cmd/compile/internal/noder: write V2 bitstream aliastypeparams=1

Enables V2 unified IR bitstreams when GOEXPERIMENT aliastypeparams
are enabled.

Allows pkgbits.NewPkgEncoder to set the output version.
Reenables support for writing V0 streams.

Updates #68778
Updates #68526

Change-Id: I590c494d81ab7db148232ceaba52229068d1e986
Reviewed-on: https://go-review.googlesource.com/c/go/+/608595
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

7 files changed, 62 insertions, 47 deletions

diff --git a/src/cmd/compile/internal/noder/unified.go b/src/cmd/compile/internal/noder/unified.go
index ead348f0c1..c8dbc43e67 100644
--- a/src/cmd/compile/internal/noder/unified.go
+++ b/src/cmd/compile/internal/noder/unified.go
@@ -6,6 +6,7 @@ package noder
 
 import (
 	"fmt"
+	"internal/buildcfg"
 	"internal/pkgbits"
 	"internal/types/errors"
 	"io"
@@ -462,8 +463,13 @@ func readPackage(pr *pkgReader, importpkg *types.Pkg, localStub bool) {
 // writeUnifiedExport writes to `out` the finalized, self-contained
 // Unified IR export data file for the current compilation unit.
 func writeUnifiedExport(out io.Writer) {
+	// Use V2 as the encoded version aliastypeparams GOEXPERIMENT is enabled.
+	version := pkgbits.V1
+	if buildcfg.Experiment.AliasTypeParams {
+		version = pkgbits.V2
+	}
 	l := linker{
-		pw: pkgbits.NewPkgEncoder(base.Debug.SyncFrames),
+		pw: pkgbits.NewPkgEncoder(version, base.Debug.SyncFrames),
 
 		pkgs:   make(map[string]index),
 		decls:  make(map[*types.Sym]index),
diff --git a/src/cmd/compile/internal/noder/writer.go b/src/cmd/compile/internal/noder/writer.go
index 695fdcceea..564087d912 100644
--- a/src/cmd/compile/internal/noder/writer.go
+++ b/src/cmd/compile/internal/noder/writer.go
@@ -96,8 +96,13 @@ type pkgWriter struct {
 // newPkgWriter returns an initialized pkgWriter for the specified
 // package.
 func newPkgWriter(m posMap, pkg *types2.Package, info *types2.Info, otherInfo map[*syntax.FuncLit]bool) *pkgWriter {
+	// Use V2 as the encoded version aliastypeparams GOEXPERIMENT is enabled.
+	version := pkgbits.V1
+	if buildcfg.Experiment.AliasTypeParams {
+		version = pkgbits.V2
+	}
 	return &pkgWriter{
-		PkgEncoder: pkgbits.NewPkgEncoder(base.Debug.SyncFrames),
+		PkgEncoder: pkgbits.NewPkgEncoder(version, base.Debug.SyncFrames),
 
 		m:                     m,
 		curpkg:                pkg,
@@ -864,8 +869,7 @@ func (w *writer) doObj(wext *writer, obj types2.Object) pkgbits.CodeObj {
 			if w.Version().Has(pkgbits.AliasTypeParamNames) {
 				w.typeParamNames(tparams)
 			}
-			// TODO(taking): enable this assertion once this is not intended to be a nop.
-			// assert(w.Version().Has(pkgbits.AliasTypeParamNames) || tparams.Len() == 0)
+			assert(w.Version().Has(pkgbits.AliasTypeParamNames) || tparams.Len() == 0)
 			w.typ(rhs)
 			return pkgbits.ObjAlias
 		}
diff --git a/src/internal/pkgbits/decoder.go b/src/internal/pkgbits/decoder.go
index ca66446dba..09f26a84bd 100644
--- a/src/internal/pkgbits/decoder.go
+++ b/src/internal/pkgbits/decoder.go
@@ -82,8 +82,8 @@ func NewPkgDecoder(pkgPath, input string) PkgDecoder {
 	assert(binary.Read(r, binary.LittleEndian, &ver) == nil)
 	pr.version = Version(ver)
 
-	if pr.version >= V2 { // TODO(taking): Switch to numVersions.
-		panic(fmt.Errorf("cannot decode %q, export data version %d is too new", pkgPath, pr.version))
+	if pr.version >= numVersions {
+		panic(fmt.Errorf("cannot decode %q, export data version %d is greater than maximum supported version %d", pkgPath, pr.version, numVersions-1))
 	}
 
 	if pr.version.Has(Flags) {
@@ -101,7 +101,9 @@ func NewPkgDecoder(pkgPath, input string) PkgDecoder {
 	assert(err == nil)
 
 	pr.elemData = input[pos:]
-	assert(len(pr.elemData)-8 == int(pr.elemEnds[len(pr.elemEnds)-1]))
+
+	const fingerprintSize = 8
+	assert(len(pr.elemData)-fingerprintSize == int(pr.elemEnds[len(pr.elemEnds)-1]))
 
 	return pr
 }
diff --git a/src/internal/pkgbits/encoder.go b/src/internal/pkgbits/encoder.go
index b632b58ca0..c17a12399d 100644
--- a/src/internal/pkgbits/encoder.go
+++ b/src/internal/pkgbits/encoder.go
@@ -15,9 +15,6 @@ import (
 	"strings"
 )
 
-// currentVersion is the current version number written.
-const currentVersion = V1
-
 // A PkgEncoder provides methods for encoding a package's Unified IR
 // export data.
 type PkgEncoder struct {
@@ -47,10 +44,9 @@ func (pw *PkgEncoder) SyncMarkers() bool { return pw.syncFrames >= 0 }
 // export data files, but can help diagnosing desync errors in
 // higher-level Unified IR reader/writer code. If syncFrames is
 // negative, then sync markers are omitted entirely.
-func NewPkgEncoder(syncFrames int) PkgEncoder {
+func NewPkgEncoder(version Version, syncFrames int) PkgEncoder {
 	return PkgEncoder{
-		// TODO(taking): Change NewPkgEncoder to take a version as an argument, and remove currentVersion.
-		version:    currentVersion,
+		version:    version,
 		stringsIdx: make(map[string]Index),
 		syncFrames: syncFrames,
 	}
@@ -68,11 +64,13 @@ func (pw *PkgEncoder) DumpTo(out0 io.Writer) (fingerprint [8]byte) {
 
 	writeUint32(uint32(pw.version))
 
-	var flags uint32
-	if pw.SyncMarkers() {
-		flags |= flagSyncMarkers
+	if pw.version.Has(Flags) {
+		var flags uint32
+		if pw.SyncMarkers() {
+			flags |= flagSyncMarkers
+		}
+		writeUint32(flags)
 	}
-	writeUint32(flags)
 
 	// Write elemEndsEnds.
 	var sum uint32
diff --git a/src/internal/pkgbits/pkgbits_test.go b/src/internal/pkgbits/pkgbits_test.go
index f4c3719446..6f4004741b 100644
--- a/src/internal/pkgbits/pkgbits_test.go
+++ b/src/internal/pkgbits/pkgbits_test.go
@@ -11,19 +11,25 @@ import (
 )
 
 func TestRoundTrip(t *testing.T) {
-	pw := pkgbits.NewPkgEncoder(-1)
-	w := pw.NewEncoder(pkgbits.RelocMeta, pkgbits.SyncPublic)
-	w.Flush()
+	for _, version := range []pkgbits.Version{
+		pkgbits.V0,
+		pkgbits.V1,
+		pkgbits.V2,
+	} {
+		pw := pkgbits.NewPkgEncoder(version, -1)
+		w := pw.NewEncoder(pkgbits.RelocMeta, pkgbits.SyncPublic)
+		w.Flush()
 
-	var b strings.Builder
-	_ = pw.DumpTo(&b)
-	input := b.String()
+		var b strings.Builder
+		_ = pw.DumpTo(&b)
+		input := b.String()
 
-	pr := pkgbits.NewPkgDecoder("package_id", input)
-	r := pr.NewDecoder(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)
+		pr := pkgbits.NewPkgDecoder("package_id", input)
+		r := pr.NewDecoder(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)
 
-	if r.Version() != w.Version() {
-		t.Errorf("Expected reader version %q to be the writer version %q", r.Version(), w.Version())
+		if r.Version() != w.Version() {
+			t.Errorf("Expected reader version %q to be the writer version %q", r.Version(), w.Version())
+		}
 	}
 }
 
diff --git a/test/fixedbugs/issue68526.dir/a/a.go b/test/fixedbugs/issue68526.dir/a/a.go
index 7c2961c28f..83462c7fb9 100644
--- a/test/fixedbugs/issue68526.dir/a/a.go
+++ b/test/fixedbugs/issue68526.dir/a/a.go
@@ -6,8 +6,7 @@
 
 package a
 
-// TODO(#68778): enable once type parameterized aliases are allowed in exportdata.
-// type A[T any] = struct{ F T }
+type A[T any] = struct{ F T }
 
 type B = struct{ F int }
 
diff --git a/test/fixedbugs/issue68526.dir/main.go b/test/fixedbugs/issue68526.dir/main.go
index 0353ca5daa..966efd7190 100644
--- a/test/fixedbugs/issue68526.dir/main.go
+++ b/test/fixedbugs/issue68526.dir/main.go
@@ -7,12 +7,14 @@
 package main
 
 import (
+	"fmt"
+
 	"issue68526.dir/a"
 )
 
 func main() {
 	unexported()
-	// exported()
+	exported()
 }
 
 func unexported() {
@@ -23,23 +25,21 @@ func unexported() {
 	}
 }
 
-// TODO(#68778): enable once type parameterized aliases are allowed in exportdata.
-
-// func exported() {
-// 	var (
-// 		astr a.A[string]
-// 		aint a.A[int]
-// 	)
+func exported() {
+	var (
+		astr a.A[string]
+		aint a.A[int]
+	)
 
-// 	if any(astr) != any(struct{ F string }{}) || any(aint) != any(struct{ F int }{}) {
-// 		panic("zero value of alias and concrete type not identical")
-// 	}
+	if any(astr) != any(struct{ F string }{}) || any(aint) != any(struct{ F int }{}) {
+		panic("zero value of alias and concrete type not identical")
+	}
 
-// 	if any(astr) == any(aint) {
-// 		panic("zero value of struct{ F string } and struct{ F int } are not distinct")
-// 	}
+	if any(astr) == any(aint) {
+		panic("zero value of struct{ F string } and struct{ F int } are not distinct")
+	}
 
-// 	if got := fmt.Sprintf("%T", astr); got != "struct { F string }" {
-// 		panic(got)
-// 	}
-// }
+	if got := fmt.Sprintf("%T", astr); got != "struct { F string }" {
+		panic(got)
+	}
+}