wasmtime/crates/environ/src/component/translate.rs

use crate::component::*;
use crate::ScopeVec;
use crate::{
    EntityIndex, ModuleEnvironment, ModuleTranslation, PrimaryMap, SignatureIndex, Tunables,
};
use anyhow::{bail, Result};
use indexmap::IndexMap;
use std::collections::HashMap;
use std::mem;
use wasmparser::{Chunk, Encoding, Parser, Payload, Validator};

mod adapt;
pub use self::adapt::*;
mod inline;

/// Structure used to translate a component and parse it.
pub struct Translator<'a, 'data> {
    /// The current component being translated.
    ///
    /// This will get swapped out as translation traverses the body of a
    /// component and a sub-component is entered or left.
    result: Translation<'data>,

    /// Current state of parsing a binary component. Note that like `result`
    /// this will change as the component is traversed.
    parser: Parser,

    /// Stack of lexical scopes that are in-progress but not finished yet.
    ///
    /// This is pushed to whenever a component is entered and popped from
    /// whenever a component is left. Each lexical scope also contains
    /// information about the variables that it is currently required to close
    /// over which is threaded into the current in-progress translation of
    /// the sub-component which pushed a scope here.
    lexical_scopes: Vec<LexicalScope<'data>>,

    /// The validator in use to verify that the raw input binary is a valid
    /// component.
    validator: &'a mut Validator,

    /// Type information shared for the entire component.
    ///
    /// This builder is also used for all core wasm modules found to intern
    /// signatures across all modules.
    types: &'a mut ComponentTypesBuilder,

    /// The compiler configuration provided by the embedder.
    tunables: &'a Tunables,

    /// Auxiliary location to push generated adapter modules onto.
    scope_vec: &'data ScopeVec<u8>,

    /// Completely translated core wasm modules that have been found so far.
    ///
    /// Note that this translation only involves learning about type
    /// information and functions are not actually compiled here.
    static_modules: PrimaryMap<StaticModuleIndex, ModuleTranslation<'data>>,

    /// Completely translated components that have been found so far.
    ///
    /// As frames are popped from `lexical_scopes` their completed component
    /// will be pushed onto this list.
    static_components: PrimaryMap<StaticComponentIndex, Translation<'data>>,

    /// Storage for type information used by `ComponentInstanceType::Synthetic`
    /// which is thrown away after compilation is finished.
    synthetic_instance_types:
        PrimaryMap<SyntheticInstanceTypeIndex, HashMap<&'data str, ComponentItemType>>,
}

/// Representation of the syntactic scope of a component meaning where it is
/// and what its state is at in the binary format.
///
/// These scopes are pushed and popped when a sub-component starts being
/// parsed and finishes being parsed. The main purpose of this frame is to
/// have a `ClosedOverVars` field which encapsulates data that is inherited
/// from the scope specified into the component being translated just beneath
/// it.
///
/// This structure exists to implement outer aliases to components and modules.
/// When a component or module is closed over then that means it needs to be
/// inherited in a sense to the component which actually had the alias. This is
/// achieved with a deceptively simple scheme where each parent of the
/// component with the alias will inherit the component from the desired
/// location.
///
/// For example with a component structure that looks like:
///
/// ```wasm
/// (component $A
///     (core module $M)
///     (component $B
///         (component $C
///             (alias outer $A $M (core module))
///         )
///     )
/// )
/// ```
///
/// here the `C` component is closing over `M` located in the root component
/// `A`. When `C` is being translated the `lexical_scopes` field will look like
/// `[A, B]`. When the alias is encountered (for module index 0) this will
/// place a `ClosedOverModule::Local(0)` entry into the `closure_args` field of
/// `A`'s frame. This will in turn give a `ModuleUpvarIndex` which is then
/// inserted into `closure_args` in `B`'s frame. This produces yet another
/// `ModuleUpvarIndex` which is finally inserted into `C`'s module index space
/// via `LocalInitializer::AliasModuleUpvar` with the last index.
///
/// All of these upvar indices and such are interpreted in the "inline" phase
/// of compilation and not at runtime. This means that when `A` is being
/// instantiated one of its initializers will be
/// `LocalInitializer::ComponentStatic`. This starts to create `B` and the
/// variables captured for `B` are listed as local module 0, or `M`. This list
/// is then preserved in the definition of the component `B` and later reused
/// by `C` again to finally get access to the closed over component.
///
/// Effectively the scopes are managed hierarchically where a reference to an
/// outer variable automatically injects references into all parents up to
/// where the reference is. This variable scopes are the processed during
/// inlining where a component definition is a reference to the static
/// component information (`Translation`) plus closed over variables
/// (`ComponentClosure` during inlining).
struct LexicalScope<'data> {
    /// Current state of translating the `translation` below.
    parser: Parser,
    /// Current state of the component's translation as found so far.
    translation: Translation<'data>,
    /// List of captures that `translation` will need to process to create the
    /// sub-component which is directly beneath this lexical scope.
    closure_args: ClosedOverVars,
}

/// A "local" translation of a component.
///
/// This structure is used as a sort of in-progress translation of a component.
/// This is not `Component` which is the final form as consumed by Wasmtime
/// at runtime. Instead this is a fairly simple representation of a component
/// where almost everything is ordered as a list of initializers. The binary
/// format is translated to a list of initializers here which is later processed
/// during "inlining" to produce a final component with the final set of
/// initializers.
#[derive(Default)]
struct Translation<'data> {
    /// Instructions which form this component.
    ///
    /// There is one initializer for all members of each index space, and all
    /// index spaces are incrementally built here as the initializer list is
    /// processed.
    initializers: Vec<LocalInitializer<'data>>,

    /// The list of exports from this component, as pairs of names and an
    /// index into an index space of what's being exported.
    exports: IndexMap<&'data str, ComponentItem>,

    /// Type information (in Wasmtime's representation) for various
    /// component-model index spaces.
    funcs: PrimaryMap<FuncIndex, SignatureIndex>,
    components: PrimaryMap<ComponentIndex, ComponentType>,
    component_funcs: PrimaryMap<ComponentFuncIndex, TypeFuncIndex>,
    component_instances: PrimaryMap<ComponentInstanceIndex, ComponentInstanceType>,
}

#[allow(missing_docs)]
enum LocalInitializer<'data> {
    // imports
    Import(&'data str, TypeDef),

    // canonical function sections
    Lower(ComponentFuncIndex, LocalCanonicalOptions),
    Lift(TypeFuncIndex, FuncIndex, LocalCanonicalOptions),

    // core wasm modules
    ModuleStatic(StaticModuleIndex),

    // core wasm module instances
    ModuleInstantiate(ModuleIndex, HashMap<&'data str, ModuleInstanceIndex>),
    ModuleSynthetic(HashMap<&'data str, EntityIndex>),

    // components
    ComponentStatic(StaticComponentIndex, ClosedOverVars),

    // component instances
    ComponentInstantiate(ComponentIndex, HashMap<&'data str, ComponentItem>),
    ComponentSynthetic(HashMap<&'data str, ComponentItem>),

    // alias section
    AliasExportFunc(ModuleInstanceIndex, &'data str),
    AliasExportTable(ModuleInstanceIndex, &'data str),
    AliasExportGlobal(ModuleInstanceIndex, &'data str),
    AliasExportMemory(ModuleInstanceIndex, &'data str),
    AliasComponentExport(ComponentInstanceIndex, &'data str),
    AliasModule(ClosedOverModule),
    AliasComponent(ClosedOverComponent),
}

/// The "closure environment" of components themselves.
///
/// For more information see `LexicalScope`.
#[derive(Default)]
struct ClosedOverVars {
    components: PrimaryMap<ComponentUpvarIndex, ClosedOverComponent>,
    modules: PrimaryMap<ModuleUpvarIndex, ClosedOverModule>,
}

/// Description how a component is closed over when the closure variables for
/// a component are being created.
///
/// For more information see `LexicalScope`.
enum ClosedOverComponent {
    /// A closed over component is coming from the local component's index
    /// space, meaning a previously defined component is being captured.
    Local(ComponentIndex),
    /// A closed over component is coming from our own component's list of
    /// upvars. This list was passed to us by our enclosing component, which
    /// will eventually have bottomed out in closing over a `Local` component
    /// index for some parent component.
    Upvar(ComponentUpvarIndex),
}

/// Same as `ClosedOverComponent`, but for modules.
enum ClosedOverModule {
    Local(ModuleIndex),
    Upvar(ModuleUpvarIndex),
}

/// Representation of canonical ABI options.
struct LocalCanonicalOptions {
    string_encoding: StringEncoding,
    memory: Option<MemoryIndex>,
    realloc: Option<FuncIndex>,
    post_return: Option<FuncIndex>,
}

#[derive(Copy, Clone)]
enum ComponentType {
    /// A component was imported from so its type is listed by an index.
    Index(TypeComponentIndex),
    /// A component was defined statically inline so its type information can be
    /// found in the `Translation` itself.
    Static(StaticComponentIndex),
}

#[derive(Copy, Clone)]
enum ComponentInstanceType {
    /// An instance was imported so its type information is listed by index.
    Index(TypeComponentInstanceIndex),
    /// An instance was created through instantiating an imported component, so
    /// the type of the index is inferred from the type of the component.
    InstantiatedIndex(TypeComponentIndex),
    /// An instance was created through instantiation of a statically defined
    /// component, so the type information is inferred from a `Translation`.
    InstantiatedStatic(StaticComponentIndex),
    /// An instance was created from a list of other items, and the list can be
    /// found in the `synthetic_instance_types` map.
    Synthetic(SyntheticInstanceTypeIndex),
}

/// Only used as part of `synthetic_instance_types` which is used to infer type
/// information for component-model items. This intentionally doesn't cover
/// everything (e.g. modules are missing at this time since they aren't needed).
#[derive(Copy, Clone)]
enum ComponentItemType {
    Func(TypeFuncIndex),
    Component(ComponentType),
    Instance(ComponentInstanceType),
}

#[derive(Copy, Clone, PartialEq, Eq)]
struct SyntheticInstanceTypeIndex(u32);
cranelift_entity::entity_impl!(SyntheticInstanceTypeIndex);

enum Action {
    KeepGoing,
    Skip(usize),
    Done,
}

impl<'a, 'data> Translator<'a, 'data> {
    /// Creates a new translation state ready to translate a component.
    pub fn new(
        tunables: &'a Tunables,
        validator: &'a mut Validator,
        types: &'a mut ComponentTypesBuilder,
        scope_vec: &'data ScopeVec<u8>,
    ) -> Self {
        Self {
            result: Translation::default(),
            tunables,
            validator,
            types,
            parser: Parser::new(0),
            lexical_scopes: Vec::new(),
            static_components: Default::default(),
            static_modules: Default::default(),
            synthetic_instance_types: Default::default(),
            scope_vec,
        }
    }

    /// Translates the binary `component`.
    ///
    /// This is the workhorse of compilation which will parse all of
    /// `component` and create type information for Wasmtime and such. The
    /// `component` does not have to be valid and it will be validated during
    /// compilation.
    ///
    /// THe result of this function is a tuple of the final component's
    /// description plus a list of core wasm modules found within the
    /// component. The component's description actually erases internal
    /// components, instances, etc, as much as it can. Instead `Component`
    /// retains a flat list of initializers (no nesting) which was created
    /// as part of compilation from the nested structure of the original
    /// component.
    ///
    /// The list of core wasm modules found is provided to allow compiling
    /// modules externally in parallel. Additionally initializers in
    /// `Component` may refer to the modules in the map returned by index.
    ///
    /// # Errors
    ///
    /// This function will return an error if the `component` provided is
    /// invalid.
    pub fn translate(
        mut self,
        component: &'data [u8],
    ) -> Result<(
        Component,
        PrimaryMap<StaticModuleIndex, ModuleTranslation<'data>>,
    )> {
        // First up wasmparser is used to actually perform the translation and
        // validation of this component. This will produce a list of core wasm
        // modules in addition to components which are found during the
        // translation process. When doing this only a `Translation` is created
        // which is a simple representation of a component.
        let mut remaining = component;
        loop {
            let payload = match self.parser.parse(remaining, true)? {
                Chunk::Parsed { payload, consumed } => {
                    remaining = &remaining[consumed..];
                    payload
                }
                Chunk::NeedMoreData(_) => unreachable!(),
            };

            match self.translate_payload(payload, component)? {
                Action::KeepGoing => {}
                Action::Skip(n) => remaining = &remaining[n..],
                Action::Done => break,
            }
        }
        assert!(remaining.is_empty());
        assert!(self.lexical_scopes.is_empty());

        // ... after translation initially finishes the next pass is performed
        // which we're calling "inlining". This will "instantiate" the root
        // component, following nested component instantiations, creating a
        // global list of initializers along the way. This phase uses the simple
        // initializers in each component to track dataflow of host imports and
        // internal references to items throughout a component at compile-time.
        // The produce initializers in the final `Component` are intended to be
        // much simpler than the original component and more efficient for
        // Wasmtime to process at runtime as well (e.g. no string lookups as
        // most everything is done through indices instead).
        let (mut component, mut adapters) = inline::run(
            &self.types,
            &self.result,
            &self.static_modules,
            &self.static_components,
        )?;
        self.insert_adapter_module_initializers(&mut component, &mut adapters);
        Ok((component, self.static_modules))
    }

    fn translate_payload(
        &mut self,
        payload: Payload<'data>,
        component: &'data [u8],
    ) -> Result<Action> {
        match payload {
            Payload::Version {
                num,
                encoding,
                range,
            } => {
                self.validator.version(num, encoding, &range)?;

                match encoding {
                    Encoding::Component => {}
                    Encoding::Module => {
                        bail!("attempted to parse a wasm module with a component parser");
                    }
                }

                // Push a new scope for component types so outer aliases know
                // that the 0th level is this new component.
                self.types.push_type_scope();
            }

            Payload::End(offset) => {
                let types = self.validator.end(offset)?;

                // Record type information for this component now that we'll
                // have it from wasmparser.
                //
                // Note that this uses type information from `wasmparser` to
                // lookup signature of all core wasm functions in this
                // component.  This avoids us having to reimplement the
                // translate-interface-types-to-the-canonical-abi logic. The
                // type of the function is then intern'd to get a
                // `SignatureIndex` which is later used at runtime for a
                // `VMSharedSignatureIndex`.
                for idx in 0.. {
                    let lowered_function_type = match types.function_at(idx) {
                        Some(ty) => ty,
                        None => break,
                    };
                    let ty = self
                        .types
                        .module_types_builder()
                        .wasm_func_type(lowered_function_type.clone().try_into()?);
                    self.result.funcs.push(ty);
                }

                // When leaving a module be sure to pop the types scope to
                // ensure that when we go back to the previous module outer
                // type alias indices work correctly again.
                self.types.pop_type_scope();

                // Exit the current lexical scope. If there is no parent (no
                // frame currently on the stack) then translation is finished.
                // Otherwise that means that a nested component has been
                // completed and is recorded as such.
                let LexicalScope {
                    parser,
                    translation,
                    closure_args,
                } = match self.lexical_scopes.pop() {
                    Some(frame) => frame,
                    None => return Ok(Action::Done),
                };
                self.parser = parser;
                let component = mem::replace(&mut self.result, translation);
                let static_idx = self.static_components.push(component);
                self.result
                    .initializers
                    .push(LocalInitializer::ComponentStatic(static_idx, closure_args));
                self.result
                    .components
                    .push(ComponentType::Static(static_idx));
            }

            // When we see a type section the types are validated and then
            // translated into Wasmtime's representation. Each active type
            // definition is recorded in the `ComponentTypesBuilder` tables, or
            // this component's active scope.
            //
            // Note that the push/pop of the component types scope happens above
            // in `Version` and `End` since multiple type sections can appear
            // within a component.
            Payload::ComponentTypeSection(s) => {
                self.validator.component_type_section(&s)?;
                for ty in s {
                    let ty = self.types.intern_component_type(&ty?)?;
                    self.types.push_component_typedef(ty);
                }
            }
            Payload::CoreTypeSection(s) => {
                self.validator.core_type_section(&s)?;
                for ty in s {
                    let ty = self.types.intern_core_type(&ty?)?;
                    self.types.push_core_typedef(ty);
                }
            }

            // Processing the import section at this point is relatively simple
            // which is to simply record the name of the import and the type
            // information associated with it.
            Payload::ComponentImportSection(s) => {
                self.validator.component_import_section(&s)?;
                for import in s {
                    let import = import?;
                    let ty = self.types.component_type_ref(&import.ty);
                    self.result.push_typedef(ty);
                    self.result
                        .initializers
                        .push(LocalInitializer::Import(import.name, ty));
                }
            }

            // Entries in the canonical section will get initializers recorded
            // with the listed options for lifting/lowering.
            Payload::ComponentCanonicalSection(s) => {
                self.validator.component_canonical_section(&s)?;
                for func in s {
                    match func? {
                        wasmparser::CanonicalFunction::Lift {
                            type_index,
                            core_func_index,
                            options,
                        } => {
                            let ty = ComponentTypeIndex::from_u32(type_index);
                            let ty = match self.types.component_outer_type(0, ty) {
                                TypeDef::ComponentFunc(ty) => ty,
                                // should not be possible after validation
                                _ => unreachable!(),
                            };
                            let func = FuncIndex::from_u32(core_func_index);
                            let options = self.canonical_options(&options);
                            self.result
                                .initializers
                                .push(LocalInitializer::Lift(ty, func, options));
                            self.result.component_funcs.push(ty);
                        }
                        wasmparser::CanonicalFunction::Lower {
                            func_index,
                            options,
                        } => {
                            let func = ComponentFuncIndex::from_u32(func_index);
                            let options = self.canonical_options(&options);
                            self.result
                                .initializers
                                .push(LocalInitializer::Lower(func, options));
                        }
                    }
                }
            }

            // Core wasm modules are translated inline directly here with the
            // `ModuleEnvironment` from core wasm compilation. This will return
            // to the caller the size of the module so it knows how many bytes
            // of the input are skipped.
            //
            // Note that this is just initial type translation of the core wasm
            // module and actual function compilation is deferred until this
            // entire process has completed.
            Payload::ModuleSection { parser, range } => {
                self.validator.module_section(&range)?;
                let translation = ModuleEnvironment::new(
                    self.tunables,
                    self.validator,
                    self.types.module_types_builder(),
                )
                .translate(parser, &component[range.start..range.end])?;
                let static_idx = self.static_modules.push(translation);
                self.result
                    .initializers
                    .push(LocalInitializer::ModuleStatic(static_idx));
                return Ok(Action::Skip(range.end - range.start));
            }

            // When a sub-component is found then the current translation state
            // is pushed onto the `lexical_scopes` stack. This will subsequently
            // get popped as part of `Payload::End` processing above.
            //
            // Note that the set of closure args for this new lexical scope
            // starts empty since it will only get populated if translation of
            // the nested component ends up aliasing some outer module or
            // component.
            Payload::ComponentSection { parser, range } => {
                self.validator.component_section(&range)?;
                self.lexical_scopes.push(LexicalScope {
                    parser: mem::replace(&mut self.parser, parser),
                    translation: mem::take(&mut self.result),
                    closure_args: ClosedOverVars::default(),
                });
            }

            // Both core wasm instances and component instances record
            // initializers of what form of instantiation is performed which
            // largely just records the arguments given from wasmparser into a
            // `HashMap` for processing later during inlining.
            Payload::InstanceSection(s) => {
                self.validator.instance_section(&s)?;
                for instance in s {
                    let init = match instance? {
                        wasmparser::Instance::Instantiate { module_index, args } => {
                            let index = ModuleIndex::from_u32(module_index);
                            self.instantiate_module(index, &args)
                        }
                        wasmparser::Instance::FromExports(exports) => {
                            self.instantiate_module_from_exports(&exports)
                        }
                    };
                    self.result.initializers.push(init);
                }
            }
            Payload::ComponentInstanceSection(s) => {
                self.validator.component_instance_section(&s)?;
                for instance in s {
                    let init = match instance? {
                        wasmparser::ComponentInstance::Instantiate {
                            component_index,
                            args,
                        } => {
                            let index = ComponentIndex::from_u32(component_index);
                            self.instantiate_component(index, &args)
                        }
                        wasmparser::ComponentInstance::FromExports(exports) => {
                            self.instantiate_component_from_exports(&exports)
                        }
                    };
                    self.result.initializers.push(init);
                }
            }

            // Exports don't actually fill out the `initializers` array but
            // instead fill out the one other field in a `Translation`, the
            // `exports` field (as one might imagine). This for now simply
            // records the index of what's exported and that's tracked further
            // later during inlining.
            Payload::ComponentExportSection(s) => {
                self.validator.component_export_section(&s)?;
                for export in s {
                    let export = export?;

                    // TODO: https://github.com/bytecodealliance/wasmtime/issues/4494
                    // Currently, wit-component-based tooling creates components that
                    // export types to represent the interface of a component so that
                    // bindings can (potentially) be generated directly from the component
                    // itself without a wit file. For now, we ignore these exports in Wasmtime.
                    if wasmparser::ComponentExternalKind::Type == export.kind {
                        continue;
                    }

                    let item = self.kind_to_item(export.kind, export.index);
                    let prev = self.result.exports.insert(export.name, item);
                    assert!(prev.is_none());
                }
            }

            Payload::ComponentStartSection(s) => {
                self.validator.component_start_section(&s)?;
                unimplemented!("component start section");
            }

            // Aliases of instance exports (either core or component) will be
            // recorded as an initializer of the appropriate type with outer
            // aliases handled specially via upvars and type processing.
            Payload::AliasSection(s) => {
                self.validator.alias_section(&s)?;
                for alias in s {
                    let init = match alias? {
                        wasmparser::Alias::InstanceExport {
                            kind,
                            instance_index,
                            name,
                        } => {
                            let instance = ModuleInstanceIndex::from_u32(instance_index);
                            self.alias_module_instance_export(kind, instance, name)
                        }
                        wasmparser::Alias::Outer {
                            kind: wasmparser::OuterAliasKind::Type,
                            count,
                            index,
                        } => {
                            let index = TypeIndex::from_u32(index);
                            let ty = self.types.core_outer_type(count, index);
                            self.types.push_core_typedef(ty);
                            continue;
                        }
                    };
                    self.result.initializers.push(init);
                }
            }
            Payload::ComponentAliasSection(s) => {
                self.validator.component_alias_section(&s)?;
                for alias in s {
                    let init = match alias? {
                        wasmparser::ComponentAlias::InstanceExport {
                            kind,
                            instance_index,
                            name,
                        } => {
                            let instance = ComponentInstanceIndex::from_u32(instance_index);
                            drop(kind);
                            self.alias_component_instance_export(instance, name);
                            LocalInitializer::AliasComponentExport(instance, name)
                        }
                        wasmparser::ComponentAlias::Outer { kind, count, index } => {
                            self.alias_component_outer(kind, count, index);
                            continue;
                        }
                    };
                    self.result.initializers.push(init);
                }
            }

            // All custom sections are ignored by Wasmtime at this time.
            //
            // FIXME(WebAssembly/component-model#14): probably want to specify
            // and parse a `name` section here.
            Payload::CustomSection { .. } => {}

            // Anything else is either not reachable since we never enable the
            // feature in Wasmtime or we do enable it and it's a bug we don't
            // implement it, so let validation take care of most errors here and
            // if it gets past validation provide a helpful error message to
            // debug.
            other => {
                self.validator.payload(&other)?;
                panic!("unimplemented section {other:?}");
            }
        }

        Ok(Action::KeepGoing)
    }

    fn instantiate_module(
        &mut self,
        module: ModuleIndex,
        raw_args: &[wasmparser::InstantiationArg<'data>],
    ) -> LocalInitializer<'data> {
        let mut args = HashMap::with_capacity(raw_args.len());
        for arg in raw_args {
            match arg.kind {
                wasmparser::InstantiationArgKind::Instance => {
                    let idx = ModuleInstanceIndex::from_u32(arg.index);
                    args.insert(arg.name, idx);
                }
            }
        }
        LocalInitializer::ModuleInstantiate(module, args)
    }

    /// Creates a synthetic module from the list of items currently in the
    /// module and their given names.
    fn instantiate_module_from_exports(
        &mut self,
        exports: &[wasmparser::Export<'data>],
    ) -> LocalInitializer<'data> {
        let mut map = HashMap::with_capacity(exports.len());
        for export in exports {
            let idx = match export.kind {
                wasmparser::ExternalKind::Func => {
                    let index = FuncIndex::from_u32(export.index);
                    EntityIndex::Function(index)
                }
                wasmparser::ExternalKind::Table => {
                    let index = TableIndex::from_u32(export.index);
                    EntityIndex::Table(index)
                }
                wasmparser::ExternalKind::Memory => {
                    let index = MemoryIndex::from_u32(export.index);
                    EntityIndex::Memory(index)
                }
                wasmparser::ExternalKind::Global => {
                    let index = GlobalIndex::from_u32(export.index);
                    EntityIndex::Global(index)
                }

                // doesn't get past validation
                wasmparser::ExternalKind::Tag => unimplemented!("wasm exceptions"),
            };
            map.insert(export.name, idx);
        }
        LocalInitializer::ModuleSynthetic(map)
    }

    fn instantiate_component(
        &mut self,
        component: ComponentIndex,
        raw_args: &[wasmparser::ComponentInstantiationArg<'data>],
    ) -> LocalInitializer<'data> {
        let mut args = HashMap::with_capacity(raw_args.len());
        for arg in raw_args {
            let idx = self.kind_to_item(arg.kind, arg.index);
            args.insert(arg.name, idx);
        }

        self.result
            .component_instances
            .push(match self.result.components[component] {
                ComponentType::Index(i) => ComponentInstanceType::InstantiatedIndex(i),
                ComponentType::Static(i) => ComponentInstanceType::InstantiatedStatic(i),
            });

        LocalInitializer::ComponentInstantiate(component, args)
    }

    /// Creates a synthetic module from the list of items currently in the
    /// module and their given names.
    fn instantiate_component_from_exports(
        &mut self,
        exports: &[wasmparser::ComponentExport<'data>],
    ) -> LocalInitializer<'data> {
        let mut map = HashMap::with_capacity(exports.len());
        let mut types = HashMap::with_capacity(exports.len());
        for export in exports {
            let idx = self.kind_to_item(export.kind, export.index);
            let ty = match idx {
                ComponentItem::Func(i) => {
                    Some(ComponentItemType::Func(self.result.component_funcs[i]))
                }
                ComponentItem::Component(i) => {
                    Some(ComponentItemType::Component(self.result.components[i]))
                }
                ComponentItem::ComponentInstance(i) => Some(ComponentItemType::Instance(
                    self.result.component_instances[i],
                )),
                ComponentItem::Module(_) => None,
            };
            map.insert(export.name, idx);
            if let Some(ty) = ty {
                types.insert(export.name, ty);
            }
        }

        let index = self.synthetic_instance_types.push(types);
        self.result
            .component_instances
            .push(ComponentInstanceType::Synthetic(index));

        LocalInitializer::ComponentSynthetic(map)
    }

    fn kind_to_item(&self, kind: wasmparser::ComponentExternalKind, index: u32) -> ComponentItem {
        match kind {
            wasmparser::ComponentExternalKind::Func => {
                let index = ComponentFuncIndex::from_u32(index);
                ComponentItem::Func(index)
            }
            wasmparser::ComponentExternalKind::Module => {
                let index = ModuleIndex::from_u32(index);
                ComponentItem::Module(index)
            }
            wasmparser::ComponentExternalKind::Instance => {
                let index = ComponentInstanceIndex::from_u32(index);
                ComponentItem::ComponentInstance(index)
            }
            wasmparser::ComponentExternalKind::Component => {
                let index = ComponentIndex::from_u32(index);
                ComponentItem::Component(index)
            }
            wasmparser::ComponentExternalKind::Value => {
                unimplemented!("component values");
            }
            wasmparser::ComponentExternalKind::Type => {
                unimplemented!("component type export");
            }
        }
    }

    fn alias_module_instance_export(
        &mut self,
        kind: wasmparser::ExternalKind,
        instance: ModuleInstanceIndex,
        name: &'data str,
    ) -> LocalInitializer<'data> {
        match kind {
            wasmparser::ExternalKind::Func => LocalInitializer::AliasExportFunc(instance, name),
            wasmparser::ExternalKind::Memory => LocalInitializer::AliasExportMemory(instance, name),
            wasmparser::ExternalKind::Table => LocalInitializer::AliasExportTable(instance, name),
            wasmparser::ExternalKind::Global => LocalInitializer::AliasExportGlobal(instance, name),
            wasmparser::ExternalKind::Tag => {
                unimplemented!("wasm exceptions");
            }
        }
    }

    fn alias_component_instance_export(
        &mut self,
        instance: ComponentInstanceIndex,
        name: &'data str,
    ) {
        match self.result.component_instances[instance] {
            // An imported component instance is being aliased, so the type of
            // the aliased item is directly available from the instance type.
            ComponentInstanceType::Index(ty) => {
                self.result.push_typedef(self.types[ty].exports[name])
            }

            // An imported component was instantiated so the type of the aliased
            // export is available through the type of the export on the
            // original component.
            ComponentInstanceType::InstantiatedIndex(ty) => {
                self.result.push_typedef(self.types[ty].exports[name])
            }

            // A static nested component was instantiated which means that the
            // type of the export can be looked up directly from the translation
            // that was finished prior.
            ComponentInstanceType::InstantiatedStatic(idx) => {
                let translation = &self.static_components[idx];

                match translation.exports[name] {
                    ComponentItem::Func(idx) => {
                        self.result
                            .component_funcs
                            .push(translation.component_funcs[idx]);
                    }
                    ComponentItem::Component(idx) => {
                        self.result.components.push(translation.components[idx]);
                    }
                    ComponentItem::ComponentInstance(idx) => {
                        self.result
                            .component_instances
                            .push(translation.component_instances[idx]);
                    }

                    // ignored during this type pass
                    ComponentItem::Module(_) => {}
                }
            }

            // A synthetic instance is being aliased which means the global list
            // of synthetic instance types can be consulted for the type
            // information.
            ComponentInstanceType::Synthetic(index) => {
                let map = &self.synthetic_instance_types[index];
                match map[name] {
                    ComponentItemType::Func(ty) => {
                        self.result.component_funcs.push(ty);
                    }
                    ComponentItemType::Component(ty) => {
                        self.result.components.push(ty);
                    }
                    ComponentItemType::Instance(ty) => {
                        self.result.component_instances.push(ty);
                    }
                }
            }
        }
    }

    fn alias_component_outer(
        &mut self,
        kind: wasmparser::ComponentOuterAliasKind,
        count: u32,
        index: u32,
    ) {
        match kind {
            // When aliasing a type the `ComponentTypesBuilder` is used to
            // resolve the outer `count` plus the index, and then once it's
            // resolved we push the type information into our local index
            // space.
            //
            // Note that this is just copying indices around as all type
            // information is basically a pointer back into the `TypesBuilder`
            // structure (and the eventual `TypeTables` that it produces).
            wasmparser::ComponentOuterAliasKind::CoreType => {
                let index = TypeIndex::from_u32(index);
                let ty = self.types.core_outer_type(count, index);
                self.types.push_core_typedef(ty);
            }
            wasmparser::ComponentOuterAliasKind::Type => {
                let index = ComponentTypeIndex::from_u32(index);
                let ty = self.types.component_outer_type(count, index);
                self.types.push_component_typedef(ty);
            }

            // For more information about the implementation of outer aliases
            // see the documentation of `LexicalScope`. Otherwise though the
            // main idea here is that the data to close over starts as `Local`
            // and then transitions to `Upvar` as its inserted into the parents
            // in order from target we're aliasing back to the current
            // component.
            wasmparser::ComponentOuterAliasKind::CoreModule => {
                let index = ModuleIndex::from_u32(index);
                let mut module = ClosedOverModule::Local(index);
                let depth = self.lexical_scopes.len() - (count as usize);
                for frame in self.lexical_scopes[depth..].iter_mut() {
                    module = ClosedOverModule::Upvar(frame.closure_args.modules.push(module));
                }

                // If the `module` is still `Local` then the `depth` was 0 and
                // it's an alias into our own space. Otherwise it's switched to
                // an upvar and will index into the upvar space. Either way
                // it's just plumbed directly into the initializer.
                self.result
                    .initializers
                    .push(LocalInitializer::AliasModule(module));
            }
            wasmparser::ComponentOuterAliasKind::Component => {
                let index = ComponentIndex::from_u32(index);
                let mut component = ClosedOverComponent::Local(index);
                let depth = self.lexical_scopes.len() - (count as usize);
                for frame in self.lexical_scopes[depth..].iter_mut() {
                    component =
                        ClosedOverComponent::Upvar(frame.closure_args.components.push(component));
                }
                let component_ty = match self.lexical_scopes.get(depth) {
                    Some(frame) => frame.translation.components[index],
                    None => self.result.components[index],
                };

                self.result
                    .initializers
                    .push(LocalInitializer::AliasComponent(component));
                self.result.components.push(component_ty);
            }
        }
    }

    fn canonical_options(&mut self, opts: &[wasmparser::CanonicalOption]) -> LocalCanonicalOptions {
        let mut ret = LocalCanonicalOptions {
            string_encoding: StringEncoding::Utf8,
            memory: None,
            realloc: None,
            post_return: None,
        };
        for opt in opts {
            match opt {
                wasmparser::CanonicalOption::UTF8 => {
                    ret.string_encoding = StringEncoding::Utf8;
                }
                wasmparser::CanonicalOption::UTF16 => {
                    ret.string_encoding = StringEncoding::Utf16;
                }
                wasmparser::CanonicalOption::CompactUTF16 => {
                    ret.string_encoding = StringEncoding::CompactUtf16;
                }
                wasmparser::CanonicalOption::Memory(idx) => {
                    let idx = MemoryIndex::from_u32(*idx);
                    ret.memory = Some(idx);
                }
                wasmparser::CanonicalOption::Realloc(idx) => {
                    let idx = FuncIndex::from_u32(*idx);
                    ret.realloc = Some(idx);
                }
                wasmparser::CanonicalOption::PostReturn(idx) => {
                    let idx = FuncIndex::from_u32(*idx);
                    ret.post_return = Some(idx);
                }
            }
        }
        return ret;
    }
}

impl Translation<'_> {
    fn push_typedef(&mut self, ty: TypeDef) {
        match ty {
            TypeDef::ComponentInstance(idx) => {
                self.component_instances
                    .push(ComponentInstanceType::Index(idx));
            }
            TypeDef::ComponentFunc(idx) => {
                self.component_funcs.push(idx);
            }
            TypeDef::Component(idx) => {
                self.components.push(ComponentType::Index(idx));
            }

            // not processed here
            TypeDef::Interface(_) | TypeDef::CoreFunc(_) | TypeDef::Module(_) => {}
        }
    }
}