Initial reorg.

This is largely the same as #305, but updated for the current tree.

crates/jit/src/namespace.rs

@@ -0,0 +1,47 @@
+//! The core WebAssembly spec does not specify how imports are to be resolved
+//! to exports. This file provides one possible way to manage multiple instances
+//! and resolve imports to exports among them.
+
+use super::HashMap;
+use crate::resolver::Resolver;
+use alloc::string::String;
+use wasmtime_runtime::{Export, InstanceHandle};
+
+/// A namespace containing instances keyed by name.
+///
+/// Note that `Namespace` implements the `Resolver` trait, so it can resolve
+/// imports using defined exports.
+pub struct Namespace {
+    /// Mapping from identifiers to indices in `self.instances`.
+    names: HashMap<String, InstanceHandle>,
+}
+
+impl Namespace {
+    /// Construct a new `Namespace`.
+    pub fn new() -> Self {
+        Self {
+            names: HashMap::new(),
+        }
+    }
+
+    /// Install a new `InstanceHandle` in this `Namespace`, optionally with the
+    /// given name.
+    pub fn name_instance(&mut self, name: String, instance: InstanceHandle) {
+        self.names.insert(name, instance);
+    }
+
+    /// Get the instance registered with the given `instance_name`.
+    pub fn get_instance(&mut self, name: &str) -> Option<&mut InstanceHandle> {
+        self.names.get_mut(name)
+    }
+}
+
+impl Resolver for Namespace {
+    fn resolve(&mut self, name: &str, field: &str) -> Option<Export> {
+        if let Some(instance) = self.names.get_mut(name) {
+            instance.lookup(field)
+        } else {
+            None
+        }
+    }
+}