facet_deserialize/

error.rs

#[cfg(feature = "rich-diagnostics")]
use ariadne::{Color, Config, IndexType, Label, Report, ReportKind, Source};

use alloc::string::String;

use facet_core::{Def, Shape};
use facet_reflect::ReflectError;
use owo_colors::OwoColorize;

use crate::{Outcome, Span};

/// A JSON parse error, with context. Never would've guessed huh.
#[derive(Debug)]
pub struct DeserError<'input> {
    /// The input associated with the error.
    pub input: alloc::borrow::Cow<'input, [u8]>,

    /// Where the error occured
    pub span: Span,

    /// The specific error that occurred while parsing the JSON.
    pub kind: DeserErrorKind,
}

impl DeserError<'_> {
    /// Converts the error into an owned error.
    pub fn into_owned(self) -> DeserError<'static> {
        DeserError {
            input: self.input.into_owned().into(),
            span: self.span,
            kind: self.kind,
        }
    }

    /// Sets the span of this error
    pub fn with_span(mut self, span: Span) -> Self {
        self.span = span;
        self
    }
}

/// An error kind for JSON parsing.
#[derive(Debug, PartialEq, Clone)]
pub enum DeserErrorKind {
    /// An unexpected byte was encountered in the input.
    UnexpectedByte {
        /// The byte that was found.
        got: u8,
        /// The expected value as a string description.
        wanted: &'static str,
    },
    /// An unexpected character was encountered in the input.
    UnexpectedChar {
        /// The character that was found.
        got: char,
        /// The expected value as a string description.
        wanted: &'static str,
    },
    /// An unexpected outcome was encountered in the input.
    UnexpectedOutcome {
        /// The outcome that was found.
        got: Outcome<'static>,
        /// The expected value as a string description.
        wanted: &'static str,
    },
    /// The input ended unexpectedly while parsing JSON.
    UnexpectedEof {
        /// The expected value as a string description.
        wanted: &'static str,
    },
    /// A required struct field was missing at the end of JSON input.
    MissingField(&'static str),
    /// A number is out of range.
    NumberOutOfRange(f64),
    /// An unexpected String was encountered in the input.
    StringAsNumber(String),
    /// An unexpected field name was encountered in the input.
    UnknownField {
        /// The name of the field that was not recognized
        field_name: String,
        /// The shape definition where the unknown field was encountered
        shape: &'static Shape,
    },
    /// A string that could not be built into valid UTF-8 Unicode
    InvalidUtf8(String),
    /// An error occurred while reflecting a type.
    ReflectError(ReflectError),
    /// Some feature is not yet implemented (under development).
    Unimplemented(&'static str),
    /// An unsupported type was encountered.
    UnsupportedType {
        /// The shape we got
        got: &'static Shape,

        /// The shape we wanted
        wanted: &'static str,
    },
    /// An enum variant name that doesn't exist in the enum definition.
    NoSuchVariant {
        /// The name of the variant that was not found
        name: String,

        /// The enum shape definition where the variant was looked up
        enum_shape: &'static Shape,
    },
}

impl<'input> DeserError<'input> {
    /// Creates a new deser error, preserving input and location context for accurate reporting.
    pub fn new(kind: DeserErrorKind, input: &'input [u8], span: Span) -> Self {
        Self {
            input: alloc::borrow::Cow::Borrowed(input),
            span,
            kind,
        }
    }

    /// Constructs a reflection-related deser error, keeping contextual information intact.
    pub(crate) fn new_reflect(e: ReflectError, input: &'input [u8], span: Span) -> Self {
        DeserError::new(DeserErrorKind::ReflectError(e), input, span)
    }

    /// Provides a human-friendly message wrapper to improve error readability.
    pub fn message(&self) -> DeserErrorMessage<'_> {
        DeserErrorMessage(self)
    }
}

/// A wrapper type for displaying deser error messages
pub struct DeserErrorMessage<'a>(&'a DeserError<'a>);

impl core::fmt::Display for DeserErrorMessage<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        match &self.0.kind {
            DeserErrorKind::UnexpectedByte { got, wanted } => write!(
                f,
                "Unexpected byte: got 0x{:02X}, wanted {}",
                got.red(),
                wanted.yellow()
            ),
            DeserErrorKind::UnexpectedChar { got, wanted } => write!(
                f,
                "Unexpected character: got '{}', wanted {}",
                got.red(),
                wanted.yellow()
            ),
            DeserErrorKind::UnexpectedOutcome { got, wanted } => {
                write!(f, "Unexpected {}, wanted {}", got.red(), wanted.yellow())
            }
            DeserErrorKind::UnexpectedEof { wanted } => {
                write!(f, "Unexpected end of file: wanted {}", wanted.red())
            }
            DeserErrorKind::MissingField(fld) => write!(f, "Missing required field: {}", fld.red()),
            DeserErrorKind::NumberOutOfRange(n) => {
                write!(f, "Number out of range: {}", n.red())
            }
            DeserErrorKind::StringAsNumber(s) => {
                write!(f, "Expected a string but got number: {}", s.red())
            }
            DeserErrorKind::UnknownField { field_name, shape } => {
                write!(
                    f,
                    "Unknown field: {} for shape {}",
                    field_name.red(),
                    shape.yellow()
                )
            }
            DeserErrorKind::InvalidUtf8(e) => write!(f, "Invalid UTF-8 encoding: {}", e.red()),
            DeserErrorKind::ReflectError(e) => write!(f, "{e}"),
            DeserErrorKind::Unimplemented(s) => {
                write!(f, "Feature not yet implemented: {}", s.yellow())
            }
            DeserErrorKind::UnsupportedType { got, wanted } => {
                write!(
                    f,
                    "Unsupported type: got {}, wanted {}",
                    got.red(),
                    wanted.green()
                )
            }
            DeserErrorKind::NoSuchVariant { name, enum_shape } => match enum_shape.def {
                Def::Enum(ed) => {
                    write!(
                        f,
                        "Enum variant not found: {} in enum {}. Available variants: [",
                        name.red(),
                        enum_shape.yellow()
                    )?;

                    let mut first = true;
                    for variant in ed.variants.iter() {
                        if !first {
                            write!(f, ", ")?;
                        }
                        write!(f, "{}", variant.name.green())?;
                        first = false;
                    }

                    write!(f, "]")
                }
                _ => {
                    write!(
                        f,
                        "Enum variant not found: {} in enum {}. No variants available (not an enum)",
                        name.red(),
                        enum_shape.yellow()
                    )
                }
            },
        }
    }
}

#[cfg(not(feature = "rich-diagnostics"))]
impl core::fmt::Display for DeserError<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "{} at byte {}", self.message(), self.span.start(),)
    }
}

#[cfg(feature = "rich-diagnostics")]
impl core::fmt::Display for DeserError<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        let Ok(input_str) = core::str::from_utf8(&self.input[..]) else {
            return write!(f, "(JSON input was invalid UTF-8)");
        };

        let source_id = "json";
        let span_start = self.span.start();
        let span_end = self.span.end();

        let mut report = Report::build(ReportKind::Error, (source_id, span_start..span_end))
            .with_config(Config::new().with_index_type(IndexType::Byte));

        let label = Label::new((source_id, span_start..span_end))
            .with_message(self.message())
            .with_color(Color::Red);

        report = report.with_label(label);

        let source = Source::from(input_str);

        struct FmtWriter<'a, 'b: 'a> {
            f: &'a mut core::fmt::Formatter<'b>,
            error: Option<core::fmt::Error>,
        }

        impl core::fmt::Write for FmtWriter<'_, '_> {
            fn write_str(&mut self, s: &str) -> core::fmt::Result {
                if self.error.is_some() {
                    // Already failed, do nothing
                    return Err(core::fmt::Error);
                }
                if let Err(e) = self.f.write_str(s) {
                    self.error = Some(e);
                    Err(core::fmt::Error)
                } else {
                    Ok(())
                }
            }
        }

        struct IoWriter<'a, 'b: 'a> {
            inner: FmtWriter<'a, 'b>,
        }

        impl std::io::Write for IoWriter<'_, '_> {
            fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
                match core::str::from_utf8(buf) {
                    Ok(s) => match core::fmt::Write::write_str(&mut self.inner, s) {
                        Ok(()) => Ok(buf.len()),
                        Err(_) => Err(std::io::ErrorKind::Other.into()),
                    },
                    Err(_) => Err(std::io::ErrorKind::InvalidData.into()),
                }
            }
            fn flush(&mut self) -> std::io::Result<()> {
                Ok(())
            }
        }

        let cache = (source_id, &source);

        let fmt_writer = FmtWriter { f, error: None };
        let mut io_writer = IoWriter { inner: fmt_writer };

        if report.finish().write(cache, &mut io_writer).is_err() {
            return write!(f, "Error formatting with ariadne");
        }

        // Check if our adapter ran into a formatting error
        if io_writer.inner.error.is_some() {
            return write!(f, "Error writing ariadne output to fmt::Formatter");
        }

        Ok(())
    }
}

impl core::error::Error for DeserError<'_> {}