Refactor (#1524)

* Compute instance exports on demand.

Instead having instances eagerly compute a Vec of Externs, and bumping
the refcount for each Extern, compute Externs on demand.

This also enables `Instance::get_export` to avoid doing a linear search.

This also means that the closure returned by `get0` and friends now
holds an `InstanceHandle` to dynamically hold the instance live rather
than being scoped to a lifetime.

* Compute module imports and exports on demand too.

And compute Extern::ty on demand too.

* Add a utility function for computing an ExternType.

* Add a utility function for looking up a function's signature.

* Add a utility function for computing the ValType of a Global.

* Rename wasmtime_environ::Export to EntityIndex.

This helps differentiate it from other Export types in the tree, and
describes what it is.

* Fix a typo in a comment.

* Simplify module imports and exports.

* Make `Instance::exports` return the export names.

This significantly simplifies the public API, as it's relatively common
to need the names, and this avoids the need to do a zip with
`Module::exports`.

This also changes `ImportType` and `ExportType` to have public members
instead of private members and accessors, as I find that simplifies the
usage particularly in cases where there are temporary instances.

* Remove `Instance::module`.

This doesn't quite remove `Instance`'s `module` member, it gets a step
closer.

* Use a InstanceHandle utility function.

* Don't consume self in the `Func::get*` methods.

Instead, just create a closure containing the instance handle and the
export for them to call.

* Use `ExactSizeIterator` to avoid needing separate `num_*` methods.

* Rename `Extern::func()` etc. to `into_func()` etc.

* Revise examples to avoid using `nth`.

* Add convenience methods to instance for getting specific extern types.

* Use the convenience functions in more tests and examples.

* Avoid cloning strings for `ImportType` and `ExportType`.

* Remove more obviated clone() calls.

* Simplify `Func`'s closure state.

* Make wasmtime::Export's fields private.

This makes them more consistent with ExportType.

* Fix compilation error.

* Make a lifetime parameter explicit, and use better lifetime names.

Instead of 'me, use 'instance and 'module to make it clear what the
lifetime is.

* More lifetime cleanups.

crates/api/src/trampoline/func.rs

@@ -10,7 +10,7 @@ use std::mem;
 use std::panic::{self, AssertUnwindSafe};
 use wasmtime_environ::entity::PrimaryMap;
 use wasmtime_environ::isa::TargetIsa;
-use wasmtime_environ::{ir, settings, CompiledFunction, Export, Module};
+use wasmtime_environ::{ir, settings, CompiledFunction, EntityIndex, Module};
 use wasmtime_jit::trampoline::ir::{
     ExternalName, Function, InstBuilder, MemFlags, StackSlotData, StackSlotKind,
 };
@@ -212,7 +212,7 @@ pub fn create_handle_with_function(
 
     let pointer_type = isa.pointer_type();
     let sig = match ft.get_wasmtime_signature(pointer_type) {
-        Some(sig) => sig.clone(),
+        Some(sig) => sig,
         None => bail!("not a supported core wasm signature {:?}", ft),
     };
 
@@ -228,7 +228,7 @@ pub fn create_handle_with_function(
     let func_id = module.local.functions.push(sig_id);
     module
         .exports
-        .insert("trampoline".to_string(), Export::Function(func_id));
+        .insert("trampoline".to_string(), EntityIndex::Function(func_id));
     let trampoline = make_trampoline(isa.as_ref(), &mut code_memory, &mut fn_builder_ctx, &sig);
     finished_functions.push(trampoline);
 
@@ -276,7 +276,7 @@ pub unsafe fn create_handle_with_raw_function(
 
     let pointer_type = isa.pointer_type();
     let sig = match ft.get_wasmtime_signature(pointer_type) {
-        Some(sig) => sig.clone(),
+        Some(sig) => sig,
         None => bail!("not a supported core wasm signature {:?}", ft),
     };
 
@@ -288,7 +288,7 @@ pub unsafe fn create_handle_with_raw_function(
     let func_id = module.local.functions.push(sig_id);
     module
         .exports
-        .insert("trampoline".to_string(), Export::Function(func_id));
+        .insert("trampoline".to_string(), EntityIndex::Function(func_id));
     finished_functions.push(func);
     let sig_id = store.compiler().signatures().register(&sig);
     trampolines.insert(sig_id, trampoline);

crates/api/src/trampoline/global.rs

@@ -3,7 +3,7 @@ use crate::Store;
 use crate::{GlobalType, Mutability, Val};
 use anyhow::{bail, Result};
 use wasmtime_environ::entity::PrimaryMap;
-use wasmtime_environ::{wasm, Module};
+use wasmtime_environ::{wasm, EntityIndex, Module};
 use wasmtime_runtime::InstanceHandle;
 
 pub fn create_global(store: &Store, gt: &GlobalType, val: Val) -> Result<InstanceHandle> {
@@ -26,10 +26,9 @@ pub fn create_global(store: &Store, gt: &GlobalType, val: Val) -> Result<Instanc
     };
     let mut module = Module::new();
     let global_id = module.local.globals.push(global);
-    module.exports.insert(
-        "global".to_string(),
-        wasmtime_environ::Export::Global(global_id),
-    );
+    module
+        .exports
+        .insert("global".to_string(), EntityIndex::Global(global_id));
     let handle = create_handle(
         module,
         store,

crates/api/src/trampoline/memory.rs

@@ -4,7 +4,7 @@ use crate::Store;
 use crate::{Limits, MemoryType};
 use anyhow::Result;
 use wasmtime_environ::entity::PrimaryMap;
-use wasmtime_environ::{wasm, MemoryPlan, Module, WASM_PAGE_SIZE};
+use wasmtime_environ::{wasm, EntityIndex, MemoryPlan, Module, WASM_PAGE_SIZE};
 use wasmtime_runtime::{
     InstanceHandle, RuntimeLinearMemory, RuntimeMemoryCreator, VMMemoryDefinition,
 };
@@ -23,10 +23,9 @@ pub fn create_handle_with_memory(store: &Store, memory: &MemoryType) -> Result<I
 
     let memory_plan = wasmtime_environ::MemoryPlan::for_memory(memory, &tunable);
     let memory_id = module.local.memory_plans.push(memory_plan);
-    module.exports.insert(
-        "memory".to_string(),
-        wasmtime_environ::Export::Memory(memory_id),
-    );
+    module
+        .exports
+        .insert("memory".to_string(), EntityIndex::Memory(memory_id));
 
     create_handle(
         module,

crates/api/src/trampoline/table.rs

@@ -3,7 +3,7 @@ use crate::Store;
 use crate::{TableType, ValType};
 use anyhow::{bail, Result};
 use wasmtime_environ::entity::PrimaryMap;
-use wasmtime_environ::{wasm, Module};
+use wasmtime_environ::{wasm, EntityIndex, Module};
 use wasmtime_runtime::InstanceHandle;
 
 pub fn create_handle_with_table(store: &Store, table: &TableType) -> Result<InstanceHandle> {
@@ -21,10 +21,9 @@ pub fn create_handle_with_table(store: &Store, table: &TableType) -> Result<Inst
 
     let table_plan = wasmtime_environ::TablePlan::for_table(table, &tunable);
     let table_id = module.local.table_plans.push(table_plan);
-    module.exports.insert(
-        "table".to_string(),
-        wasmtime_environ::Export::Table(table_id),
-    );
+    module
+        .exports
+        .insert("table".to_string(), EntityIndex::Table(table_id));
 
     create_handle(
         module,