wiggle: emit a metadata module containing witx document (#1387)

* wiggle: emit a metadata module containing witx document

* wiggle: put metadata module behind a wiggle_metadata feature

* wasi-common: add wiggle_metadata feature and optional witx dep

* refactor according to alex's advice

* wasi-common: make snapshots pub

* wasi-common: i do need a wiggle_metadata feature to be available

* Tweak features and such

* wiggle: fix tests by passing metadata flag to wiggle-runtime

* wiggle: need to move wiggle-runtime to a non-dev dependency

so that the feature resolves for external users of the crates

Co-authored-by: Alex Crichton <alex@alexcrichton.com>

Cargo.lock

@@ -2705,6 +2705,7 @@ name = "wiggle-runtime"
 version = "0.1.0"
 dependencies = [
  "thiserror",
+ "witx",
 ]
 
 [[package]]

crates/wasi-common/Cargo.toml

@@ -21,7 +21,7 @@ filetime = "0.2.7"
 lazy_static = "1.4.0"
 num = { version = "0.2.0", default-features = false }
 wig = { path = "wig", version = "0.12.0" }
-wiggle = { path = "../wiggle" }
+wiggle = { path = "../wiggle", default-features = false }
 wiggle-runtime = { path = "../wiggle/crates/runtime" }
 
 [target.'cfg(unix)'.dependencies]
@@ -34,3 +34,8 @@ cpu-time = "1.0"
 
 [badges]
 maintenance = { status = "actively-developed" }
+
+[features]
+# Need to make the wiggle_metadata feature available to consumers of this
+# crate if they want the snapshots to have metadata available.
+wiggle_metadata = ["wiggle/wiggle_metadata", "wiggle-runtime/wiggle_metadata"]

crates/wasi-common/src/lib.rs

@@ -31,7 +31,7 @@ pub mod old;
 mod path;
 mod poll;
 mod sandboxed_tty_writer;
-mod snapshots;
+pub mod snapshots;
 mod sys;
 mod virtfs;
 pub mod wasi;

crates/wasi-common/src/snapshots/mod.rs

@@ -1 +1 @@
-mod wasi_snapshot_preview1;
+pub mod wasi_snapshot_preview1;

crates/wiggle/Cargo.toml

@@ -16,10 +16,22 @@ proc-macro = true
 
 [dependencies]
 wiggle-generate = { path = "crates/generate", version = "0.1.0" }
+wiggle-runtime = { path = "crates/runtime", version = "0.1.0" }
 witx = { path = "../wasi-common/wig/WASI/tools/witx", version = "0.8.4" }
 syn = { version = "1.0", features = ["full"] }
 
 [dev-dependencies]
-wiggle-runtime = { path = "crates/runtime", version = "0.1.0" }
 wiggle-test = { path = "crates/test", version = "0.1.0" }
 proptest = "0.9"
+
+[features]
+# These features have no effect on the users of this crate. They are only
+# necessary for testing.
+# The wiggle proc-macro emits some code (inside `pub mod metadata`) guarded
+# by the `wiggle_metadata` feature flag. We use this feature flag so that
+# users of wiggle are not forced to take a direct dependency on the `witx`
+# crate unless they want it.
+wiggle_metadata = ["wiggle-runtime/wiggle_metadata"]
+# In order to test that the contents of this metadata module meet
+# expectations, we must have this feature enabled for the crate by default.
+default = ["wiggle_metadata"]

crates/wiggle/crates/generate/src/config.rs

@@ -12,6 +12,7 @@ use syn::{
 pub struct Config {
     pub witx: WitxConf,
     pub ctx: CtxConf,
+    pub emit_metadata: bool,
 }
 
 #[derive(Debug, Clone)]
@@ -59,6 +60,7 @@ impl Config {
             ctx: ctx
                 .take()
                 .ok_or_else(|| Error::new(err_loc, "`ctx` field required"))?,
+            emit_metadata: false,
         })
     }
 }

crates/wiggle/crates/generate/src/lib.rs

@@ -35,10 +35,25 @@ pub fn generate(doc: &witx::Document, config: &Config) -> TokenStream {
         )
     });
 
+    let metadata = if config.emit_metadata {
+        let doc_text = &format!("{}", doc);
+        quote! {
+            pub mod metadata {
+                pub const DOC_TEXT: &str = #doc_text;
+                pub fn document() -> wiggle_runtime::witx::Document {
+                    wiggle_runtime::witx::parse(DOC_TEXT).unwrap()
+                }
+            }
+        }
+    } else {
+        quote!()
+    };
+
     quote!(
         pub mod types {
             #(#types)*
         }
         #(#modules)*
+        #metadata
     )
 }

crates/wiggle/crates/runtime/Cargo.toml

@@ -12,6 +12,10 @@ include = ["src/**/*", "LICENSE"]
 
 [dependencies]
 thiserror = "1"
+witx = { path = "../../../wasi-common/wig/WASI/tools/witx", version = "0.8.4", optional = true }
 
 [badges]
 maintenance = { status = "actively-developed" }
+
+[features]
+wiggle_metadata = ['witx']

crates/wiggle/crates/runtime/src/lib.rs

@@ -6,6 +6,9 @@ use std::slice;
 use std::str;
 use std::sync::Arc;
 
+#[cfg(feature = "wiggle_metadata")]
+pub use witx;
+
 mod borrow;
 mod error;
 mod guest_type;

crates/wiggle/src/lib.rs

@@ -87,6 +87,12 @@ pub fn from_witx(args: TokenStream) -> TokenStream {
     config.witx.make_paths_relative_to(
         std::env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR env var"),
     );
+
+    #[cfg(feature = "wiggle_metadata")]
+    {
+        config.emit_metadata = true;
+    }
+
     let doc = witx::load(&config.witx.paths).expect("loading witx");
     TokenStream::from(wiggle_generate::generate(&doc, &config))
 }

crates/wiggle/tests/wasi.rs

@@ -1,11 +1,26 @@
 use wiggle_runtime::{GuestBorrows, GuestError, GuestErrorType, GuestPtr};
 use wiggle_test::WasiCtx;
 
+// This test file exists to make sure that the entire `wasi.witx` file can be
+// handled by wiggle, producing code that compiles correctly.
+// The trait impls here are never executed, and just exist to validate that the
+// witx is exposed with the type signatures that we expect.
+
 wiggle::from_witx!({
     witx: ["tests/wasi.witx"],
     ctx: WasiCtx,
 });
 
+// The only test in this file is to verify that the witx document provided by the
+// proc macro in the `metadata` module is equal to the document on the disk.
+#[test]
+fn document_equivelant() {
+    let macro_doc = metadata::document();
+    let disk_doc = witx::load(&["tests/wasi.witx"]).expect("load wasi.witx from disk");
+
+    assert_eq!(macro_doc, disk_doc);
+}
+
 type Result<T> = std::result::Result<T, types::Errno>;
 
 impl<'a> GuestErrorType<'a> for types::Errno {