Quelle  mod.rs   Sprache: unbekannt

use crate::diagnostic_filter::{
    self, DiagnosticFilter, DiagnosticFilterMap, DiagnosticFilterNode, FilterableTriggeringRule,
    ShouldConflictOnFullDuplicate, StandardFilterableTriggeringRule,
};
use crate::front::wgsl::error::{DiagnosticAttributeNotSupportedPosition, Error, ExpectedToken};
use crate::front::wgsl::parse::directive::enable_extension::{
    EnableExtension, EnableExtensions, UnimplementedEnableExtension,
};
use crate::front::wgsl::parse::directive::language_extension::LanguageExtension;
use crate::front::wgsl::parse::directive::DirectiveKind;
use crate::front::wgsl::parse::lexer::{Lexer, Token};
use crate::front::wgsl::parse::number::Number;
use crate::front::wgsl::Scalar;
use crate::front::SymbolTable;
use crate::{Arena, FastIndexSet, Handle, ShaderStage, Span};

pub mod ast;
pub mod conv;
pub mod directive;
pub mod lexer;
pub mod number;

/// State for constructing an AST expression.
///
/// Not to be confused with [`lower::ExpressionContext`], which is for producing
/// Naga IR from the AST we produce here.
///
/// [`lower::ExpressionContext`]: super::lower::ExpressionContext
struct ExpressionContext<'input, 'temp, 'out> {
    /// The [`TranslationUnit::expressions`] arena to which we should contribute
    /// expressions.
    ///
    /// [`TranslationUnit::expressions`]: ast::TranslationUnit::expressions
    expressions: &'out mut Arena<ast::Expression<'input>>,

    /// The [`TranslationUnit::types`] arena to which we should contribute new
    /// types.
    ///
    /// [`TranslationUnit::types`]: ast::TranslationUnit::types
    types: &'out mut Arena<ast::Type<'input>>,

    /// A map from identifiers in scope to the locals/arguments they represent.
    ///
    /// The handles refer to the [`locals`] arena; see that field's
    /// documentation for details.
    ///
    /// [`locals`]: ExpressionContext::locals
    local_table: &'temp mut SymbolTable<&'input str, Handle<ast::Local>>,

    /// Local variable and function argument arena for the function we're building.
    ///
    /// Note that the [`ast::Local`] here is actually a zero-sized type. This
    /// `Arena`'s only role is to assign a unique `Handle` to each local
    /// identifier, and track its definition's span for use in diagnostics. All
    /// the detailed information about locals - names, types, etc. - is kept in
    /// the [`LocalDecl`] statements we parsed from their declarations. For
    /// arguments, that information is kept in [`arguments`].
    ///
    /// In the AST, when an [`Ident`] expression refers to a local variable or
    /// argument, its [`IdentExpr`] holds the referent's `Handle<Local>` in this
    /// arena.
    ///
    /// During lowering, [`LocalDecl`] statements add entries to a per-function
    /// table that maps `Handle<Local>` values to their Naga representations,
    /// accessed via [`StatementContext::local_table`] and
    /// [`LocalExpressionContext::local_table`]. This table is then consulted when
    /// lowering subsequent [`Ident`] expressions.
    ///
    /// [`LocalDecl`]: ast::StatementKind::LocalDecl
    /// [`arguments`]: ast::Function::arguments
    /// [`Ident`]: ast::Expression::Ident
    /// [`IdentExpr`]: ast::IdentExpr
    /// [`StatementContext::local_table`]: super::lower::StatementContext::local_table
    /// [`LocalExpressionContext::local_table`]: super::lower::LocalExpressionContext::local_table
    locals: &'out mut Arena<ast::Local>,

    /// Identifiers used by the current global declaration that have no local definition.
    ///
    /// This becomes the [`GlobalDecl`]'s [`dependencies`] set.
    ///
    /// Note that we don't know at parse time what kind of [`GlobalDecl`] the
    /// name refers to. We can't look up names until we've seen the entire
    /// translation unit.
    ///
    /// [`GlobalDecl`]: ast::GlobalDecl
    /// [`dependencies`]: ast::GlobalDecl::dependencies
    unresolved: &'out mut FastIndexSet<ast::Dependency<'input>>,
}

impl<'a> ExpressionContext<'a, '_, '_> {
    fn parse_binary_op(
        &mut self,
        lexer: &mut Lexer<'a>,
        classifier: impl Fn(Token<'a>) -> Option<crate::BinaryOperator>,
        mut parser: impl FnMut(
            &mut Lexer<'a>,
            &mut Self,
        ) -> Result<Handle<ast::Expression<'a>>, Error<'a>>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        let start = lexer.start_byte_offset();
        let mut accumulator = parser(lexer, self)?;
        while let Some(op) = classifier(lexer.peek().0) {
            let _ = lexer.next();
            let left = accumulator;
            let right = parser(lexer, self)?;
            accumulator = self.expressions.append(
                ast::Expression::Binary { op, left, right },
                lexer.span_from(start),
            );
        }
        Ok(accumulator)
    }

    fn declare_local(&mut self, name: ast::Ident<'a>) -> Result<Handle<ast::Local>, Error<'a>> {
        let handle = self.locals.append(ast::Local, name.span);
        if let Some(old) = self.local_table.add(name.name, handle) {
            Err(Error::Redefinition {
                previous: self.locals.get_span(old),
                current: name.span,
            })
        } else {
            Ok(handle)
        }
    }

    fn new_scalar(&mut self, scalar: Scalar) -> Handle<ast::Type<'a>> {
        self.types
            .append(ast::Type::Scalar(scalar), Span::UNDEFINED)
    }
}

/// Which grammar rule we are in the midst of parsing.
///
/// This is used for error checking. `Parser` maintains a stack of
/// these and (occasionally) checks that it is being pushed and popped
/// as expected.
#[derive(Copy, Clone, Debug, PartialEq)]
enum Rule {
    Attribute,
    VariableDecl,
    TypeDecl,
    FunctionDecl,
    Block,
    Statement,
    PrimaryExpr,
    SingularExpr,
    UnaryExpr,
    GeneralExpr,
    Directive,
    GenericExpr,
    EnclosedExpr,
}

struct ParsedAttribute<T> {
    value: Option<T>,
}

impl<T> Default for ParsedAttribute<T> {
    fn default() -> Self {
        Self { value: None }
    }
}

impl<T> ParsedAttribute<T> {
    fn set(&mut self, value: T, name_span: Span) -> Result<(), Error<'static>> {
        if self.value.is_some() {
            return Err(Error::RepeatedAttribute(name_span));
        }
        self.value = Some(value);
        Ok(())
    }
}

#[derive(Default)]
struct BindingParser<'a> {
    location: ParsedAttribute<Handle<ast::Expression<'a>>>,
    second_blend_source: ParsedAttribute<bool>,
    built_in: ParsedAttribute<crate::BuiltIn>,
    interpolation: ParsedAttribute<crate::Interpolation>,
    sampling: ParsedAttribute<crate::Sampling>,
    invariant: ParsedAttribute<bool>,
}

impl<'a> BindingParser<'a> {
    fn parse(
        &mut self,
        parser: &mut Parser,
        lexer: &mut Lexer<'a>,
        name: &'a str,
        name_span: Span,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<(), Error<'a>> {
        match name {
            "location" => {
                lexer.expect(Token::Paren('('))?;
                self.location
                    .set(parser.general_expression(lexer, ctx)?, name_span)?;
                lexer.expect(Token::Paren(')'))?;
            }
            "builtin" => {
                lexer.expect(Token::Paren('('))?;
                let (raw, span) = lexer.next_ident_with_span()?;
                self.built_in
                    .set(conv::map_built_in(raw, span)?, name_span)?;
                lexer.expect(Token::Paren(')'))?;
            }
            "interpolate" => {
                lexer.expect(Token::Paren('('))?;
                let (raw, span) = lexer.next_ident_with_span()?;
                self.interpolation
                    .set(conv::map_interpolation(raw, span)?, name_span)?;
                if lexer.skip(Token::Separator(',')) {
                    let (raw, span) = lexer.next_ident_with_span()?;
                    self.sampling
                        .set(conv::map_sampling(raw, span)?, name_span)?;
                }
                lexer.expect(Token::Paren(')'))?;
            }
            "second_blend_source" => {
                self.second_blend_source.set(true, name_span)?;
            }
            "invariant" => {
                self.invariant.set(true, name_span)?;
            }
            _ => return Err(Error::UnknownAttribute(name_span)),
        }
        Ok(())
    }

    fn finish(self, span: Span) -> Result<Option<ast::Binding<'a>>, Error<'a>> {
        match (
            self.location.value,
            self.built_in.value,
            self.interpolation.value,
            self.sampling.value,
            self.invariant.value.unwrap_or_default(),
        ) {
            (None, None, None, None, false) => Ok(None),
            (Some(location), None, interpolation, sampling, false) => {
                // Before handing over the completed `Module`, we call
                // `apply_default_interpolation` to ensure that the interpolation and
                // sampling have been explicitly specified on all vertex shader output and fragment
                // shader input user bindings, so leaving them potentially `None` here is fine.
                Ok(Some(ast::Binding::Location {
                    location,
                    interpolation,
                    sampling,
                    second_blend_source: self.second_blend_source.value.unwrap_or(false),
                }))
            }
            (None, Some(crate::BuiltIn::Position { .. }), None, None, invariant) => {
                Ok(Some(ast::Binding::BuiltIn(crate::BuiltIn::Position {
                    invariant,
                })))
            }
            (None, Some(built_in), None, None, false) => Ok(Some(ast::Binding::BuiltIn(built_in))),
            (_, _, _, _, _) => Err(Error::InconsistentBinding(span)),
        }
    }
}

pub struct Parser {
    rules: Vec<(Rule, usize)>,
}

impl Parser {
    pub const fn new() -> Self {
        Parser { rules: Vec::new() }
    }

    fn reset(&mut self) {
        self.rules.clear();
    }

    fn push_rule_span(&mut self, rule: Rule, lexer: &mut Lexer<'_>) {
        self.rules.push((rule, lexer.start_byte_offset()));
    }

    fn pop_rule_span(&mut self, lexer: &Lexer<'_>) -> Span {
        let (_, initial) = self.rules.pop().unwrap();
        lexer.span_from(initial)
    }

    fn peek_rule_span(&mut self, lexer: &Lexer<'_>) -> Span {
        let &(_, initial) = self.rules.last().unwrap();
        lexer.span_from(initial)
    }

    fn race_rules(&self, rule0: Rule, rule1: Rule) -> Option<Rule> {
        Some(
            self.rules
                .iter()
                .rev()
                .find(|&x| x.0 == rule0 || x.0 == rule1)?
                .0,
        )
    }

    fn switch_value<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<ast::SwitchValue<'a>, Error<'a>> {
        if let Token::Word("default") = lexer.peek().0 {
            let _ = lexer.next();
            return Ok(ast::SwitchValue::Default);
        }

        let expr = self.general_expression(lexer, ctx)?;
        Ok(ast::SwitchValue::Expr(expr))
    }

    /// Decide if we're looking at a construction expression, and return its
    /// type if so.
    ///
    /// If the identifier `word` is a [type-defining keyword], then return a
    /// [`ConstructorType`] value describing the type to build. Return an error
    /// if the type is not constructible (like `sampler`).
    ///
    /// If `word` isn't a type name, then return `None`.
    ///
    /// [type-defining keyword]: https://gpuweb.github.io/gpuweb/wgsl/#type-defining-keywords
    /// [`ConstructorType`]: ast::ConstructorType
    fn constructor_type<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        word: &'a str,
        span: Span,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Option<ast::ConstructorType<'a>>, Error<'a>> {
        if let Some(scalar) = conv::get_scalar_type(word) {
            return Ok(Some(ast::ConstructorType::Scalar(scalar)));
        }

        let partial = match word {
            "vec2" => ast::ConstructorType::PartialVector {
                size: crate::VectorSize::Bi,
            },
            "vec2i" => {
                return Ok(Some(ast::ConstructorType::Vector {
                    size: crate::VectorSize::Bi,
                    ty: ctx.new_scalar(Scalar::I32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "vec2u" => {
                return Ok(Some(ast::ConstructorType::Vector {
                    size: crate::VectorSize::Bi,
                    ty: ctx.new_scalar(Scalar::U32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "vec2f" => {
                return Ok(Some(ast::ConstructorType::Vector {
                    size: crate::VectorSize::Bi,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "vec3" => ast::ConstructorType::PartialVector {
                size: crate::VectorSize::Tri,
            },
            "vec3i" => {
                return Ok(Some(ast::ConstructorType::Vector {
                    size: crate::VectorSize::Tri,
                    ty: ctx.new_scalar(Scalar::I32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "vec3u" => {
                return Ok(Some(ast::ConstructorType::Vector {
                    size: crate::VectorSize::Tri,
                    ty: ctx.new_scalar(Scalar::U32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "vec3f" => {
                return Ok(Some(ast::ConstructorType::Vector {
                    size: crate::VectorSize::Tri,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "vec4" => ast::ConstructorType::PartialVector {
                size: crate::VectorSize::Quad,
            },
            "vec4i" => {
                return Ok(Some(ast::ConstructorType::Vector {
                    size: crate::VectorSize::Quad,
                    ty: ctx.new_scalar(Scalar::I32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "vec4u" => {
                return Ok(Some(ast::ConstructorType::Vector {
                    size: crate::VectorSize::Quad,
                    ty: ctx.new_scalar(Scalar::U32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "vec4f" => {
                return Ok(Some(ast::ConstructorType::Vector {
                    size: crate::VectorSize::Quad,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "mat2x2" => ast::ConstructorType::PartialMatrix {
                columns: crate::VectorSize::Bi,
                rows: crate::VectorSize::Bi,
            },
            "mat2x2f" => {
                return Ok(Some(ast::ConstructorType::Matrix {
                    columns: crate::VectorSize::Bi,
                    rows: crate::VectorSize::Bi,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "mat2x3" => ast::ConstructorType::PartialMatrix {
                columns: crate::VectorSize::Bi,
                rows: crate::VectorSize::Tri,
            },
            "mat2x3f" => {
                return Ok(Some(ast::ConstructorType::Matrix {
                    columns: crate::VectorSize::Bi,
                    rows: crate::VectorSize::Tri,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "mat2x4" => ast::ConstructorType::PartialMatrix {
                columns: crate::VectorSize::Bi,
                rows: crate::VectorSize::Quad,
            },
            "mat2x4f" => {
                return Ok(Some(ast::ConstructorType::Matrix {
                    columns: crate::VectorSize::Bi,
                    rows: crate::VectorSize::Quad,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "mat3x2" => ast::ConstructorType::PartialMatrix {
                columns: crate::VectorSize::Tri,
                rows: crate::VectorSize::Bi,
            },
            "mat3x2f" => {
                return Ok(Some(ast::ConstructorType::Matrix {
                    columns: crate::VectorSize::Tri,
                    rows: crate::VectorSize::Bi,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "mat3x3" => ast::ConstructorType::PartialMatrix {
                columns: crate::VectorSize::Tri,
                rows: crate::VectorSize::Tri,
            },
            "mat3x3f" => {
                return Ok(Some(ast::ConstructorType::Matrix {
                    columns: crate::VectorSize::Tri,
                    rows: crate::VectorSize::Tri,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "mat3x4" => ast::ConstructorType::PartialMatrix {
                columns: crate::VectorSize::Tri,
                rows: crate::VectorSize::Quad,
            },
            "mat3x4f" => {
                return Ok(Some(ast::ConstructorType::Matrix {
                    columns: crate::VectorSize::Tri,
                    rows: crate::VectorSize::Quad,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "mat4x2" => ast::ConstructorType::PartialMatrix {
                columns: crate::VectorSize::Quad,
                rows: crate::VectorSize::Bi,
            },
            "mat4x2f" => {
                return Ok(Some(ast::ConstructorType::Matrix {
                    columns: crate::VectorSize::Quad,
                    rows: crate::VectorSize::Bi,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "mat4x3" => ast::ConstructorType::PartialMatrix {
                columns: crate::VectorSize::Quad,
                rows: crate::VectorSize::Tri,
            },
            "mat4x3f" => {
                return Ok(Some(ast::ConstructorType::Matrix {
                    columns: crate::VectorSize::Quad,
                    rows: crate::VectorSize::Tri,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "mat4x4" => ast::ConstructorType::PartialMatrix {
                columns: crate::VectorSize::Quad,
                rows: crate::VectorSize::Quad,
            },
            "mat4x4f" => {
                return Ok(Some(ast::ConstructorType::Matrix {
                    columns: crate::VectorSize::Quad,
                    rows: crate::VectorSize::Quad,
                    ty: ctx.new_scalar(Scalar::F32),
                    ty_span: Span::UNDEFINED,
                }))
            }
            "array" => ast::ConstructorType::PartialArray,
            "atomic"
            | "binding_array"
            | "sampler"
            | "sampler_comparison"
            | "texture_1d"
            | "texture_1d_array"
            | "texture_2d"
            | "texture_2d_array"
            | "texture_3d"
            | "texture_cube"
            | "texture_cube_array"
            | "texture_multisampled_2d"
            | "texture_multisampled_2d_array"
            | "texture_depth_2d"
            | "texture_depth_2d_array"
            | "texture_depth_cube"
            | "texture_depth_cube_array"
            | "texture_depth_multisampled_2d"
            | "texture_storage_1d"
            | "texture_storage_1d_array"
            | "texture_storage_2d"
            | "texture_storage_2d_array"
            | "texture_storage_3d" => return Err(Error::TypeNotConstructible(span)),
            _ => return Ok(None),
        };

        // parse component type if present
        match (lexer.peek().0, partial) {
            (Token::Paren('<'), ast::ConstructorType::PartialVector { size }) => {
                let (ty, ty_span) = self.singular_generic(lexer, ctx)?;
                Ok(Some(ast::ConstructorType::Vector { size, ty, ty_span }))
            }
            (Token::Paren('<'), ast::ConstructorType::PartialMatrix { columns, rows }) => {
                let (ty, ty_span) = self.singular_generic(lexer, ctx)?;
                Ok(Some(ast::ConstructorType::Matrix {
                    columns,
                    rows,
                    ty,
                    ty_span,
                }))
            }
            (Token::Paren('<'), ast::ConstructorType::PartialArray) => {
                lexer.expect_generic_paren('<')?;
                let base = self.type_decl(lexer, ctx)?;
                let size = if lexer.skip(Token::Separator(',')) {
                    let expr = self.const_generic_expression(lexer, ctx)?;
                    ast::ArraySize::Constant(expr)
                } else {
                    ast::ArraySize::Dynamic
                };
                lexer.expect_generic_paren('>')?;

                Ok(Some(ast::ConstructorType::Array { base, size }))
            }
            (_, partial) => Ok(Some(partial)),
        }
    }

    /// Expects `name` to be consumed (not in lexer).
    fn arguments<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Vec<Handle<ast::Expression<'a>>>, Error<'a>> {
        self.push_rule_span(Rule::EnclosedExpr, lexer);
        lexer.open_arguments()?;
        let mut arguments = Vec::new();
        loop {
            if !arguments.is_empty() {
                if !lexer.next_argument()? {
                    break;
                }
            } else if lexer.skip(Token::Paren(')')) {
                break;
            }
            let arg = self.general_expression(lexer, ctx)?;
            arguments.push(arg);
        }

        self.pop_rule_span(lexer);
        Ok(arguments)
    }

    fn enclosed_expression<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        self.push_rule_span(Rule::EnclosedExpr, lexer);
        let expr = self.general_expression(lexer, ctx)?;
        self.pop_rule_span(lexer);
        Ok(expr)
    }

    /// Expects [`Rule::PrimaryExpr`] or [`Rule::SingularExpr`] on top; does not pop it.
    /// Expects `name` to be consumed (not in lexer).
    fn function_call<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        name: &'a str,
        name_span: Span,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        assert!(self.rules.last().is_some());

        let expr = match name {
            // bitcast looks like a function call, but it's an operator and must be handled differently.
            "bitcast" => {
                let (to, span) = self.singular_generic(lexer, ctx)?;

                lexer.open_arguments()?;
                let expr = self.general_expression(lexer, ctx)?;
                lexer.close_arguments()?;

                ast::Expression::Bitcast {
                    expr,
                    to,
                    ty_span: span,
                }
            }
            // everything else must be handled later, since they can be hidden by user-defined functions.
            _ => {
                let arguments = self.arguments(lexer, ctx)?;
                ctx.unresolved.insert(ast::Dependency {
                    ident: name,
                    usage: name_span,
                });
                ast::Expression::Call {
                    function: ast::Ident {
                        name,
                        span: name_span,
                    },
                    arguments,
                }
            }
        };

        let span = self.peek_rule_span(lexer);
        let expr = ctx.expressions.append(expr, span);
        Ok(expr)
    }

    fn ident_expr<'a>(
        &mut self,
        name: &'a str,
        name_span: Span,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> ast::IdentExpr<'a> {
        match ctx.local_table.lookup(name) {
            Some(&local) => ast::IdentExpr::Local(local),
            None => {
                ctx.unresolved.insert(ast::Dependency {
                    ident: name,
                    usage: name_span,
                });
                ast::IdentExpr::Unresolved(name)
            }
        }
    }

    fn primary_expression<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        self.push_rule_span(Rule::PrimaryExpr, lexer);
        const fn literal_ray_flag<'b>(flag: crate::RayFlag) -> ast::Expression<'b> {
            ast::Expression::Literal(ast::Literal::Number(Number::U32(flag.bits())))
        }
        const fn literal_ray_intersection<'b>(
            intersection: crate::RayQueryIntersection,
        ) -> ast::Expression<'b> {
            ast::Expression::Literal(ast::Literal::Number(Number::U32(intersection as u32)))
        }

        let expr = match lexer.peek() {
            (Token::Paren('('), _) => {
                let _ = lexer.next();
                let expr = self.enclosed_expression(lexer, ctx)?;
                lexer.expect(Token::Paren(')'))?;
                self.pop_rule_span(lexer);
                return Ok(expr);
            }
            (Token::Word("true"), _) => {
                let _ = lexer.next();
                ast::Expression::Literal(ast::Literal::Bool(true))
            }
            (Token::Word("false"), _) => {
                let _ = lexer.next();
                ast::Expression::Literal(ast::Literal::Bool(false))
            }
            (Token::Number(res), span) => {
                let _ = lexer.next();
                let num = res.map_err(|err| match err {
                    super::error::NumberError::UnimplementedF16 => {
                        Error::EnableExtensionNotEnabled {
                            kind: EnableExtension::Unimplemented(UnimplementedEnableExtension::F16),
                            span,
                        }
                    }
                    err => Error::BadNumber(span, err),
                })?;
                ast::Expression::Literal(ast::Literal::Number(num))
            }
            (Token::Word("RAY_FLAG_NONE"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::empty())
            }
            (Token::Word("RAY_FLAG_FORCE_OPAQUE"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::FORCE_OPAQUE)
            }
            (Token::Word("RAY_FLAG_FORCE_NO_OPAQUE"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::FORCE_NO_OPAQUE)
            }
            (Token::Word("RAY_FLAG_TERMINATE_ON_FIRST_HIT"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::TERMINATE_ON_FIRST_HIT)
            }
            (Token::Word("RAY_FLAG_SKIP_CLOSEST_HIT_SHADER"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::SKIP_CLOSEST_HIT_SHADER)
            }
            (Token::Word("RAY_FLAG_CULL_BACK_FACING"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::CULL_BACK_FACING)
            }
            (Token::Word("RAY_FLAG_CULL_FRONT_FACING"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::CULL_FRONT_FACING)
            }
            (Token::Word("RAY_FLAG_CULL_OPAQUE"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::CULL_OPAQUE)
            }
            (Token::Word("RAY_FLAG_CULL_NO_OPAQUE"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::CULL_NO_OPAQUE)
            }
            (Token::Word("RAY_FLAG_SKIP_TRIANGLES"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::SKIP_TRIANGLES)
            }
            (Token::Word("RAY_FLAG_SKIP_AABBS"), _) => {
                let _ = lexer.next();
                literal_ray_flag(crate::RayFlag::SKIP_AABBS)
            }
            (Token::Word("RAY_QUERY_INTERSECTION_NONE"), _) => {
                let _ = lexer.next();
                literal_ray_intersection(crate::RayQueryIntersection::None)
            }
            (Token::Word("RAY_QUERY_INTERSECTION_TRIANGLE"), _) => {
                let _ = lexer.next();
                literal_ray_intersection(crate::RayQueryIntersection::Triangle)
            }
            (Token::Word("RAY_QUERY_INTERSECTION_GENERATED"), _) => {
                let _ = lexer.next();
                literal_ray_intersection(crate::RayQueryIntersection::Generated)
            }
            (Token::Word("RAY_QUERY_INTERSECTION_AABB"), _) => {
                let _ = lexer.next();
                literal_ray_intersection(crate::RayQueryIntersection::Aabb)
            }
            (Token::Word(word), span) => {
                let start = lexer.start_byte_offset();
                let _ = lexer.next();

                if let Some(ty) = self.constructor_type(lexer, word, span, ctx)? {
                    let ty_span = lexer.span_from(start);
                    let components = self.arguments(lexer, ctx)?;
                    ast::Expression::Construct {
                        ty,
                        ty_span,
                        components,
                    }
                } else if let Token::Paren('(') = lexer.peek().0 {
                    self.pop_rule_span(lexer);
                    return self.function_call(lexer, word, span, ctx);
                } else if word == "bitcast" {
                    self.pop_rule_span(lexer);
                    return self.function_call(lexer, word, span, ctx);
                } else {
                    let ident = self.ident_expr(word, span, ctx);
                    ast::Expression::Ident(ident)
                }
            }
            other => return Err(Error::Unexpected(other.1, ExpectedToken::PrimaryExpression)),
        };

        let span = self.pop_rule_span(lexer);
        let expr = ctx.expressions.append(expr, span);
        Ok(expr)
    }

    fn postfix<'a>(
        &mut self,
        span_start: usize,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
        expr: Handle<ast::Expression<'a>>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        let mut expr = expr;

        loop {
            let expression = match lexer.peek().0 {
                Token::Separator('.') => {
                    let _ = lexer.next();
                    let field = lexer.next_ident()?;

                    ast::Expression::Member { base: expr, field }
                }
                Token::Paren('[') => {
                    let _ = lexer.next();
                    let index = self.enclosed_expression(lexer, ctx)?;
                    lexer.expect(Token::Paren(']'))?;

                    ast::Expression::Index { base: expr, index }
                }
                _ => break,
            };

            let span = lexer.span_from(span_start);
            expr = ctx.expressions.append(expression, span);
        }

        Ok(expr)
    }

    fn const_generic_expression<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        self.push_rule_span(Rule::GenericExpr, lexer);
        let expr = self.general_expression(lexer, ctx)?;
        self.pop_rule_span(lexer);
        Ok(expr)
    }

    /// Parse a `unary_expression`.
    fn unary_expression<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        self.push_rule_span(Rule::UnaryExpr, lexer);
        //TODO: refactor this to avoid backing up
        let expr = match lexer.peek().0 {
            Token::Operation('-') => {
                let _ = lexer.next();
                let expr = self.unary_expression(lexer, ctx)?;
                let expr = ast::Expression::Unary {
                    op: crate::UnaryOperator::Negate,
                    expr,
                };
                let span = self.peek_rule_span(lexer);
                ctx.expressions.append(expr, span)
            }
            Token::Operation('!') => {
                let _ = lexer.next();
                let expr = self.unary_expression(lexer, ctx)?;
                let expr = ast::Expression::Unary {
                    op: crate::UnaryOperator::LogicalNot,
                    expr,
                };
                let span = self.peek_rule_span(lexer);
                ctx.expressions.append(expr, span)
            }
            Token::Operation('~') => {
                let _ = lexer.next();
                let expr = self.unary_expression(lexer, ctx)?;
                let expr = ast::Expression::Unary {
                    op: crate::UnaryOperator::BitwiseNot,
                    expr,
                };
                let span = self.peek_rule_span(lexer);
                ctx.expressions.append(expr, span)
            }
            Token::Operation('*') => {
                let _ = lexer.next();
                let expr = self.unary_expression(lexer, ctx)?;
                let expr = ast::Expression::Deref(expr);
                let span = self.peek_rule_span(lexer);
                ctx.expressions.append(expr, span)
            }
            Token::Operation('&') => {
                let _ = lexer.next();
                let expr = self.unary_expression(lexer, ctx)?;
                let expr = ast::Expression::AddrOf(expr);
                let span = self.peek_rule_span(lexer);
                ctx.expressions.append(expr, span)
            }
            _ => self.singular_expression(lexer, ctx)?,
        };

        self.pop_rule_span(lexer);
        Ok(expr)
    }

    /// Parse a `singular_expression`.
    fn singular_expression<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        let start = lexer.start_byte_offset();
        self.push_rule_span(Rule::SingularExpr, lexer);
        let primary_expr = self.primary_expression(lexer, ctx)?;
        let singular_expr = self.postfix(start, lexer, ctx, primary_expr)?;
        self.pop_rule_span(lexer);

        Ok(singular_expr)
    }

    fn equality_expression<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        context: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        // equality_expression
        context.parse_binary_op(
            lexer,
            |token| match token {
                Token::LogicalOperation('=') => Some(crate::BinaryOperator::Equal),
                Token::LogicalOperation('!') => Some(crate::BinaryOperator::NotEqual),
                _ => None,
            },
            // relational_expression
            |lexer, context| {
                let enclosing = self.race_rules(Rule::GenericExpr, Rule::EnclosedExpr);
                context.parse_binary_op(
                    lexer,
                    match enclosing {
                        Some(Rule::GenericExpr) => |token| match token {
                            Token::LogicalOperation('<') => Some(crate::BinaryOperator::LessEqual),
                            Token::LogicalOperation('>') => {
                                Some(crate::BinaryOperator::GreaterEqual)
                            }
                            _ => None,
                        },
                        _ => |token| match token {
                            Token::Paren('<') => Some(crate::BinaryOperator::Less),
                            Token::Paren('>') => Some(crate::BinaryOperator::Greater),
                            Token::LogicalOperation('<') => Some(crate::BinaryOperator::LessEqual),
                            Token::LogicalOperation('>') => {
                                Some(crate::BinaryOperator::GreaterEqual)
                            }
                            _ => None,
                        },
                    },
                    // shift_expression
                    |lexer, context| {
                        context.parse_binary_op(
                            lexer,
                            match enclosing {
                                Some(Rule::GenericExpr) => |token| match token {
                                    Token::ShiftOperation('<') => {
                                        Some(crate::BinaryOperator::ShiftLeft)
                                    }
                                    _ => None,
                                },
                                _ => |token| match token {
                                    Token::ShiftOperation('<') => {
                                        Some(crate::BinaryOperator::ShiftLeft)
                                    }
                                    Token::ShiftOperation('>') => {
                                        Some(crate::BinaryOperator::ShiftRight)
                                    }
                                    _ => None,
                                },
                            },
                            // additive_expression
                            |lexer, context| {
                                context.parse_binary_op(
                                    lexer,
                                    |token| match token {
                                        Token::Operation('+') => Some(crate::BinaryOperator::Add),
                                        Token::Operation('-') => {
                                            Some(crate::BinaryOperator::Subtract)
                                        }
                                        _ => None,
                                    },
                                    // multiplicative_expression
                                    |lexer, context| {
                                        context.parse_binary_op(
                                            lexer,
                                            |token| match token {
                                                Token::Operation('*') => {
                                                    Some(crate::BinaryOperator::Multiply)
                                                }
                                                Token::Operation('/') => {
                                                    Some(crate::BinaryOperator::Divide)
                                                }
                                                Token::Operation('%') => {
                                                    Some(crate::BinaryOperator::Modulo)
                                                }
                                                _ => None,
                                            },
                                            |lexer, context| self.unary_expression(lexer, context),
                                        )
                                    },
                                )
                            },
                        )
                    },
                )
            },
        )
    }

    fn general_expression<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Handle<ast::Expression<'a>>, Error<'a>> {
        self.general_expression_with_span(lexer, ctx)
            .map(|(expr, _)| expr)
    }

    fn general_expression_with_span<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        context: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<(Handle<ast::Expression<'a>>, Span), Error<'a>> {
        self.push_rule_span(Rule::GeneralExpr, lexer);
        // logical_or_expression
        let handle = context.parse_binary_op(
            lexer,
            |token| match token {
                Token::LogicalOperation('|') => Some(crate::BinaryOperator::LogicalOr),
                _ => None,
            },
            // logical_and_expression
            |lexer, context| {
                context.parse_binary_op(
                    lexer,
                    |token| match token {
                        Token::LogicalOperation('&') => Some(crate::BinaryOperator::LogicalAnd),
                        _ => None,
                    },
                    // inclusive_or_expression
                    |lexer, context| {
                        context.parse_binary_op(
                            lexer,
                            |token| match token {
                                Token::Operation('|') => Some(crate::BinaryOperator::InclusiveOr),
                                _ => None,
                            },
                            // exclusive_or_expression
                            |lexer, context| {
                                context.parse_binary_op(
                                    lexer,
                                    |token| match token {
                                        Token::Operation('^') => {
                                            Some(crate::BinaryOperator::ExclusiveOr)
                                        }
                                        _ => None,
                                    },
                                    // and_expression
                                    |lexer, context| {
                                        context.parse_binary_op(
                                            lexer,
                                            |token| match token {
                                                Token::Operation('&') => {
                                                    Some(crate::BinaryOperator::And)
                                                }
                                                _ => None,
                                            },
                                            |lexer, context| {
                                                self.equality_expression(lexer, context)
                                            },
                                        )
                                    },
                                )
                            },
                        )
                    },
                )
            },
        )?;
        Ok((handle, self.pop_rule_span(lexer)))
    }

    fn variable_decl<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<ast::GlobalVariable<'a>, Error<'a>> {
        self.push_rule_span(Rule::VariableDecl, lexer);
        let mut space = crate::AddressSpace::Handle;

        if lexer.skip(Token::Paren('<')) {
            let (class_str, span) = lexer.next_ident_with_span()?;
            space = match class_str {
                "storage" => {
                    let access = if lexer.skip(Token::Separator(',')) {
                        lexer.next_storage_access()?
                    } else {
                        // defaulting to `read`
                        crate::StorageAccess::LOAD
                    };
                    crate::AddressSpace::Storage { access }
                }
                _ => conv::map_address_space(class_str, span)?,
            };
            lexer.expect(Token::Paren('>'))?;
        }
        let name = lexer.next_ident()?;

        let ty = if lexer.skip(Token::Separator(':')) {
            Some(self.type_decl(lexer, ctx)?)
        } else {
            None
        };

        let init = if lexer.skip(Token::Operation('=')) {
            let handle = self.general_expression(lexer, ctx)?;
            Some(handle)
        } else {
            None
        };
        lexer.expect(Token::Separator(';'))?;
        self.pop_rule_span(lexer);

        Ok(ast::GlobalVariable {
            name,
            space,
            binding: None,
            ty,
            init,
        })
    }

    fn struct_body<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Vec<ast::StructMember<'a>>, Error<'a>> {
        let mut members = Vec::new();

        lexer.expect(Token::Paren('{'))?;
        let mut ready = true;
        while !lexer.skip(Token::Paren('}')) {
            if !ready {
                return Err(Error::Unexpected(
                    lexer.next().1,
                    ExpectedToken::Token(Token::Separator(',')),
                ));
            }
            let (mut size, mut align) = (ParsedAttribute::default(), ParsedAttribute::default());
            self.push_rule_span(Rule::Attribute, lexer);
            let mut bind_parser = BindingParser::default();
            while lexer.skip(Token::Attribute) {
                match lexer.next_ident_with_span()? {
                    ("size", name_span) => {
                        lexer.expect(Token::Paren('('))?;
                        let expr = self.general_expression(lexer, ctx)?;
                        lexer.expect(Token::Paren(')'))?;
                        size.set(expr, name_span)?;
                    }
                    ("align", name_span) => {
                        lexer.expect(Token::Paren('('))?;
                        let expr = self.general_expression(lexer, ctx)?;
                        lexer.expect(Token::Paren(')'))?;
                        align.set(expr, name_span)?;
                    }
                    (word, word_span) => bind_parser.parse(self, lexer, word, word_span, ctx)?,
                }
            }

            let bind_span = self.pop_rule_span(lexer);
            let binding = bind_parser.finish(bind_span)?;

            let name = lexer.next_ident()?;
            lexer.expect(Token::Separator(':'))?;
            let ty = self.type_decl(lexer, ctx)?;
            ready = lexer.skip(Token::Separator(','));

            members.push(ast::StructMember {
                name,
                ty,
                binding,
                size: size.value,
                align: align.value,
            });
        }

        Ok(members)
    }

    /// Parses `<T>`, returning T and span of T
    fn singular_generic<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<(Handle<ast::Type<'a>>, Span), Error<'a>> {
        lexer.expect_generic_paren('<')?;
        let start = lexer.start_byte_offset();
        let ty = self.type_decl(lexer, ctx)?;
        let span = lexer.span_from(start);
        lexer.expect_generic_paren('>')?;
        Ok((ty, span))
    }

    fn matrix_with_type<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
        columns: crate::VectorSize,
        rows: crate::VectorSize,
    ) -> Result<ast::Type<'a>, Error<'a>> {
        let (ty, ty_span) = self.singular_generic(lexer, ctx)?;
        Ok(ast::Type::Matrix {
            columns,
            rows,
            ty,
            ty_span,
        })
    }

    fn type_decl_impl<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        word: &'a str,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Option<ast::Type<'a>>, Error<'a>> {
        if let Some(scalar) = conv::get_scalar_type(word) {
            return Ok(Some(ast::Type::Scalar(scalar)));
        }

        Ok(Some(match word {
            "vec2" => {
                let (ty, ty_span) = self.singular_generic(lexer, ctx)?;
                ast::Type::Vector {
                    size: crate::VectorSize::Bi,
                    ty,
                    ty_span,
                }
            }
            "vec2i" => ast::Type::Vector {
                size: crate::VectorSize::Bi,
                ty: ctx.new_scalar(Scalar::I32),
                ty_span: Span::UNDEFINED,
            },
            "vec2u" => ast::Type::Vector {
                size: crate::VectorSize::Bi,
                ty: ctx.new_scalar(Scalar::U32),
                ty_span: Span::UNDEFINED,
            },
            "vec2f" => ast::Type::Vector {
                size: crate::VectorSize::Bi,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "vec3" => {
                let (ty, ty_span) = self.singular_generic(lexer, ctx)?;
                ast::Type::Vector {
                    size: crate::VectorSize::Tri,
                    ty,
                    ty_span,
                }
            }
            "vec3i" => ast::Type::Vector {
                size: crate::VectorSize::Tri,
                ty: ctx.new_scalar(Scalar::I32),
                ty_span: Span::UNDEFINED,
            },
            "vec3u" => ast::Type::Vector {
                size: crate::VectorSize::Tri,
                ty: ctx.new_scalar(Scalar::U32),
                ty_span: Span::UNDEFINED,
            },
            "vec3f" => ast::Type::Vector {
                size: crate::VectorSize::Tri,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "vec4" => {
                let (ty, ty_span) = self.singular_generic(lexer, ctx)?;
                ast::Type::Vector {
                    size: crate::VectorSize::Quad,
                    ty,
                    ty_span,
                }
            }
            "vec4i" => ast::Type::Vector {
                size: crate::VectorSize::Quad,
                ty: ctx.new_scalar(Scalar::I32),
                ty_span: Span::UNDEFINED,
            },
            "vec4u" => ast::Type::Vector {
                size: crate::VectorSize::Quad,
                ty: ctx.new_scalar(Scalar::U32),
                ty_span: Span::UNDEFINED,
            },
            "vec4f" => ast::Type::Vector {
                size: crate::VectorSize::Quad,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "mat2x2" => {
                self.matrix_with_type(lexer, ctx, crate::VectorSize::Bi, crate::VectorSize::Bi)?
            }
            "mat2x2f" => ast::Type::Matrix {
                columns: crate::VectorSize::Bi,
                rows: crate::VectorSize::Bi,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "mat2x3" => {
                self.matrix_with_type(lexer, ctx, crate::VectorSize::Bi, crate::VectorSize::Tri)?
            }
            "mat2x3f" => ast::Type::Matrix {
                columns: crate::VectorSize::Bi,
                rows: crate::VectorSize::Tri,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "mat2x4" => {
                self.matrix_with_type(lexer, ctx, crate::VectorSize::Bi, crate::VectorSize::Quad)?
            }
            "mat2x4f" => ast::Type::Matrix {
                columns: crate::VectorSize::Bi,
                rows: crate::VectorSize::Quad,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "mat3x2" => {
                self.matrix_with_type(lexer, ctx, crate::VectorSize::Tri, crate::VectorSize::Bi)?
            }
            "mat3x2f" => ast::Type::Matrix {
                columns: crate::VectorSize::Tri,
                rows: crate::VectorSize::Bi,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "mat3x3" => {
                self.matrix_with_type(lexer, ctx, crate::VectorSize::Tri, crate::VectorSize::Tri)?
            }
            "mat3x3f" => ast::Type::Matrix {
                columns: crate::VectorSize::Tri,
                rows: crate::VectorSize::Tri,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "mat3x4" => {
                self.matrix_with_type(lexer, ctx, crate::VectorSize::Tri, crate::VectorSize::Quad)?
            }
            "mat3x4f" => ast::Type::Matrix {
                columns: crate::VectorSize::Tri,
                rows: crate::VectorSize::Quad,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "mat4x2" => {
                self.matrix_with_type(lexer, ctx, crate::VectorSize::Quad, crate::VectorSize::Bi)?
            }
            "mat4x2f" => ast::Type::Matrix {
                columns: crate::VectorSize::Quad,
                rows: crate::VectorSize::Bi,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "mat4x3" => {
                self.matrix_with_type(lexer, ctx, crate::VectorSize::Quad, crate::VectorSize::Tri)?
            }
            "mat4x3f" => ast::Type::Matrix {
                columns: crate::VectorSize::Quad,
                rows: crate::VectorSize::Tri,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "mat4x4" => {
                self.matrix_with_type(lexer, ctx, crate::VectorSize::Quad, crate::VectorSize::Quad)?
            }
            "mat4x4f" => ast::Type::Matrix {
                columns: crate::VectorSize::Quad,
                rows: crate::VectorSize::Quad,
                ty: ctx.new_scalar(Scalar::F32),
                ty_span: Span::UNDEFINED,
            },
            "atomic" => {
                let scalar = lexer.next_scalar_generic()?;
                ast::Type::Atomic(scalar)
            }
            "ptr" => {
                lexer.expect_generic_paren('<')?;
                let (ident, span) = lexer.next_ident_with_span()?;
                let mut space = conv::map_address_space(ident, span)?;
                lexer.expect(Token::Separator(','))?;
                let base = self.type_decl(lexer, ctx)?;
                if let crate::AddressSpace::Storage { ref mut access } = space {
                    *access = if lexer.skip(Token::Separator(',')) {
                        lexer.next_storage_access()?
                    } else {
                        crate::StorageAccess::LOAD
                    };
                }
                lexer.expect_generic_paren('>')?;
                ast::Type::Pointer { base, space }
            }
            "array" => {
                lexer.expect_generic_paren('<')?;
                let base = self.type_decl(lexer, ctx)?;
                let size = if lexer.skip(Token::Separator(',')) {
                    let size = self.const_generic_expression(lexer, ctx)?;
                    ast::ArraySize::Constant(size)
                } else {
                    ast::ArraySize::Dynamic
                };
                lexer.expect_generic_paren('>')?;

                ast::Type::Array { base, size }
            }
            "binding_array" => {
                lexer.expect_generic_paren('<')?;
                let base = self.type_decl(lexer, ctx)?;
                let size = if lexer.skip(Token::Separator(',')) {
                    let size = self.unary_expression(lexer, ctx)?;
                    ast::ArraySize::Constant(size)
                } else {
                    ast::ArraySize::Dynamic
                };
                lexer.expect_generic_paren('>')?;

                ast::Type::BindingArray { base, size }
            }
            "sampler" => ast::Type::Sampler { comparison: false },
            "sampler_comparison" => ast::Type::Sampler { comparison: true },
            "texture_1d" => {
                let (scalar, span) = lexer.next_scalar_generic_with_span()?;
                Self::check_texture_sample_type(scalar, span)?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D1,
                    arrayed: false,
                    class: crate::ImageClass::Sampled {
                        kind: scalar.kind,
                        multi: false,
                    },
                }
            }
            "texture_1d_array" => {
                let (scalar, span) = lexer.next_scalar_generic_with_span()?;
                Self::check_texture_sample_type(scalar, span)?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D1,
                    arrayed: true,
                    class: crate::ImageClass::Sampled {
                        kind: scalar.kind,
                        multi: false,
                    },
                }
            }
            "texture_2d" => {
                let (scalar, span) = lexer.next_scalar_generic_with_span()?;
                Self::check_texture_sample_type(scalar, span)?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D2,
                    arrayed: false,
                    class: crate::ImageClass::Sampled {
                        kind: scalar.kind,
                        multi: false,
                    },
                }
            }
            "texture_2d_array" => {
                let (scalar, span) = lexer.next_scalar_generic_with_span()?;
                Self::check_texture_sample_type(scalar, span)?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D2,
                    arrayed: true,
                    class: crate::ImageClass::Sampled {
                        kind: scalar.kind,
                        multi: false,
                    },
                }
            }
            "texture_3d" => {
                let (scalar, span) = lexer.next_scalar_generic_with_span()?;
                Self::check_texture_sample_type(scalar, span)?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D3,
                    arrayed: false,
                    class: crate::ImageClass::Sampled {
                        kind: scalar.kind,
                        multi: false,
                    },
                }
            }
            "texture_cube" => {
                let (scalar, span) = lexer.next_scalar_generic_with_span()?;
                Self::check_texture_sample_type(scalar, span)?;
                ast::Type::Image {
                    dim: crate::ImageDimension::Cube,
                    arrayed: false,
                    class: crate::ImageClass::Sampled {
                        kind: scalar.kind,
                        multi: false,
                    },
                }
            }
            "texture_cube_array" => {
                let (scalar, span) = lexer.next_scalar_generic_with_span()?;
                Self::check_texture_sample_type(scalar, span)?;
                ast::Type::Image {
                    dim: crate::ImageDimension::Cube,
                    arrayed: true,
                    class: crate::ImageClass::Sampled {
                        kind: scalar.kind,
                        multi: false,
                    },
                }
            }
            "texture_multisampled_2d" => {
                let (scalar, span) = lexer.next_scalar_generic_with_span()?;
                Self::check_texture_sample_type(scalar, span)?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D2,
                    arrayed: false,
                    class: crate::ImageClass::Sampled {
                        kind: scalar.kind,
                        multi: true,
                    },
                }
            }
            "texture_multisampled_2d_array" => {
                let (scalar, span) = lexer.next_scalar_generic_with_span()?;
                Self::check_texture_sample_type(scalar, span)?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D2,
                    arrayed: true,
                    class: crate::ImageClass::Sampled {
                        kind: scalar.kind,
                        multi: true,
                    },
                }
            }
            "texture_depth_2d" => ast::Type::Image {
                dim: crate::ImageDimension::D2,
                arrayed: false,
                class: crate::ImageClass::Depth { multi: false },
            },
            "texture_depth_2d_array" => ast::Type::Image {
                dim: crate::ImageDimension::D2,
                arrayed: true,
                class: crate::ImageClass::Depth { multi: false },
            },
            "texture_depth_cube" => ast::Type::Image {
                dim: crate::ImageDimension::Cube,
                arrayed: false,
                class: crate::ImageClass::Depth { multi: false },
            },
            "texture_depth_cube_array" => ast::Type::Image {
                dim: crate::ImageDimension::Cube,
                arrayed: true,
                class: crate::ImageClass::Depth { multi: false },
            },
            "texture_depth_multisampled_2d" => ast::Type::Image {
                dim: crate::ImageDimension::D2,
                arrayed: false,
                class: crate::ImageClass::Depth { multi: true },
            },
            "texture_storage_1d" => {
                let (format, access) = lexer.next_format_generic()?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D1,
                    arrayed: false,
                    class: crate::ImageClass::Storage { format, access },
                }
            }
            "texture_storage_1d_array" => {
                let (format, access) = lexer.next_format_generic()?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D1,
                    arrayed: true,
                    class: crate::ImageClass::Storage { format, access },
                }
            }
            "texture_storage_2d" => {
                let (format, access) = lexer.next_format_generic()?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D2,
                    arrayed: false,
                    class: crate::ImageClass::Storage { format, access },
                }
            }
            "texture_storage_2d_array" => {
                let (format, access) = lexer.next_format_generic()?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D2,
                    arrayed: true,
                    class: crate::ImageClass::Storage { format, access },
                }
            }
            "texture_storage_3d" => {
                let (format, access) = lexer.next_format_generic()?;
                ast::Type::Image {
                    dim: crate::ImageDimension::D3,
                    arrayed: false,
                    class: crate::ImageClass::Storage { format, access },
                }
            }
            "acceleration_structure" => ast::Type::AccelerationStructure,
            "ray_query" => ast::Type::RayQuery,
            "RayDesc" => ast::Type::RayDesc,
            "RayIntersection" => ast::Type::RayIntersection,
            _ => return Ok(None),
        }))
    }

    const fn check_texture_sample_type(scalar: Scalar, span: Span) -> Result<(), Error<'static>> {
        use crate::ScalarKind::*;
        // Validate according to https://gpuweb.github.io/gpuweb/wgsl/#sampled-texture-type
        match scalar {
            Scalar {
                kind: Float | Sint | Uint,
                width: 4,
            } => Ok(()),
            _ => Err(Error::BadTextureSampleType { span, scalar }),
        }
    }

    /// Parse type declaration of a given name.
    fn type_decl<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
    ) -> Result<Handle<ast::Type<'a>>, Error<'a>> {
        self.push_rule_span(Rule::TypeDecl, lexer);

        let (name, span) = lexer.next_ident_with_span()?;

        let ty = match self.type_decl_impl(lexer, name, ctx)? {
            Some(ty) => ty,
            None => {
                ctx.unresolved.insert(ast::Dependency {
                    ident: name,
                    usage: span,
                });
                ast::Type::User(ast::Ident { name, span })
            }
        };

        self.pop_rule_span(lexer);

        let handle = ctx.types.append(ty, Span::UNDEFINED);
        Ok(handle)
    }

    fn assignment_op_and_rhs<'a>(
        &mut self,
        lexer: &mut Lexer<'a>,
        ctx: &mut ExpressionContext<'a, '_, '_>,
        block: &mut ast::Block<'a>,
        target: Handle<ast::Expression<'a>>,
        span_start: usize,
    ) -> Result<(), Error<'a>> {
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