      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
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305
    306
    307
    308
    309
    310
    311
    312
    313
    314
    315
    316
    317
    318
    319
    320
    321
    322
    323
    324
    325
    326
    327
    328
    329
    330
    331
    332
    333
    334
    335
    336
    337
    338
    339
    340
    341
    342
    343
    344
    345
    346
    347
    348
    349
    350
    351
    352
    353
    354
    355
    356
    357
    358
    359
    360
    361
    362
    363
    364
    365
    366
    367
    368
    369
    370
    371
    372
    373
    374
    375
    376
    377
    378
    379
    380
    381
    382
    383
    384
    385
    386
    387
    388
    389
    390
    391
    392
    393
    394
    395
    396
    397
    398
    399
    400
    401
    402
    403
    404
    405
    406
    407
    408
    409
    410
    411
    412

    #[cfg(feature = "parsing")]
    use crate::buffer::Cursor;
    use crate::thread::ThreadBound;
    use proc_macro2::{
        Delimiter, Group, Ident, LexError, Literal, Punct, Spacing, Span, TokenStream, TokenTree,
    };
    #[cfg(feature = "printing")]
    use quote::ToTokens;
    use std::fmt::{self, Debug, Display};
    use std::iter::FromIterator;
    use std::slice;
    use std::vec;

    /// The result of a Syn parser.
    pub type Result<T> = std::result::Result<T, Error>;

    /// Error returned when a Syn parser cannot parse the input tokens.
    ///
    /// # Error reporting in proc macros
    ///
    /// The correct way to report errors back to the compiler from a procedural
    /// macro is by emitting an appropriately spanned invocation of
    /// [`compile_error!`] in the generated code. This produces a better diagnostic
    /// message than simply panicking the macro.
    ///
    /// [`compile_error!`]: std::compile_error!
    ///
    /// When parsing macro input, the [`parse_macro_input!`] macro handles the
    /// conversion to `compile_error!` automatically.
    ///
    /// ```
    /// # extern crate proc_macro;
    /// #
    /// use proc_macro::TokenStream;
    /// use syn::{parse_macro_input, AttributeArgs, ItemFn};
    ///
    /// # const IGNORE: &str = stringify! {
    /// #[proc_macro_attribute]
    /// # };
    /// pub fn my_attr(args: TokenStream, input: TokenStream) -> TokenStream {
    ///     let args = parse_macro_input!(args as AttributeArgs);
    ///     let input = parse_macro_input!(input as ItemFn);
    ///
    ///     /* ... */
    ///     # TokenStream::new()
    /// }
    /// ```
    ///
    /// For errors that arise later than the initial parsing stage, the
    /// [`.to_compile_error()`] method can be used to perform an explicit conversion
    /// to `compile_error!`.
    ///
    /// [`.to_compile_error()`]: Error::to_compile_error
    ///
    /// ```
    /// # extern crate proc_macro;
    /// #
    /// # use proc_macro::TokenStream;
    /// # use syn::{parse_macro_input, DeriveInput};
    /// #
    /// # const IGNORE: &str = stringify! {
    /// #[proc_macro_derive(MyDerive)]
    /// # };
    /// pub fn my_derive(input: TokenStream) -> TokenStream {
    ///     let input = parse_macro_input!(input as DeriveInput);
    ///
    ///     // fn(DeriveInput) -> syn::Result<proc_macro2::TokenStream>
    ///     expand::my_derive(input)
    ///         .unwrap_or_else(|err| err.to_compile_error())
    ///         .into()
    /// }
    /// #
    /// # mod expand {
    /// #     use proc_macro2::TokenStream;
    /// #     use syn::{DeriveInput, Result};
    /// #
    /// #     pub fn my_derive(input: DeriveInput) -> Result<TokenStream> {
    /// #         unimplemented!()
    /// #     }
    /// # }
    /// ```
    pub struct Error {
        messages: Vec<ErrorMessage>,
    }

    struct ErrorMessage {
        // Span is implemented as an index into a thread-local interner to keep the
        // size small. It is not safe to access from a different thread. We want
        // errors to be Send and Sync to play nicely with the Failure crate, so pin
        // the span we're given to its original thread and assume it is
        // Span::call_site if accessed from any other thread.
        start_span: ThreadBound<Span>,
        end_span: ThreadBound<Span>,
        message: String,
    }

    #[cfg(test)]
    struct _Test
    where
        Error: Send + Sync;

    impl Error {
        /// Usually the [`ParseStream::error`] method will be used instead, which
        /// automatically uses the correct span from the current position of the
        /// parse stream.
        ///
        /// Use `Error::new` when the error needs to be triggered on some span other
        /// than where the parse stream is currently positioned.
        ///
        /// [`ParseStream::error`]: crate::parse::ParseBuffer::error
        ///
        /// # Example
        ///
        /// ```
        /// use syn::{Error, Ident, LitStr, Result, Token};
        /// use syn::parse::ParseStream;
        ///
        /// // Parses input that looks like `name = "string"` where the key must be
        /// // the identifier `name` and the value may be any string literal.
        /// // Returns the string literal.
        /// fn parse_name(input: ParseStream) -> Result<LitStr> {
        ///     let name_token: Ident = input.parse()?;
        ///     if name_token != "name" {
        ///         // Trigger an error not on the current position of the stream,
        ///         // but on the position of the unexpected identifier.
        ///         return Err(Error::new(name_token.span(), "expected `name`"));
        ///     }
        ///     input.parse::<Token![=]>()?;
        ///     let s: LitStr = input.parse()?;
        ///     Ok(s)
        /// }
        /// ```
        pub fn new<T: Display>(span: Span, message: T) -> Self {
            Error {
                messages: vec![ErrorMessage {
                    start_span: ThreadBound::new(span),
                    end_span: ThreadBound::new(span),
                    message: message.to_string(),
                }],
            }
        }

        /// Creates an error with the specified message spanning the given syntax
        /// tree node.
        ///
        /// Unlike the `Error::new` constructor, this constructor takes an argument
        /// `tokens` which is a syntax tree node. This allows the resulting `Error`
        /// to attempt to span all tokens inside of `tokens`. While you would
        /// typically be able to use the `Spanned` trait with the above `Error::new`
        /// constructor, implementation limitations today mean that
        /// `Error::new_spanned` may provide a higher-quality error message on
        /// stable Rust.
        ///
        /// When in doubt it's recommended to stick to `Error::new` (or
        /// `ParseStream::error`)!
        #[cfg(feature = "printing")]
        pub fn new_spanned<T: ToTokens, U: Display>(tokens: T, message: U) -> Self {
            let mut iter = tokens.into_token_stream().into_iter();
            let start = iter.next().map_or_else(Span::call_site, |t| t.span());
            let end = iter.last().map_or(start, |t| t.span());
            Error {
                messages: vec![ErrorMessage {
                    start_span: ThreadBound::new(start),
                    end_span: ThreadBound::new(end),
                    message: message.to_string(),
                }],
            }
        }

        /// The source location of the error.
        ///
        /// Spans are not thread-safe so this function returns `Span::call_site()`
        /// if called from a different thread than the one on which the `Error` was
        /// originally created.
        pub fn span(&self) -> Span {
            let start = match self.messages[0].start_span.get() {
                Some(span) => *span,
                None => return Span::call_site(),
            };
            let end = match self.messages[0].end_span.get() {
                Some(span) => *span,
                None => return Span::call_site(),
            };
            start.join(end).unwrap_or(start)
        }

        /// Render the error as an invocation of [`compile_error!`].
        ///
        /// The [`parse_macro_input!`] macro provides a convenient way to invoke
        /// this method correctly in a procedural macro.
        ///
        /// [`compile_error!`]: std::compile_error!
        pub fn to_compile_error(&self) -> TokenStream {
            self.messages
                .iter()
                .map(ErrorMessage::to_compile_error)
                .collect()
        }

        /// Render the error as an invocation of [`compile_error!`].
        ///
        /// [`compile_error!`]: std::compile_error!
        ///
        /// # Example
        ///
        /// ```
        /// # extern crate proc_macro;
        /// #
        /// use proc_macro::TokenStream;
        /// use syn::{parse_macro_input, DeriveInput, Error};
        ///
        /// # const _: &str = stringify! {
        /// #[proc_macro_derive(MyTrait)]
        /// # };
        /// pub fn derive_my_trait(input: TokenStream) -> TokenStream {
        ///     let input = parse_macro_input!(input as DeriveInput);
        ///     my_trait::expand(input)
        ///         .unwrap_or_else(Error::into_compile_error)
        ///         .into()
        /// }
        ///
        /// mod my_trait {
        ///     use proc_macro2::TokenStream;
        ///     use syn::{DeriveInput, Result};
        ///
        ///     pub(crate) fn expand(input: DeriveInput) -> Result<TokenStream> {
        ///         /* ... */
        ///         # unimplemented!()
        ///     }
        /// }
        /// ```
        pub fn into_compile_error(self) -> TokenStream {
            self.to_compile_error()
        }

        /// Add another error message to self such that when `to_compile_error()` is
        /// called, both errors will be emitted together.
        pub fn combine(&mut self, another: Error) {
            self.messages.extend(another.messages)
        }
    }

    impl ErrorMessage {
        fn to_compile_error(&self) -> TokenStream {
            let start = self
                .start_span
                .get()
                .cloned()
                .unwrap_or_else(Span::call_site);
            let end = self.end_span.get().cloned().unwrap_or_else(Span::call_site);

            // compile_error!($message)
            TokenStream::from_iter(vec![
                TokenTree::Ident(Ident::new("compile_error", start)),
                TokenTree::Punct({
                    let mut punct = Punct::new('!', Spacing::Alone);
                    punct.set_span(start);
                    punct
                }),
                TokenTree::Group({
                    let mut group = Group::new(Delimiter::Brace, {
                        TokenStream::from_iter(vec![TokenTree::Literal({
                            let mut string = Literal::string(&self.message);
                            string.set_span(end);
                            string
                        })])
                    });
                    group.set_span(end);
                    group
                }),
            ])
        }
    }

    #[cfg(feature = "parsing")]
    pub fn new_at<T: Display>(scope: Span, cursor: Cursor, message: T) -> Error {
        if cursor.eof() {
            Error::new(scope, format!("unexpected end of input, {}", message))
        } else {
            let span = crate::buffer::open_span_of_group(cursor);
            Error::new(span, message)
        }
    }

    #[cfg(all(feature = "parsing", any(feature = "full", feature = "derive")))]
    pub fn new2<T: Display>(start: Span, end: Span, message: T) -> Error {
        Error {
            messages: vec![ErrorMessage {
                start_span: ThreadBound::new(start),
                end_span: ThreadBound::new(end),
                message: message.to_string(),
            }],
        }
    }

    impl Debug for Error {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            if self.messages.len() == 1 {
                formatter
                    .debug_tuple("Error")
                    .field(&self.messages[0])
                    .finish()
            } else {
                formatter
                    .debug_tuple("Error")
                    .field(&self.messages)
                    .finish()
            }
        }
    }

    impl Debug for ErrorMessage {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            Debug::fmt(&self.message, formatter)
        }
    }

    impl Display for Error {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str(&self.messages[0].message)
        }
    }

    impl Clone for Error {
        fn clone(&self) -> Self {
            Error {
                messages: self.messages.clone(),
            }
        }
    }

    impl Clone for ErrorMessage {
        fn clone(&self) -> Self {
            let start = self
                .start_span
                .get()
                .cloned()
                .unwrap_or_else(Span::call_site);
            let end = self.end_span.get().cloned().unwrap_or_else(Span::call_site);
            ErrorMessage {
                start_span: ThreadBound::new(start),
                end_span: ThreadBound::new(end),
                message: self.message.clone(),
            }
        }
    }

    impl std::error::Error for Error {}

    impl From<LexError> for Error {
        fn from(err: LexError) -> Self {
            Error::new(Span::call_site(), format!("{:?}", err))
        }
    }

    impl IntoIterator for Error {
        type Item = Error;
        type IntoIter = IntoIter;

        fn into_iter(self) -> Self::IntoIter {
            IntoIter {
                messages: self.messages.into_iter(),
            }
        }
    }

    pub struct IntoIter {
        messages: vec::IntoIter<ErrorMessage>,
    }

    impl Iterator for IntoIter {
        type Item = Error;

        fn next(&mut self) -> Option<Self::Item> {
            Some(Error {
                messages: vec![self.messages.next()?],
            })
        }
    }

    impl<'a> IntoIterator for &'a Error {
        type Item = Error;
        type IntoIter = Iter<'a>;

        fn into_iter(self) -> Self::IntoIter {
            Iter {
                messages: self.messages.iter(),
            }
        }
    }

    pub struct Iter<'a> {
        messages: slice::Iter<'a, ErrorMessage>,
    }

    impl<'a> Iterator for Iter<'a> {
        type Item = Error;

        fn next(&mut self) -> Option<Self::Item> {
            Some(Error {
                messages: vec![self.messages.next()?.clone()],
            })
        }
    }

    impl Extend<Error> for Error {
        fn extend<T: IntoIterator<Item = Error>>(&mut self, iter: T) {
            for err in iter {
                self.combine(err);
            }
        }
    }