Make more code work with no_std. (#407)

* Make more code work with no_std.

no_std support is still incomplete, but this patch takes care of the
bulk of the straightforward parts.

misc/wasmtime-py/src/function.rs

@@ -1,11 +1,13 @@
 //! Support for a calling of a bounds (exported) function.
 
+extern crate alloc;
+
 use pyo3::prelude::*;
 use pyo3::types::PyTuple;
 
 use crate::value::{pyobj_to_value, value_to_pyobj};
-use std::cell::RefCell;
-use std::rc::Rc;
+use alloc::rc::Rc;
+use core::cell::RefCell;
 
 use cranelift_codegen::ir;
 use wasmtime_interface_types::ModuleData;

misc/wasmtime-py/src/import.rs

@@ -1,5 +1,7 @@
 //! Support for a calling of an imported function.
 
+extern crate alloc;
+
 use pyo3::prelude::*;
 use pyo3::types::{PyAny, PyDict, PyTuple};
 
@@ -18,10 +20,10 @@ use target_lexicon::HOST;
 use wasmtime_environ::{Export, Module};
 use wasmtime_runtime::{Imports, InstanceHandle, VMContext, VMFunctionBody};
 
+use alloc::rc::Rc;
+use core::cell::RefCell;
 use core::cmp;
-use std::cell::RefCell;
 use std::collections::{HashMap, HashSet};
-use std::rc::Rc;
 
 struct BoundPyFunction {
     name: String,

misc/wasmtime-py/src/instance.rs

@@ -1,12 +1,14 @@
 //! WebAssembly Instance API object.
 
+extern crate alloc;
+
 use pyo3::prelude::*;
 use pyo3::types::PyDict;
 
 use crate::function::Function;
 use crate::memory::Memory;
-use std::cell::RefCell;
-use std::rc::Rc;
+use alloc::rc::Rc;
+use core::cell::RefCell;
 
 use cranelift_codegen::ir;
 use cranelift_codegen::ir::types;

misc/wasmtime-py/src/lib.rs

@@ -7,7 +7,7 @@ use crate::import::into_instance_from_obj;
 use crate::instance::Instance;
 use crate::memory::Memory;
 use crate::module::Module;
-use std::cell::RefCell;
+use core::cell::RefCell;
 use std::rc::Rc;
 use wasmtime_interface_types::ModuleData;
 

misc/wasmtime-py/src/memory.rs

@@ -1,15 +1,17 @@
 //! WebAssembly Memory API object.
 
+extern crate alloc;
+
 use pyo3::class::PyBufferProtocol;
 use pyo3::exceptions::BufferError;
 use pyo3::ffi;
 use pyo3::prelude::*;
 
-use std::cell::RefCell;
+use alloc::rc::Rc;
+use core::cell::RefCell;
+use core::ptr;
 use std::ffi::CStr;
 use std::os::raw::{c_int, c_void};
-use std::ptr;
-use std::rc::Rc;
 
 use wasmtime_environ::MemoryPlan;
 use wasmtime_jit::{Context, InstanceHandle};

misc/wasmtime-py/src/module.rs

@@ -1,8 +1,10 @@
 //! WebAssembly Module API object.
 
+extern crate alloc;
+
 use pyo3::prelude::*;
 
-use std::rc::Rc;
+use alloc::rc::Rc;
 
 #[pyclass]
 pub struct Module {

misc/wasmtime-py/src/value.rs

@@ -4,8 +4,8 @@ use pyo3::exceptions::Exception;
 use pyo3::prelude::*;
 use pyo3::types::PyAny;
 
+use core::ptr;
 use cranelift_codegen::ir;
-use std::ptr;
 use wasmtime_interface_types::Value;
 
 pub fn pyobj_to_value(_: Python, p: &PyAny) -> PyResult<Value> {