Use Result in idiomatic wrappers, mark most wrappers as unsafe fn

Cargo.toml

@@ -15,10 +15,13 @@ documentation = "https://docs.rs/wasi"
 # When built as part of libstd
 compiler_builtins = { version = "0.1", optional = true }
 core = { version = "1.0", optional = true, package = "rustc-std-workspace-core" }
+rustc-std-workspace-alloc = { version = "1.0", optional = true }
 
 [features]
+default = ["alloc"]
+alloc = []
 # Unstable feature to support being a libstd dependency
-rustc-dep-of-std = ["compiler_builtins", "core"]
+rustc-dep-of-std = ["compiler_builtins", "core", "rustc-std-workspace-alloc"]
 
 [badges]
 maintenance = { status = "experimental" }

src/lib.rs

@@ -12,5 +12,9 @@
     )
 )]
 #![no_std]
+#[cfg(all(feature = "alloc", not(feature = "rustc-std-workspace-alloc")))]
+extern crate alloc;
+#[cfg(all(feature = "alloc", feature = "rustc-std-workspace-alloc"))]
+extern crate rustc_std_workspace_alloc as alloc;
 
 pub mod wasi_unstable;