vendor/syn/src/stmt.rs

   1 use super::*;
   2
   3 ast_struct! {
   4     /// A braced block containing Rust statements.
   5     ///
   6     /// *This type is available only if Syn is built with the `"full"` feature.*
   7     #[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
   8     pub struct Block {
   9         pub brace_token: token::Brace,
  10         /// Statements in a block
  11         pub stmts: Vec<Stmt>,
  12     }
  13 }
  14
  15 ast_enum! {
  16     /// A statement, usually ending in a semicolon.
  17     ///
  18     /// *This type is available only if Syn is built with the `"full"` feature.*
  19     #[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
  20     pub enum Stmt {
  21         /// A local (let) binding.
  22         Local(Local),
  23
  24         /// An item definition.
  25         Item(Item),
  26
  27         /// Expr without trailing semicolon.
  28         Expr(Expr),
  29
  30         /// Expression with trailing semicolon.
  31         Semi(Expr, Token![;]),
  32     }
  33 }
  34
  35 ast_struct! {
  36     /// A local `let` binding: `let x: u64 = s.parse()?`.
  37     ///
  38     /// *This type is available only if Syn is built with the `"full"` feature.*
  39     #[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
  40     pub struct Local {
  41         pub attrs: Vec<Attribute>,
  42         pub let_token: Token![let],
  43         pub pat: Pat,
  44         pub init: Option<(Token![=], Box<Expr>)>,
  45         pub semi_token: Token![;],
  46     }
  47 }
  48
  49 #[cfg(feature = "parsing")]
  50 pub mod parsing {
  51     use super::*;
  52     use crate::parse::discouraged::Speculative;
  53     use crate::parse::{Parse, ParseStream, Result};
  54     use proc_macro2::TokenStream;
  55
  56     impl Block {
  57         /// Parse the body of a block as zero or more statements, possibly
  58         /// including one trailing expression.
  59         ///
  60         /// *This function is available only if Syn is built with the `"parsing"`
  61         /// feature.*
  62         ///
  63         /// # Example
  64         ///
  65         /// ```
  66         /// use syn::{braced, token, Attribute, Block, Ident, Result, Stmt, Token};
  67         /// use syn::parse::{Parse, ParseStream};
  68         ///
  69         /// // Parse a function with no generics or parameter list.
  70         /// //
  71         /// //     fn playground {
  72         /// //         let mut x = 1;
  73         /// //         x += 1;
  74         /// //         println!("{}", x);
  75         /// //     }
  76         /// struct MiniFunction {
  77         ///     attrs: Vec<Attribute>,
  78         ///     fn_token: Token![fn],
  79         ///     name: Ident,
  80         ///     brace_token: token::Brace,
  81         ///     stmts: Vec<Stmt>,
  82         /// }
  83         ///
  84         /// impl Parse for MiniFunction {
  85         ///     fn parse(input: ParseStream) -> Result<Self> {
  86         ///         let outer_attrs = input.call(Attribute::parse_outer)?;
  87         ///         let fn_token: Token![fn] = input.parse()?;
  88         ///         let name: Ident = input.parse()?;
  89         ///
  90         ///         let content;
  91         ///         let brace_token = braced!(content in input);
  92         ///         let inner_attrs = content.call(Attribute::parse_inner)?;
  93         ///         let stmts = content.call(Block::parse_within)?;
  94         ///
  95         ///         Ok(MiniFunction {
  96         ///             attrs: {
  97         ///                 let mut attrs = outer_attrs;
  98         ///                 attrs.extend(inner_attrs);
  99         ///                 attrs
 100         ///             },
 101         ///             fn_token,
 102         ///             name,
 103         ///             brace_token,
 104         ///             stmts,
 105         ///         })
 106         ///     }
 107         /// }
 108         /// ```
 109         #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
 110         pub fn parse_within(input: ParseStream) -> Result<Vec<Stmt>> {
 111             let mut stmts = Vec::new();
 112             loop {
 113                 while let Some(semi) = input.parse::<Option<Token![;]>>()? {
 114                     stmts.push(Stmt::Semi(Expr::Verbatim(TokenStream::new()), semi));
 115                 }
 116                 if input.is_empty() {
 117                     break;
 118                 }
 119                 let s = parse_stmt(input, true)?;
 120                 let requires_semicolon = if let Stmt::Expr(s) = &s {
 121                     expr::requires_terminator(s)
 122                 } else {
 123                     false
 124                 };
 125                 stmts.push(s);
 126                 if input.is_empty() {
 127                     break;
 128                 } else if requires_semicolon {
 129                     return Err(input.error("unexpected token"));
 130                 }
 131             }
 132             Ok(stmts)
 133         }
 134     }
 135
 136     #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
 137     impl Parse for Block {
 138         fn parse(input: ParseStream) -> Result<Self> {
 139             let content;
 140             Ok(Block {
 141                 brace_token: braced!(content in input),
 142                 stmts: content.call(Block::parse_within)?,
 143             })
 144         }
 145     }
 146
 147     #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
 148     impl Parse for Stmt {
 149         fn parse(input: ParseStream) -> Result<Self> {
 150             parse_stmt(input, false)
 151         }
 152     }
 153
 154     fn parse_stmt(input: ParseStream, allow_nosemi: bool) -> Result<Stmt> {
 155         let mut attrs = input.call(Attribute::parse_outer)?;
 156
 157         // brace-style macros; paren and bracket macros get parsed as
 158         // expression statements.
 159         let ahead = input.fork();
 160         if let Ok(path) = ahead.call(Path::parse_mod_style) {
 161             if ahead.peek(Token![!]) && (ahead.peek2(token::Brace) || ahead.peek2(Ident)) {
 162                 input.advance_to(&ahead);
 163                 return stmt_mac(input, attrs, path);
 164             }
 165         }
 166
 167         if input.peek(Token![let]) {
 168             stmt_local(input, attrs).map(Stmt::Local)
 169         } else if input.peek(Token![pub])
 170             || input.peek(Token![crate]) && !input.peek2(Token![::])
 171             || input.peek(Token![extern])
 172             || input.peek(Token![use])
 173             || input.peek(Token![static]) && (input.peek2(Token![mut]) || input.peek2(Ident))
 174             || input.peek(Token![const]) && !input.peek2(token::Brace)
 175             || input.peek(Token![unsafe]) && !input.peek2(token::Brace)
 176             || input.peek(Token![async])
 177                 && (input.peek2(Token![unsafe])
 178                     || input.peek2(Token![extern])
 179                     || input.peek2(Token![fn]))
 180             || input.peek(Token![fn])
 181             || input.peek(Token![mod])
 182             || input.peek(Token![type])
 183             || input.peek(item::parsing::existential) && input.peek2(Token![type])
 184             || input.peek(Token![struct])
 185             || input.peek(Token![enum])
 186             || input.peek(Token![union]) && input.peek2(Ident)
 187             || input.peek(Token![auto]) && input.peek2(Token![trait])
 188             || input.peek(Token![trait])
 189             || input.peek(Token![default])
 190                 && (input.peek2(Token![unsafe]) || input.peek2(Token![impl]))
 191             || input.peek(Token![impl])
 192             || input.peek(Token![macro])
 193         {
 194             let mut item: Item = input.parse()?;
 195             attrs.extend(item.replace_attrs(Vec::new()));
 196             item.replace_attrs(attrs);
 197             Ok(Stmt::Item(item))
 198         } else {
 199             stmt_expr(input, allow_nosemi, attrs)
 200         }
 201     }
 202
 203     fn stmt_mac(input: ParseStream, attrs: Vec<Attribute>, path: Path) -> Result<Stmt> {
 204         let bang_token: Token![!] = input.parse()?;
 205         let ident: Option<Ident> = input.parse()?;
 206         let (delimiter, tokens) = mac::parse_delimiter(input)?;
 207         let semi_token: Option<Token![;]> = input.parse()?;
 208
 209         Ok(Stmt::Item(Item::Macro(ItemMacro {
 210             attrs,
 211             ident,
 212             mac: Macro {
 213                 path,
 214                 bang_token,
 215                 delimiter,
 216                 tokens,
 217             },
 218             semi_token,
 219         })))
 220     }
 221
 222     fn stmt_local(input: ParseStream, attrs: Vec<Attribute>) -> Result<Local> {
 223         Ok(Local {
 224             attrs,
 225             let_token: input.parse()?,
 226             pat: {
 227                 let mut pat: Pat = pat::parsing::multi_pat_with_leading_vert(input)?;
 228                 if input.peek(Token![:]) {
 229                     let colon_token: Token![:] = input.parse()?;
 230                     let ty: Type = input.parse()?;
 231                     pat = Pat::Type(PatType {
 232                         attrs: Vec::new(),
 233                         pat: Box::new(pat),
 234                         colon_token,
 235                         ty: Box::new(ty),
 236                     });
 237                 }
 238                 pat
 239             },
 240             init: {
 241                 if input.peek(Token![=]) {
 242                     let eq_token: Token![=] = input.parse()?;
 243                     let init: Expr = input.parse()?;
 244                     Some((eq_token, Box::new(init)))
 245                 } else {
 246                     None
 247                 }
 248             },
 249             semi_token: input.parse()?,
 250         })
 251     }
 252
 253     fn stmt_expr(
 254         input: ParseStream,
 255         allow_nosemi: bool,
 256         mut attrs: Vec<Attribute>,
 257     ) -> Result<Stmt> {
 258         let mut e = expr::parsing::expr_early(input)?;
 259
 260         let mut attr_target = &mut e;
 261         while let Expr::Binary(e) = attr_target {
 262             attr_target = &mut e.left;
 263         }
 264         attrs.extend(attr_target.replace_attrs(Vec::new()));
 265         attr_target.replace_attrs(attrs);
 266
 267         if input.peek(Token![;]) {
 268             return Ok(Stmt::Semi(e, input.parse()?));
 269         }
 270
 271         if allow_nosemi || !expr::requires_terminator(&e) {
 272             Ok(Stmt::Expr(e))
 273         } else {
 274             Err(input.error("expected semicolon"))
 275         }
 276     }
 277 }
 278
 279 #[cfg(feature = "printing")]
 280 mod printing {
 281     use super::*;
 282     use proc_macro2::TokenStream;
 283     use quote::{ToTokens, TokenStreamExt};
 284
 285     #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
 286     impl ToTokens for Block {
 287         fn to_tokens(&self, tokens: &mut TokenStream) {
 288             self.brace_token.surround(tokens, |tokens| {
 289                 tokens.append_all(&self.stmts);
 290             });
 291         }
 292     }
 293
 294     #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
 295     impl ToTokens for Stmt {
 296         fn to_tokens(&self, tokens: &mut TokenStream) {
 297             match self {
 298                 Stmt::Local(local) => local.to_tokens(tokens),
 299                 Stmt::Item(item) => item.to_tokens(tokens),
 300                 Stmt::Expr(expr) => expr.to_tokens(tokens),
 301                 Stmt::Semi(expr, semi) => {
 302                     expr.to_tokens(tokens);
 303                     semi.to_tokens(tokens);
 304                 }
 305             }
 306         }
 307     }
 308
 309     #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
 310     impl ToTokens for Local {
 311         fn to_tokens(&self, tokens: &mut TokenStream) {
 312             expr::printing::outer_attrs_to_tokens(&self.attrs, tokens);
 313             self.let_token.to_tokens(tokens);
 314             self.pat.to_tokens(tokens);
 315             if let Some((eq_token, init)) = &self.init {
 316                 eq_token.to_tokens(tokens);
 317                 init.to_tokens(tokens);
 318             }
 319             self.semi_token.to_tokens(tokens);
 320         }
 321     }
 322 }