Move the C API to a separate crate (#818)

* Move the C API to a separate crate

This commit moves the C API from `crates/api/src/wasm.rs` to
`crates/capi/src/lib.rs` to be located in a separate crate. There's a
number of reasons for this:

* When a Rust program depends on the `wasmtime` crate, there's no need
  to compile in the C API.
* This should improve compile times of the `wasmtime` crate since it's
  not producing artifacts which aren't always used.
* The development of the C API can be guaranteed to only use the public
  API of the `wasmtime` crate itself.

Some CI pieces are tweaked and this overall shouldn't have much impact
on users, it's intended that it's a cleanup/speedup for developers!

* Disable rustdoc/tests for capi

* Review feedback

* Add back in accidentally deleted comment

* More renamings

* Try to fix dotnet build

.github/workflows/main.yml

@@ -302,7 +302,7 @@ jobs:
     - run: $CENTOS cargo build --release --bin wasmtime --bin wasm2obj
       shell: bash
     # Build `libwasmtime.so`
-    - run: $CENTOS cargo build --release --manifest-path crates/api/Cargo.toml
+    - run: $CENTOS cargo build --release --manifest-path crates/c-api/Cargo.toml
       shell: bash
     # Test what we just built
     - run: $CENTOS cargo test --features test_programs --release --all --exclude lightbeam --exclude wasmtime --exclude wasmtime-fuzzing

.gitmodules

@@ -1,8 +1,8 @@
 [submodule "spec_testsuite"]
 	path = tests/spec_testsuite
 	url = https://github.com/WebAssembly/testsuite
-[submodule "crates/api/c-examples/wasm-c-api"]
+[submodule "crates/c-api/examples/wasm-c-api"]
-	path = crates/api/c-examples/wasm-c-api
+	path = crates/c-api/examples/wasm-c-api
 	url = https://github.com/WebAssembly/wasm-c-api
 [submodule "crates/wasi-common/WASI"]
 	path = crates/wasi-common/wig/WASI

Cargo.lock

@@ -2007,6 +2007,13 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "wasmtime-c-api"
+version = "0.9.0"
+dependencies = [
+ "wasmtime",
+]
+
 [[package]]
 name = "wasmtime-cli"
 version = "0.9.0"

Cargo.toml

@@ -55,6 +55,7 @@ members = [
   "crates/fuzzing",
   "crates/misc/rust",
   "crates/misc/py",
+  "crates/c-api",
   "fuzz",
 ]
 

ci/build-tarballs.sh

@@ -48,7 +48,7 @@ mkdir tmp/$api_pkgname/lib
 mkdir tmp/$api_pkgname/include
 cp LICENSE README.md tmp/$api_pkgname
 mv bins-$src/* tmp/$api_pkgname/lib
-cp crates/api/c-examples/wasm-c-api/include/wasm.h tmp/$api_pkgname/include
+cp crates/c-api/examples/wasm-c-api/include/wasm.h tmp/$api_pkgname/include
 mktarball $api_pkgname
 
 # Move wheels to dist folder

crates/api/Cargo.toml

@@ -8,10 +8,6 @@ repository = "https://github.com/bytecodealliance/wasmtime"
 readme = "README.md"
 edition = "2018"
 
-[lib]
-name = "wasmtime"
-crate-type = ["lib", "staticlib", "cdylib"]
-
 [dependencies]
 wasmtime-runtime = { path = "../runtime", version = "0.9.0" }
 wasmtime-environ = { path = "../environ", version = "0.9.0" }

crates/api/README.md

@@ -1,3 +1,8 @@
-# Implementation of wasm-c-api in Rust
+## Wasmtime Embedding API
 
-https://github.com/WebAssembly/wasm-c-api
+The `wasmtime` crate is an embedding API of the `wasmtime` WebAssembly runtime.
+This is intended to be used in Rust projects and provides a high-level API of
+working with WebAssembly modules.
+
+If you're interested in embedding `wasmtime` in other languages, you may wish to
+take a look a the [C embedding API](../c-api) instead!

crates/api/src/lib.rs

@@ -18,13 +18,11 @@ mod trap;
 mod types;
 mod values;
 
-pub mod wasm;
-
 pub use crate::callable::Callable;
 pub use crate::externals::*;
 pub use crate::instance::Instance;
 pub use crate::module::Module;
-pub use crate::r#ref::AnyRef;
+pub use crate::r#ref::{AnyRef, HostInfo, HostRef};
 pub use crate::runtime::{Config, Engine, OptLevel, Store, Strategy};
 pub use crate::trap::{FrameInfo, Trap};
 pub use crate::types::*;

crates/api/src/runtime.rs

@@ -398,7 +398,13 @@ impl Store {
             .cloned()
     }
 
-    pub(crate) fn ptr_eq(a: &Store, b: &Store) -> bool {
+    /// Returns whether the stores `a` and `b` refer to the same underlying
+    /// `Store`.
+    ///
+    /// Because the `Store` type is reference counted multiple clones may point
+    /// to the same underlying storage, and this method can be used to determine
+    /// whether two stores are indeed the same.
+    pub fn same(a: &Store, b: &Store) -> bool {
         Rc::ptr_eq(&a.inner, &b.inner)
     }
 }

crates/c-api/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "wasmtime-c-api"
+version = "0.9.0"
+authors = ["The Wasmtime Project Developers"]
+description = "C API to expose the Wasmtime runtime"
+license = "Apache-2.0 WITH LLVM-exception"
+repository = "https://github.com/bytecodealliance/wasmtime"
+readme = "README.md"
+edition = "2018"
+publish = false
+
+[lib]
+name = "wasmtime"
+crate-type = ["staticlib", "cdylib"]
+doc = false
+test = false
+doctest = false
+
+[dependencies]
+wasmtime = { path = "../api" }

crates/c-api/LICENSE

@@ -0,0 +1,220 @@
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crates/c-api/README.md

@@ -0,0 +1,3 @@
+# Implementation of wasm-c-api in Rust
+
+https://github.com/WebAssembly/wasm-c-api

crates/c-api/src/lib.rs

@@ -5,15 +5,14 @@
 
 // TODO complete the C API
 
-use super::{
-    AnyRef, Callable, Engine, ExportType, Extern, ExternType, Func, FuncType, Global, GlobalType,
-    ImportType, Instance, Limits, Memory, MemoryType, Module, Store, Table, TableType, Trap, Val,
-    ValType,
-};
-use crate::r#ref::{HostInfo, HostRef};
 use std::cell::RefCell;
 use std::rc::Rc;
 use std::{mem, ptr, slice};
+use wasmtime::{
+    AnyRef, Callable, Engine, ExportType, Extern, ExternType, Func, FuncType, Global, GlobalType,
+    HostInfo, HostRef, ImportType, Instance, Limits, Memory, MemoryType, Module, Store, Table,
+    TableType, Trap, Val, ValType,
+};
 
 macro_rules! declare_vec {
     ($name:ident, $elem_ty:path) => {
@@ -569,14 +568,18 @@ impl wasm_val_t {
     }
 }
 
-impl Callable for wasm_func_callback_t {
+struct Callback {
+    callback: wasm_func_callback_t,
+}
+
+impl Callable for Callback {
     fn call(&self, params: &[Val], results: &mut [Val]) -> Result<(), Trap> {
         let params = params
             .iter()
             .map(|p| wasm_val_t::from_val(p))
             .collect::<Vec<_>>();
         let mut out_results = vec![wasm_val_t::default(); results.len()];
-        let func = self.expect("wasm_func_callback_t fn");
+        let func = self.callback.expect("wasm_func_callback_t fn");
         let out = unsafe { func(params.as_ptr(), out_results.as_mut_ptr()) };
         if !out.is_null() {
             let trap: Box<wasm_trap_t> = unsafe { Box::from_raw(out) };
@@ -633,7 +636,7 @@ pub unsafe extern "C" fn wasm_func_new(
 ) -> *mut wasm_func_t {
     let store = &(*store).store.borrow();
     let ty = (*ty).functype.clone();
-    let callback = Rc::new(callback);
+    let callback = Rc::new(Callback { callback });
     let func = Box::new(wasm_func_t {
         ext: wasm_extern_t {
             which: ExternHost::Func(HostRef::new(Func::new(store, ty, callback))),
@@ -700,7 +703,7 @@ pub unsafe extern "C" fn wasm_instance_new(
     let module = &(*module).module.borrow();
     // FIXME(WebAssembly/wasm-c-api#126) what else can we do with the `store`
     // argument?
-    if !Store::ptr_eq(&store, module.store()) {
+    if !Store::same(&store, module.store()) {
         if !result.is_null() {
             let trap = Trap::new("wasm_store_t must match store in wasm_module_t");
             let trap = Box::new(wasm_trap_t {
@@ -1254,7 +1257,7 @@ pub unsafe extern "C" fn wasm_globaltype_content(
 pub unsafe extern "C" fn wasm_globaltype_mutability(
     gt: *const wasm_globaltype_t,
 ) -> wasm_mutability_t {
-    use super::Mutability::*;
+    use wasmtime::Mutability::*;
     match (*gt).globaltype.mutability() {
         Const => 0,
         Var => 1,
@@ -1411,7 +1414,7 @@ pub unsafe extern "C" fn wasm_globaltype_new(
     ty: *mut wasm_valtype_t,
     mutability: wasm_mutability_t,
 ) -> *mut wasm_globaltype_t {
-    use super::Mutability::*;
+    use wasmtime::Mutability::*;
     let ty = Box::from_raw(ty);
     let mutability = match mutability {
         0 => Const,

crates/misc/dotnet/Directory.Build.props

@@ -2,5 +2,6 @@
   <PropertyGroup>
     <WasmtimeVersion>0.8.0</WasmtimeVersion>
     <WasmtimeLibraryName>wasmtime</WasmtimeLibraryName>
+    <WasmtimePackageName>wasmtime-c-api</WasmtimePackageName>
   </PropertyGroup>
 </Project>

crates/misc/dotnet/Directory.Build.targets

@@ -6,7 +6,7 @@
     <LibraryExtension Condition="'$(LibraryExtension)' == ''">.so</LibraryExtension>
     <WasmtimeLibraryFilename>$(LibraryPrefix)$(WasmtimeLibraryName)$(LibraryExtension)</WasmtimeLibraryFilename>
     <WasmtimeOutputPath>$(MSBuildThisFileDirectory)../../../target/$(Configuration.ToLower())</WasmtimeOutputPath>
-    <BuildWasmtimeCommand Condition="'$(Configuration)' == 'Release'">cargo build --release -p $(WasmtimeLibraryName)</BuildWasmtimeCommand> 
+    <BuildWasmtimeCommand Condition="'$(Configuration)' == 'Release'">cargo build --release -p $(WasmtimePackageName)</BuildWasmtimeCommand>
-    <BuildWasmtimeCommand Condition="'$(BuildWasmtimeCommand)' == ''">cargo build -p $(WasmtimeLibraryName)</BuildWasmtimeCommand> 
+    <BuildWasmtimeCommand Condition="'$(BuildWasmtimeCommand)' == ''">cargo build -p $(WasmtimePackageName)</BuildWasmtimeCommand>
   </PropertyGroup>
 </Project>