pkg: generate register.go automatically as well

Resolves a TODO, and avoids us having to maintain the file manually.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I79d852f1822fedb89a63b810115b5dd8fbee4c78
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1201391
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

pkg/gen.go

@@ -28,8 +28,6 @@
 // Be sure to also update an entry in pkg/pkg.go, if so desired.
 package main
 
-// TODO generate ../register.go too.
-
 import (
 	"bytes"
 	_ "embed"
@@ -55,8 +53,6 @@ import (
 	"cuelang.org/go/internal"
 )
 
-const genFile = "pkg.go"
-
 type headerParams struct {
 	GoPkg  string
 	CUEPkg string
@@ -104,23 +100,34 @@ func main() {
 	if packages.PrintErrors(pkgs) > 0 {
 		os.Exit(1)
 	}
+	regBuf := new(bytes.Buffer)
+	fmt.Fprintf(regBuf, "// Code generated by cuelang.org/go/pkg/gen. DO NOT EDIT.\n\n")
+	fmt.Fprintf(regBuf, "package pkg\n\n")
+	fmt.Fprintf(regBuf, "import (\n")
 	for _, pkg := range pkgs {
 		switch {
 		case pkg.PkgPath == pkgParent:
 			// The pkg package itself should not be generated.
 		case strings.Contains(pkg.PkgPath, "/internal"):
 			// Internal packages are not for public use.
-		case pkg.PkgPath == "cuelang.org/go/pkg/path":
-			// TODO remove this special case. Currently the path
-			// pkg.go file cannot be generated automatically but that
-			// will be possible when we can attach arbitrary signatures
-			// to builtin functions.
 		default:
+			fmt.Fprintf(regBuf, "\t_ %q\n", pkg.PkgPath)
+			if pkg.PkgPath == "cuelang.org/go/pkg/path" {
+				// TODO remove this special case. Currently the path
+				// pkg.go file cannot be generated automatically but that
+				// will be possible when we can attach arbitrary signatures
+				// to builtin functions.
+				break
+			}
 			if err := generate(pkg); err != nil {
 				log.Fatalf("%s: %v", pkg, err)
 			}
 		}
 	}
+	fmt.Fprintf(regBuf, ")\n")
+	if err := os.WriteFile("register.go", regBuf.Bytes(), 0o666); err != nil {
+		log.Fatal(err)
+	}
 }
 
 type generator struct {
@@ -190,7 +197,7 @@ func generate(pkg *packages.Package) error {
 		b = g.w.Bytes() // write the unformatted source
 	}
 
-	filename := filepath.Join(pkgDir, genFile)
+	filename := filepath.Join(pkgDir, "pkg.go")
 
 	if err := os.WriteFile(filename, b, 0666); err != nil {
 		return err