[dev.unified] cmd/compile: move "has init" to private metadata

Currently, there's a "has init" bool in the public metadata section,
which is only needed by cmd/compile; but because it's in the public
metadata section, it's known to the go/types importers too. This CL
moves it instead to the new compiler-only private metadata section
added in the last CL for the inline bodies index.

The existing bool in the public metadata section is left in place, and
just always set to false, to avoid breaking the x/tools importer. The
next time we bump the export version number, we can remove the bool
properly. But no urgency just yet.

Change-Id: I380f358652374b5a221f85020a53dc65912ddb29
Reviewed-on: https://go-review.googlesource.com/c/go/+/419676
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/importer/ureader.go

@@ -39,7 +39,7 @@ func ReadPackage(ctxt *types2.Context, imports map[string]*types2.Package, input
 
 	r := pr.newReader(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)
 	pkg := r.pkg()
-	r.Bool() // has init
+	r.Bool() // TODO(mdempsky): Remove; was "has init"
 
 	for i, n := 0, r.Len(); i < n; i++ {
 		// As if r.obj(), but avoiding the Scope.Lookup call,

src/cmd/compile/internal/noder/unified.go

@@ -161,7 +161,7 @@ func writePkgStub(noders []*noder) string {
 	{
 		w := publicRootWriter
 		w.pkg(pkg)
-		w.Bool(false) // has init; XXX
+		w.Bool(false) // TODO(mdempsky): Remove; was "has init"
 
 		scope := pkg.Scope()
 		names := scope.Names()
@@ -237,12 +237,7 @@ func readPackage(pr *pkgReader, importpkg *types.Pkg, localStub bool) {
 		pkg := r.pkg()
 		base.Assertf(pkg == importpkg, "have package %q (%p), want package %q (%p)", pkg.Path, pkg, importpkg.Path, importpkg)
 
-		if r.Bool() {
-			sym := pkg.Lookup(".inittask")
-			task := ir.NewNameAt(src.NoXPos, sym)
-			task.Class = ir.PEXTERN
-			sym.Def = task
-		}
+		r.Bool() // TODO(mdempsky): Remove; was "has init"
 
 		for i, n := 0, r.Len(); i < n; i++ {
 			r.Sync(pkgbits.SyncObject)
@@ -262,6 +257,13 @@ func readPackage(pr *pkgReader, importpkg *types.Pkg, localStub bool) {
 	if !localStub {
 		r := pr.newReader(pkgbits.RelocMeta, pkgbits.PrivateRootIdx, pkgbits.SyncPrivate)
 
+		if r.Bool() {
+			sym := importpkg.Lookup(".inittask")
+			task := ir.NewNameAt(src.NoXPos, sym)
+			task.Class = ir.PEXTERN
+			sym.Def = task
+		}
+
 		for i, n := 0, r.Len(); i < n; i++ {
 			path := r.String()
 			name := r.String()
@@ -302,7 +304,7 @@ func writeUnifiedExport(out io.Writer) {
 		r.Sync(pkgbits.SyncPkg)
 		selfPkgIdx = l.relocIdx(pr, pkgbits.RelocPkg, r.Reloc(pkgbits.RelocPkg))
 
-		r.Bool() // has init
+		r.Bool() // TODO(mdempsky): Remove; was "has init"
 
 		for i, n := 0, r.Len(); i < n; i++ {
 			r.Sync(pkgbits.SyncObject)
@@ -333,8 +335,7 @@ func writeUnifiedExport(out io.Writer) {
 
 		w.Sync(pkgbits.SyncPkg)
 		w.Reloc(pkgbits.RelocPkg, selfPkgIdx)
-
-		w.Bool(typecheck.Lookup(".inittask").Def != nil)
+		w.Bool(false) // TODO(mdempsky): Remove; was "has init"
 
 		w.Len(len(idxs))
 		for _, idx := range idxs {
@@ -361,6 +362,8 @@ func writeUnifiedExport(out io.Writer) {
 
 		w := privateRootWriter
 
+		w.Bool(typecheck.Lookup(".inittask").Def != nil)
+
 		w.Len(len(bodies))
 		for _, body := range bodies {
 			w.String(body.sym.Pkg.Path)

src/go/internal/gcimporter/ureader.go

@@ -60,7 +60,7 @@ func readUnifiedPackage(fset *token.FileSet, ctxt *types.Context, imports map[st
 
 	r := pr.newReader(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)
 	pkg := r.pkg()
-	r.Bool() // has init
+	r.Bool() // TODO(mdempsky): Remove; was "has init"
 
 	for i, n := 0, r.Len(); i < n; i++ {
 		// As if r.obj(), but avoiding the Scope.Lookup call,

src/internal/pkgbits/encoder.go

@@ -19,6 +19,10 @@ import (
 //   - v0: initial prototype
 //
 //   - v1: adds the flags uint32 word
+//
+// TODO(mdempsky): For the next version bump:
+//   - remove the unused dict.derived.needed bool
+//   - remove the legacy "has init" bool from the public root
 const currentVersion uint32 = 1
 
 // A PkgEncoder provides methods for encoding a package's Unified IR