Make WASI and wat support optional in the C API (#1419)

Add some crate features to compile out support for these features of the
C API. Avoiding these two features if they're not necessary shaves about
2MB off the final shared object in some local tests!

crates/c-api/src/lib.rs

@@ -21,8 +21,6 @@ mod trap;
 mod types;
 mod val;
 mod vec;
-mod wasi;
-mod wat2wasm;
 
 pub use crate::config::*;
 pub use crate::engine::*;
@@ -40,7 +38,15 @@ pub use crate::trap::*;
 pub use crate::types::*;
 pub use crate::val::*;
 pub use crate::vec::*;
+
+#[cfg(feature = "wasi")]
+mod wasi;
+#[cfg(feature = "wasi")]
 pub use crate::wasi::*;
+
+#[cfg(feature = "wat")]
+mod wat2wasm;
+#[cfg(feature = "wat")]
 pub use crate::wat2wasm::*;
 
 #[repr(C)]

crates/c-api/src/linker.rs

@@ -1,4 +1,4 @@
-use crate::{wasi_instance_t, wasm_extern_t, wasm_store_t, ExternHost};
+use crate::{wasm_extern_t, wasm_store_t, ExternHost};
 use crate::{wasm_instance_t, wasm_module_t, wasm_name_t, wasm_trap_t};
 use std::str;
 use wasmtime::{Extern, Linker};
@@ -51,10 +51,11 @@ pub extern "C" fn wasmtime_linker_define(
     linker.define(module, name, item).is_ok()
 }
 
+#[cfg(feature = "wasi")]
 #[no_mangle]
 pub extern "C" fn wasmtime_linker_define_wasi(
     linker: &mut wasmtime_linker_t,
-    instance: &wasi_instance_t,
+    instance: &crate::wasi_instance_t,
 ) -> bool {
     let linker = &mut linker.linker;
     instance.add_to_linker(linker).is_ok()

crates/c-api/src/wat2wasm.rs

@@ -1,5 +1,4 @@
 use crate::wasm_byte_vec_t;
-use std::str;
 
 #[no_mangle]
 pub extern "C" fn wasmtime_wat2wasm(
@@ -7,7 +6,7 @@ pub extern "C" fn wasmtime_wat2wasm(
     ret: &mut wasm_byte_vec_t,
     error: Option<&mut wasm_byte_vec_t>,
 ) -> bool {
-    let wat = match str::from_utf8(wat.as_slice()) {
+    let wat = match std::str::from_utf8(wat.as_slice()) {
         Ok(s) => s,
         Err(_) => {
             if let Some(error) = error {