wit/bindgen: cgo + linker tricks WIP

Author: ydnar

wit/bindgen/generator.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"go/token"
 	"io"
+	"os/exec"
 	"path"
 	"path/filepath"
 	"runtime"
@@ -248,8 +249,8 @@ func (g *generator) defineWorld(w *wit.World) error {
 	}
 
 	// Write WIT file for this world
-	witFile := g.witFileFor(w)
-	witFile.WriteString(g.res.WIT(wit.Filter(w, nil), ""))
+	// witFile := g.witFileFor(w)
+	// witFile.WriteString(g.res.WIT(wit.Filter(w, nil), ""))
 
 	// Write Go package docs
 	file := g.fileFor(w)
@@ -2319,23 +2320,53 @@ func (g *generator) newPackage(w *wit.World, i *wit.Interface, name string) (*ge
 	g.exportScopes[owner] = gen.NewScope(nil)
 	pkg.DeclareName("Exports")
 
-	// Write a Cgo file that adds a library to the linker arguments.
+	// Write a Cgo file and a .wasm library to the linker arguments.
 	// The library is a WebAssembly file that includes a custom section
 	// with a name prefixed with "component-type:". The contents are the
 	// Component Model definition for a world that encapsulates the
 	// Component Model types and functions imported into and/or exported
 	// from this Go package.
 	if false {
-		cgoFile := g.cgoFileFor(owner)
+		// Synthesize a unique-ish library name
 		lib := id.String()
 		if name != id.Extension {
 			lib += "-" + name
 		}
 		lib = strings.ReplaceAll(lib, "/", "-")
 		lib = strings.ReplaceAll(lib, ":", "-")
+		libFile := pkg.File("lib" + lib + ".a")
+
+		// Generate
+		witText := g.res.WIT(wit.FilterFor(w, i), "")
+		witFile := g.witFileFor(owner)
+		witFile.WriteString(witText)
+		content, err := g.componentEmbed(witText)
+		if err != nil {
+			// return nil, err
+		}
+		libFile.Write(content)
+
+		// Write Cgo file
+		cgoFile := g.cgoFileFor(owner)
 		stringio.Write(cgoFile, "// #cgo LDFLAGS: -L. -l", lib, "\n")
 		stringio.Write(cgoFile, "import \"C\"\n")
 	}
 
 	return pkg, nil
 }
+
+// componentEmbed runs generated WIT through wasm-tools to generate a wasm file with a component-type custom section.
+func (g *generator) componentEmbed(witData string) ([]byte, error) {
+	// TODO: --all-features?
+	cmd := exec.Command("wasm-tools", "component", "embed", "--only-custom", "/dev/stdin")
+	cmd.Stdin = strings.NewReader(witData)
+	stdout := &bytes.Buffer{}
+	stderr := &bytes.Buffer{}
+	cmd.Stdout = stdout
+	cmd.Stderr = stderr
+	err := cmd.Run()
+	if err != nil {
+		g.opts.logger.Errorf("wasm-tools: %s", stderr.String())
+	}
+	return stdout.Bytes(), err
+}