// Copyright (c) 2021 The Vulkano developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or https://opensource.org/licenses/MIT>,
// at your option. All files in the project carrying such
// notice may not be copied, modified, or distributed except
// according to those terms.

//! Parsing and analysis utilities for SPIR-V shader binaries.
//!
//! This can be used to inspect and validate a SPIR-V module at runtime. The `Spirv` type does some
//! validation, but you should not assume that code that is read successfully is valid.
//!
//! For more information about SPIR-V modules, instructions and types, see the
//! [SPIR-V specification](https://www.khronos.org/registry/SPIR-V/specs/unified1/SPIRV.html).

use crate::Version;
use std::{
    collections::HashMap,
    error::Error,
    fmt::{self, Display, Formatter},
    ops::Range,
    string::FromUtf8Error,
};

// Generated by build.rs
include!(concat!(env!("OUT_DIR"), "/spirv_parse.rs"));

/// A parsed and analyzed SPIR-V module.
#[derive(Clone, Debug)]
pub struct Spirv {
    version: Version,
    bound: u32,
    instructions: Vec<Instruction>,
    ids: HashMap<Id, IdDataIndices>,

    // Items described in the spec section "Logical Layout of a Module"
    range_capability: Range<usize>,
    range_extension: Range<usize>,
    range_ext_inst_import: Range<usize>,
    memory_model: usize,
    range_entry_point: Range<usize>,
    range_execution_mode: Range<usize>,
    range_name: Range<usize>,
    range_decoration: Range<usize>,
    range_global: Range<usize>,
}

impl Spirv {
    /// Parses a SPIR-V document from a list of words.
    pub fn new(words: &[u32]) -> Result<Spirv, SpirvError> {
        if words.len() < 5 {
            return Err(SpirvError::InvalidHeader);
        }

        if words[0] != 0x07230203 {
            return Err(SpirvError::InvalidHeader);
        }

        let version = Version {
            major: (words[1] & 0x00ff0000) >> 16,
            minor: (words[1] & 0x0000ff00) >> 8,
            patch: words[1] & 0x000000ff,
        };

        let bound = words[3];

        let instructions = {
            let mut ret = Vec::new();
            let mut rest = &words[5..];
            while !rest.is_empty() {
                let word_count = (rest[0] >> 16) as usize;
                assert!(word_count >= 1);

                if rest.len() < word_count {
                    return Err(ParseError {
                        instruction: ret.len(),
                        word: rest.len(),
                        error: ParseErrors::UnexpectedEOF,
                        words: rest.to_owned(),
                    }
                    .into());
                }

                let mut reader = InstructionReader::new(&rest[0..word_count], ret.len());
                let instruction = Instruction::parse(&mut reader)?;

                if !reader.is_empty() {
                    return Err(reader.map_err(ParseErrors::LeftoverOperands).into());
                }

                ret.push(instruction);
                rest = &rest[word_count..];
            }
            ret
        };

        // It is impossible for a valid SPIR-V file to contain more Ids than instructions, so put
        // a sane upper limit on the allocation. This prevents a malicious file from causing huge
        // memory allocations.
        let mut ids = HashMap::with_capacity(instructions.len().min(bound as usize));
        let mut range_capability: Option<Range<usize>> = None;
        let mut range_extension: Option<Range<usize>> = None;
        let mut range_ext_inst_import: Option<Range<usize>> = None;
        let mut range_memory_model: Option<Range<usize>> = None;
        let mut range_entry_point: Option<Range<usize>> = None;
        let mut range_execution_mode: Option<Range<usize>> = None;
        let mut range_name: Option<Range<usize>> = None;
        let mut range_decoration: Option<Range<usize>> = None;
        let mut range_global: Option<Range<usize>> = None;
        let mut in_function = false;

        fn set_range(range: &mut Option<Range<usize>>, index: usize) -> Result<(), SpirvError> {
            if let Some(range) = range {
                if range.end != index {
                    return Err(SpirvError::BadLayout { index });
                }

                range.end = index + 1;
            } else {
                *range = Some(Range {
                    start: index,
                    end: index + 1,
                });
            }

            Ok(())
        }

        for (index, instruction) in instructions.iter().enumerate() {
            if let Some(id) = instruction.result_id() {
                if u32::from(id) >= bound {
                    return Err(SpirvError::IdOutOfBounds { id, index, bound });
                }

                let members = if let Instruction::TypeStruct { member_types, .. } = instruction {
                    member_types
                        .iter()
                        .map(|_| StructMemberDataIndices::default())
                        .collect()
                } else {
                    Vec::new()
                };
                let data = IdDataIndices {
                    index,
                    names: Vec::new(),
                    decorations: Vec::new(),
                    members,
                };
                if let Some(first) = ids.insert(id, data) {
                    return Err(SpirvError::DuplicateId {
                        id,
                        first_index: first.index,
                        second_index: index,
                    });
                }
            }

            match instruction {
                Instruction::Capability { .. } => set_range(&mut range_capability, index)?,
                Instruction::Extension { .. } => set_range(&mut range_extension, index)?,
                Instruction::ExtInstImport { .. } => set_range(&mut range_ext_inst_import, index)?,
                Instruction::MemoryModel { .. } => set_range(&mut range_memory_model, index)?,
                Instruction::EntryPoint { .. } => set_range(&mut range_entry_point, index)?,
                Instruction::ExecutionMode { .. } | Instruction::ExecutionModeId { .. } => {
                    set_range(&mut range_execution_mode, index)?
                }
                Instruction::Name { .. } | Instruction::MemberName { .. } => {
                    set_range(&mut range_name, index)?
                }
                Instruction::Decorate { .. }
                | Instruction::MemberDecorate { .. }
                | Instruction::DecorationGroup { .. }
                | Instruction::GroupDecorate { .. }
                | Instruction::GroupMemberDecorate { .. }
                | Instruction::DecorateId { .. }
                | Instruction::DecorateString { .. }
                | Instruction::MemberDecorateString { .. } => {
                    set_range(&mut range_decoration, index)?
                }
                Instruction::TypeVoid { .. }
                | Instruction::TypeBool { .. }
                | Instruction::TypeInt { .. }
                | Instruction::TypeFloat { .. }
                | Instruction::TypeVector { .. }
                | Instruction::TypeMatrix { .. }
                | Instruction::TypeImage { .. }
                | Instruction::TypeSampler { .. }
                | Instruction::TypeSampledImage { .. }
                | Instruction::TypeArray { .. }
                | Instruction::TypeRuntimeArray { .. }
                | Instruction::TypeStruct { .. }
                | Instruction::TypeOpaque { .. }
                | Instruction::TypePointer { .. }
                | Instruction::TypeFunction { .. }
                | Instruction::TypeEvent { .. }
                | Instruction::TypeDeviceEvent { .. }
                | Instruction::TypeReserveId { .. }
                | Instruction::TypeQueue { .. }
                | Instruction::TypePipe { .. }
                | Instruction::TypeForwardPointer { .. }
                | Instruction::TypePipeStorage { .. }
                | Instruction::TypeNamedBarrier { .. }
                | Instruction::TypeRayQueryKHR { .. }
                | Instruction::TypeAccelerationStructureKHR { .. }
                | Instruction::TypeCooperativeMatrixNV { .. }
                | Instruction::TypeVmeImageINTEL { .. }
                | Instruction::TypeAvcImePayloadINTEL { .. }
                | Instruction::TypeAvcRefPayloadINTEL { .. }
                | Instruction::TypeAvcSicPayloadINTEL { .. }
                | Instruction::TypeAvcMcePayloadINTEL { .. }
                | Instruction::TypeAvcMceResultINTEL { .. }
                | Instruction::TypeAvcImeResultINTEL { .. }
                | Instruction::TypeAvcImeResultSingleReferenceStreamoutINTEL { .. }
                | Instruction::TypeAvcImeResultDualReferenceStreamoutINTEL { .. }
                | Instruction::TypeAvcImeSingleReferenceStreaminINTEL { .. }
                | Instruction::TypeAvcImeDualReferenceStreaminINTEL { .. }
                | Instruction::TypeAvcRefResultINTEL { .. }
                | Instruction::TypeAvcSicResultINTEL { .. }
                | Instruction::ConstantTrue { .. }
                | Instruction::ConstantFalse { .. }
                | Instruction::Constant { .. }
                | Instruction::ConstantComposite { .. }
                | Instruction::ConstantSampler { .. }
                | Instruction::ConstantNull { .. }
                | Instruction::ConstantPipeStorage { .. }
                | Instruction::SpecConstantTrue { .. }
                | Instruction::SpecConstantFalse { .. }
                | Instruction::SpecConstant { .. }
                | Instruction::SpecConstantComposite { .. }
                | Instruction::SpecConstantOp { .. } => set_range(&mut range_global, index)?,
                Instruction::Undef { .. } if !in_function => set_range(&mut range_global, index)?,
                Instruction::Variable { storage_class, .. }
                    if *storage_class != StorageClass::Function =>
                {
                    set_range(&mut range_global, index)?
                }
                Instruction::Function { .. } => {
                    in_function = true;
                }
                Instruction::Line { .. } | Instruction::NoLine { .. } => {
                    if !in_function {
                        set_range(&mut range_global, index)?
                    }
                }
                _ => (),
            }
        }

        let mut spirv = Spirv {
            version,
            bound,
            instructions,
            ids,

            range_capability: range_capability.unwrap_or_default(),
            range_extension: range_extension.unwrap_or_default(),
            range_ext_inst_import: range_ext_inst_import.unwrap_or_default(),
            memory_model: if let Some(range) = range_memory_model {
                if range.end - range.start != 1 {
                    return Err(SpirvError::MemoryModelInvalid);
                }

                range.start
            } else {
                return Err(SpirvError::MemoryModelInvalid);
            },
            range_entry_point: range_entry_point.unwrap_or_default(),
            range_execution_mode: range_execution_mode.unwrap_or_default(),
            range_name: range_name.unwrap_or_default(),
            range_decoration: range_decoration.unwrap_or_default(),
            range_global: range_global.unwrap_or_default(),
        };

        for index in spirv.range_name.clone() {
            match &spirv.instructions[index] {
                Instruction::Name { target, .. } => {
                    spirv.ids.get_mut(target).unwrap().names.push(index);
                }
                Instruction::MemberName { ty, member, .. } => {
                    spirv.ids.get_mut(ty).unwrap().members[*member as usize]
                        .names
                        .push(index);
                }
                _ => unreachable!(),
            }
        }

        // First handle all regular decorations, including those targeting decoration groups.
        for index in spirv.range_decoration.clone() {
            match &spirv.instructions[index] {
                Instruction::Decorate { target, .. }
                | Instruction::DecorateId { target, .. }
                | Instruction::DecorateString { target, .. } => {
                    spirv.ids.get_mut(target).unwrap().decorations.push(index);
                }
                Instruction::MemberDecorate {
                    structure_type: target,
                    member,
                    ..
                }
                | Instruction::MemberDecorateString {
                    struct_type: target,
                    member,
                    ..
                } => {
                    spirv.ids.get_mut(target).unwrap().members[*member as usize]
                        .decorations
                        .push(index);
                }
                _ => (),
            }
        }

        // Then, with decoration groups having their lists complete, handle group decorates.
        for index in spirv.range_decoration.clone() {
            match &spirv.instructions[index] {
                Instruction::GroupDecorate {
                    decoration_group,
                    targets,
                    ..
                } => {
                    let indices = {
                        let data = &spirv.ids[decoration_group];
                        if !matches!(
                            spirv.instructions[data.index],
                            Instruction::DecorationGroup { .. }
                        ) {
                            return Err(SpirvError::GroupDecorateNotGroup { index });
                        };
                        data.decorations.clone()
                    };

                    for target in targets {
                        spirv
                            .ids
                            .get_mut(target)
                            .unwrap()
                            .decorations
                            .extend(&indices);
                    }
                }
                Instruction::GroupMemberDecorate {
                    decoration_group,
                    targets,
                    ..
                } => {
                    let indices = {
                        let data = &spirv.ids[decoration_group];
                        if !matches!(
                            spirv.instructions[data.index],
                            Instruction::DecorationGroup { .. }
                        ) {
                            return Err(SpirvError::GroupDecorateNotGroup { index });
                        };
                        data.decorations.clone()
                    };

                    for (target, member) in targets {
                        spirv.ids.get_mut(target).unwrap().members[*member as usize]
                            .decorations
                            .extend(&indices);
                    }
                }
                _ => (),
            }
        }

        Ok(spirv)
    }

    /// Returns a reference to the instructions in the module.
    #[inline]
    pub fn instructions(&self) -> &[Instruction] {
        &self.instructions
    }

    /// Returns the SPIR-V version that the module is compiled for.
    #[inline]
    pub fn version(&self) -> Version {
        self.version
    }

    /// Returns the upper bound of `Id`s. All `Id`s should have a numeric value strictly less than
    /// this value.
    #[inline]
    pub fn bound(&self) -> u32 {
        self.bound
    }

    /// Returns information about an `Id`.
    ///
    /// # Panics
    ///
    /// - Panics if `id` is not defined in this module. This can in theory only happpen if you are
    ///   mixing `Id`s from different modules.
    #[inline]
    pub fn id<'a>(&'a self, id: Id) -> IdInfo<'a> {
        IdInfo {
            data_indices: &self.ids[&id],
            instructions: &self.instructions,
        }
    }

    /// Returns an iterator over all `Capability` instructions.
    #[inline]
    pub fn iter_capability(&self) -> impl ExactSizeIterator<Item = &Instruction> {
        self.instructions[self.range_capability.clone()].iter()
    }

    /// Returns an iterator over all `Extension` instructions.
    #[inline]
    pub fn iter_extension(&self) -> impl ExactSizeIterator<Item = &Instruction> {
        self.instructions[self.range_extension.clone()].iter()
    }

    /// Returns an iterator over all `ExtInstImport` instructions.
    #[inline]
    pub fn iter_ext_inst_import(&self) -> impl ExactSizeIterator<Item = &Instruction> {
        self.instructions[self.range_ext_inst_import.clone()].iter()
    }

    /// Returns the `MemoryModel` instruction.
    #[inline]
    pub fn memory_model(&self) -> &Instruction {
        &self.instructions[self.memory_model]
    }

    /// Returns an iterator over all `EntryPoint` instructions.
    #[inline]
    pub fn iter_entry_point(&self) -> impl ExactSizeIterator<Item = &Instruction> {
        self.instructions[self.range_entry_point.clone()].iter()
    }

    /// Returns an iterator over all execution mode instructions.
    #[inline]
    pub fn iter_execution_mode(&self) -> impl ExactSizeIterator<Item = &Instruction> {
        self.instructions[self.range_execution_mode.clone()].iter()
    }

    /// Returns an iterator over all name debug instructions.
    #[inline]
    pub fn iter_name(&self) -> impl ExactSizeIterator<Item = &Instruction> {
        self.instructions[self.range_name.clone()].iter()
    }

    /// Returns an iterator over all decoration instructions.
    #[inline]
    pub fn iter_decoration(&self) -> impl ExactSizeIterator<Item = &Instruction> {
        self.instructions[self.range_decoration.clone()].iter()
    }

    /// Returns an iterator over all global declaration instructions: types,
    /// constants and global variables.
    ///
    /// Note: This can also include `Line` and `NoLine` instructions.
    #[inline]
    pub fn iter_global(&self) -> impl ExactSizeIterator<Item = &Instruction> {
        self.instructions[self.range_global.clone()].iter()
    }
}

#[derive(Clone, Debug)]
struct IdDataIndices {
    index: usize,
    names: Vec<usize>,
    decorations: Vec<usize>,
    members: Vec<StructMemberDataIndices>,
}

#[derive(Clone, Debug, Default)]
struct StructMemberDataIndices {
    names: Vec<usize>,
    decorations: Vec<usize>,
}

/// Information associated with an `Id`.
#[derive(Clone, Debug)]
pub struct IdInfo<'a> {
    data_indices: &'a IdDataIndices,
    instructions: &'a [Instruction],
}

impl<'a> IdInfo<'a> {
    /// Returns the instruction that defines this `Id` with a `result_id` operand.
    #[inline]
    pub fn instruction(&self) -> &'a Instruction {
        &self.instructions[self.data_indices.index]
    }

    /// Returns an iterator over all name debug instructions that target this `Id`.
    #[inline]
    pub fn iter_name(&self) -> impl ExactSizeIterator<Item = &'a Instruction> {
        let instructions = self.instructions;
        self.data_indices
            .names
            .iter()
            .map(move |&index| &instructions[index])
    }

    /// Returns an iterator over all decorate instructions, that target this `Id`. This includes any
    /// decorate instructions that target this `Id` indirectly via a `DecorationGroup`.
    #[inline]
    pub fn iter_decoration(&self) -> impl ExactSizeIterator<Item = &'a Instruction> {
        let instructions = self.instructions;
        self.data_indices
            .decorations
            .iter()
            .map(move |&index| &instructions[index])
    }

    /// If this `Id` refers to a `TypeStruct`, returns an iterator of information about each member
    /// of the struct. Empty otherwise.
    #[inline]
    pub fn iter_members(&self) -> impl ExactSizeIterator<Item = StructMemberInfo<'a>> {
        let instructions = self.instructions;
        self.data_indices
            .members
            .iter()
            .map(move |data_indices| StructMemberInfo {
                data_indices,
                instructions,
            })
    }
}

/// Information associated with a member of a `TypeStruct` instruction.
#[derive(Clone, Debug)]
pub struct StructMemberInfo<'a> {
    data_indices: &'a StructMemberDataIndices,
    instructions: &'a [Instruction],
}

impl<'a> StructMemberInfo<'a> {
    /// Returns an iterator over all name debug instructions that target this struct member.
    #[inline]
    pub fn iter_name(&self) -> impl ExactSizeIterator<Item = &'a Instruction> {
        let instructions = self.instructions;
        self.data_indices
            .names
            .iter()
            .map(move |&index| &instructions[index])
    }

    /// Returns an iterator over all decorate instructions that target this struct member. This
    /// includes any decorate instructions that target this member indirectly via a
    /// `DecorationGroup`.
    #[inline]
    pub fn iter_decoration(&self) -> impl ExactSizeIterator<Item = &'a Instruction> {
        let instructions = self.instructions;
        self.data_indices
            .decorations
            .iter()
            .map(move |&index| &instructions[index])
    }
}

/// Used in SPIR-V to refer to the result of another instruction.
///
/// Ids are global across a module, and are always assigned by exactly one instruction.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
#[repr(transparent)]
pub struct Id(u32);

impl From<Id> for u32 {
    #[inline]
    fn from(id: Id) -> u32 {
        id.0
    }
}

impl Display for Id {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        write!(f, "%{}", self.0)
    }
}

/// Helper type for parsing the words of an instruction.
#[derive(Debug)]
struct InstructionReader<'a> {
    words: &'a [u32],
    next_word: usize,
    instruction: usize,
}

impl<'a> InstructionReader<'a> {
    /// Constructs a new reader from a slice of words for a single instruction, including the opcode
    /// word. `instruction` is the number of the instruction currently being read, and is used for
    /// error reporting.
    #[inline]
    fn new(words: &'a [u32], instruction: usize) -> Self {
        debug_assert!(!words.is_empty());
        Self {
            words,
            next_word: 0,
            instruction,
        }
    }

    /// Returns whether the reader has reached the end of the current instruction.
    #[inline]
    fn is_empty(&self) -> bool {
        self.next_word >= self.words.len()
    }

    /// Converts the `ParseErrors` enum to the `ParseError` struct, adding contextual information.
    #[inline]
    fn map_err(&self, error: ParseErrors) -> ParseError {
        ParseError {
            instruction: self.instruction,
            word: self.next_word - 1, // -1 because the word has already been read
            error,
            words: self.words.to_owned(),
        }
    }

    /// Returns the next word in the sequence.
    #[inline]
    fn next_u32(&mut self) -> Result<u32, ParseError> {
        let word = *self.words.get(self.next_word).ok_or(ParseError {
            instruction: self.instruction,
            word: self.next_word, // No -1 because we didn't advance yet
            error: ParseErrors::MissingOperands,
            words: self.words.to_owned(),
        })?;
        self.next_word += 1;
        Ok(word)
    }

    /// Returns the next two words as a single `u64`.
    #[inline]
    fn next_u64(&mut self) -> Result<u64, ParseError> {
        Ok(self.next_u32()? as u64 | (self.next_u32()? as u64) << 32)
    }

    /// Reads a nul-terminated string.
    fn next_string(&mut self) -> Result<String, ParseError> {
        let mut bytes = Vec::new();
        loop {
            let word = self.next_u32()?.to_le_bytes();

            if let Some(nul) = word.iter().position(|&b| b == 0) {
                bytes.extend(&word[0..nul]);
                break;
            } else {
                bytes.extend(word);
            }
        }
        String::from_utf8(bytes).map_err(|err| self.map_err(ParseErrors::FromUtf8Error(err)))
    }

    /// Reads all remaining words.
    #[inline]
    fn remainder(&mut self) -> Vec<u32> {
        let vec = self.words[self.next_word..].to_owned();
        self.next_word = self.words.len();
        vec
    }
}

/// Error that can happen when reading a SPIR-V module.
#[derive(Clone, Debug)]
pub enum SpirvError {
    BadLayout {
        index: usize,
    },
    DuplicateId {
        id: Id,
        first_index: usize,
        second_index: usize,
    },
    GroupDecorateNotGroup {
        index: usize,
    },
    IdOutOfBounds {
        id: Id,
        index: usize,
        bound: u32,
    },
    InvalidHeader,
    MemoryModelInvalid,
    ParseError(ParseError),
}

impl Display for SpirvError {
    #[inline]
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        match self {
            Self::BadLayout { index } => write!(
                f,
                "the instruction at index {} does not follow the logical layout of a module",
                index
            ),
            Self::DuplicateId {
                id,
                first_index,
                second_index,
            } => write!(
                f,
                "id {} is assigned more than once, by instructions {} and {}",
                id, first_index, second_index
            ),
            Self::GroupDecorateNotGroup { index } => write!(f, "a GroupDecorate or GroupMemberDecorate instruction at index {} referred to an Id that was not a DecorationGroup", index),
            Self::IdOutOfBounds { id, bound, index, } => write!(f, "id {}, assigned at instruction {}, is not below the maximum bound {}", id, index, bound),
            Self::InvalidHeader => write!(f, "the SPIR-V module header is invalid"),
            Self::MemoryModelInvalid => {
                write!(f, "the MemoryModel instruction is not present exactly once")
            }
            Self::ParseError(_) => write!(f, "parse error"),
        }
    }
}

impl Error for SpirvError {
    #[inline]
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        match self {
            Self::ParseError(err) => Some(err),
            _ => None,
        }
    }
}

impl From<ParseError> for SpirvError {
    #[inline]
    fn from(err: ParseError) -> Self {
        Self::ParseError(err)
    }
}

/// Error that can happen when parsing SPIR-V instructions into Rust data structures.
#[derive(Clone, Debug)]
pub struct ParseError {
    /// The instruction number the error happened at, starting from 0.
    pub instruction: usize,
    /// The word from the start of the instruction that the error happened at, starting from 0.
    pub word: usize,
    /// The error.
    pub error: ParseErrors,
    /// The words of the instruction.
    pub words: Vec<u32>,
}

impl Display for ParseError {
    #[inline]
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "at instruction {}, word {}: {}",
            self.instruction, self.word, self.error
        )
    }
}

impl Error for ParseError {}

/// Individual types of parse error that can happen.
#[derive(Clone, Debug)]
pub enum ParseErrors {
    FromUtf8Error(FromUtf8Error),
    LeftoverOperands,
    MissingOperands,
    UnexpectedEOF,
    UnknownEnumerant(&'static str, u32),
    UnknownOpcode(u16),
    UnknownSpecConstantOpcode(u16),
}

impl Display for ParseErrors {
    #[inline]
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        match self {
            Self::FromUtf8Error(err) => write!(f, "invalid UTF-8 in string literal"),
            Self::LeftoverOperands => write!(f, "unparsed operands remaining"),
            Self::MissingOperands => write!(f, "the instruction and its operands require more words than are present in the instruction"),
            Self::UnexpectedEOF => write!(f, "encountered unexpected end of file"),
            Self::UnknownEnumerant(ty, enumerant) => write!(f, "invalid enumerant {} for enum {}", enumerant, ty),
            Self::UnknownOpcode(opcode) => write!(f, "invalid instruction opcode {}", opcode),
            Self::UnknownSpecConstantOpcode(opcode) => write!(f, "invalid spec constant instruction opcode {}", opcode),
        }
    }
}