //
/// // #[path = "s.tmpl"]
/// // struct S;
/// struct UnitStruct {
/// attrs: Vec<Attribute>,
/// struct_token: Token![struct],
/// name: Ident,
/// semi_token: Token![;],
/// }
///
/// impl Parse for UnitStruct {
/// fn parse(input: ParseStream) -> Result<Self> {
/// Ok(UnitStruct {
/// attrs: input.call(Attribute::parse_outer)?,
/// struct_token: input.parse()?,
/// name: input.parse()?,
/// semi_token: input.parse()?,
/// })
/// }
/// }
/// ```
pub fn call<T>(&self, function: fn(ParseStream) -> Result<T>) -> Result<T> {
function(self)
}
/// Looks at the next token in the parse stream to determine whether it
/// matches the requested type of token.
///
/// Does not advance the position of the parse stream.
///
/// # Syntax
///
/// Note that this method does not use turbofish syntax. Pass the peek type
/// inside of parentheses.
///
/// - `input.peek(Token![struct])`
/// - `input.peek(Token![==])`
/// - `input.peek(Ident)` *(does not accept keywords)*
/// - `input.peek(Ident::peek_any)`
/// - `input.peek(Lifetime)`
/// - `input.peek(token::Brace)`
///
/// # Example
///
/// In this example we finish parsing the list of supertraits when the next
/// token in the input is either `where` or an opening curly brace.
///
/// ```
/// use syn::{braced, token, Generics, Ident, Result, Token, TypeParamBound};
/// use syn::parse::{Parse, ParseStream};
/// use syn::punctuated::Punctuated;
///
/// // Parses a trait definition containing no associated items.
/// //
/// // trait Marker<'de, T>: A + B<'de> where Box<T>: Clone {}
/// struct MarkerTrait {
/// trait_token: Token![trait],
/// ident: Ident,
/// generics: Generics,
/// colon_token: Option<Token![:]>,
/// supertraits: Punctuated<TypeParamBound, Token![+]>,
/// brace_token: token::Brace,
/// }
///
/// impl Parse for MarkerTrait {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let trait_token: Token![trait] = input.parse()?;
/// let ident: Ident = input.parse()?;
/// let mut generics: Generics = input.parse()?;
/// let colon_token: Option<Token![:]> = input.parse()?;
///
/// let mut supertraits = Punctuated::new();
/// if colon_token.is_some() {
/// loop {
/// supertraits.push_value(input.parse()?);
/// if input.peek(Token![where]) || input.peek(token::Brace) {
/// break;
/// }
/// supertraits.push_punct(input.parse()?);
/// }
/// }
///
/// generics.where_clause = input.parse()?;
/// let content;
/// let empty_brace_token = braced!(content in input);
///
/// Ok(MarkerTrait {
/// trait_token,
/// ident,
/// generics,
/// colon_token,
/// supertraits,
/// brace_token: empty_brace_token,
/// })
/// }
/// }
/// ```
pub fn peek<T: Peek>(&self, token: T) -> bool {
let _ = token;
T::Token::peek(self.cursor())
}
/// Looks at the second-next token in the parse stream.
///
/// This is commonly useful as a way to implement contextual keywords.
///
/// # Example
///
/// This example needs to use `peek2` because the symbol `union` is not a
/// keyword in Rust. We can't use just `peek` and decide to parse a union if
/// the very next token is `union`, because someone is free to write a `mod
/// union` and a macro invocation that looks like `union::some_macro! { ...
/// }`. In other words `union` is a contextual keyword.
///
/// ```
/// use syn::{Ident, ItemUnion, Macro, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses either a union or a macro invocation.
/// enum UnionOrMacro {
/// // union MaybeUninit<T> { uninit: (), value: T }
/// Union(ItemUnion),
/// // lazy_static! { ... }
/// Macro(Macro),
/// }
///
/// impl Parse for UnionOrMacro {
/// fn parse(input: ParseStream) -> Result<Self> {
/// if input.peek(Token![union]) && input.peek2(Ident) {
/// input.parse().map(UnionOrMacro::Union)
/// } else {
/// input.parse().map(UnionOrMacro::Macro)
/// }
/// }
/// }
/// ```
pub fn peek2<T: Peek>(&self, token: T) -> bool {
fn peek2(buffer: &ParseBuffer, peek: fn(Cursor) -> bool) -> bool {
if let Some(group) = buffer.cursor().group(Delimiter::None) {
if group.0.skip().map_or(false, peek) {
return true;
}
}
buffer.cursor().skip().map_or(false, peek)
}
let _ = token;
peek2(self, T::Token::peek)
}
/// Looks at the third-next token in the parse stream.
pub fn peek3<T: Peek>(&self, token: T) -> bool {
fn peek3(buffer: &ParseBuffer, peek: fn(Cursor) -> bool) -> bool {
if let Some(group) = buffer.cursor().group(Delimiter::None) {
if group.0.skip().and_then(Cursor::skip).map_or(false, peek) {
return true;
}
}
buffer
.cursor()
.skip()
.and_then(Cursor::skip)
.map_or(false, peek)
}
let _ = token;
peek3(self, T::Token::peek)
}
/// Parses zero or more occurrences of `T` separated by punctuation of type
/// `P`, with optional trailing punctuation.
///
/// Parsing continues until the end of this parse stream. The entire content
/// of this parse stream must consist of `T` and `P`.
///
/// # Example
///
/// ```
/// # use quote::quote;
/// #
/// use syn::{parenthesized, token, Ident, Result, Token, Type};
/// use syn::parse::{Parse, ParseStream};
/// use syn::punctuated::Punctuated;
///
/// // Parse a simplified tuple struct syntax like:
/// //
/// // struct S(A, B);
/// struct TupleStruct {
/// struct_token: Token![struct],
/// ident: Ident,
/// paren_token: token::Paren,
/// fields: Punctuated<Type, Token![,]>,
/// semi_token: Token![;],
/// }
///
/// impl Parse for TupleStruct {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let content;
/// Ok(TupleStruct {
/// struct_token: input.parse()?,
/// ident: input.parse()?,
/// paren_token: parenthesized!(content in input),
/// fields: content.parse_terminated(Type::parse)?,
/// semi_token: input.parse()?,
/// })
/// }
/// }
/// #
/// # let input = quote! {
/// # struct S(A, B);
/// # };
/// # syn::parse2::<TupleStruct>(input).unwrap();
/// ```
pub fn parse_terminated<T, P: Parse>(
&self,
parser: fn(ParseStream) -> Result<T>,
) -> Result<Punctuated<T, P>> {
Punctuated::parse_terminated_with(self, parser)
}
/// Returns whether there are tokens remaining in this stream.
///
/// This method returns true at the end of the content of a set of
/// delimiters, as well as at the very end of the complete macro input.
///
/// # Example
///
/// ```
/// use syn::{braced, token, Ident, Item, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses a Rust `mod m { ... }` containing zero or more items.
/// struct Mod {
/// mod_token: Token![mod],
/// name: Ident,
/// brace_token: token::Brace,
/// items: Vec<Item>,
/// }
///
/// impl Parse for Mod {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let content;
/// Ok(Mod {
/// mod_token: input.parse()?,
/// name: input.parse()?,
/// brace_token: braced!(content in input),
/// items: {
/// let mut items = Vec::new();
/// while !content.is_empty() {
/// items.push(content.parse()?);
/// }
/// items
/// },
/// })
/// }
/// }
/// ```
pub fn is_empty(&self) -> bool {
self.cursor().eof()
}
/// Constructs a helper for peeking at the next token in this stream and
/// building an error message if it is not one of a set of expected tokens.
///
/// # Example
///
/// ```
/// use syn::{ConstParam, Ident, Lifetime, LifetimeDef, Result, Token, TypeParam};
/// use syn::parse::{Parse, ParseStream};
///
/// // A generic parameter, a single one of the comma-separated elements inside
/// // angle brackets in:
/// //
/// // fn f<T: Clone, 'a, 'b: 'a, const N: usize>() { ... }
/// //
/// // On invalid input, lookahead gives us a reasonable error message.
/// //
/// // error: expected one of: identifier, lifetime, `const`
/// // |
/// // 5 | fn f<!Sized>() {}
/// // | ^
/// enum GenericParam {
/// Type(TypeParam),
/// Lifetime(LifetimeDef),
/// Const(ConstParam),
/// }
///
/// impl Parse for GenericParam {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let lookahead = input.lookahead1();
/// if lookahead.peek(Ident) {
/// input.parse().map(GenericParam::Type)
/// } else if lookahead.peek(Lifetime) {
/// input.parse().map(GenericParam::Lifetime)
/// } else if lookahead.peek(Token![const]) {
/// input.parse().map(GenericParam::Const)
/// } else {
/// Err(lookahead.error())
/// }
/// }
/// }
/// ```
pub fn lookahead1(&self) -> Lookahead1<'a> {
lookahead::new(self.scope, self.cursor())
}
/// Forks a parse stream so that parsing tokens out of either the original
/// or the fork does not advance the position of the other.
///
/// # Performance
///
/// Forking a parse stream is a cheap fixed amount of work and does not
/// involve copying token buffers. Where you might hit performance problems
/// is if your macro ends up parsing a large amount of content more than
/// once.
///
/// ```
/// # use syn::{Expr, Result};
/// # use syn::parse::ParseStream;
/// #
/// # fn bad(input: ParseStream) -> Result<Expr> {
/// // Do not do this.
/// if input.fork().parse::<Expr>().is_ok() {
/// return input.parse::<Expr>();
/// }
/// # unimplemented!()
/// # }
/// ```
///
/// As a rule, avoid parsing an unbounded amount of tokens out of a forked
/// parse stream. Only use a fork when the amount of work performed against
/// the fork is small and bounded.
///
/// When complex speculative parsing against the forked stream is
/// unavoidable, use [`parse::discouraged::Speculative`] to advance the
/// original stream once the fork's parse is determined to have been
/// successful.
///
/// For a lower level way to perform speculative parsing at the token level,
/// consider using [`ParseStream::step`] instead.
///
/// [`parse::discouraged::Speculative`]: discouraged::Speculative
/// [`ParseStream::step`]: ParseBuffer::step
///
/// # Example
///
/// The parse implementation shown here parses possibly restricted `pub`
/// visibilities.
///
/// - `pub`
/// - `pub(crate)`
/// - `pub(self)`
/// - `pub(super)`
/// - `pub(in some::path)`
///
/// To handle the case of visibilities inside of tuple structs, the parser
/// needs to distinguish parentheses that specify visibility restrictions
/// from parentheses that form part of a tuple type.
///
/// ```
/// # struct A;
/// # struct B;
/// # struct C;
/// #
/// struct S(pub(crate) A, pub (B, C));
/// ```
///
/// In this example input the first tuple struct element of `S` has
/// `pub(crate)` visibility while the second tuple struct element has `pub`
/// visibility; the parentheses around `(B, C)` are part of the type rather
/// than part of a visibility restriction.
///
/// The parser uses a forked parse stream to check the first token inside of
/// parentheses after the `pub` keyword. This is a small bounded amount of
/// work performed against the forked parse stream.
///
/// ```
/// use syn::{parenthesized, token, Ident, Path, Result, Token};
/// use syn::ext::IdentExt;
/// use syn::parse::{Parse, ParseStream};
///
/// struct PubVisibility {
/// pub_token: Token![pub],
/// restricted: Option<Restricted>,
/// }
///
/// struct Restricted {
/// paren_token: token::Paren,
/// in_token: Option<Token![in]>,
/// path: Path,
/// }
///
/// impl Parse for PubVisibility {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let pub_token: Token![pub] = input.parse()?;
///
/// if input.peek(token::Paren) {
/// let ahead = input.fork();
/// let mut content;
/// parenthesized!(content in ahead);
///
/// if content.peek(Token![crate])
/// || content.peek(Token![self])
/// || content.peek(Token![super])
/// {
/// return Ok(PubVisibility {
/// pub_token,
/// restricted: Some(Restricted {
/// paren_token: parenthesized!(content in input),
/// in_token: None,
/// path: Path::from(content.call(Ident::parse_any)?),
/// }),
/// });
/// } else if content.peek(Token![in]) {
/// return Ok(PubVisibility {
/// pub_token,
/// restricted: Some(Restricted {
/// paren_token: parenthesized!(content in input),
/// in_token: Some(content.parse()?),
/// path: content.call(Path::parse_mod_style)?,
/// }),
/// });
/// }
/// }
///
/// Ok(PubVisibility {
/// pub_token,
/// restricted: None,
/// })
/// }
/// }
/// ```
pub fn fork(&self) -> Self {
ParseBuffer {
scope: self.scope,
cell: self.cell.clone(),
marker: PhantomData,
// Not the parent's unexpected. Nothing cares whether the clone
// parses all the way unless we `advance_to`.
unexpected: Cell::new(Some(Rc::new(Cell::new(Unexpected::None)))),
}
}
/// Triggers an error at the current position of the parse stream.
///
/// # Example
///
/// ```
/// use syn::{Expr, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Some kind of loop: `while` or `for` or `loop`.
/// struct Loop {
/// expr: Expr,
/// }
///
/// impl Parse for Loop {
/// fn parse(input: ParseStream) -> Result<Self> {
/// if input.peek(Token![while])
/// || input.peek(Token![for])
/// || input.peek(Token![loop])
/// {
/// Ok(Loop {
/// expr: input.parse()?,
/// })
/// } else {
/// Err(input.error("expected some kind of loop"))
/// }
/// }
/// }
/// ```
pub fn error<T: Display>(&self, message: T) -> Error {
error::new_at(self.scope, self.cursor(), message)
}
/// Speculatively parses tokens from this parse stream, advancing the
/// position of this stream only if parsing succeeds.
///
/// This is a powerful low-level API used for defining the `Parse` impls of
/// the basic built-in token types. It is not something that will be used
/// widely outside of the Syn codebase.
///
/// # Example
///
/// ```
/// use proc_macro2::TokenTree;
/// use syn::Result;
/// use syn::parse::ParseStream;
///
/// // This function advances the stream past the next occurrence of `@`. If
/// // no `@` is present in the stream, the stream position is unchanged and
/// // an error is returned.
/// fn skip_past_next_at(input: ParseStream) -> Result<()> {
/// input.step(|cursor| {
/// let mut rest = *cursor;
/// while let Some((tt, next)) = rest.token_tree() {
/// match &tt {
/// TokenTree::Punct(punct) if punct.as_char() == '@' => {
/// return Ok(((), next));
/// }
/// _ => rest = next,
/// }
/// }
/// Err(cursor.error("no `@` was found after this point"))
/// })
/// }
/// #
/// # fn remainder_after_skipping_past_next_at(
/// # input: ParseStream,
/// # ) -> Result<proc_macro2::TokenStream> {
/// # skip_past_next_at(input)?;
/// # input.parse()
/// # }
/// #
/// # use syn::parse::Parser;
/// # let remainder = remainder_after_skipping_past_next_at
/// # .parse_str("a @ b c")
/// # .unwrap();
/// # assert_eq!(remainder.to_string(), "b c");
/// ```
pub fn step<F, R>(&self, function: F) -> Result<R>
where
F: for<'c> FnOnce(StepCursor<'c, 'a>) -> Result<(R, Cursor<'c>)>,
{
// Since the user's function is required to work for any 'c, we know
// that the Cursor<'c> they return is either derived from the input
// StepCursor<'c, 'a> or from a Cursor<'static>.
//
// It would not be legal to write this function without the invariant
// lifetime 'c in StepCursor<'c, 'a>. If this function were written only
// in terms of 'a, the user could take our ParseBuffer<'a>, upcast it to
// a ParseBuffer<'short> which some shorter lifetime than 'a, invoke
// `step` on their ParseBuffer<'short> with a closure that returns
// Cursor<'short>, and we would wrongly write that Cursor<'short> into
// the Cell intended to hold Cursor<'a>.
//
// In some cases it may be necessary for R to contain a Cursor<'a>.
// Within Syn we solve this using `advance_step_cursor` which uses the
// existence of a StepCursor<'c, 'a> as proof that it is safe to cast
// from Cursor<'c> to Cursor<'a>. If needed outside of Syn, it would be
// safe to expose that API as a method on StepCursor.
let (node, rest) = function(StepCursor {
scope: self.scope,
cursor: self.cell.get(),
marker: PhantomData,
})?;
self.cell.set(rest);
Ok(node)
}
/// Returns the `Span` of the next token in the parse stream, or
/// `Span::call_site()` if this parse stream has completely exhausted its
/// input `TokenStream`.
pub fn span(&self) -> Span {
let cursor = self.cursor();
if cursor.eof() {
self.scope
} else {
crate::buffer::open_span_of_group(cursor)
}
}
/// Provides low-level access to the token representation underlying this
/// parse stream.
///
/// Cursors are immutable so no operations you perform against the cursor
/// will affect the state of this parse stream.
pub fn cursor(&self) -> Cursor<'a> {
self.cell.get()
}
fn check_unexpected(&self) -> Result<()> {
match inner_unexpected(self).1 {
Some(span) => Err(Error::new(span, "unexpected token")),
None => Ok(()),
}
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl<T: Parse> Parse for Box<T> {
fn parse(input: ParseStream) -> Result<Self> {
input.parse().map(Box::new)
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl<T: Parse + Token> Parse for Option<T> {
fn parse(input: ParseStream) -> Result<Self> {
if T::peek(input.cursor()) {
Ok(Some(input.parse()?))
} else {
Ok(None)
}
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl Parse for TokenStream {
fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| Ok((cursor.token_stream(), Cursor::empty())))
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl Parse for TokenTree {
fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| match cursor.token_tree() {
Some((tt, rest)) => Ok((tt, rest)),
None => Err(cursor.error("expected token tree")),
})
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl Parse for Group {
fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
for delim in &[Delimiter::Parenthesis, Delimiter::Brace, Delimiter::Bracket] {
if let Some((inside, span, rest)) = cursor.group(*delim) {
let mut group = Group::new(*delim, inside.token_stream());
group.set_span(span);
return Ok((group, rest));
}
}
Err(cursor.error("expected group token"))
})
}sourcepub fn token_tree(self) -> Option<(TokenTree, Cursor<'a>)>
pub fn token_tree(self) -> Option<(TokenTree, Cursor<'a>)>
If the cursor is pointing at a TokenTree, returns it along with a
cursor pointing at the next TokenTree.
Returns None if the cursor has reached the end of its stream.
This method does not treat None-delimited groups as transparent, and
will return a Group(None, ..) if the cursor is looking at one.
Examples found in repository?
More examples
src/mac.rs (line 155)
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pub fn parse_delimiter(input: ParseStream) -> Result<(MacroDelimiter, TokenStream)> {
input.step(|cursor| {
if let Some((TokenTree::Group(g), rest)) = cursor.token_tree() {
let span = g.span();
let delimiter = match g.delimiter() {
Delimiter::Parenthesis => MacroDelimiter::Paren(Paren(span)),
Delimiter::Brace => MacroDelimiter::Brace(Brace(span)),
Delimiter::Bracket => MacroDelimiter::Bracket(Bracket(span)),
Delimiter::None => {
return Err(cursor.error("expected delimiter"));
}
};
Ok(((delimiter, g.stream()), rest))
} else {
Err(cursor.error("expected delimiter"))
}
})
}src/verbatim.rs (line 13)
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
pub fn between<'a>(begin: ParseBuffer<'a>, end: ParseStream<'a>) -> TokenStream {
let end = end.cursor();
let mut cursor = begin.cursor();
assert!(crate::buffer::same_buffer(end, cursor));
let mut tokens = TokenStream::new();
while cursor != end {
let (tt, next) = cursor.token_tree().unwrap();
if crate::buffer::cmp_assuming_same_buffer(end, next) == Ordering::Less {
// A syntax node can cross the boundary of a None-delimited group
// due to such groups being transparent to the parser in most cases.
// Any time this occurs the group is known to be semantically
// irrelevant. https://github.com/dtolnay/syn/issues/1235
if let Some((inside, _span, after)) = cursor.group(Delimiter::None) {
assert!(next == after);
cursor = inside;
continue;
} else {
panic!("verbatim end must not be inside a delimited group");
}
}
tokens.extend(iter::once(tt));
cursor = next;
}
tokens
}sourcepub fn span(self) -> Span
pub fn span(self) -> Span
Returns the Span of the current token, or Span::call_site() if this
cursor points to eof.
Examples found in repository?
src/buffer.rs (line 389)
386 387 388 389 390 391 392 393 394 395 396 397 398
pub(crate) fn open_span_of_group(cursor: Cursor) -> Span {
match cursor.entry() {
Entry::Group(group, _) => group.span_open(),
_ => cursor.span(),
}
}
pub(crate) fn close_span_of_group(cursor: Cursor) -> Span {
match cursor.entry() {
Entry::Group(group, _) => group.span_close(),
_ => cursor.span(),
}
}More examples
src/parse.rs (line 460)
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fn span_of_unexpected_ignoring_nones(mut cursor: Cursor) -> Option<Span> {
if cursor.eof() {
return None;
}
while let Some((inner, _span, rest)) = cursor.group(Delimiter::None) {
if let Some(unexpected) = span_of_unexpected_ignoring_nones(inner) {
return Some(unexpected);
}
cursor = rest;
}
if cursor.eof() {
None
} else {
Some(cursor.span())
}
}src/lookahead.rs (line 119)
112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136
pub fn error(self) -> Error {
let comparisons = self.comparisons.borrow();
match comparisons.len() {
0 => {
if self.cursor.eof() {
Error::new(self.scope, "unexpected end of input")
} else {
Error::new(self.cursor.span(), "unexpected token")
}
}
1 => {
let message = format!("expected {}", comparisons[0]);
error::new_at(self.scope, self.cursor, message)
}
2 => {
let message = format!("expected {} or {}", comparisons[0], comparisons[1]);
error::new_at(self.scope, self.cursor, message)
}
_ => {
let join = comparisons.join(", ");
let message = format!("expected one of: {}", join);
error::new_at(self.scope, self.cursor, message)
}
}
}Trait Implementations§
source§impl<'a> PartialOrd<Cursor<'a>> for Cursor<'a>
impl<'a> PartialOrd<Cursor<'a>> for Cursor<'a>
1.0.0 · source§fn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
This method tests less than or equal to (for
self and other) and is used by the <=
operator. Read more