function.rs

use crate::arena::{Arena, UniqueArena};
use crate::arena::{Handle, HandleSet};

use super::validate_atomic_compare_exchange_struct;

use super::{
    analyzer::{UniformityDisruptor, UniformityRequirements},
    ExpressionError, FunctionInfo, ModuleInfo,
};
use crate::span::WithSpan;
use crate::span::{AddSpan as _, MapErrWithSpan as _};

#[derive(Clone, Debug, thiserror::Error)]
#[cfg_attr(test, derive(PartialEq))]
pub enum CallError {
    #[error("Argument {index} expression is invalid")]
    Argument {
        index: usize,
        source: ExpressionError,
    },
    #[error("Result expression {0:?} has already been introduced earlier")]
    ResultAlreadyInScope(Handle<crate::Expression>),
    #[error("Result expression {0:?} is populated by multiple `Call` statements")]
    ResultAlreadyPopulated(Handle<crate::Expression>),
    #[error("Result value is invalid")]
    ResultValue(#[source] ExpressionError),
    #[error("Requires {required} arguments, but {seen} are provided")]
    ArgumentCount { required: usize, seen: usize },
    #[error("Argument {index} value {seen_expression:?} doesn't match the type {required:?}")]
    ArgumentType {
        index: usize,
        required: Handle<crate::Type>,
        seen_expression: Handle<crate::Expression>,
    },
    #[error("The emitted expression doesn't match the call")]
    ExpressionMismatch(Option<Handle<crate::Expression>>),
}

#[derive(Clone, Debug, thiserror::Error)]
#[cfg_attr(test, derive(PartialEq))]
pub enum AtomicError {
    #[error("Pointer {0:?} to atomic is invalid.")]
    InvalidPointer(Handle<crate::Expression>),
    #[error("Address space {0:?} does not support 64bit atomics.")]
    InvalidAddressSpace(crate::AddressSpace),
    #[error("Operand {0:?} has invalid type.")]
    InvalidOperand(Handle<crate::Expression>),
    #[error("Result expression {0:?} is not an `AtomicResult` expression")]
    InvalidResultExpression(Handle<crate::Expression>),
    #[error("Result expression {0:?} is marked as an `exchange`")]
    ResultExpressionExchange(Handle<crate::Expression>),
    #[error("Result expression {0:?} is not marked as an `exchange`")]
    ResultExpressionNotExchange(Handle<crate::Expression>),
    #[error("Result type for {0:?} doesn't match the statement")]
    ResultTypeMismatch(Handle<crate::Expression>),
    #[error("Exchange operations must return a value")]
    MissingReturnValue,
    #[error("Capability {0:?} is required")]
    MissingCapability(super::Capabilities),
    #[error("Result expression {0:?} is populated by multiple `Atomic` statements")]
    ResultAlreadyPopulated(Handle<crate::Expression>),
}

#[derive(Clone, Debug, thiserror::Error)]
#[cfg_attr(test, derive(PartialEq))]
pub enum SubgroupError {
    #[error("Operand {0:?} has invalid type.")]
    InvalidOperand(Handle<crate::Expression>),
    #[error("Result type for {0:?} doesn't match the statement")]
    ResultTypeMismatch(Handle<crate::Expression>),
    #[error("Support for subgroup operation {0:?} is required")]
    UnsupportedOperation(super::SubgroupOperationSet),
    #[error("Unknown operation")]
    UnknownOperation,
}

#[derive(Clone, Debug, thiserror::Error)]
#[cfg_attr(test, derive(PartialEq))]
pub enum LocalVariableError {
    #[error("Local variable has a type {0:?} that can't be stored in a local variable.")]
    InvalidType(Handle<crate::Type>),
    #[error("Initializer doesn't match the variable type")]
    InitializerType,
    #[error("Initializer is not a const or override expression")]
    NonConstOrOverrideInitializer,
}

#[derive(Clone, Debug, thiserror::Error)]
#[cfg_attr(test, derive(PartialEq))]
pub enum FunctionError {
    #[error("Expression {handle:?} is invalid")]
    Expression {
        handle: Handle<crate::Expression>,
        source: ExpressionError,
    },
    #[error("Expression {0:?} can't be introduced - it's already in scope")]
    ExpressionAlreadyInScope(Handle<crate::Expression>),
    #[error("Local variable {handle:?} '{name}' is invalid")]
    LocalVariable {
        handle: Handle<crate::LocalVariable>,
        name: String,
        source: LocalVariableError,
    },
    #[error("Argument '{name}' at index {index} has a type that can't be passed into functions.")]
    InvalidArgumentType { index: usize, name: String },
    #[error("The function's given return type cannot be returned from functions")]
    NonConstructibleReturnType,
    #[error("Argument '{name}' at index {index} is a pointer of space {space:?}, which can't be passed into functions.")]
    InvalidArgumentPointerSpace {
        index: usize,
        name: String,
        space: crate::AddressSpace,
    },
    #[error("There are instructions after `return`/`break`/`continue`")]
    InstructionsAfterReturn,
    #[error("The `break` is used outside of a `loop` or `switch` context")]
    BreakOutsideOfLoopOrSwitch,
    #[error("The `continue` is used outside of a `loop` context")]
    ContinueOutsideOfLoop,
    #[error("The `return` is called within a `continuing` block")]
    InvalidReturnSpot,
    #[error("The `return` value {0:?} does not match the function return value")]
    InvalidReturnType(Option<Handle<crate::Expression>>),
    #[error("The `if` condition {0:?} is not a boolean scalar")]
    InvalidIfType(Handle<crate::Expression>),
    #[error("The `switch` value {0:?} is not an integer scalar")]
    InvalidSwitchType(Handle<crate::Expression>),
    #[error("Multiple `switch` cases for {0:?} are present")]
    ConflictingSwitchCase(crate::SwitchValue),
    #[error("The `switch` contains cases with conflicting types")]
    ConflictingCaseType,
    #[error("The `switch` is missing a `default` case")]
    MissingDefaultCase,
    #[error("Multiple `default` cases are present")]
    MultipleDefaultCases,
    #[error("The last `switch` case contains a `fallthrough`")]
    LastCaseFallTrough,
    #[error("The pointer {0:?} doesn't relate to a valid destination for a store")]
    InvalidStorePointer(Handle<crate::Expression>),
    #[error("The value {0:?} can not be stored")]
    InvalidStoreValue(Handle<crate::Expression>),
    #[error("The type of {value:?} doesn't match the type stored in {pointer:?}")]
    InvalidStoreTypes {
        pointer: Handle<crate::Expression>,
        value: Handle<crate::Expression>,
    },
    #[error("Image store parameters are invalid")]
    InvalidImageStore(#[source] ExpressionError),
    #[error("Image atomic parameters are invalid")]
    InvalidImageAtomic(#[source] ExpressionError),
    #[error("Image atomic function is invalid")]
    InvalidImageAtomicFunction(crate::AtomicFunction),
    #[error("Image atomic value is invalid")]
    InvalidImageAtomicValue(Handle<crate::Expression>),
    #[error("Call to {function:?} is invalid")]
    InvalidCall {
        function: Handle<crate::Function>,
        #[source]
        error: CallError,
    },
    #[error("Atomic operation is invalid")]
    InvalidAtomic(#[from] AtomicError),
    #[error("Ray Query {0:?} is not a local variable")]
    InvalidRayQueryExpression(Handle<crate::Expression>),
    #[error("Acceleration structure {0:?} is not a matching expression")]
    InvalidAccelerationStructure(Handle<crate::Expression>),
    #[error("Ray descriptor {0:?} is not a matching expression")]
    InvalidRayDescriptor(Handle<crate::Expression>),
    #[error("Ray Query {0:?} does not have a matching type")]
    InvalidRayQueryType(Handle<crate::Type>),
    #[error("Shader requires capability {0:?}")]
    MissingCapability(super::Capabilities),
    #[error(
        "Required uniformity of control flow for {0:?} in {1:?} is not fulfilled because of {2:?}"
    )]
    NonUniformControlFlow(
        UniformityRequirements,
        Handle<crate::Expression>,
        UniformityDisruptor,
    ),
    #[error("Functions that are not entry points cannot have `@location` or `@builtin` attributes on their arguments: \"{name}\" has attributes")]
    PipelineInputRegularFunction { name: String },
    #[error("Functions that are not entry points cannot have `@location` or `@builtin` attributes on their return value types")]
    PipelineOutputRegularFunction,
    #[error("Required uniformity for WorkGroupUniformLoad is not fulfilled because of {0:?}")]
    // The actual load statement will be "pointed to" by the span
    NonUniformWorkgroupUniformLoad(UniformityDisruptor),
    // This is only possible with a misbehaving frontend
    #[error("The expression {0:?} for a WorkGroupUniformLoad isn't a WorkgroupUniformLoadResult")]
    WorkgroupUniformLoadExpressionMismatch(Handle<crate::Expression>),
    #[error("The expression {0:?} is not valid as a WorkGroupUniformLoad argument. It should be a Pointer in Workgroup address space")]
    WorkgroupUniformLoadInvalidPointer(Handle<crate::Expression>),
    #[error("Subgroup operation is invalid")]
    InvalidSubgroup(#[from] SubgroupError),
    #[error("Emit statement should not cover \"result\" expressions like {0:?}")]
    EmitResult(Handle<crate::Expression>),
    #[error("Expression not visited by the appropriate statement")]
    UnvisitedExpression(Handle<crate::Expression>),
}

bitflags::bitflags! {
    #[repr(transparent)]
    #[derive(Clone, Copy)]
    struct ControlFlowAbility: u8 {
        /// The control can return out of this block.
        const RETURN = 0x1;
        /// The control can break.
        const BREAK = 0x2;
        /// The control can continue.
        const CONTINUE = 0x4;
    }
}

struct BlockInfo {
    stages: super::ShaderStages,
    finished: bool,
}

struct BlockContext<'a> {
    abilities: ControlFlowAbility,
    info: &'a FunctionInfo,
    expressions: &'a Arena<crate::Expression>,
    types: &'a UniqueArena<crate::Type>,
    local_vars: &'a Arena<crate::LocalVariable>,
    global_vars: &'a Arena<crate::GlobalVariable>,
    functions: &'a Arena<crate::Function>,
    special_types: &'a crate::SpecialTypes,
    prev_infos: &'a [FunctionInfo],
    return_type: Option<Handle<crate::Type>>,
}

impl<'a> BlockContext<'a> {
    fn new(
        fun: &'a crate::Function,
        module: &'a crate::Module,
        info: &'a FunctionInfo,
        prev_infos: &'a [FunctionInfo],
    ) -> Self {
        Self {
            abilities: ControlFlowAbility::RETURN,
            info,
            expressions: &fun.expressions,
            types: &module.types,
            local_vars: &fun.local_variables,
            global_vars: &module.global_variables,
            functions: &module.functions,
            special_types: &module.special_types,
            prev_infos,
            return_type: fun.result.as_ref().map(|fr| fr.ty),
        }
    }

    const fn with_abilities(&self, abilities: ControlFlowAbility) -> Self {
        BlockContext { abilities, ..*self }
    }

    fn get_expression(&self, handle: Handle<crate::Expression>) -> &'a crate::Expression {
        &self.expressions[handle]
    }

    fn resolve_type_impl(
        &self,
        handle: Handle<crate::Expression>,
        valid_expressions: &HandleSet<crate::Expression>,
    ) -> Result<&crate::TypeInner, WithSpan<ExpressionError>> {
        if !valid_expressions.contains(handle) {
            Err(ExpressionError::NotInScope.with_span_handle(handle, self.expressions))
        } else {
            Ok(self.info[handle].ty.inner_with(self.types))
        }
    }

    fn resolve_type(
        &self,
        handle: Handle<crate::Expression>,
        valid_expressions: &HandleSet<crate::Expression>,
    ) -> Result<&crate::TypeInner, WithSpan<FunctionError>> {
        self.resolve_type_impl(handle, valid_expressions)
            .map_err_inner(|source| FunctionError::Expression { handle, source }.with_span())
    }

    fn resolve_pointer_type(&self, handle: Handle<crate::Expression>) -> &crate::TypeInner {
        self.info[handle].ty.inner_with(self.types)
    }
}

impl super::Validator {
    fn validate_call(
        &mut self,
        function: Handle<crate::Function>,
        arguments: &[Handle<crate::Expression>],
        result: Option<Handle<crate::Expression>>,
        context: &BlockContext,
    ) -> Result<super::ShaderStages, WithSpan<CallError>> {
        let fun = &context.functions[function];
        if fun.arguments.len() != arguments.len() {
            return Err(CallError::ArgumentCount {
                required: fun.arguments.len(),
                seen: arguments.len(),
            }
            .with_span());
        }
        for (index, (arg, &expr)) in fun.arguments.iter().zip(arguments).enumerate() {
            let ty = context
                .resolve_type_impl(expr, &self.valid_expression_set)
                .map_err_inner(|source| {
                    CallError::Argument { index, source }
                        .with_span_handle(expr, context.expressions)
                })?;
            let arg_inner = &context.types[arg.ty].inner;
            if !ty.equivalent(arg_inner, context.types) {
                return Err(CallError::ArgumentType {
                    index,
                    required: arg.ty,
                    seen_expression: expr,
                }
                .with_span_handle(expr, context.expressions));
            }
        }

        if let Some(expr) = result {
            if self.valid_expression_set.insert(expr) {
                self.valid_expression_list.push(expr);
            } else {
                return Err(CallError::ResultAlreadyInScope(expr)
                    .with_span_handle(expr, context.expressions));
            }
            match context.expressions[expr] {
                crate::Expression::CallResult(callee)
                    if fun.result.is_some() && callee == function =>
                {
                    if !self.needs_visit.remove(expr) {
                        return Err(CallError::ResultAlreadyPopulated(expr)
                            .with_span_handle(expr, context.expressions));
                    }
                }
                _ => {
                    return Err(CallError::ExpressionMismatch(result)
                        .with_span_handle(expr, context.expressions))
                }
            }
        } else if fun.result.is_some() {
            return Err(CallError::ExpressionMismatch(result).with_span());
        }

        let callee_info = &context.prev_infos[function.index()];
        Ok(callee_info.available_stages)
    }

    fn emit_expression(
        &mut self,
        handle: Handle<crate::Expression>,
        context: &BlockContext,
    ) -> Result<(), WithSpan<FunctionError>> {
        if self.valid_expression_set.insert(handle) {
            self.valid_expression_list.push(handle);
            Ok(())
        } else {
            Err(FunctionError::ExpressionAlreadyInScope(handle)
                .with_span_handle(handle, context.expressions))
        }
    }

    fn validate_atomic(
        &mut self,
        pointer: Handle<crate::Expression>,
        fun: &crate::AtomicFunction,
        value: Handle<crate::Expression>,
        result: Option<Handle<crate::Expression>>,
        span: crate::Span,
        context: &BlockContext,
    ) -> Result<(), WithSpan<FunctionError>> {
        // The `pointer` operand must be a pointer to an atomic value.
        let pointer_inner = context.resolve_type(pointer, &self.valid_expression_set)?;
        let crate::TypeInner::Pointer {
            base: pointer_base,
            space: pointer_space,
        } = *pointer_inner
        else {
            log::error!("Atomic operation on type {:?}", *pointer_inner);
            return Err(AtomicError::InvalidPointer(pointer)
                .with_span_handle(pointer, context.expressions)
                .into_other());
        };
        let crate::TypeInner::Atomic(pointer_scalar) = context.types[pointer_base].inner else {
            log::error!(
                "Atomic pointer to type {:?}",
                context.types[pointer_base].inner
            );
            return Err(AtomicError::InvalidPointer(pointer)
                .with_span_handle(pointer, context.expressions)
                .into_other());
        };

        // The `value` operand must be a scalar of the same type as the atomic.
        let value_inner = context.resolve_type(value, &self.valid_expression_set)?;
        let crate::TypeInner::Scalar(value_scalar) = *value_inner else {
            log::error!("Atomic operand type {:?}", *value_inner);
            return Err(AtomicError::InvalidOperand(value)
                .with_span_handle(value, context.expressions)
                .into_other());
        };
        if pointer_scalar != value_scalar {
            log::error!("Atomic operand type {:?}", *value_inner);
            return Err(AtomicError::InvalidOperand(value)
                .with_span_handle(value, context.expressions)
                .into_other());
        }

        // Check for the special restrictions on 64-bit atomic operations.
        //
        // We don't need to consider other widths here: this function has already checked
        // that `pointer`'s type is an `Atomic`, and `validate_type` has already checked
        // that that `Atomic` type has a permitted scalar width.
        if pointer_scalar.width == 8 {
            // `Capabilities::SHADER_INT64_ATOMIC_ALL_OPS` enables all sorts of 64-bit
            // atomic operations.
            if self
                .capabilities
                .contains(super::Capabilities::SHADER_INT64_ATOMIC_ALL_OPS)
            {
                // okay
            } else {
                // `Capabilities::SHADER_INT64_ATOMIC_MIN_MAX` allows `Min` and
                // `Max` on operations in `Storage`, without a return value.
                if matches!(
                    *fun,
                    crate::AtomicFunction::Min | crate::AtomicFunction::Max
                ) && matches!(pointer_space, crate::AddressSpace::Storage { .. })
                    && result.is_none()
                {
                    if !self
                        .capabilities
                        .contains(super::Capabilities::SHADER_INT64_ATOMIC_MIN_MAX)
                    {
                        log::error!("Int64 min-max atomic operations are not supported");
                        return Err(AtomicError::MissingCapability(
                            super::Capabilities::SHADER_INT64_ATOMIC_MIN_MAX,
                        )
                        .with_span_handle(value, context.expressions)
                        .into_other());
                    }
                } else {
                    // Otherwise, we require the full 64-bit atomic capability.
                    log::error!("Int64 atomic operations are not supported");
                    return Err(AtomicError::MissingCapability(
                        super::Capabilities::SHADER_INT64_ATOMIC_ALL_OPS,
                    )
                    .with_span_handle(value, context.expressions)
                    .into_other());
                }
            }
        }

        // The result expression must be appropriate to the operation.
        match result {
            Some(result) => {
                // The `result` handle must refer to an `AtomicResult` expression.
                let crate::Expression::AtomicResult {
                    ty: result_ty,
                    comparison,
                } = context.expressions[result]
                else {
                    return Err(AtomicError::InvalidResultExpression(result)
                        .with_span_handle(result, context.expressions)
                        .into_other());
                };

                // Note that this expression has been visited by the proper kind
                // of statement.
                if !self.needs_visit.remove(result) {
                    return Err(AtomicError::ResultAlreadyPopulated(result)
                        .with_span_handle(result, context.expressions)
                        .into_other());
                }

                // The constraints on the result type depend on the atomic function.
                if let crate::AtomicFunction::Exchange {
                    compare: Some(compare),
                } = *fun
                {
                    // The comparison value must be a scalar of the same type as the
                    // atomic we're operating on.
                    let compare_inner =
                        context.resolve_type(compare, &self.valid_expression_set)?;
                    if !compare_inner.equivalent(value_inner, context.types) {
                        log::error!(
                            "Atomic exchange comparison has a different type from the value"
                        );
                        return Err(AtomicError::InvalidOperand(compare)
                            .with_span_handle(compare, context.expressions)
                            .into_other());
                    }

                    // The result expression must be an `__atomic_compare_exchange_result`
                    // struct whose `old_value` member is of the same type as the atomic
                    // we're operating on.
                    let crate::TypeInner::Struct { ref members, .. } =
                        context.types[result_ty].inner
                    else {
                        return Err(AtomicError::ResultTypeMismatch(result)
                            .with_span_handle(result, context.expressions)
                            .into_other());
                    };
                    if !validate_atomic_compare_exchange_struct(
                        context.types,
                        members,
                        |ty: &crate::TypeInner| *ty == crate::TypeInner::Scalar(pointer_scalar),
                    ) {
                        return Err(AtomicError::ResultTypeMismatch(result)
                            .with_span_handle(result, context.expressions)
                            .into_other());
                    }

                    // The result expression must be for a comparison operation.
                    if !comparison {
                        return Err(AtomicError::ResultExpressionNotExchange(result)
                            .with_span_handle(result, context.expressions)
                            .into_other());
                    }
                } else {
                    // The result expression must be a scalar of the same type as the
                    // atomic we're operating on.
                    let result_inner = &context.types[result_ty].inner;
                    if !result_inner.equivalent(value_inner, context.types) {
                        return Err(AtomicError::ResultTypeMismatch(result)
                            .with_span_handle(result, context.expressions)
                            .into_other());
                    }

                    // The result expression must not be for a comparison.
                    if comparison {
                        return Err(AtomicError::ResultExpressionExchange(result)
                            .with_span_handle(result, context.expressions)
                            .into_other());
                    }
                }
                self.emit_expression(result, context)?;
            }

            None => {
                // Exchange operations must always produce a value.
                if let crate::AtomicFunction::Exchange { compare: None } = *fun {
                    log::error!("Atomic exchange's value is unused");
                    return Err(AtomicError::MissingReturnValue
                        .with_span_static(span, "atomic exchange operation")
                        .into_other());
                }
            }
        }

        Ok(())
    }
    fn validate_subgroup_operation(
        &mut self,
        op: &crate::SubgroupOperation,
        collective_op: &crate::CollectiveOperation,
        argument: Handle<crate::Expression>,
        result: Handle<crate::Expression>,
        context: &BlockContext,
    ) -> Result<(), WithSpan<FunctionError>> {
        let argument_inner = context.resolve_type(argument, &self.valid_expression_set)?;

        let (is_scalar, scalar) = match *argument_inner {
            crate::TypeInner::Scalar(scalar) => (true, scalar),
            crate::TypeInner::Vector { scalar, .. } => (false, scalar),
            _ => {
                log::error!("Subgroup operand type {:?}", argument_inner);
                return Err(SubgroupError::InvalidOperand(argument)
                    .with_span_handle(argument, context.expressions)
                    .into_other());
            }
        };

        use crate::ScalarKind as sk;
        use crate::SubgroupOperation as sg;
        match (scalar.kind, *op) {
            (sk::Bool, sg::All | sg::Any) if is_scalar => {}
            (sk::Sint | sk::Uint | sk::Float, sg::Add | sg::Mul | sg::Min | sg::Max) => {}
            (sk::Sint | sk::Uint, sg::And | sg::Or | sg::Xor) => {}

            (_, _) => {
                log::error!("Subgroup operand type {:?}", argument_inner);
                return Err(SubgroupError::InvalidOperand(argument)
                    .with_span_handle(argument, context.expressions)
                    .into_other());
            }
        };

        use crate::CollectiveOperation as co;
        match (*collective_op, *op) {
            (
                co::Reduce,
                sg::All
                | sg::Any
                | sg::Add
                | sg::Mul
                | sg::Min
                | sg::Max
                | sg::And
                | sg::Or
                | sg::Xor,
            ) => {}
            (co::InclusiveScan | co::ExclusiveScan, sg::Add | sg::Mul) => {}

            (_, _) => {
                return Err(SubgroupError::UnknownOperation.with_span().into_other());
            }
        };

        self.emit_expression(result, context)?;
        match context.expressions[result] {
            crate::Expression::SubgroupOperationResult { ty }
                if { &context.types[ty].inner == argument_inner } => {}
            _ => {
                return Err(SubgroupError::ResultTypeMismatch(result)
                    .with_span_handle(result, context.expressions)
                    .into_other())
            }
        }
        Ok(())
    }
    fn validate_subgroup_gather(
        &mut self,
        mode: &crate::GatherMode,
        argument: Handle<crate::Expression>,
        result: Handle<crate::Expression>,
        context: &BlockContext,
    ) -> Result<(), WithSpan<FunctionError>> {
        match *mode {
            crate::GatherMode::BroadcastFirst => {}
            crate::GatherMode::Broadcast(index)
            | crate::GatherMode::Shuffle(index)
            | crate::GatherMode::ShuffleDown(index)
            | crate::GatherMode::ShuffleUp(index)
            | crate::GatherMode::ShuffleXor(index) => {
                let index_ty = context.resolve_type(index, &self.valid_expression_set)?;
                match *index_ty {
                    crate::TypeInner::Scalar(crate::Scalar::U32) => {}
                    _ => {
                        log::error!(
                            "Subgroup gather index type {:?}, expected unsigned int",
                            index_ty
                        );
                        return Err(SubgroupError::InvalidOperand(argument)
                            .with_span_handle(index, context.expressions)
                            .into_other());
                    }
                }
            }
        }
        let argument_inner = context.resolve_type(argument, &self.valid_expression_set)?;
        if !matches!(*argument_inner,
            crate::TypeInner::Scalar ( scalar, .. ) | crate::TypeInner::Vector { scalar, .. }
            if matches!(scalar.kind, crate::ScalarKind::Uint | crate::ScalarKind::Sint | crate::ScalarKind::Float)
        ) {
            log::error!("Subgroup gather operand type {:?}", argument_inner);
            return Err(SubgroupError::InvalidOperand(argument)
                .with_span_handle(argument, context.expressions)
                .into_other());
        }

        self.emit_expression(result, context)?;
        match context.expressions[result] {
            crate::Expression::SubgroupOperationResult { ty }
                if { &context.types[ty].inner == argument_inner } => {}
            _ => {
                return Err(SubgroupError::ResultTypeMismatch(result)
                    .with_span_handle(result, context.expressions)
                    .into_other())
            }
        }
        Ok(())
    }

    fn validate_block_impl(
        &mut self,
        statements: &crate::Block,
        context: &BlockContext,
    ) -> Result<BlockInfo, WithSpan<FunctionError>> {
        use crate::{AddressSpace, Statement as S, TypeInner as Ti};
        let mut finished = false;
        let mut stages = super::ShaderStages::all();
        for (statement, &span) in statements.span_iter() {
            if finished {
                return Err(FunctionError::InstructionsAfterReturn
                    .with_span_static(span, "instructions after return"));
            }
            match *statement {
                S::Emit(ref range) => {
                    for handle in range.clone() {
                        use crate::Expression as Ex;
                        match context.expressions[handle] {
                            Ex::Literal(_)
                            | Ex::Constant(_)
                            | Ex::Override(_)
                            | Ex::ZeroValue(_)
                            | Ex::Compose { .. }
                            | Ex::Access { .. }
                            | Ex::AccessIndex { .. }
                            | Ex::Splat { .. }
                            | Ex::Swizzle { .. }
                            | Ex::FunctionArgument(_)
                            | Ex::GlobalVariable(_)
                            | Ex::LocalVariable(_)
                            | Ex::Load { .. }
                            | Ex::ImageSample { .. }
                            | Ex::ImageLoad { .. }
                            | Ex::ImageQuery { .. }
                            | Ex::Unary { .. }
                            | Ex::Binary { .. }
                            | Ex::Select { .. }
                            | Ex::Derivative { .. }
                            | Ex::Relational { .. }
                            | Ex::Math { .. }
                            | Ex::As { .. }
                            | Ex::ArrayLength(_)
                            | Ex::RayQueryGetIntersection { .. } => {
                                self.emit_expression(handle, context)?
                            }
                            Ex::CallResult(_)
                            | Ex::AtomicResult { .. }
                            | Ex::WorkGroupUniformLoadResult { .. }
                            | Ex::RayQueryProceedResult
                            | Ex::SubgroupBallotResult
                            | Ex::SubgroupOperationResult { .. } => {
                                return Err(FunctionError::EmitResult(handle)
                                    .with_span_handle(handle, context.expressions));
                            }
                        }
                    }
                }
                S::Block(ref block) => {
                    let info = self.validate_block(block, context)?;
                    stages &= info.stages;
                    finished = info.finished;
                }
                S::If {
                    condition,
                    ref accept,
                    ref reject,
                } => {
                    match *context.resolve_type(condition, &self.valid_expression_set)? {
                        Ti::Scalar(crate::Scalar {
                            kind: crate::ScalarKind::Bool,
                            width: _,
                        }) => {}
                        _ => {
                            return Err(FunctionError::InvalidIfType(condition)
                                .with_span_handle(condition, context.expressions))
                        }
                    }
                    stages &= self.validate_block(accept, context)?.stages;
                    stages &= self.validate_block(reject, context)?.stages;
                }
                S::Switch {
                    selector,
                    ref cases,
                } => {
                    let uint = match context
                        .resolve_type(selector, &self.valid_expression_set)?
                        .scalar_kind()
                    {
                        Some(crate::ScalarKind::Uint) => true,
                        Some(crate::ScalarKind::Sint) => false,
                        _ => {
                            return Err(FunctionError::InvalidSwitchType(selector)
                                .with_span_handle(selector, context.expressions))
                        }
                    };
                    self.switch_values.clear();
                    for case in cases {
                        match case.value {
                            crate::SwitchValue::I32(_) if !uint => {}
                            crate::SwitchValue::U32(_) if uint => {}
                            crate::SwitchValue::Default => {}
                            _ => {
                                return Err(FunctionError::ConflictingCaseType.with_span_static(
                                    case.body
                                        .span_iter()
                                        .next()
                                        .map_or(Default::default(), |(_, s)| *s),
                                    "conflicting switch arm here",
                                ));
                            }
                        };
                        if !self.switch_values.insert(case.value) {
                            return Err(match case.value {
                                crate::SwitchValue::Default => FunctionError::MultipleDefaultCases
                                    .with_span_static(
                                        case.body
                                            .span_iter()
                                            .next()
                                            .map_or(Default::default(), |(_, s)| *s),
                                        "duplicated switch arm here",
                                    ),
                                _ => FunctionError::ConflictingSwitchCase(case.value)
                                    .with_span_static(
                                        case.body
                                            .span_iter()
                                            .next()
                                            .map_or(Default::default(), |(_, s)| *s),
                                        "conflicting switch arm here",
                                    ),
                            });
                        }
                    }
                    if !self.switch_values.contains(&crate::SwitchValue::Default) {
                        return Err(FunctionError::MissingDefaultCase
                            .with_span_static(span, "missing default case"));
                    }
                    if let Some(case) = cases.last() {
                        if case.fall_through {
                            return Err(FunctionError::LastCaseFallTrough.with_span_static(
                                case.body
                                    .span_iter()
                                    .next()
                                    .map_or(Default::default(), |(_, s)| *s),
                                "bad switch arm here",
                            ));
                        }
                    }
                    let pass_through_abilities = context.abilities
                        & (ControlFlowAbility::RETURN | ControlFlowAbility::CONTINUE);
                    let sub_context =
                        context.with_abilities(pass_through_abilities | ControlFlowAbility::BREAK);
                    for case in cases {
                        stages &= self.validate_block(&case.body, &sub_context)?.stages;
                    }
                }
                S::Loop {
                    ref body,
                    ref continuing,
                    break_if,
                } => {
                    // special handling for block scoping is needed here,
                    // because the continuing{} block inherits the scope
                    let base_expression_count = self.valid_expression_list.len();
                    let pass_through_abilities = context.abilities & ControlFlowAbility::RETURN;
                    stages &= self
                        .validate_block_impl(
                            body,
                            &context.with_abilities(
                                pass_through_abilities
                                    | ControlFlowAbility::BREAK
                                    | ControlFlowAbility::CONTINUE,
                            ),
                        )?
                        .stages;
                    stages &= self
                        .validate_block_impl(
                            continuing,
                            &context.with_abilities(ControlFlowAbility::empty()),
                        )?
                        .stages;

                    if let Some(condition) = break_if {
                        match *context.resolve_type(condition, &self.valid_expression_set)? {
                            Ti::Scalar(crate::Scalar {
                                kind: crate::ScalarKind::Bool,
                                width: _,
                            }) => {}
                            _ => {
                                return Err(FunctionError::InvalidIfType(condition)
                                    .with_span_handle(condition, context.expressions))
                            }
                        }
                    }

                    for handle in self.valid_expression_list.drain(base_expression_count..) {
                        self.valid_expression_set.remove(handle);
                    }
                }
                S::Break => {
                    if !context.abilities.contains(ControlFlowAbility::BREAK) {
                        return Err(FunctionError::BreakOutsideOfLoopOrSwitch
                            .with_span_static(span, "invalid break"));
                    }
                    finished = true;
                }
                S::Continue => {
                    if !context.abilities.contains(ControlFlowAbility::CONTINUE) {
                        return Err(FunctionError::ContinueOutsideOfLoop
                            .with_span_static(span, "invalid continue"));
                    }
                    finished = true;
                }
                S::Return { value } => {
                    if !context.abilities.contains(ControlFlowAbility::RETURN) {
                        return Err(FunctionError::InvalidReturnSpot
                            .with_span_static(span, "invalid return"));
                    }
                    let value_ty = value
                        .map(|expr| context.resolve_type(expr, &self.valid_expression_set))
                        .transpose()?;
                    let expected_ty = context.return_type.map(|ty| &context.types[ty].inner);
                    // We can't return pointers, but it seems best not to embed that
                    // assumption here, so use `TypeInner::equivalent` for comparison.
                    let okay = match (value_ty, expected_ty) {
                        (None, None) => true,
                        (Some(value_inner), Some(expected_inner)) => {
                            value_inner.equivalent(expected_inner, context.types)
                        }
                        (_, _) => false,
                    };

                    if !okay {
                        log::error!(
                            "Returning {:?} where {:?} is expected",
                            value_ty,
                            expected_ty
                        );
                        if let Some(handle) = value {
                            return Err(FunctionError::InvalidReturnType(value)
                                .with_span_handle(handle, context.expressions));
                        } else {
                            return Err(FunctionError::InvalidReturnType(value)
                                .with_span_static(span, "invalid return"));
                        }
                    }
                    finished = true;
                }
                S::Kill => {
                    stages &= super::ShaderStages::FRAGMENT;
                    finished = true;
                }
                S::Barrier(barrier) => {
                    stages &= super::ShaderStages::COMPUTE;
                    if barrier.contains(crate::Barrier::SUB_GROUP) {
                        if !self.capabilities.contains(
                            super::Capabilities::SUBGROUP | super::Capabilities::SUBGROUP_BARRIER,
                        ) {
                            return Err(FunctionError::MissingCapability(
                                super::Capabilities::SUBGROUP
                                    | super::Capabilities::SUBGROUP_BARRIER,
                            )
                            .with_span_static(span, "missing capability for this operation"));
                        }
                        if !self
                            .subgroup_operations
                            .contains(super::SubgroupOperationSet::BASIC)
                        {
                            return Err(FunctionError::InvalidSubgroup(
                                SubgroupError::UnsupportedOperation(
                                    super::SubgroupOperationSet::BASIC,
                                ),
                            )
                            .with_span_static(span, "support for this operation is not present"));
                        }
                    }
                }
                S::Store { pointer, value } => {
                    let mut current = pointer;
                    loop {
                        match context.expressions[current] {
                            crate::Expression::Access { base, .. }
                            | crate::Expression::AccessIndex { base, .. } => current = base,
                            crate::Expression::LocalVariable(_)
                            | crate::Expression::GlobalVariable(_)
                            | crate::Expression::FunctionArgument(_) => break,
                            _ => {
                                return Err(FunctionError::InvalidStorePointer(current)
                                    .with_span_handle(pointer, context.expressions))
                            }
                        }
                    }

                    let value_ty = context.resolve_type(value, &self.valid_expression_set)?;
                    match *value_ty {
                        Ti::Image { .. } | Ti::Sampler { .. } => {
                            return Err(FunctionError::InvalidStoreValue(value)
                                .with_span_handle(value, context.expressions));
                        }
                        _ => {}
                    }

                    let pointer_ty = context.resolve_pointer_type(pointer);

                    let good = match *pointer_ty {
                        Ti::Pointer { base, space: _ } => match context.types[base].inner {
                            Ti::Atomic(scalar) => *value_ty == Ti::Scalar(scalar),
                            ref other => value_ty == other,
                        },
                        Ti::ValuePointer {
                            size: Some(size),
                            scalar,
                            space: _,
                        } => *value_ty == Ti::Vector { size, scalar },
                        Ti::ValuePointer {
                            size: None,
                            scalar,
                            space: _,
                        } => *value_ty == Ti::Scalar(scalar),
                        _ => false,
                    };
                    if !good {
                        return Err(FunctionError::InvalidStoreTypes { pointer, value }
                            .with_span()
                            .with_handle(pointer, context.expressions)
                            .with_handle(value, context.expressions));
                    }

                    if let Some(space) = pointer_ty.pointer_space() {
                        if !space.access().contains(crate::StorageAccess::STORE) {
                            return Err(FunctionError::InvalidStorePointer(pointer)
                                .with_span_static(
                                    context.expressions.get_span(pointer),
                                    "writing to this location is not permitted",
                                ));
                        }
                    }
                }
                S::ImageStore {
                    image,
                    coordinate,
                    array_index,
                    value,
                } => {
                    //Note: this code uses a lot of `FunctionError::InvalidImageStore`,
                    // and could probably be refactored.
                    let var = match *context.get_expression(image) {
                        crate::Expression::GlobalVariable(var_handle) => {
                            &context.global_vars[var_handle]
                        }
                        // We're looking at a binding index situation, so punch through the index and look at the global behind it.
                        crate::Expression::Access { base, .. }
                        | crate::Expression::AccessIndex { base, .. } => {
                            match *context.get_expression(base) {
                                crate::Expression::GlobalVariable(var_handle) => {
                                    &context.global_vars[var_handle]
                                }
                                _ => {
                                    return Err(FunctionError::InvalidImageStore(
                                        ExpressionError::ExpectedGlobalVariable,
                                    )
                                    .with_span_handle(image, context.expressions))
                                }
                            }
                        }
                        _ => {
                            return Err(FunctionError::InvalidImageStore(
                                ExpressionError::ExpectedGlobalVariable,
                            )
                            .with_span_handle(image, context.expressions))
                        }
                    };

                    // Punch through a binding array to get the underlying type
                    let global_ty = match context.types[var.ty].inner {
                        Ti::BindingArray { base, .. } => &context.types[base].inner,
                        ref inner => inner,
                    };

                    let value_ty = match *global_ty {
                        Ti::Image {
                            class,
                            arrayed,
                            dim,
                        } => {
                            match context
                                .resolve_type(coordinate, &self.valid_expression_set)?
                                .image_storage_coordinates()
                            {
                                Some(coord_dim) if coord_dim == dim => {}
                                _ => {
                                    return Err(FunctionError::InvalidImageStore(
                                        ExpressionError::InvalidImageCoordinateType(
                                            dim, coordinate,
                                        ),
                                    )
                                    .with_span_handle(coordinate, context.expressions));
                                }
                            };
                            if arrayed != array_index.is_some() {
                                return Err(FunctionError::InvalidImageStore(
                                    ExpressionError::InvalidImageArrayIndex,
                                )
                                .with_span_handle(coordinate, context.expressions));
                            }
                            if let Some(expr) = array_index {
                                match *context.resolve_type(expr, &self.valid_expression_set)? {
                                    Ti::Scalar(crate::Scalar {
                                        kind: crate::ScalarKind::Sint | crate::ScalarKind::Uint,
                                        width: _,
                                    }) => {}
                                    _ => {
                                        return Err(FunctionError::InvalidImageStore(
                                            ExpressionError::InvalidImageArrayIndexType(expr),
                                        )
                                        .with_span_handle(expr, context.expressions));
                                    }
                                }
                            }
                            match class {
                                crate::ImageClass::Storage { format, .. } => {
                                    crate::TypeInner::Vector {
                                        size: crate::VectorSize::Quad,
                                        scalar: format.into(),
                                    }
                                }
                                _ => {
                                    return Err(FunctionError::InvalidImageStore(
                                        ExpressionError::InvalidImageClass(class),
                                    )
                                    .with_span_handle(image, context.expressions));
                                }
                            }
                        }
                        _ => {
                            return Err(FunctionError::InvalidImageStore(
                                ExpressionError::ExpectedImageType(var.ty),
                            )
                            .with_span()
                            .with_handle(var.ty, context.types)
                            .with_handle(image, context.expressions))
                        }
                    };

                    if *context.resolve_type(value, &self.valid_expression_set)? != value_ty {
                        return Err(FunctionError::InvalidStoreValue(value)
                            .with_span_handle(value, context.expressions));
                    }
                }
                S::Call {
                    function,
                    ref arguments,
                    result,
                } => match self.validate_call(function, arguments, result, context) {
                    Ok(callee_stages) => stages &= callee_stages,
                    Err(error) => {
                        return Err(error.and_then(|error| {
                            FunctionError::InvalidCall { function, error }
                                .with_span_static(span, "invalid function call")
                        }))
                    }
                },
                S::Atomic {
                    pointer,
                    ref fun,
                    value,
                    result,
                } => {
                    self.validate_atomic(pointer, fun, value, result, span, context)?;
                }
                S::ImageAtomic {
                    image,
                    coordinate,
                    sample: _,
                    fun,
                    value,
                } => {
                    let var = match *context.get_expression(image) {
                        crate::Expression::GlobalVariable(var_handle) => {
                            &context.global_vars[var_handle]
                        }
                        // We're looking at a binding index situation, so punch through the index and look at the global behind it.
                        crate::Expression::Access { base, .. }
                        | crate::Expression::AccessIndex { base, .. } => {
                            match *context.get_expression(base) {
                                crate::Expression::GlobalVariable(var_handle) => {
                                    &context.global_vars[var_handle]
                                }
                                _ => {
                                    return Err(FunctionError::InvalidImageAtomic(
                                        ExpressionError::ExpectedGlobalVariable,
                                    )
                                    .with_span_handle(image, context.expressions))
                                }
                            }
                        }
                        _ => {
                            return Err(FunctionError::InvalidImageAtomic(
                                ExpressionError::ExpectedGlobalVariable,
                            )
                            .with_span_handle(image, context.expressions))
                        }
                    };

                    // Punch through a binding array to get the underlying type
                    let global_ty = match context.types[var.ty].inner {
                        Ti::BindingArray { base, .. } => &context.types[base].inner,
                        ref inner => inner,
                    };

                    let value_ty = match *global_ty {
                        Ti::Image {
                            class,
                            arrayed: _,
                            dim,
                        } => {
                            match context
                                .resolve_type(coordinate, &self.valid_expression_set)?
                                .image_storage_coordinates()
                            {
                                Some(coord_dim) if coord_dim == dim => {}
                                _ => {
                                    return Err(FunctionError::InvalidImageAtomic(
                                        ExpressionError::InvalidImageCoordinateType(
                                            dim, coordinate,
                                        ),
                                    )
                                    .with_span_handle(coordinate, context.expressions));
                                }
                            };

                            match class {
                                crate::ImageClass::Storage { format, access } => {
                                    if access != crate::StorageAccess::ATOMIC {
                                        return Err(FunctionError::InvalidImageAtomic(
                                            ExpressionError::InvalidImageStorageAccess(access),
                                        )
                                        .with_span_handle(image, context.expressions));
                                    }
                                    match format {
                                        crate::StorageFormat::R32Sint
                                        | crate::StorageFormat::R32Uint => {
                                            if !self
                                                .capabilities
                                                .intersects(super::Capabilities::TEXTURE_ATOMIC)
                                            {
                                                return Err(FunctionError::MissingCapability(
                                                    super::Capabilities::TEXTURE_ATOMIC,
                                                )
                                                .with_span_static(
                                                    span,
                                                    "missing capability for this operation",
                                                ));
                                            }
                                            match fun {
                                                crate::AtomicFunction::Add
                                                | crate::AtomicFunction::And
                                                | crate::AtomicFunction::ExclusiveOr
                                                | crate::AtomicFunction::InclusiveOr
                                                | crate::AtomicFunction::Min
                                                | crate::AtomicFunction::Max => {}
                                                _ => {
                                                    return Err(
                                                        FunctionError::InvalidImageAtomicFunction(
                                                            fun,
                                                        )
                                                        .with_span_handle(
                                                            image,
                                                            context.expressions,
                                                        ),
                                                    );
                                                }
                                            }
                                        }
                                        _ => {
                                            return Err(FunctionError::InvalidImageAtomic(
                                                ExpressionError::InvalidImageFormat(format),
                                            )
                                            .with_span_handle(image, context.expressions));
                                        }
                                    }
                                    crate::TypeInner::Scalar(format.into())
                                }
                                _ => {
                                    return Err(FunctionError::InvalidImageAtomic(
                                        ExpressionError::InvalidImageClass(class),
                                    )
                                    .with_span_handle(image, context.expressions));
                                }
                            }
                        }
                        _ => {
                            return Err(FunctionError::InvalidImageAtomic(
                                ExpressionError::ExpectedImageType(var.ty),
                            )
                            .with_span()
                            .with_handle(var.ty, context.types)
                            .with_handle(image, context.expressions))
                        }
                    };

                    if *context.resolve_type(value, &self.valid_expression_set)? != value_ty {
                        return Err(FunctionError::InvalidImageAtomicValue(value)
                            .with_span_handle(value, context.expressions));
                    }
                }
                S::WorkGroupUniformLoad { pointer, result } => {
                    stages &= super::ShaderStages::COMPUTE;
                    let pointer_inner =
                        context.resolve_type(pointer, &self.valid_expression_set)?;
                    match *pointer_inner {
                        Ti::Pointer {
                            space: AddressSpace::WorkGroup,
                            ..
                        } => {}
                        Ti::ValuePointer {
                            space: AddressSpace::WorkGroup,
                            ..
                        } => {}
                        _ => {
                            return Err(FunctionError::WorkgroupUniformLoadInvalidPointer(pointer)
                                .with_span_static(span, "WorkGroupUniformLoad"))
                        }
                    }
                    self.emit_expression(result, context)?;
                    let ty = match &context.expressions[result] {
                        &crate::Expression::WorkGroupUniformLoadResult { ty } => ty,
                        _ => {
                            return Err(FunctionError::WorkgroupUniformLoadExpressionMismatch(
                                result,
                            )
                            .with_span_static(span, "WorkGroupUniformLoad"));
                        }
                    };
                    let expected_pointer_inner = Ti::Pointer {
                        base: ty,
                        space: AddressSpace::WorkGroup,
                    };
                    if !expected_pointer_inner.equivalent(pointer_inner, context.types) {
                        return Err(FunctionError::WorkgroupUniformLoadInvalidPointer(pointer)
                            .with_span_static(span, "WorkGroupUniformLoad"));
                    }
                }
                S::RayQuery { query, ref fun } => {
                    let query_var = match *context.get_expression(query) {
                        crate::Expression::LocalVariable(var) => &context.local_vars[var],
                        ref other => {
                            log::error!("Unexpected ray query expression {other:?}");
                            return Err(FunctionError::InvalidRayQueryExpression(query)
                                .with_span_static(span, "invalid query expression"));
                        }
                    };
                    match context.types[query_var.ty].inner {
                        Ti::RayQuery => {}
                        ref other => {
                            log::error!("Unexpected ray query type {other:?}");
                            return Err(FunctionError::InvalidRayQueryType(query_var.ty)
                                .with_span_static(span, "invalid query type"));
                        }
                    }
                    match *fun {
                        crate::RayQueryFunction::Initialize {
                            acceleration_structure,
                            descriptor,
                        } => {
                            match *context
                                .resolve_type(acceleration_structure, &self.valid_expression_set)?
                            {
                                Ti::AccelerationStructure => {}
                                _ => {
                                    return Err(FunctionError::InvalidAccelerationStructure(
                                        acceleration_structure,
                                    )
                                    .with_span_static(span, "invalid acceleration structure"))
                                }
                            }
                            let desc_ty_given =
                                context.resolve_type(descriptor, &self.valid_expression_set)?;
                            let desc_ty_expected = context
                                .special_types
                                .ray_desc
                                .map(|handle| &context.types[handle].inner);
                            if Some(desc_ty_given) != desc_ty_expected {
                                return Err(FunctionError::InvalidRayDescriptor(descriptor)
                                    .with_span_static(span, "invalid ray descriptor"));
                            }
                        }
                        crate::RayQueryFunction::Proceed { result } => {
                            self.emit_expression(result, context)?;
                        }
                        crate::RayQueryFunction::Terminate => {}
                    }
                }
                S::SubgroupBallot { result, predicate } => {
                    stages &= self.subgroup_stages;
                    if !self.capabilities.contains(super::Capabilities::SUBGROUP) {
                        return Err(FunctionError::MissingCapability(
                            super::Capabilities::SUBGROUP,
                        )
                        .with_span_static(span, "missing capability for this operation"));
                    }
                    if !self
                        .subgroup_operations
                        .contains(super::SubgroupOperationSet::BALLOT)
                    {
                        return Err(FunctionError::InvalidSubgroup(
                            SubgroupError::UnsupportedOperation(
                                super::SubgroupOperationSet::BALLOT,
                            ),
                        )
                        .with_span_static(span, "support for this operation is not present"));
                    }
                    if let Some(predicate) = predicate {
                        let predicate_inner =
                            context.resolve_type(predicate, &self.valid_expression_set)?;
                        if !matches!(
                            *predicate_inner,
                            crate::TypeInner::Scalar(crate::Scalar::BOOL,)
                        ) {
                            log::error!(
                                "Subgroup ballot predicate type {:?} expected bool",
                                predicate_inner
                            );
                            return Err(SubgroupError::InvalidOperand(predicate)
                                .with_span_handle(predicate, context.expressions)
                                .into_other());
                        }
                    }
                    self.emit_expression(result, context)?;
                }
                S::SubgroupCollectiveOperation {
                    ref op,
                    ref collective_op,
                    argument,
                    result,
                } => {
                    stages &= self.subgroup_stages;
                    if !self.capabilities.contains(super::Capabilities::SUBGROUP) {
                        return Err(FunctionError::MissingCapability(
                            super::Capabilities::SUBGROUP,
                        )
                        .with_span_static(span, "missing capability for this operation"));
                    }
                    let operation = op.required_operations();
                    if !self.subgroup_operations.contains(operation) {
                        return Err(FunctionError::InvalidSubgroup(
                            SubgroupError::UnsupportedOperation(operation),
                        )
                        .with_span_static(span, "support for this operation is not present"));
                    }
                    self.validate_subgroup_operation(op, collective_op, argument, result, context)?;
                }
                S::SubgroupGather {
                    ref mode,
                    argument,
                    result,
                } => {
                    stages &= self.subgroup_stages;
                    if !self.capabilities.contains(super::Capabilities::SUBGROUP) {
                        return Err(FunctionError::MissingCapability(
                            super::Capabilities::SUBGROUP,
                        )
                        .with_span_static(span, "missing capability for this operation"));
                    }
                    let operation = mode.required_operations();
                    if !self.subgroup_operations.contains(operation) {
                        return Err(FunctionError::InvalidSubgroup(
                            SubgroupError::UnsupportedOperation(operation),
                        )
                        .with_span_static(span, "support for this operation is not present"));
                    }
                    self.validate_subgroup_gather(mode, argument, result, context)?;
                }
            }
        }
        Ok(BlockInfo { stages, finished })
    }

    fn validate_block(
        &mut self,
        statements: &crate::Block,
        context: &BlockContext,
    ) -> Result<BlockInfo, WithSpan<FunctionError>> {
        let base_expression_count = self.valid_expression_list.len();
        let info = self.validate_block_impl(statements, context)?;
        for handle in self.valid_expression_list.drain(base_expression_count..) {
            self.valid_expression_set.remove(handle);
        }
        Ok(info)
    }

    fn validate_local_var(
        &self,
        var: &crate::LocalVariable,
        gctx: crate::proc::GlobalCtx,
        fun_info: &FunctionInfo,
        local_expr_kind: &crate::proc::ExpressionKindTracker,
    ) -> Result<(), LocalVariableError> {
        log::debug!("var {:?}", var);
        let type_info = self
            .types
            .get(var.ty.index())
            .ok_or(LocalVariableError::InvalidType(var.ty))?;
        if !type_info.flags.contains(super::TypeFlags::CONSTRUCTIBLE) {
            return Err(LocalVariableError::InvalidType(var.ty));
        }

        if let Some(init) = var.init {
            let decl_ty = &gctx.types[var.ty].inner;
            let init_ty = fun_info[init].ty.inner_with(gctx.types);
            if !decl_ty.equivalent(init_ty, gctx.types) {
                return Err(LocalVariableError::InitializerType);
            }

            if !local_expr_kind.is_const_or_override(init) {
                return Err(LocalVariableError::NonConstOrOverrideInitializer);
            }
        }

        Ok(())
    }

    pub(super) fn validate_function(
        &mut self,
        fun: &crate::Function,
        module: &crate::Module,
        mod_info: &ModuleInfo,
        entry_point: bool,
        global_expr_kind: &crate::proc::ExpressionKindTracker,
    ) -> Result<FunctionInfo, WithSpan<FunctionError>> {
        let mut info = mod_info.process_function(fun, module, self.flags, self.capabilities)?;

        let local_expr_kind = crate::proc::ExpressionKindTracker::from_arena(&fun.expressions);

        for (var_handle, var) in fun.local_variables.iter() {
            self.validate_local_var(var, module.to_ctx(), &info, &local_expr_kind)
                .map_err(|source| {
                    FunctionError::LocalVariable {
                        handle: var_handle,
                        name: var.name.clone().unwrap_or_default(),
                        source,
                    }
                    .with_span_handle(var.ty, &module.types)
                    .with_handle(var_handle, &fun.local_variables)
                })?;
        }

        for (index, argument) in fun.arguments.iter().enumerate() {
            match module.types[argument.ty].inner.pointer_space() {
                Some(crate::AddressSpace::Private | crate::AddressSpace::Function) | None => {}
                Some(other) => {
                    return Err(FunctionError::InvalidArgumentPointerSpace {
                        index,
                        name: argument.name.clone().unwrap_or_default(),
                        space: other,
                    }
                    .with_span_handle(argument.ty, &module.types))
                }
            }
            // Check for the least informative error last.
            if !self.types[argument.ty.index()]
                .flags
                .contains(super::TypeFlags::ARGUMENT)
            {
                return Err(FunctionError::InvalidArgumentType {
                    index,
                    name: argument.name.clone().unwrap_or_default(),
                }
                .with_span_handle(argument.ty, &module.types));
            }

            if !entry_point && argument.binding.is_some() {
                return Err(FunctionError::PipelineInputRegularFunction {
                    name: argument.name.clone().unwrap_or_default(),
                }
                .with_span_handle(argument.ty, &module.types));
            }
        }

        if let Some(ref result) = fun.result {
            if !self.types[result.ty.index()]
                .flags
                .contains(super::TypeFlags::CONSTRUCTIBLE)
            {
                return Err(FunctionError::NonConstructibleReturnType
                    .with_span_handle(result.ty, &module.types));
            }

            if !entry_point && result.binding.is_some() {
                return Err(FunctionError::PipelineOutputRegularFunction
                    .with_span_handle(result.ty, &module.types));
            }
        }

        self.valid_expression_set.clear_for_arena(&fun.expressions);
        self.valid_expression_list.clear();
        self.needs_visit.clear_for_arena(&fun.expressions);
        for (handle, expr) in fun.expressions.iter() {
            if expr.needs_pre_emit() {
                self.valid_expression_set.insert(handle);
            }
            if self.flags.contains(super::ValidationFlags::EXPRESSIONS) {
                // Mark expressions that need to be visited by a particular kind of
                // statement.
                if let crate::Expression::CallResult(_) | crate::Expression::AtomicResult { .. } =
                    *expr
                {
                    self.needs_visit.insert(handle);
                }

                match self.validate_expression(
                    handle,
                    expr,
                    fun,
                    module,
                    &info,
                    mod_info,
                    global_expr_kind,
                ) {
                    Ok(stages) => info.available_stages &= stages,
                    Err(source) => {
                        return Err(FunctionError::Expression { handle, source }
                            .with_span_handle(handle, &fun.expressions))
                    }
                }
            }
        }

        if self.flags.contains(super::ValidationFlags::BLOCKS) {
            let stages = self
                .validate_block(
                    &fun.body,
                    &BlockContext::new(fun, module, &info, &mod_info.functions),
                )?
                .stages;
            info.available_stages &= stages;

            if self.flags.contains(super::ValidationFlags::EXPRESSIONS) {
                if let Some(handle) = self.needs_visit.iter().next() {
                    return Err(FunctionError::UnvisitedExpression(handle)
                        .with_span_handle(handle, &fun.expressions));
                }
            }
        }
        Ok(info)
    }
}