Struct syn::Macro

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pub struct Macro {
    pub path: Path,
    pub bang_token: Not,
    pub delimiter: MacroDelimiter,
    pub tokens: TokenStream,
}
Expand description

A macro invocation: println!("{}", mac).

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§path: Path§bang_token: Not§delimiter: MacroDelimiter§tokens: TokenStream

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impl Macro

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pub fn parse_body<T: Parse>(&self) -> Result<T>

Parse the tokens within the macro invocation’s delimiters into a syntax tree.

This is equivalent to syn::parse2::<T>(mac.tokens) except that it produces a more useful span when tokens is empty.

Example
use syn::{parse_quote, Expr, ExprLit, Ident, Lit, LitStr, Macro, Token};
use syn::ext::IdentExt;
use syn::parse::{Error, Parse, ParseStream, Result};
use syn::punctuated::Punctuated;

// The arguments expected by libcore's format_args macro, and as a
// result most other formatting and printing macros like println.
//
//     println!("{} is {number:.prec$}", "x", prec=5, number=0.01)
struct FormatArgs {
    format_string: Expr,
    positional_args: Vec<Expr>,
    named_args: Vec<(Ident, Expr)>,
}

impl Parse for FormatArgs {
    fn parse(input: ParseStream) -> Result<Self> {
        let format_string: Expr;
        let mut positional_args = Vec::new();
        let mut named_args = Vec::new();

        format_string = input.parse()?;
        while !input.is_empty() {
            input.parse::<Token![,]>()?;
            if input.is_empty() {
                break;
            }
            if input.peek(Ident::peek_any) && input.peek2(Token![=]) {
                while !input.is_empty() {
                    let name: Ident = input.call(Ident::parse_any)?;
                    input.parse::<Token![=]>()?;
                    let value: Expr = input.parse()?;
                    named_args.push((name, value));
                    if input.is_empty() {
                        break;
                    }
                    input.parse::<Token![,]>()?;
                }
                break;
            }
            positional_args.push(input.parse()?);
        }

        Ok(FormatArgs {
            format_string,
            positional_args,
            named_args,
        })
    }
}

// Extract the first argument, the format string literal, from an
// invocation of a formatting or printing macro.
fn get_format_string(m: &Macro) -> Result<LitStr> {
    let args: FormatArgs = m.parse_body()?;
    match args.format_string {
        Expr::Lit(ExprLit { lit: Lit::Str(lit), .. }) => Ok(lit),
        other => {
            // First argument was not a string literal expression.
            // Maybe something like: println!(concat!(...), ...)
            Err(Error::new_spanned(other, "format string must be a string literal"))
        }
    }
}

fn main() {
    let invocation = parse_quote! {
        println!("{:?}", Instant::now())
    };
    let lit = get_format_string(&invocation).unwrap();
    assert_eq!(lit.value(), "{:?}");
}
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pub fn parse_body_with<F: Parser>(&self, parser: F) -> Result<F::Output>

Parse the tokens within the macro invocation’s delimiters using the given parser.

Trait Implementations§

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impl Clone for Macro

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fn clone(&self) -> Self

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for Macro

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fn fmt(&self, formatter: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl Hash for Macro

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fn hash<H>(&self, state: &mut H)
where H: Hasher,

Feeds this value into the given Hasher. Read more
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fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl Parse for Macro

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fn parse(input: ParseStream<'_>) -> Result<Self>

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impl PartialEq for Macro

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fn eq(&self, other: &Self) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl ToTokens for Macro

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fn to_tokens(&self, tokens: &mut TokenStream)

Write self to the given TokenStream. Read more
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fn to_token_stream(&self) -> TokenStream

Convert self directly into a TokenStream object. Read more
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fn into_token_stream(self) -> TokenStream
where Self: Sized,

Convert self directly into a TokenStream object. Read more
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impl Eq for Macro

Auto Trait Implementations§

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impl RefUnwindSafe for Macro

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impl !Send for Macro

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impl !Sync for Macro

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impl Unpin for Macro

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impl UnwindSafe for Macro

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> Spanned for T
where T: Spanned + ?Sized,

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fn span(&self) -> Span

Returns a Span covering the complete contents of this syntax tree node, or Span::call_site() if this node is empty.
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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.