feat: preliminary support for WIT templates

This is a minimum viable implementation of WIT templates per
WebAssembly/component-model#172.  It
supports interfaces with at most one wildcard function, which may be
expanded (i.e. monomorphized) with a set of substitutions provided by
the application developer when generating guest bindings.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

Author: fibonacci1729

Cargo.lock

@@ -32,8 +32,8 @@ indexmap = "1.9.1"
 wasm-encoder = "0.25.0"
 wasm-metadata = "0.3.1"
 wat = "1.0.61"
-wit-parser = "0.6.3"
-wit-component = "0.7.2"
+wit-parser = "0.6.4"
+wit-component = "0.7.3"
 
 wit-bindgen-core = { path = 'crates/core', version = '0.4.0' }
 wit-bindgen-c = { path = 'crates/c', version = '0.4.0' }
@@ -60,6 +60,7 @@ wit-bindgen-go = { workspace = true, features = ['clap'], optional = true }
 wat = { workspace = true }
 wit-component = { workspace = true }
 wasm-encoder = { workspace = true }
+toml = "0.7.2"
 
 [features]
 default = ['c', 'rust', 'markdown', 'teavm-java', 'go']
@@ -71,6 +72,13 @@ go = ['dep:wit-bindgen-go']
 
 [dev-dependencies]
 heck = { workspace = true }
-wasmtime = { version = "6", features = ['component-model'] }
+wasmtime = { version = "8", features = ['component-model'] }
 test-artifacts = { path = 'crates/test-rust-wasm/artifacts' }
 wit-parser = { workspace = true }
+
+[patch.crates-io]
+wit-component = { git = "https://github.com/dicej/wasm-tools", branch = "wit-templates" }
+wit-parser = { git = "https://github.com/dicej/wasm-tools", branch = "wit-templates" }
+wasm-metadata = { git = "https://github.com/dicej/wasm-tools", branch = "wit-templates" }
+wasmtime = { git = "https://github.com/dicej/wasmtime", branch = "wit-templates-minimal" }
+wasmtime-wit-bindgen = { git = "https://github.com/dicej/wasmtime", branch = "wit-templates-minimal" }

Cargo.toml

@@ -22,3 +22,4 @@ wit-bindgen-core = { workspace = true }
 wit-bindgen-rust = { workspace = true }
 wit-component = { workspace = true }
 anyhow = { workspace = true }
+toml = "0.7.2"

crates/rust-macro/Cargo.toml

@@ -1,9 +1,10 @@
 use proc_macro2::{Span, TokenStream};
+use std::fs;
 use std::path::{Path, PathBuf};
 use syn::parse::{Error, Parse, ParseStream, Result};
 use syn::punctuated::Punctuated;
 use syn::{token, Token};
-use wit_bindgen_core::wit_parser::{PackageId, Resolve, UnresolvedPackage, WorldId};
+use wit_bindgen_core::wit_parser::{self, PackageId, Resolve, UnresolvedPackage, WorldId};
 use wit_bindgen_rust::Opts;
 
 #[proc_macro]
@@ -32,6 +33,7 @@ impl Parse for Config {
         let mut opts = Opts::default();
         let mut world = None;
         let mut source = None;
+        let mut substitutions = None;
 
         if input.peek(token::Brace) {
             let content;
@@ -57,6 +59,24 @@ impl Parse for Config {
                         }
                         source = Some(Source::Inline(s.value()));
                     }
+                    Opt::SubstitutionsPath(s) => {
+                        if substitutions.is_some() {
+                            return Err(Error::new(
+                                s.span(),
+                                "cannot specify second substitutions",
+                            ));
+                        }
+                        substitutions = Some(Source::Path(s.value()));
+                    }
+                    Opt::SubstitutionsInline(s) => {
+                        if substitutions.is_some() {
+                            return Err(Error::new(
+                                s.span(),
+                                "cannot specify second substitutions",
+                            ));
+                        }
+                        substitutions = Some(Source::Inline(s.value()));
+                    }
                     Opt::UseStdFeature => opts.std_feature = true,
                     Opt::RawStrings => opts.raw_strings = true,
                     Opt::MacroExport => opts.macro_export = true,
@@ -71,8 +91,8 @@ impl Parse for Config {
                 source = Some(Source::Path(input.parse::<syn::LitStr>()?.value()));
             }
         }
-        let (resolve, pkg, files) =
-            parse_source(&source).map_err(|err| Error::new(call_site, format!("{err:?}")))?;
+        let (resolve, pkg, files) = parse_source(&source, &substitutions)
+            .map_err(|err| Error::new(call_site, format!("{err:?}")))?;
         let world = resolve
             .select_world(pkg, world.as_deref())
             .map_err(|e| Error::new(call_site, format!("{e:?}")))?;
@@ -85,7 +105,10 @@ impl Parse for Config {
     }
 }
 
-fn parse_source(source: &Option<Source>) -> anyhow::Result<(Resolve, PackageId, Vec<PathBuf>)> {
+fn parse_source(
+    source: &Option<Source>,
+    substitutions: &Option<Source>,
+) -> anyhow::Result<(Resolve, PackageId, Vec<PathBuf>)> {
     let mut resolve = Resolve::default();
     let mut files = Vec::new();
     let root = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap());
@@ -108,7 +131,14 @@ fn parse_source(source: &Option<Source>) -> anyhow::Result<(Resolve, PackageId,
         Some(Source::Path(s)) => parse(&root.join(&s))?,
         None => parse(&root.join("wit"))?,
     };
-
+    match substitutions {
+        Some(Source::Inline(s)) => wit_parser::expand(&mut resolve, toml::from_str(s)?)?,
+        Some(Source::Path(s)) => wit_parser::expand(
+            &mut resolve,
+            toml::from_str(&fs::read_to_string(&root.join(&s))?)?,
+        )?,
+        None => (),
+    }
     Ok((resolve, pkg, files))
 }
 
@@ -146,12 +176,16 @@ mod kw {
     syn::custom_keyword!(world);
     syn::custom_keyword!(path);
     syn::custom_keyword!(inline);
+    syn::custom_keyword!(substitutions_path);
+    syn::custom_keyword!(substitutions_inline);
 }
 
 enum Opt {
     World(syn::LitStr),
     Path(syn::LitStr),
     Inline(syn::LitStr),
+    SubstitutionsPath(syn::LitStr),
+    SubstitutionsInline(syn::LitStr),
     UseStdFeature,
     RawStrings,
     MacroExport,
@@ -171,6 +205,14 @@ impl Parse for Opt {
             input.parse::<kw::inline>()?;
             input.parse::<Token![:]>()?;
             Ok(Opt::Inline(input.parse()?))
+        } else if l.peek(kw::substitutions_path) {
+            input.parse::<kw::substitutions_path>()?;
+            input.parse::<Token![:]>()?;
+            Ok(Opt::SubstitutionsPath(input.parse()?))
+        } else if l.peek(kw::substitutions_inline) {
+            input.parse::<kw::substitutions_inline>()?;
+            input.parse::<Token![:]>()?;
+            Ok(Opt::SubstitutionsInline(input.parse()?))
         } else if l.peek(kw::world) {
             input.parse::<kw::world>()?;
             input.parse::<Token![:]>()?;

crates/rust-macro/src/lib.rs

@@ -47,3 +47,7 @@ test = false
 [[bin]]
 name = "results"
 test = false
+
+[[bin]]
+name = "wildcards"
+test = false

crates/test-rust-wasm/Cargo.toml

@@ -0,0 +1,3 @@
+include!("../../../../tests/runtime/wildcards/wasm.rs");
+
+fn main() {}

crates/test-rust-wasm/src/bin/wildcards.rs

@@ -1,7 +1,7 @@
 use anyhow::{bail, Context, Result};
 use clap::Parser;
 use std::path::PathBuf;
-use std::str;
+use std::{fs, str};
 use wit_bindgen_core::{wit_parser, Files, WorldGenerator};
 use wit_parser::{Resolve, UnresolvedPackage};
 
@@ -78,6 +78,10 @@ struct Common {
     /// they're up-to-date with the source files.
     #[clap(long)]
     check: bool,
+
+    /// Path to template substitutions for expansion.
+    #[clap(long)]
+    expand: Option<PathBuf>,
 }
 
 fn main() -> Result<()> {
@@ -143,6 +147,15 @@ fn gen_world(
     opts: &Common,
     files: &mut Files,
 ) -> Result<()> {
+    let substitutions = match &opts.expand {
+        Some(path) => {
+            let input =
+                fs::read_to_string(path).context("failed to read substitutions from file")?;
+            toml::from_str(&input).context("failed to parse substitutions from TOML")?
+        }
+        None => Default::default(),
+    };
+
     let mut resolve = Resolve::default();
     let pkg = if opts.wit.is_dir() {
         resolve.push_dir(&opts.wit)?.0
@@ -152,6 +165,8 @@ fn gen_world(
             &Default::default(),
         )?
     };
+
+    wit_parser::expand(&mut resolve, substitutions)?;
     let world = resolve.select_world(pkg, opts.world.as_deref())?;
     generator.generate(&resolve, world, files);
     Ok(())

src/bin/wit-bindgen.rs

@@ -9,7 +9,7 @@ pub struct MyImports {
     errored: bool,
 }
 
-impl imports::Imports for MyImports {
+impl imports::Host for MyImports {
     fn f_list_in_record1(&mut self, ty: imports::ListInRecord1Result) -> Result<()> {
         assert_eq!(ty.a, "list_in_record1");
         Ok(())

tests/runtime/flavorful.rs

@@ -8,7 +8,7 @@ use imports::*;
 #[derive(Default)]
 pub struct MyImports;
 
-impl Imports for MyImports {
+impl Host for MyImports {
     fn empty_list_param(&mut self, a: Vec<u8>) -> Result<()> {
         assert_eq!(a, []);
         Ok(())

tests/runtime/lists.rs

@@ -18,13 +18,14 @@ mod smoke;
 mod strings;
 mod unions;
 mod variants;
+mod wildcards;
 
 wasmtime::component::bindgen!("testwasi" in "crates/wasi_snapshot_preview1/wit");
 
 #[derive(Default)]
 struct Wasi<T>(T);
 
-impl<T> testwasi::Testwasi for Wasi<T> {
+impl<T> testwasi::Host for Wasi<T> {
     fn log(&mut self, bytes: Vec<u8>) -> Result<()> {
         std::io::stdout().write_all(&bytes)?;
         Ok(())