go/internal/gcimporter: indexed format imports for type parameters aliases

Add support for importing a new 'B' tag for type parameters aliases
in the indexed data format.

Updates #68778

Change-Id: I3bd82870d4c4619a3771de30baf6d54f6ee5959e
Reviewed-on: https://go-review.googlesource.com/c/go/+/604635
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: David Chase <[email protected]>

Author: timothy-king

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

@@ -321,10 +321,14 @@ func (r *importReader) obj(name string) {
 	pos := r.pos()
 
 	switch tag {
-	case 'A':
-		typ := r.typ()
-
-		r.declare(types2.NewTypeName(pos, r.currPkg, name, typ))
+	case 'A', 'B':
+		var tparams []*types2.TypeParam
+		if tag == 'B' {
+			tparams = r.tparamList()
+		}
+		rhs := r.typ()
+		const enabled = true // This is now always enabled within the compiler.
+		r.declare(newAliasTypeName(enabled, pos, r.currPkg, name, rhs, tparams))
 
 	case 'C':
 		typ, val := r.value()

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

@@ -410,8 +410,9 @@ 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.
 			typ := r.typ()
-			return newAliasTypeName(pr.enableAlias, pos, objPkg, objName, typ)
+			return newAliasTypeName(pr.enableAlias, pos, objPkg, objName, typ, tparams)
 
 		case pkgbits.ObjConst:
 			pos := r.pos()
@@ -537,13 +538,15 @@ func (r *reader) ident(marker pkgbits.SyncMarker) (*types2.Package, string) {
 }
 
 // newAliasTypeName returns a new TypeName, with a materialized *types2.Alias if supported.
-func newAliasTypeName(aliases bool, pos syntax.Pos, pkg *types2.Package, name string, rhs types2.Type) *types2.TypeName {
+func newAliasTypeName(aliases bool, pos syntax.Pos, pkg *types2.Package, name string, rhs types2.Type, tparams []*types2.TypeParam) *types2.TypeName {
 	// Copied from x/tools/internal/aliases.NewAlias via
 	// GOROOT/src/go/internal/gcimporter/ureader.go.
 	if aliases {
 		tname := types2.NewTypeName(pos, pkg, name, nil)
-		_ = types2.NewAlias(tname, rhs) // form TypeName -> Alias cycle
+		a := types2.NewAlias(tname, rhs) // form TypeName -> Alias cycle
+		a.SetTypeParams(tparams)
 		return tname
 	}
+	assert(len(tparams) == 0)
 	return types2.NewTypeName(pos, pkg, name, rhs)
 }

src/cmd/compile/internal/typecheck/iexport.go

@@ -90,8 +90,9 @@
 //     }
 //
 //     type Alias struct {
-//         Tag  byte // 'A'
+//         Tag  byte // 'A' or 'B'
 //         Pos  Pos
+//         TypeParams []typeOff  // only present if Tag == 'B'
 //         Type typeOff
 //     }
 //

src/go/internal/gcimporter/iimport.go

@@ -333,10 +333,13 @@ func (r *importReader) obj(name string) {
 	pos := r.pos()
 
 	switch tag {
-	case 'A':
-		typ := r.typ()
-
-		r.declare(types.NewTypeName(pos, r.currPkg, name, typ))
+	case 'A', 'B':
+		var tparams []*types.TypeParam
+		if tag == 'B' {
+			tparams = r.tparamList()
+		}
+		rhs := r.typ()
+		r.declare(newAliasTypeName(pos, r.currPkg, name, rhs, tparams))
 
 	case 'C':
 		typ, val := r.value()

src/go/internal/gcimporter/ureader.go

@@ -482,8 +482,9 @@ 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.
 			typ := r.typ()
-			declare(newAliasTypeName(pos, objPkg, objName, typ))
+			declare(newAliasTypeName(pos, objPkg, objName, typ, tparams))
 
 		case pkgbits.ObjConst:
 			pos := r.pos()
@@ -661,14 +662,16 @@ func pkgScope(pkg *types.Package) *types.Scope {
 }
 
 // newAliasTypeName returns a new TypeName, with a materialized *types.Alias if supported.
-func newAliasTypeName(pos token.Pos, pkg *types.Package, name string, rhs types.Type) *types.TypeName {
+func newAliasTypeName(pos token.Pos, pkg *types.Package, name string, rhs types.Type, tparams []*types.TypeParam) *types.TypeName {
 	// When GODEBUG=gotypesalias=1 or unset, the Type() of the return value is a
 	// *types.Alias. Copied from x/tools/internal/aliases.NewAlias.
 	switch godebug.New("gotypesalias").Value() {
 	case "", "1":
 		tname := types.NewTypeName(pos, pkg, name, nil)
-		_ = types.NewAlias(tname, rhs) // form TypeName -> Alias cycle
+		a := types.NewAlias(tname, rhs) // form TypeName -> Alias cycle
+		a.SetTypeParams(tparams)
 		return tname
 	}
+	assert(len(tparams) == 0)
 	return types.NewTypeName(pos, pkg, name, rhs)
 }