syn/stmt.rs
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use super::*;
ast_struct! {
/// A braced block containing Rust statements.
///
/// *This type is available only if Syn is built with the `"full"` feature.*
#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
pub struct Block {
pub brace_token: token::Brace,
/// Statements in a block
pub stmts: Vec<Stmt>,
}
}
ast_enum! {
/// A statement, usually ending in a semicolon.
///
/// *This type is available only if Syn is built with the `"full"` feature.*
#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
pub enum Stmt {
/// A local (let) binding.
Local(Local),
/// An item definition.
Item(Item),
/// Expr without trailing semicolon.
Expr(Expr),
/// Expression with trailing semicolon.
Semi(Expr, Token![;]),
}
}
ast_struct! {
/// A local `let` binding: `let x: u64 = s.parse()?`.
///
/// *This type is available only if Syn is built with the `"full"` feature.*
#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
pub struct Local {
pub attrs: Vec<Attribute>,
pub let_token: Token![let],
pub pat: Pat,
pub init: Option<(Token![=], Box<Expr>)>,
pub semi_token: Token![;],
}
}
#[cfg(feature = "parsing")]
pub mod parsing {
use super::*;
use crate::parse::discouraged::Speculative;
use crate::parse::{Parse, ParseBuffer, ParseStream, Result};
use proc_macro2::TokenStream;
impl Block {
/// Parse the body of a block as zero or more statements, possibly
/// including one trailing expression.
///
/// *This function is available only if Syn is built with the `"parsing"`
/// feature.*
///
/// # Example
///
/// ```
/// use syn::{braced, token, Attribute, Block, Ident, Result, Stmt, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parse a function with no generics or parameter list.
/// //
/// // fn playground {
/// // let mut x = 1;
/// // x += 1;
/// // println!("{}", x);
/// // }
/// struct MiniFunction {
/// attrs: Vec<Attribute>,
/// fn_token: Token![fn],
/// name: Ident,
/// brace_token: token::Brace,
/// stmts: Vec<Stmt>,
/// }
///
/// impl Parse for MiniFunction {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let outer_attrs = input.call(Attribute::parse_outer)?;
/// let fn_token: Token![fn] = input.parse()?;
/// let name: Ident = input.parse()?;
///
/// let content;
/// let brace_token = braced!(content in input);
/// let inner_attrs = content.call(Attribute::parse_inner)?;
/// let stmts = content.call(Block::parse_within)?;
///
/// Ok(MiniFunction {
/// attrs: {
/// let mut attrs = outer_attrs;
/// attrs.extend(inner_attrs);
/// attrs
/// },
/// fn_token,
/// name,
/// brace_token,
/// stmts,
/// })
/// }
/// }
/// ```
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
pub fn parse_within(input: ParseStream) -> Result<Vec<Stmt>> {
let mut stmts = Vec::new();
loop {
while let Some(semi) = input.parse::<Option<Token![;]>>()? {
stmts.push(Stmt::Semi(Expr::Verbatim(TokenStream::new()), semi));
}
if input.is_empty() {
break;
}
let s = parse_stmt(input, true)?;
let requires_semicolon = if let Stmt::Expr(s) = &s {
expr::requires_terminator(s)
} else {
false
};
stmts.push(s);
if input.is_empty() {
break;
} else if requires_semicolon {
return Err(input.error("unexpected token"));
}
}
Ok(stmts)
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl Parse for Block {
fn parse(input: ParseStream) -> Result<Self> {
let content;
Ok(Block {
brace_token: braced!(content in input),
stmts: content.call(Block::parse_within)?,
})
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
impl Parse for Stmt {
fn parse(input: ParseStream) -> Result<Self> {
parse_stmt(input, false)
}
}
fn parse_stmt(input: ParseStream, allow_nosemi: bool) -> Result<Stmt> {
let begin = input.fork();
let mut attrs = input.call(Attribute::parse_outer)?;
// brace-style macros; paren and bracket macros get parsed as
// expression statements.
let ahead = input.fork();
if let Ok(path) = ahead.call(Path::parse_mod_style) {
if ahead.peek(Token![!])
&& (ahead.peek2(token::Brace)
&& !(ahead.peek3(Token![.]) || ahead.peek3(Token![?]))
|| ahead.peek2(Ident))
{
input.advance_to(&ahead);
return stmt_mac(input, attrs, path);
}
}
if input.peek(Token![let]) {
stmt_local(input, attrs, begin)
} else if input.peek(Token![pub])
|| input.peek(Token![crate]) && !input.peek2(Token![::])
|| input.peek(Token![extern])
|| input.peek(Token![use])
|| input.peek(Token![static])
&& (input.peek2(Token![mut])
|| input.peek2(Ident)
&& !(input.peek2(Token![async])
&& (input.peek3(Token![move]) || input.peek3(Token![|]))))
|| input.peek(Token![const]) && !input.peek2(token::Brace)
|| input.peek(Token![unsafe]) && !input.peek2(token::Brace)
|| input.peek(Token![async])
&& (input.peek2(Token![unsafe])
|| input.peek2(Token![extern])
|| input.peek2(Token![fn]))
|| input.peek(Token![fn])
|| input.peek(Token![mod])
|| input.peek(Token![type])
|| input.peek(Token![struct])
|| input.peek(Token![enum])
|| input.peek(Token![union]) && input.peek2(Ident)
|| input.peek(Token![auto]) && input.peek2(Token![trait])
|| input.peek(Token![trait])
|| input.peek(Token![default])
&& (input.peek2(Token![unsafe]) || input.peek2(Token![impl]))
|| input.peek(Token![impl])
|| input.peek(Token![macro])
{
let mut item: Item = input.parse()?;
attrs.extend(item.replace_attrs(Vec::new()));
item.replace_attrs(attrs);
Ok(Stmt::Item(item))
} else {
stmt_expr(input, allow_nosemi, attrs)
}
}
fn stmt_mac(input: ParseStream, attrs: Vec<Attribute>, path: Path) -> Result<Stmt> {
let bang_token: Token![!] = input.parse()?;
let ident: Option<Ident> = input.parse()?;
let (delimiter, tokens) = mac::parse_delimiter(input)?;
let semi_token: Option<Token![;]> = input.parse()?;
Ok(Stmt::Item(Item::Macro(ItemMacro {
attrs,
ident,
mac: Macro {
path,
bang_token,
delimiter,
tokens,
},
semi_token,
})))
}
fn stmt_local(input: ParseStream, attrs: Vec<Attribute>, begin: ParseBuffer) -> Result<Stmt> {
let let_token: Token![let] = input.parse()?;
let mut pat: Pat = pat::parsing::multi_pat_with_leading_vert(input)?;
if input.peek(Token![:]) {
let colon_token: Token![:] = input.parse()?;
let ty: Type = input.parse()?;
pat = Pat::Type(PatType {
attrs: Vec::new(),
pat: Box::new(pat),
colon_token,
ty: Box::new(ty),
});
}
let init = if input.peek(Token![=]) {
let eq_token: Token![=] = input.parse()?;
let init: Expr = input.parse()?;
if input.peek(Token![else]) {
input.parse::<Token![else]>()?;
let content;
braced!(content in input);
content.call(Block::parse_within)?;
let verbatim = Expr::Verbatim(verbatim::between(begin, input));
let semi_token: Token![;] = input.parse()?;
return Ok(Stmt::Semi(verbatim, semi_token));
}
Some((eq_token, Box::new(init)))
} else {
None
};
let semi_token: Token![;] = input.parse()?;
Ok(Stmt::Local(Local {
attrs,
let_token,
pat,
init,
semi_token,
}))
}
fn stmt_expr(
input: ParseStream,
allow_nosemi: bool,
mut attrs: Vec<Attribute>,
) -> Result<Stmt> {
let mut e = expr::parsing::expr_early(input)?;
let mut attr_target = &mut e;
loop {
attr_target = match attr_target {
Expr::Assign(e) => &mut e.left,
Expr::AssignOp(e) => &mut e.left,
Expr::Binary(e) => &mut e.left,
_ => break,
};
}
attrs.extend(attr_target.replace_attrs(Vec::new()));
attr_target.replace_attrs(attrs);
if input.peek(Token![;]) {
return Ok(Stmt::Semi(e, input.parse()?));
}
if allow_nosemi || !expr::requires_terminator(&e) {
Ok(Stmt::Expr(e))
} else {
Err(input.error("expected semicolon"))
}
}
}
#[cfg(feature = "printing")]
mod printing {
use super::*;
use proc_macro2::TokenStream;
use quote::{ToTokens, TokenStreamExt};
#[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
impl ToTokens for Block {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.brace_token.surround(tokens, |tokens| {
tokens.append_all(&self.stmts);
});
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
impl ToTokens for Stmt {
fn to_tokens(&self, tokens: &mut TokenStream) {
match self {
Stmt::Local(local) => local.to_tokens(tokens),
Stmt::Item(item) => item.to_tokens(tokens),
Stmt::Expr(expr) => expr.to_tokens(tokens),
Stmt::Semi(expr, semi) => {
expr.to_tokens(tokens);
semi.to_tokens(tokens);
}
}
}
}
#[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
impl ToTokens for Local {
fn to_tokens(&self, tokens: &mut TokenStream) {
expr::printing::outer_attrs_to_tokens(&self.attrs, tokens);
self.let_token.to_tokens(tokens);
self.pat.to_tokens(tokens);
if let Some((eq_token, init)) = &self.init {
eq_token.to_tokens(tokens);
init.to_tokens(tokens);
}
self.semi_token.to_tokens(tokens);
}
}
}