Add a component model example

This adds the 'Hello World' example from here[0]. The runtime is in Rust
and the component is in C.

This requires some new tools

  - https://github.com/bytecodealliance/wit-bindgen
  - https://github.com/bytecodealliance/wasm-tools

You can use the pre-built packages, once downloaded and untar'd, edit

  rust/hello_world/component/Makefile

and adjust the paths for the above tools.

To build the component with make you may need to specify where the WASI
sysroot is

  $ make WASI_SYSROOT=/path/to/wasi-sysroot

[0]: <https://docs.rs/wasmtime/latest/wasmtime/component/macro.bindgen.html>

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/README b/README
index 822d1df..7e13c9a 100644
--- a/README
+++ b/README
@@ -70,3 +70,35 @@ Getting function exports...
     [cabi_realloc]
 Shutting down...
 Done.
+
+
+Component Model
+===============
+
+You can play with the component model under rust/hello_world
+
+This requires some new tools
+
+   - https://github.com/bytecodealliance/wit-bindgen
+   - https://github.com/bytecodealliance/wasm-tools
+
+ You can use the pre-built packages, once downloaded and untar'd, edit
+
+   rust/hello_world/component/Makefile
+
+ and adjust the paths for the above tools.
+
+ To build the component with make you may need to specify where the WASI
+ sysroot is
+
+   $ make WASI_SYSROOT=/path/to/wasi-sysroot
+
+You can then build the Rust runtime under rust/hello_world with
+
+  $ cargo build
+
+after a while (sheesh) it should finish... then you can run it with
+
+  $ target/debug/hello_world
+
+it won't actually print anything, but also shouldn't give an error.