Overhaul and refactor some internals of wit-component (#1810)

* Overhaul and refactor some internals of `wit-component`

This commit is a lead-up to the changes proposed in #1774. The
`wit-component` crate is quite old and has gone through many iterations
of the component model and it's very much showing its age in a few
places. Namely the correlation between component model names and core
wasm names is open-coded in many places throughout validation and
encoding of a component. This makes the changes in #1774 where the names
may be different (e.g. core wasm 0.2.0 might import component 0.2.1).

Making this change was inevitably going to require quite a lot of
refactoring of `wit-component`, so that's what this commit does. It's a
pretty large rewrite of the internals of validation of a core wasm
module and adapter prior to creating a component. The metadata produced
by this pass is now represented in a completely different format. The
metadata is extensively used throughout the encoding process so encoding
has been heavily refactored as well.

The overall idea is that the previous "grab bag" of various items here
and there produced from validation are now all unified into a single
`ImportMap` and `ExportMap` for a module. These maps track all the
various kinds of imports and exports and how they map back to core wasm
names. Notably this means that the logic to correlate core wasm names
with component model names is now happening in just one location (in
theory) as opposed to implicitly all throughout encoding. I've
additionally taken this opportunity to subjectively simplify much of the
encoding process around managing instantiations of core wasm modules and
adapters.

One of the main changes in this commit is that it does away with code
structure such as "do the thing for WIT" then "do the thing for
resources" then "do the thing for other resources" and finally "do the
thing for adapters". This was difficult to understand every time I came
back to it and I can't imagine was easy for anyone else to understand
either. All imports are now handled in a single location and it's
intended to be much better separated who's responsible for what. For
example the code satisfying an import is decoupled from what the import
is going to be named and how it's provided to the main core wasm module.

Overall the intention is that this does not either enhance the
functionality of wit-component nor regress it. Lots of tests have
changed but I've tried to verify it's just things moving around as
opposed to anything that has a different semantic meaning. A future PR
for #1774 will enhance the logic of connecting core wasm imports to WIT
imports but that's deferred for a future PR.

* Update link-related tests

* Bless some more tests

crates/wasm-encoder/src/component/builder.rs

@@ -206,20 +206,6 @@ impl ComponentBuilder {
         })
     }
 
-    /// Creates an alias to a previous core instance's exported item.
-    ///
-    /// The `instance` provided is the instance to access and the `name` is the
-    /// item to access.
-    ///
-    /// Returns the index of the new item defined.
-    pub fn alias_core_export(&mut self, instance: u32, name: &str, kind: ExportKind) -> u32 {
-        self.alias(Alias::CoreInstanceExport {
-            instance,
-            kind,
-            name,
-        })
-    }
-
     fn inc_kind(&mut self, kind: ComponentExportKind) -> u32 {
         match kind {
             ComponentExportKind::Func => inc(&mut self.funcs),

crates/wasm-encoder/src/core/exports.rs

@@ -4,7 +4,7 @@ use super::{
 use crate::{encode_section, Encode, Section, SectionId};
 
 /// Represents the kind of an export from a WebAssembly module.
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
 #[repr(u8)]
 pub enum ExportKind {
     /// The export is a function.

crates/wit-component/src/encoding/world.rs

@@ -1,13 +1,11 @@
 use super::{Adapter, ComponentEncoder, LibraryInfo, RequiredOptions};
 use crate::validation::{
-    validate_adapter_module, validate_module, RequiredImports, ValidatedAdapter, ValidatedModule,
-    BARE_FUNC_MODULE_NAME, RESOURCE_DROP,
+    validate_adapter_module, validate_module, Import, ImportMap, ValidatedModule, RESOURCE_DROP,
 };
 use anyhow::{Context, Result};
 use indexmap::{IndexMap, IndexSet};
-use std::borrow::{Borrow, Cow};
+use std::borrow::Cow;
 use std::collections::{HashMap, HashSet};
-use std::hash::Hash;
 use wasmparser::FuncType;
 use wit_parser::{
     abi::{AbiVariant, WasmSignature, WasmType},
@@ -17,7 +15,7 @@ use wit_parser::{
 
 pub struct WorldAdapter<'a> {
     pub wasm: Cow<'a, [u8]>,
-    pub info: ValidatedAdapter<'a>,
+    pub info: ValidatedModule,
     pub library_info: Option<&'a LibraryInfo>,
 }
 
@@ -31,7 +29,7 @@ pub struct ComponentWorld<'a> {
     pub encoder: &'a ComponentEncoder,
     /// Validation information of the input module, or `None` in `--types-only`
     /// mode.
-    pub info: ValidatedModule<'a>,
+    pub info: ValidatedModule,
     /// Validation information about adapters populated only for required
     /// adapters. Additionally stores the gc'd wasm for each adapter.
     pub adapters: IndexMap<&'a str, WorldAdapter<'a>>,
@@ -107,14 +105,14 @@ impl<'a> ComponentWorld<'a> {
             name,
             Adapter {
                 wasm,
-                metadata,
+                metadata: _,
                 required_exports,
                 library_info,
             },
         ) in self.encoder.adapters.iter()
         {
-            let required_by_import = self.info.adapters_required.get(name.as_str());
-            let no_required_by_import = || required_by_import.map(|m| m.is_empty()).unwrap_or(true);
+            let required_by_import = self.info.imports.required_from_adapter(name.as_str());
+            let no_required_by_import = || required_by_import.is_empty();
             let no_required_exports = || {
                 required_exports
                     .iter()
@@ -136,7 +134,7 @@ impl<'a> ComponentWorld<'a> {
                     resolve,
                     world,
                     required_exports,
-                    required_by_import,
+                    &required_by_import,
                 );
 
                 Cow::Owned(
@@ -146,7 +144,7 @@ impl<'a> ComponentWorld<'a> {
                         if self.encoder.realloc_via_memory_grow {
                             None
                         } else {
-                            self.info.realloc
+                            self.info.exports.realloc_to_import_into_adapter()
                         },
                     )
                     .context("failed to reduce input adapter module to its minimal size")?,
@@ -156,13 +154,14 @@ impl<'a> ComponentWorld<'a> {
                 &wasm,
                 resolve,
                 world,
-                metadata,
-                required_by_import,
+                &required_by_import,
                 required_exports,
-                library_info.is_some(),
+                library_info.as_ref(),
                 adapters,
             )
-            .context("failed to validate the imports of the minimized adapter module")?;
+            .with_context(|| {
+                format!("failed to validate the imports of the minimized adapter module `{name}`")
+            })?;
             self.adapters.insert(
                 name,
                 WorldAdapter {
@@ -183,15 +182,13 @@ impl<'a> ComponentWorld<'a> {
         resolve: &'r Resolve,
         world: WorldId,
         required_exports: &IndexSet<WorldKey>,
-        required_by_import: Option<&IndexMap<&str, FuncType>>,
+        required_by_import: &IndexMap<String, FuncType>,
     ) -> IndexMap<String, (FuncType, Option<&'r Function>)> {
         use wasmparser::ValType;
 
         let mut required = IndexMap::new();
-        if let Some(imports) = required_by_import {
-            for (name, ty) in imports {
-                required.insert(name.to_string(), (ty.clone(), None));
-            }
+        for (name, ty) in required_by_import {
+            required.insert(name.to_string(), (ty.clone(), None));
         }
         let mut add_func = |func: &'r Function, name: Option<&str>| {
             let name = func.core_export_name(name);
@@ -241,29 +238,40 @@ impl<'a> ComponentWorld<'a> {
     fn process_imports(&mut self) -> Result<()> {
         let resolve = &self.encoder.metadata.resolve;
         let world = self.encoder.metadata.world;
-        let mut all_required_imports = IndexMap::new();
-        for map in self.adapters.values().map(|a| &a.info.required_imports) {
-            for (k, v) in map {
-                all_required_imports
-                    .entry(k.as_str())
-                    .or_insert_with(IndexSet::new)
-                    .extend(v.funcs.iter().map(|v| v.as_str()));
+
+        // Inspect all imports of the main module and adapters to find all
+        // WIT-looking things and register those as required. This is used to
+        // prune out unneeded things in the `add_item` function below.
+        let mut required = Required::default();
+        for (_, _, import) in self
+            .adapters
+            .values()
+            .flat_map(|a| a.info.imports.imports())
+            .chain(self.info.imports.imports())
+        {
+            match import {
+                Import::WorldFunc(name) => {
+                    required
+                        .interface_funcs
+                        .entry(None)
+                        .or_default()
+                        .insert(name);
+                }
+                Import::InterfaceFunc(_, id, name) => {
+                    required
+                        .interface_funcs
+                        .entry(Some(*id))
+                        .or_default()
+                        .insert(name);
+                }
+                Import::ImportedResourceDrop(_, id) => {
+                    required.resource_drops.insert(*id);
+                }
+                _ => {}
             }
         }
-        for (k, v) in self.info.required_imports.iter() {
-            all_required_imports
-                .entry(*k)
-                .or_insert_with(IndexSet::new)
-                .extend(v.funcs.iter().map(|v| v.as_str()));
-        }
         for (name, item) in resolve.worlds[world].imports.iter() {
-            add_item(
-                &mut self.import_map,
-                resolve,
-                name,
-                item,
-                &all_required_imports,
-            )?;
+            add_item(&mut self.import_map, resolve, name, item, &required)?;
         }
         return Ok(());
 
@@ -272,11 +280,10 @@ impl<'a> ComponentWorld<'a> {
             resolve: &Resolve,
             name: &WorldKey,
             item: &WorldItem,
-            required: &IndexMap<&str, IndexSet<&str>>,
+            required: &Required<'_>,
         ) -> Result<()> {
             let name = resolve.name_world_key(name);
             log::trace!("register import `{name}`");
-            let empty = IndexSet::new();
             let import_map_key = match item {
                 WorldItem::Function(_) | WorldItem::Type(_) => None,
                 WorldItem::Interface { .. } => Some(name),
@@ -285,9 +292,6 @@ impl<'a> ComponentWorld<'a> {
                 WorldItem::Function(_) | WorldItem::Type(_) => None,
                 WorldItem::Interface { id, .. } => Some(*id),
             };
-            let required = required
-                .get(import_map_key.as_deref().unwrap_or(BARE_FUNC_MODULE_NAME))
-                .unwrap_or(&empty);
             let interface = import_map
                 .entry(import_map_key)
                 .or_insert_with(|| ImportedInterface {
@@ -324,10 +328,10 @@ impl<'a> ComponentWorld<'a> {
 
         // First use the previously calculated metadata about live imports to
         // determine the set of live types in those imports.
-        self.add_live_imports(world, &self.info.required_imports, &mut live);
+        self.add_live_imports(world, &self.info.imports, &mut live);
         for (adapter_name, adapter) in self.adapters.iter() {
             log::trace!("processing adapter `{adapter_name}`");
-            self.add_live_imports(world, &adapter.info.required_imports, &mut live);
+            self.add_live_imports(world, &adapter.info.imports, &mut live);
         }
 
         // Next any imported types used by an export must also be considered
@@ -379,43 +383,28 @@ impl<'a> ComponentWorld<'a> {
         }
     }
 
-    fn add_live_imports<S>(
-        &self,
-        world: WorldId,
-        required: &IndexMap<S, RequiredImports>,
-        live: &mut LiveTypes,
-    ) where
-        S: Borrow<str> + Hash + Eq,
-    {
+    fn add_live_imports(&self, world: WorldId, imports: &ImportMap, live: &mut LiveTypes) {
         let resolve = &self.encoder.metadata.resolve;
         for (name, item) in resolve.worlds[world].imports.iter() {
             let name = resolve.name_world_key(name);
             match item {
                 WorldItem::Function(func) => {
-                    let required = match required.get(BARE_FUNC_MODULE_NAME) {
-                        Some(set) => set,
-                        None => continue,
-                    };
-                    if !required.funcs.contains(name.as_str()) {
+                    if !imports.uses_toplevel_func(name.as_str()) {
                         continue;
                     }
                     log::trace!("add live function import `{name}`");
                     live.add_func(resolve, func);
                 }
                 WorldItem::Interface { id, .. } => {
-                    let required = match required.get(name.as_str()) {
-                        Some(set) => set,
-                        None => continue,
-                    };
                     log::trace!("add live interface import `{name}`");
                     for (name, func) in resolve.interfaces[*id].functions.iter() {
-                        if required.funcs.contains(name.as_str()) {
+                        if imports.uses_interface_func(*id, name.as_str()) {
                             log::trace!("add live func `{name}`");
                             live.add_func(resolve, func);
                         }
                     }
-                    for (name, ty) in resolve.interfaces[*id].types.iter() {
-                        if required.resources.contains(name.as_str()) {
+                    for (_name, ty) in resolve.interfaces[*id].types.iter() {
+                        if imports.uses_imported_resource_drop(*ty) {
                             live.add_type_id(resolve, *ty);
                         }
                     }
@@ -458,10 +447,17 @@ impl<'a> ComponentWorld<'a> {
     }
 }
 
+#[derive(Default)]
+struct Required<'a> {
+    interface_funcs: IndexMap<Option<InterfaceId>, IndexSet<&'a str>>,
+    resource_drops: IndexSet<TypeId>,
+}
+
 impl ImportedInterface {
-    fn add_func(&mut self, required: &IndexSet<&str>, resolve: &Resolve, func: &Function) {
-        if !required.contains(func.name.as_str()) {
-            return;
+    fn add_func(&mut self, required: &Required<'_>, resolve: &Resolve, func: &Function) {
+        match required.interface_funcs.get(&self.interface) {
+            Some(set) if set.contains(func.name.as_str()) => {}
+            _ => return,
         }
         log::trace!("add func {}", func.name);
         let options = RequiredOptions::for_import(resolve, func);
@@ -476,21 +472,18 @@ impl ImportedInterface {
         assert!(prev.is_none());
     }
 
-    fn add_type(&mut self, required: &IndexSet<&str>, resolve: &Resolve, id: TypeId) {
+    fn add_type(&mut self, required: &Required<'_>, resolve: &Resolve, id: TypeId) {
         let ty = &resolve.types[id];
         match &ty.kind {
             TypeDefKind::Resource => {}
             _ => return,
         }
         let name = ty.name.as_deref().expect("resources must be named");
 
-        let mut maybe_add = |name: String, lowering: Lowering| {
-            if !required.contains(name.as_str()) {
-                return;
-            }
-            let prev = self.lowerings.insert(name, lowering);
+        if required.resource_drops.contains(&id) {
+            let name = format!("{RESOURCE_DROP}{name}");
+            let prev = self.lowerings.insert(name, Lowering::ResourceDrop(id));
             assert!(prev.is_none());
-        };
-        maybe_add(format!("{RESOURCE_DROP}{name}"), Lowering::ResourceDrop(id));
+        }
     }
 }