cmd/compile/internal: write type parameters for aliases

Writes the field for type parameter names for aliases when
the bitstream is >= V2.

This is a no-op at the moment as the writer is hardwired to V1.

Updates #68778

Change-Id: I5887e3608239b9a6a47e3cc21cacb75b84e1d186
Reviewed-on: https://go-review.googlesource.com/c/go/+/607235
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -417,7 +417,10 @@ func (pr *pkgReader) objIdx(idx pkgbits.Index) (*types2.Package, string) {
 
 		case pkgbits.ObjAlias:
 			pos := r.pos()
-			var tparams []*types2.TypeParam // TODO(#68778): Read tparams for unified IR.
+			var tparams []*types2.TypeParam
+			if r.Version().Has(pkgbits.AliasTypeParamNames) {
+				tparams = r.typeParamNames()
+			}
 			typ := r.typ()
 			return newAliasTypeName(pr.enableAlias, pos, objPkg, objName, typ, tparams)
 

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

@@ -746,6 +746,10 @@ func (pr *pkgReader) objIdxMayFail(idx index, implicits, explicits []*types.Type
 	case pkgbits.ObjAlias:
 		name := do(ir.OTYPE, false)
 
+		if r.Version().Has(pkgbits.AliasTypeParamNames) {
+			r.typeParamNames()
+		}
+
 		// Clumsy dance: the r.typ() call here might recursively find this
 		// type alias name, before we've set its type (#66873). So we
 		// temporarily clear sym.Def and then restore it later, if still

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

@@ -855,11 +855,19 @@ func (w *writer) doObj(wext *writer, obj types2.Object) pkgbits.CodeObj {
 	case *types2.TypeName:
 		if obj.IsAlias() {
 			w.pos(obj)
-			t := obj.Type()
-			if alias, ok := t.(*types2.Alias); ok { // materialized alias
-				t = alias.Rhs()
+			rhs := obj.Type()
+			var tparams *types2.TypeParamList
+			if alias, ok := rhs.(*types2.Alias); ok { // materialized alias
+				assert(alias.TypeArgs() == nil)
+				tparams = alias.TypeParams()
+				rhs = alias.Rhs()
 			}
-			w.typ(t)
+			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)
+			w.typ(rhs)
 			return pkgbits.ObjAlias
 		}
 

src/go/internal/gcimporter/ureader.go

@@ -488,7 +488,10 @@ func (pr *pkgReader) objIdx(idx pkgbits.Index) (*types.Package, string) {
 
 		case pkgbits.ObjAlias:
 			pos := r.pos()
-			var tparams []*types.TypeParam // TODO(#68778): Read tparams for unified IR.
+			var tparams []*types.TypeParam
+			if r.Version().Has(pkgbits.AliasTypeParamNames) {
+				tparams = r.typeParamNames()
+			}
 			typ := r.typ()
 			declare(newAliasTypeName(pos, objPkg, objName, typ, tparams))