1
  2
  3
  4
  5
  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
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
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
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
use crate::iter::{self, Iter, IterImpl};
use crate::{Define, Error, Export, ExportArgs, FakeCallSite, Input, Macro, Visibility};
use proc_macro::Delimiter::{Brace, Bracket, Parenthesis};
use proc_macro::{Delimiter, Ident, Span, TokenStream, TokenTree};

pub(crate) fn parse_input(tokens: Iter) -> Result<Input, Error> {
    let attrs = parse_attributes(tokens)?;
    let vis = parse_visibility(tokens)?;
    let kw = parse_ident(tokens)?;
    if kw.to_string() == "use" {
        parse_export(attrs, vis, tokens).map(Input::Export)
    } else if kw.to_string() == "fn" {
        parse_define(attrs, vis, kw.span(), tokens).map(Input::Define)
    } else {
        Err(Error::new(
            kw.span(),
            "unexpected input to #[proc_macro_hack]",
        ))
    }
}

fn parse_export(attrs: TokenStream, vis: Visibility, tokens: Iter) -> Result<Export, Error> {
    let _ = parse_punct(tokens, ':');
    let _ = parse_punct(tokens, ':');
    let from = parse_ident(tokens)?;
    parse_punct(tokens, ':')?;
    parse_punct(tokens, ':')?;

    let mut macros = Vec::new();
    match tokens.peek() {
        Some(TokenTree::Group(group)) if group.delimiter() == Brace => {
            let ref mut content = iter::new(group.stream());
            loop {
                macros.push(parse_macro(content)?);
                if content.peek().is_none() {
                    break;
                }
                parse_punct(content, ',')?;
                if content.peek().is_none() {
                    break;
                }
            }
            tokens.next().unwrap();
        }
        _ => macros.push(parse_macro(tokens)?),
    }

    parse_punct(tokens, ';')?;
    Ok(Export {
        attrs,
        vis,
        from,
        macros,
    })
}

fn parse_punct(tokens: Iter, ch: char) -> Result<(), Error> {
    match tokens.peek() {
        Some(TokenTree::Punct(punct)) if punct.as_char() == ch => {
            tokens.next().unwrap();
            Ok(())
        }
        tt => Err(Error::new(
            tt.map_or_else(Span::call_site, TokenTree::span),
            format!("expected `{}`", ch),
        )),
    }
}

fn parse_define(
    attrs: TokenStream,
    vis: Visibility,
    fn_token: Span,
    tokens: Iter,
) -> Result<Define, Error> {
    if vis.is_none() {
        return Err(Error::new(
            fn_token,
            "functions tagged with `#[proc_macro_hack]` must be `pub`",
        ));
    }
    let name = parse_ident(tokens)?;
    let body = tokens.collect();
    Ok(Define { attrs, name, body })
}

fn parse_macro(tokens: Iter) -> Result<Macro, Error> {
    let name = parse_ident(tokens)?;
    let export_as = match tokens.peek() {
        Some(TokenTree::Ident(ident)) if ident.to_string() == "as" => {
            tokens.next().unwrap();
            parse_ident(tokens)?
        }
        _ => name.clone(),
    };
    Ok(Macro { name, export_as })
}

fn parse_ident(tokens: Iter) -> Result<Ident, Error> {
    match tokens.next() {
        Some(TokenTree::Ident(ident)) => Ok(ident),
        tt => Err(Error::new(
            tt.as_ref().map_or_else(Span::call_site, TokenTree::span),
            "expected identifier",
        )),
    }
}

fn parse_keyword(tokens: Iter, kw: &'static str) -> Result<(), Error> {
    match &tokens.next() {
        Some(TokenTree::Ident(ident)) if ident.to_string() == kw => Ok(()),
        tt => Err(Error::new(
            tt.as_ref().map_or_else(Span::call_site, TokenTree::span),
            format!("expected `{}`", kw),
        )),
    }
}

fn parse_int(tokens: Iter) -> Result<u16, Span> {
    match tokens.next() {
        Some(TokenTree::Literal(lit)) => lit.to_string().parse().map_err(|_| lit.span()),
        Some(tt) => Err(tt.span()),
        None => Err(Span::call_site()),
    }
}

fn parse_group(tokens: Iter, delimiter: Delimiter) -> Result<IterImpl, Error> {
    match &tokens.next() {
        Some(TokenTree::Group(group)) if group.delimiter() == delimiter => {
            Ok(iter::new(group.stream()))
        }
        tt => Err(Error::new(
            tt.as_ref().map_or_else(Span::call_site, TokenTree::span),
            "expected delimiter",
        )),
    }
}

fn parse_visibility(tokens: Iter) -> Result<Visibility, Error> {
    if let Some(TokenTree::Ident(ident)) = tokens.peek() {
        if ident.to_string() == "pub" {
            match tokens.next().unwrap() {
                TokenTree::Ident(vis) => return Ok(Some(vis)),
                _ => unreachable!(),
            }
        }
    }
    Ok(None)
}

fn parse_attributes(tokens: Iter) -> Result<TokenStream, Error> {
    let mut attrs = TokenStream::new();
    while let Some(TokenTree::Punct(punct)) = tokens.peek() {
        if punct.as_char() != '#' {
            break;
        }
        let span = punct.span();
        attrs.extend(tokens.next());
        match tokens.peek() {
            Some(TokenTree::Group(group)) if group.delimiter() == Bracket => {
                attrs.extend(tokens.next());
            }
            _ => return Err(Error::new(span, "unexpected input")),
        }
    }
    Ok(attrs)
}

pub(crate) fn parse_export_args(tokens: Iter) -> Result<ExportArgs, Error> {
    let mut args = ExportArgs {
        support_nested: false,
        internal_macro_calls: 0,
        fake_call_site: false,
        only_hack_old_rustc: false,
    };

    while let Some(tt) = tokens.next() {
        match &tt {
            TokenTree::Ident(ident) if ident.to_string() == "support_nested" => {
                args.support_nested = true;
            }
            TokenTree::Ident(ident) if ident.to_string() == "internal_macro_calls" => {
                parse_punct(tokens, '=')?;
                let calls = parse_int(tokens).map_err(|span| {
                    Error::new(span, "expected integer value for internal_macro_calls")
                })?;
                args.internal_macro_calls = calls;
            }
            TokenTree::Ident(ident) if ident.to_string() == "fake_call_site" => {
                args.fake_call_site = true;
            }
            TokenTree::Ident(ident) if ident.to_string() == "only_hack_old_rustc" => {
                args.only_hack_old_rustc = true;
            }
            _ => {
                return Err(Error::new(
                    tt.span(),
                    "expected one of: `support_nested`, `internal_macro_calls`, `fake_call_site`, `only_hack_old_rustc`",
                ));
            }
        }
        if tokens.peek().is_none() {
            break;
        }
        parse_punct(tokens, ',')?;
    }

    Ok(args)
}

pub(crate) fn parse_define_args(tokens: Iter) -> Result<(), Error> {
    match tokens.peek() {
        None => Ok(()),
        Some(token) => Err(Error::new(
            token.span(),
            "unexpected argument to proc_macro_hack macro implementation; args are only accepted on the macro declaration (the `pub use`)",
        )),
    }
}

pub(crate) fn parse_enum_hack(tokens: Iter) -> Result<TokenStream, Error> {
    parse_keyword(tokens, "enum")?;
    parse_ident(tokens)?;

    let ref mut braces = parse_group(tokens, Brace)?;
    parse_ident(braces)?;
    parse_punct(braces, '=')?;

    let ref mut parens = parse_group(braces, Parenthesis)?;
    parse_ident(parens)?;
    parse_punct(parens, '!')?;

    let ref mut inner = parse_group(parens, Brace)?;
    let token_stream = inner.collect();

    parse_punct(parens, ',')?;
    let _ = parens.next();
    parse_punct(braces, '.')?;
    let _ = braces.next();
    parse_punct(braces, ',')?;

    Ok(token_stream)
}

pub(crate) fn parse_fake_call_site(tokens: Iter) -> Result<FakeCallSite, Error> {
    parse_punct(tokens, '#')?;
    let ref mut attr = parse_group(tokens, Bracket)?;
    parse_keyword(attr, "derive")?;
    let ref mut path = parse_group(attr, Parenthesis)?;
    Ok(FakeCallSite {
        derive: parse_ident(path)?,
        rest: tokens.collect(),
    })
}