| 1 | // SPDX-License-Identifier: MIT or Apache-2.0 or GPL-2.0-or-later |
| 2 | |
| 3 | // shadowing is useful together with "if let" |
| 4 | #![allow(clippy::shadow_unrelated)] |
| 5 | |
| 6 | use proc_macro2::{ |
| 7 | Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree, TokenTree as TT, |
| 8 | }; |
| 9 | use syn::Error; |
| 10 | |
| 11 | pub struct BitsConstInternal { |
| 12 | typ: TokenTree, |
| 13 | } |
| 14 | |
| 15 | fn paren(ts: TokenStream) -> TokenTree { |
| 16 | TT::Group(Group::new(Delimiter::Parenthesis, ts)) |
| 17 | } |
| 18 | |
| 19 | fn ident(s: &'static str) -> TokenTree { |
| 20 | TT::Ident(Ident::new(s, Span::call_site())) |
| 21 | } |
| 22 | |
| 23 | fn punct(ch: char) -> TokenTree { |
| 24 | TT::Punct(Punct::new(ch, Spacing::Alone)) |
| 25 | } |
| 26 | |
| 27 | /// Implements a recursive-descent parser that translates Boolean expressions on |
| 28 | /// bitmasks to invocations of `const` functions defined by the `bits!` macro. |
| 29 | impl BitsConstInternal { |
| 30 | // primary ::= '(' or ')' |
| 31 | // | ident |
| 32 | // | '!' ident |
| 33 | fn parse_primary( |
| 34 | &self, |
| 35 | tok: TokenTree, |
| 36 | it: &mut dyn Iterator<Item = TokenTree>, |
| 37 | out: &mut TokenStream, |
| 38 | ) -> Result<Option<TokenTree>, Error> { |
| 39 | let next = match tok { |
| 40 | TT::Group(ref g) => { |
| 41 | if g.delimiter() != Delimiter::Parenthesis && g.delimiter() != Delimiter::None { |
| 42 | return Err(Error::new(g.span(), "expected parenthesis")); |
| 43 | } |
| 44 | let mut stream = g.stream().into_iter(); |
| 45 | let Some(first_tok) = stream.next() else { |
| 46 | return Err(Error::new(g.span(), "expected operand, found ')'")); |
| 47 | }; |
| 48 | let mut output = TokenStream::new(); |
| 49 | // start from the lowest precedence |
| 50 | let next = self.parse_or(first_tok, &mut stream, &mut output)?; |
| 51 | if let Some(tok) = next { |
| 52 | return Err(Error::new(tok.span(), format!("unexpected token {tok}"))); |
| 53 | } |
| 54 | out.extend(Some(paren(output))); |
| 55 | it.next() |
| 56 | } |
| 57 | TT::Ident(_) => { |
| 58 | let mut output = TokenStream::new(); |
| 59 | output.extend([ |
| 60 | self.typ.clone(), |
| 61 | TT::Punct(Punct::new(':', Spacing::Joint)), |
| 62 | TT::Punct(Punct::new(':', Spacing::Joint)), |
| 63 | tok, |
| 64 | ]); |
| 65 | out.extend(Some(paren(output))); |
| 66 | it.next() |
| 67 | } |
| 68 | TT::Punct(ref p) => { |
| 69 | if p.as_char() != '!' { |
| 70 | return Err(Error::new(p.span(), "expected operand")); |
| 71 | } |
| 72 | let Some(rhs_tok) = it.next() else { |
| 73 | return Err(Error::new(p.span(), "expected operand at end of input")); |
| 74 | }; |
| 75 | let next = self.parse_primary(rhs_tok, it, out)?; |
| 76 | out.extend([punct('.'), ident("invert"), paren(TokenStream::new())]); |
| 77 | next |
| 78 | } |
| 79 | _ => { |
| 80 | return Err(Error::new(tok.span(), "unexpected literal")); |
| 81 | } |
| 82 | }; |
| 83 | Ok(next) |
| 84 | } |
| 85 | |
| 86 | fn parse_binop< |
| 87 | F: Fn( |
| 88 | &Self, |
| 89 | TokenTree, |
| 90 | &mut dyn Iterator<Item = TokenTree>, |
| 91 | &mut TokenStream, |
| 92 | ) -> Result<Option<TokenTree>, Error>, |
| 93 | >( |
| 94 | &self, |
| 95 | tok: TokenTree, |
| 96 | it: &mut dyn Iterator<Item = TokenTree>, |
| 97 | out: &mut TokenStream, |
| 98 | ch: char, |
| 99 | f: F, |
| 100 | method: &'static str, |
| 101 | ) -> Result<Option<TokenTree>, Error> { |
| 102 | let mut next = f(self, tok, it, out)?; |
| 103 | while next.is_some() { |
| 104 | let op = next.as_ref().unwrap(); |
| 105 | let TT::Punct(ref p) = op else { break }; |
| 106 | if p.as_char() != ch { |
| 107 | break; |
| 108 | } |
| 109 | |
| 110 | let Some(rhs_tok) = it.next() else { |
| 111 | return Err(Error::new(p.span(), "expected operand at end of input")); |
| 112 | }; |
| 113 | let mut rhs = TokenStream::new(); |
| 114 | next = f(self, rhs_tok, it, &mut rhs)?; |
| 115 | out.extend([punct('.'), ident(method), paren(rhs)]); |
| 116 | } |
| 117 | Ok(next) |
| 118 | } |
| 119 | |
| 120 | // sub ::= primary ('-' primary)* |
| 121 | pub fn parse_sub( |
| 122 | &self, |
| 123 | tok: TokenTree, |
| 124 | it: &mut dyn Iterator<Item = TokenTree>, |
| 125 | out: &mut TokenStream, |
| 126 | ) -> Result<Option<TokenTree>, Error> { |
| 127 | self.parse_binop(tok, it, out, '-', Self::parse_primary, "difference") |
| 128 | } |
| 129 | |
| 130 | // and ::= sub ('&' sub)* |
| 131 | fn parse_and( |
| 132 | &self, |
| 133 | tok: TokenTree, |
| 134 | it: &mut dyn Iterator<Item = TokenTree>, |
| 135 | out: &mut TokenStream, |
| 136 | ) -> Result<Option<TokenTree>, Error> { |
| 137 | self.parse_binop(tok, it, out, '&', Self::parse_sub, "intersection") |
| 138 | } |
| 139 | |
| 140 | // xor ::= and ('&' and)* |
| 141 | fn parse_xor( |
| 142 | &self, |
| 143 | tok: TokenTree, |
| 144 | it: &mut dyn Iterator<Item = TokenTree>, |
| 145 | out: &mut TokenStream, |
| 146 | ) -> Result<Option<TokenTree>, Error> { |
| 147 | self.parse_binop(tok, it, out, '^', Self::parse_and, "symmetric_difference") |
| 148 | } |
| 149 | |
| 150 | // or ::= xor ('|' xor)* |
| 151 | pub fn parse_or( |
| 152 | &self, |
| 153 | tok: TokenTree, |
| 154 | it: &mut dyn Iterator<Item = TokenTree>, |
| 155 | out: &mut TokenStream, |
| 156 | ) -> Result<Option<TokenTree>, Error> { |
| 157 | self.parse_binop(tok, it, out, '|', Self::parse_xor, "union") |
| 158 | } |
| 159 | |
| 160 | pub fn parse( |
| 161 | it: &mut dyn Iterator<Item = TokenTree>, |
| 162 | ) -> Result<proc_macro2::TokenStream, Error> { |
| 163 | let mut pos = Span::call_site(); |
| 164 | let mut typ = proc_macro2::TokenStream::new(); |
| 165 | |
| 166 | // Gobble everything up to an `@` sign, which is followed by a |
| 167 | // parenthesized expression; that is, all token trees except the |
| 168 | // last two form the type. |
| 169 | let next = loop { |
| 170 | let tok = it.next(); |
| 171 | if let Some(ref t) = tok { |
| 172 | pos = t.span(); |
| 173 | } |
| 174 | match tok { |
| 175 | None => break None, |
| 176 | Some(TT::Punct(ref p)) if p.as_char() == '@' => { |
| 177 | let tok = it.next(); |
| 178 | if let Some(ref t) = tok { |
| 179 | pos = t.span(); |
| 180 | } |
| 181 | break tok; |
| 182 | } |
| 183 | Some(x) => typ.extend(Some(x)), |
| 184 | } |
| 185 | }; |
| 186 | |
| 187 | let Some(tok) = next else { |
| 188 | return Err(Error::new( |
| 189 | pos, |
| 190 | "expected expression, do not call this macro directly", |
| 191 | )); |
| 192 | }; |
| 193 | let TT::Group(ref _group) = tok else { |
| 194 | return Err(Error::new( |
| 195 | tok.span(), |
| 196 | "expected parenthesis, do not call this macro directly", |
| 197 | )); |
| 198 | }; |
| 199 | let mut out = TokenStream::new(); |
| 200 | let state = Self { |
| 201 | typ: TT::Group(Group::new(Delimiter::None, typ)), |
| 202 | }; |
| 203 | |
| 204 | let next = state.parse_primary(tok, it, &mut out)?; |
| 205 | |
| 206 | // A parenthesized expression is a single production of the grammar, |
| 207 | // so the input must have reached the last token. |
| 208 | if let Some(tok) = next { |
| 209 | return Err(Error::new(tok.span(), format!("unexpected token {tok}"))); |
| 210 | } |
| 211 | Ok(out) |
| 212 | } |
| 213 | } |