diff --git a/src/cmd/gofmt/gofmt.go b/src/cmd/gofmt/gofmt.go
index cd867bba155..2793c2c2a43 100644
--- a/src/cmd/gofmt/gofmt.go
+++ b/src/cmd/gofmt/gofmt.go
@@ -33,10 +33,6 @@ var (
 	doDiff      = flag.Bool("d", false, "display diffs instead of rewriting files")
 	allErrors   = flag.Bool("e", false, "report all errors (not just the first 10 on different lines)")
 
-	// allowTypeParams controls whether type parameters are allowed in the code
-	// being formatted. It is enabled for go1.18 in gofmt_go1.18.go.
-	allowTypeParams = false
-
 	// debugging
 	cpuprofile = flag.String("cpuprofile", "", "write cpu profile to this file")
 )
@@ -53,10 +49,6 @@ const (
 	printerNormalizeNumbers = 1 << 30
 )
 
-// parseTypeParams tells go/parser to parse type parameters. Must be kept in
-// sync with go/parser/interface.go.
-const parseTypeParams parser.Mode = 1 << 30
-
 var (
 	fileSet    = token.NewFileSet() // per process FileSet
 	exitCode   = 0
@@ -79,9 +71,6 @@ func initParserMode() {
 	if *allErrors {
 		parserMode |= parser.AllErrors
 	}
-	if allowTypeParams {
-		parserMode |= parseTypeParams
-	}
 }
 
 func isGoFile(f fs.DirEntry) bool {
diff --git a/src/cmd/gofmt/gofmt_test.go b/src/cmd/gofmt/gofmt_test.go
index 9e2239a6926..f0d3f8780f4 100644
--- a/src/cmd/gofmt/gofmt_test.go
+++ b/src/cmd/gofmt/gofmt_test.go
@@ -49,12 +49,13 @@ func gofmtFlags(filename string, maxLines int) string {
 		case scanner.EOF:
 			return ""
 		}
-
 	}
 
 	return ""
 }
 
+var typeParamsEnabled = false
+
 func runTest(t *testing.T, in, out string) {
 	// process flags
 	*simplifyAST = false
@@ -78,8 +79,10 @@ func runTest(t *testing.T, in, out string) {
 			// fake flag - pretend input is from stdin
 			stdin = true
 		case "-G":
-			// fake flag - allow parsing type parameters
-			allowTypeParams = true
+			// fake flag - test is for generic code
+			if !typeParamsEnabled {
+				return
+			}
 		default:
 			t.Errorf("unrecognized flag name: %s", name)
 		}
diff --git a/src/cmd/gofmt/gofmt_go1.18.go b/src/cmd/gofmt/gofmt_typeparams_test.go
similarity index 73%
rename from src/cmd/gofmt/gofmt_go1.18.go
rename to src/cmd/gofmt/gofmt_typeparams_test.go
index be7b46b5ede..10641a77cb2 100644
--- a/src/cmd/gofmt/gofmt_go1.18.go
+++ b/src/cmd/gofmt/gofmt_typeparams_test.go
@@ -2,11 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.18
-// +build go1.18
+//go:build typeparams
+// +build typeparams
 
 package main
 
 func init() {
-	allowTypeParams = true
+	typeParamsEnabled = true
 }
diff --git a/src/go/ast/ast.go b/src/go/ast/ast.go
index 6eb4d13f4d0..c87529ec77d 100644
--- a/src/go/ast/ast.go
+++ b/src/go/ast/ast.go
@@ -374,13 +374,6 @@ type (
 		Rparen   token.Pos // position of ")"
 	}
 
-	// A ListExpr node represents a list of expressions separated by commas.
-	// ListExpr nodes are used as index in IndexExpr nodes representing type
-	// or function instantiations with more than one type argument.
-	ListExpr struct {
-		ElemList []Expr
-	}
-
 	// A StarExpr node represents an expression of the form "*" Expression.
 	// Semantically it could be a unary "*" expression, or a pointer type.
 	//
@@ -447,14 +440,6 @@ type (
 
 	// Pointer types are represented via StarExpr nodes.
 
-	// A FuncType node represents a function type.
-	FuncType struct {
-		Func    token.Pos  // position of "func" keyword (token.NoPos if there is no "func")
-		TParams *FieldList // type parameters; or nil
-		Params  *FieldList // (incoming) parameters; non-nil
-		Results *FieldList // (outgoing) results; or nil
-	}
-
 	// An InterfaceType node represents an interface type.
 	InterfaceType struct {
 		Interface  token.Pos  // position of "interface" keyword
@@ -497,18 +482,12 @@ func (x *IndexExpr) Pos() token.Pos      { return x.X.Pos() }
 func (x *SliceExpr) Pos() token.Pos      { return x.X.Pos() }
 func (x *TypeAssertExpr) Pos() token.Pos { return x.X.Pos() }
 func (x *CallExpr) Pos() token.Pos       { return x.Fun.Pos() }
-func (x *ListExpr) Pos() token.Pos {
-	if len(x.ElemList) > 0 {
-		return x.ElemList[0].Pos()
-	}
-	return token.NoPos
-}
-func (x *StarExpr) Pos() token.Pos     { return x.Star }
-func (x *UnaryExpr) Pos() token.Pos    { return x.OpPos }
-func (x *BinaryExpr) Pos() token.Pos   { return x.X.Pos() }
-func (x *KeyValueExpr) Pos() token.Pos { return x.Key.Pos() }
-func (x *ArrayType) Pos() token.Pos    { return x.Lbrack }
-func (x *StructType) Pos() token.Pos   { return x.Struct }
+func (x *StarExpr) Pos() token.Pos       { return x.Star }
+func (x *UnaryExpr) Pos() token.Pos      { return x.OpPos }
+func (x *BinaryExpr) Pos() token.Pos     { return x.X.Pos() }
+func (x *KeyValueExpr) Pos() token.Pos   { return x.Key.Pos() }
+func (x *ArrayType) Pos() token.Pos      { return x.Lbrack }
+func (x *StructType) Pos() token.Pos     { return x.Struct }
 func (x *FuncType) Pos() token.Pos {
 	if x.Func.IsValid() || x.Params == nil { // see issue 3870
 		return x.Func
@@ -536,18 +515,12 @@ func (x *IndexExpr) End() token.Pos      { return x.Rbrack + 1 }
 func (x *SliceExpr) End() token.Pos      { return x.Rbrack + 1 }
 func (x *TypeAssertExpr) End() token.Pos { return x.Rparen + 1 }
 func (x *CallExpr) End() token.Pos       { return x.Rparen + 1 }
-func (x *ListExpr) End() token.Pos {
-	if len(x.ElemList) > 0 {
-		return x.ElemList[len(x.ElemList)-1].End()
-	}
-	return token.NoPos
-}
-func (x *StarExpr) End() token.Pos     { return x.X.End() }
-func (x *UnaryExpr) End() token.Pos    { return x.X.End() }
-func (x *BinaryExpr) End() token.Pos   { return x.Y.End() }
-func (x *KeyValueExpr) End() token.Pos { return x.Value.End() }
-func (x *ArrayType) End() token.Pos    { return x.Elt.End() }
-func (x *StructType) End() token.Pos   { return x.Fields.End() }
+func (x *StarExpr) End() token.Pos       { return x.X.End() }
+func (x *UnaryExpr) End() token.Pos      { return x.X.End() }
+func (x *BinaryExpr) End() token.Pos     { return x.Y.End() }
+func (x *KeyValueExpr) End() token.Pos   { return x.Value.End() }
+func (x *ArrayType) End() token.Pos      { return x.Elt.End() }
+func (x *StructType) End() token.Pos     { return x.Fields.End() }
 func (x *FuncType) End() token.Pos {
 	if x.Results != nil {
 		return x.Results.End()
@@ -573,7 +546,6 @@ func (*IndexExpr) exprNode()      {}
 func (*SliceExpr) exprNode()      {}
 func (*TypeAssertExpr) exprNode() {}
 func (*CallExpr) exprNode()       {}
-func (*ListExpr) exprNode()       {}
 func (*StarExpr) exprNode()       {}
 func (*UnaryExpr) exprNode()      {}
 func (*BinaryExpr) exprNode()     {}
@@ -920,16 +892,6 @@ type (
 		Values  []Expr        // initial values; or nil
 		Comment *CommentGroup // line comments; or nil
 	}
-
-	// A TypeSpec node represents a type declaration (TypeSpec production).
-	TypeSpec struct {
-		Doc     *CommentGroup // associated documentation; or nil
-		Name    *Ident        // type name
-		TParams *FieldList    // type parameters; or nil
-		Assign  token.Pos     // position of '=', if any
-		Type    Expr          // *Ident, *ParenExpr, *SelectorExpr, *StarExpr, or any of the *XxxTypes
-		Comment *CommentGroup // line comments; or nil
-	}
 )
 
 // Pos and End implementations for spec nodes.
diff --git a/src/go/ast/ast_notypeparams.go b/src/go/ast/ast_notypeparams.go
new file mode 100644
index 00000000000..fa132fba858
--- /dev/null
+++ b/src/go/ast/ast_notypeparams.go
@@ -0,0 +1,28 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !typeparams
+// +build !typeparams
+
+package ast
+
+import "go/token"
+
+type (
+	// A FuncType node represents a function type.
+	FuncType struct {
+		Func    token.Pos  // position of "func" keyword (token.NoPos if there is no "func")
+		Params  *FieldList // (incoming) parameters; non-nil
+		Results *FieldList // (outgoing) results; or nil
+	}
+
+	// A TypeSpec node represents a type declaration (TypeSpec production).
+	TypeSpec struct {
+		Doc     *CommentGroup // associated documentation; or nil
+		Name    *Ident        // type name
+		Assign  token.Pos     // position of '=', if any
+		Type    Expr          // *Ident, *ParenExpr, *SelectorExpr, *StarExpr, or any of the *XxxTypes
+		Comment *CommentGroup // line comments; or nil
+	}
+)
diff --git a/src/go/ast/ast_typeparams.go b/src/go/ast/ast_typeparams.go
new file mode 100644
index 00000000000..24fdc5f1317
--- /dev/null
+++ b/src/go/ast/ast_typeparams.go
@@ -0,0 +1,51 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build typeparams
+// +build typeparams
+
+package ast
+
+import "go/token"
+
+type (
+	// A FuncType node represents a function type.
+	FuncType struct {
+		Func    token.Pos  // position of "func" keyword (token.NoPos if there is no "func")
+		TParams *FieldList // type parameters; or nil
+		Params  *FieldList // (incoming) parameters; non-nil
+		Results *FieldList // (outgoing) results; or nil
+	}
+
+	// A TypeSpec node represents a type declaration (TypeSpec production).
+	TypeSpec struct {
+		Doc     *CommentGroup // associated documentation; or nil
+		Name    *Ident        // type name
+		TParams *FieldList    // type parameters; or nil
+		Assign  token.Pos     // position of '=', if any
+		Type    Expr          // *Ident, *ParenExpr, *SelectorExpr, *StarExpr, or any of the *XxxTypes
+		Comment *CommentGroup // line comments; or nil
+	}
+
+	// A ListExpr node represents a list of expressions separated by commas.
+	// ListExpr nodes are used as index in IndexExpr nodes representing type
+	// or function instantiations with more than one type argument.
+	ListExpr struct {
+		ElemList []Expr
+	}
+)
+
+func (*ListExpr) exprNode() {}
+func (x *ListExpr) Pos() token.Pos {
+	if len(x.ElemList) > 0 {
+		return x.ElemList[0].Pos()
+	}
+	return token.NoPos
+}
+func (x *ListExpr) End() token.Pos {
+	if len(x.ElemList) > 0 {
+		return x.ElemList[len(x.ElemList)-1].End()
+	}
+	return token.NoPos
+}
diff --git a/src/go/ast/walk.go b/src/go/ast/walk.go
index a57ff25ac5a..9224264e291 100644
--- a/src/go/ast/walk.go
+++ b/src/go/ast/walk.go
@@ -4,8 +4,6 @@
 
 package ast
 
-import "fmt"
-
 // A Visitor's Visit method is invoked for each node encountered by Walk.
 // If the result visitor w is not nil, Walk visits each of the children
 // of node with the visitor w, followed by a call of w.Visit(nil).
@@ -116,9 +114,6 @@ func Walk(v Visitor, node Node) {
 		Walk(v, n.X)
 		Walk(v, n.Index)
 
-	case *ListExpr:
-		walkExprList(v, n.ElemList)
-
 	case *SliceExpr:
 		Walk(v, n.X)
 		if n.Low != nil {
@@ -166,9 +161,7 @@ func Walk(v Visitor, node Node) {
 		Walk(v, n.Fields)
 
 	case *FuncType:
-		if n.TParams != nil {
-			Walk(v, n.TParams)
-		}
+		walkFuncTypeParams(v, n)
 		if n.Params != nil {
 			Walk(v, n.Params)
 		}
@@ -323,9 +316,7 @@ func Walk(v Visitor, node Node) {
 			Walk(v, n.Doc)
 		}
 		Walk(v, n.Name)
-		if n.TParams != nil {
-			Walk(v, n.TParams)
-		}
+		walkTypeSpecParams(v, n)
 		Walk(v, n.Type)
 		if n.Comment != nil {
 			Walk(v, n.Comment)
@@ -372,7 +363,7 @@ func Walk(v Visitor, node Node) {
 		}
 
 	default:
-		panic(fmt.Sprintf("ast.Walk: unexpected node type %T", n))
+		walkOtherNodes(v, n)
 	}
 
 	v.Visit(nil)
diff --git a/src/go/ast/walk_notypeparams.go b/src/go/ast/walk_notypeparams.go
new file mode 100644
index 00000000000..d43e13dd11a
--- /dev/null
+++ b/src/go/ast/walk_notypeparams.go
@@ -0,0 +1,17 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !typeparams
+// +build !typeparams
+
+package ast
+
+import "fmt"
+
+func walkFuncTypeParams(v Visitor, n *FuncType) {}
+func walkTypeSpecParams(v Visitor, n *TypeSpec) {}
+
+func walkOtherNodes(v Visitor, n Node) {
+	panic(fmt.Sprintf("ast.Walk: unexpected node type %T", n))
+}
diff --git a/src/go/ast/walk_typeparams.go b/src/go/ast/walk_typeparams.go
new file mode 100644
index 00000000000..77267a5b8c7
--- /dev/null
+++ b/src/go/ast/walk_typeparams.go
@@ -0,0 +1,30 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build typeparams
+// +build typeparams
+
+package ast
+
+func walkFuncTypeParams(v Visitor, n *FuncType) {
+	if n.TParams != nil {
+		Walk(v, n.TParams)
+	}
+}
+
+func walkTypeSpecParams(v Visitor, n *TypeSpec) {
+	if n.TParams != nil {
+		Walk(v, n.TParams)
+	}
+}
+
+func walkOtherNodes(v Visitor, n Node) {
+	if e, ok := n.(*ast.ListExpr); ok {
+		if e != nil {
+			Walk(v, e)
+		}
+	} else {
+		panic(fmt.Sprintf("ast.Walk: unexpected node type %T", n))
+	}
+}
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index a1a4324331c..a1ed834c715 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -278,6 +278,7 @@ var depsRules = `
 	< go/token
 	< go/scanner
 	< go/ast
+	< go/internal/typeparams
 	< go/parser;
 
 	FMT
diff --git a/src/go/internal/typeparams/common.go b/src/go/internal/typeparams/common.go
new file mode 100644
index 00000000000..47b8f7cf02f
--- /dev/null
+++ b/src/go/internal/typeparams/common.go
@@ -0,0 +1,13 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package typeparams provides functions to work with type parameter data
+// stored in the AST, while these AST changes are guarded by a build
+// constraint.
+package typeparams
+
+// DisallowParsing is the numeric value of a parsing mode that disallows type
+// parameters. This only matters if the typeparams experiment is active, and
+// may be used for running tests that disallow generics.
+const DisallowParsing = 1 << 30
diff --git a/src/go/internal/typeparams/notypeparams.go b/src/go/internal/typeparams/notypeparams.go
new file mode 100644
index 00000000000..7bd62c9efec
--- /dev/null
+++ b/src/go/internal/typeparams/notypeparams.go
@@ -0,0 +1,38 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !typeparams
+// +build !typeparams
+
+package typeparams
+
+import (
+	"go/ast"
+)
+
+const Enabled = false
+
+func PackExpr(list []ast.Expr) ast.Expr {
+	switch len(list) {
+	case 0:
+		return nil
+	case 1:
+		return list[0]
+	default:
+		// The parser should not attempt to pack multiple expressions into an
+		// IndexExpr if type params are disabled.
+		panic("multiple index expressions are unsupported without type params")
+	}
+}
+
+func UnpackExpr(expr ast.Expr) []ast.Expr {
+	return []ast.Expr{expr}
+}
+
+func Get(ast.Node) *ast.FieldList {
+	return nil
+}
+
+func Set(node ast.Node, params *ast.FieldList) {
+}
diff --git a/src/go/internal/typeparams/typeparams.go b/src/go/internal/typeparams/typeparams.go
new file mode 100644
index 00000000000..0332b6b816f
--- /dev/null
+++ b/src/go/internal/typeparams/typeparams.go
@@ -0,0 +1,61 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build typeparams
+// +build typeparams
+
+package typeparams
+
+import (
+	"fmt"
+	"go/ast"
+)
+
+const Enabled = true
+
+func PackExpr(list []ast.Expr) ast.Expr {
+	switch len(list) {
+	case 0:
+		return nil
+	case 1:
+		return list[0]
+	default:
+		return &ast.ListExpr{ElemList: list}
+	}
+}
+
+// TODO(gri) Should find a more efficient solution that doesn't
+//           require introduction of a new slice for simple
+//           expressions.
+func UnpackExpr(x ast.Expr) []ast.Expr {
+	if x, _ := x.(*ast.ListExpr); x != nil {
+		return x.ElemList
+	}
+	if x != nil {
+		return []ast.Expr{x}
+	}
+	return nil
+}
+
+func Get(n ast.Node) *ast.FieldList {
+	switch n := n.(type) {
+	case *ast.TypeSpec:
+		return n.TParams
+	case *ast.FuncType:
+		return n.TParams
+	default:
+		panic(fmt.Sprintf("node type %T has no type parameters", n))
+	}
+}
+
+func Set(n ast.Node, params *ast.FieldList) {
+	switch n := n.(type) {
+	case *ast.TypeSpec:
+		n.TParams = params
+	case *ast.FuncType:
+		n.TParams = params
+	default:
+		panic(fmt.Sprintf("node type %T has no type parameters", n))
+	}
+}
diff --git a/src/go/parser/error_test.go b/src/go/parser/error_test.go
index 3caa3571e6a..5d45a7b817b 100644
--- a/src/go/parser/error_test.go
+++ b/src/go/parser/error_test.go
@@ -23,6 +23,7 @@
 package parser
 
 import (
+	"go/internal/typeparams"
 	"go/scanner"
 	"go/token"
 	"os"
@@ -188,7 +189,11 @@ func TestErrors(t *testing.T) {
 		if !d.IsDir() && !strings.HasPrefix(name, ".") && (strings.HasSuffix(name, ".src") || strings.HasSuffix(name, ".go2")) {
 			mode := DeclarationErrors | AllErrors
 			if strings.HasSuffix(name, ".go2") {
-				mode |= parseTypeParams
+				if !typeparams.Enabled {
+					continue
+				}
+			} else {
+				mode |= typeparams.DisallowParsing
 			}
 			checkErrors(t, filepath.Join(testdata, name), nil, mode, true)
 		}
diff --git a/src/go/parser/interface.go b/src/go/parser/interface.go
index 8f306adaabd..dcc5fa6616c 100644
--- a/src/go/parser/interface.go
+++ b/src/go/parser/interface.go
@@ -56,13 +56,6 @@ const (
 	DeclarationErrors                              // report declaration errors
 	SpuriousErrors                                 // same as AllErrors, for backward-compatibility
 	AllErrors         = SpuriousErrors             // report all errors (not just the first 10 on different lines)
-
-	// parseTypeParams controls the parsing of type parameters. Must be
-	// kept in sync with:
-	//  go/printer/printer_test.go
-	//  go/types/check_test.go
-	//  cmd/gofmt/gofmt.go
-	parseTypeParams = 1 << 30
 )
 
 // ParseFile parses the source code of a single Go source file and returns
diff --git a/src/go/parser/parser.go b/src/go/parser/parser.go
index 93ab4a4600f..aff5838780d 100644
--- a/src/go/parser/parser.go
+++ b/src/go/parser/parser.go
@@ -19,6 +19,7 @@ package parser
 import (
 	"fmt"
 	"go/ast"
+	"go/internal/typeparams"
 	"go/scanner"
 	"go/token"
 	"strconv"
@@ -75,6 +76,10 @@ func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode Mod
 	p.next()
 }
 
+func (p *parser) parseTypeParams() bool {
+	return typeparams.Enabled && p.mode&typeparams.DisallowParsing == 0
+}
+
 // ----------------------------------------------------------------------------
 // Parsing support
 
@@ -494,7 +499,7 @@ func (p *parser) parseQualifiedIdent(ident *ast.Ident) ast.Expr {
 	}
 
 	typ := p.parseTypeName(ident)
-	if p.tok == token.LBRACK && p.mode&parseTypeParams != 0 {
+	if p.tok == token.LBRACK && p.parseTypeParams() {
 		typ = p.parseTypeInstance(typ)
 	}
 
@@ -553,7 +558,7 @@ func (p *parser) parseArrayFieldOrTypeInstance(x *ast.Ident) (*ast.Ident, ast.Ex
 	// TODO(rfindley): consider changing parseRhsOrType so that this function variable
 	// is not needed.
 	argparser := p.parseRhsOrType
-	if p.mode&parseTypeParams == 0 {
+	if !p.parseTypeParams() {
 		argparser = p.parseRhs
 	}
 	if p.tok != token.RBRACK {
@@ -583,19 +588,19 @@ func (p *parser) parseArrayFieldOrTypeInstance(x *ast.Ident) (*ast.Ident, ast.Ex
 			// x [P]E
 			return x, &ast.ArrayType{Lbrack: lbrack, Len: args[0], Elt: elt}
 		}
-		if p.mode&parseTypeParams == 0 {
+		if !p.parseTypeParams() {
 			p.error(rbrack, "missing element type in array type expression")
 			return nil, &ast.BadExpr{From: args[0].Pos(), To: args[0].End()}
 		}
 	}
 
-	if p.mode&parseTypeParams == 0 {
+	if !p.parseTypeParams() {
 		p.error(firstComma, "expected ']', found ','")
 		return x, &ast.BadExpr{From: args[0].Pos(), To: args[len(args)-1].End()}
 	}
 
 	// x[P], x[P1, P2], ...
-	return nil, &ast.IndexExpr{X: x, Lbrack: lbrack, Index: &ast.ListExpr{ElemList: args}, Rbrack: rbrack}
+	return nil, &ast.IndexExpr{X: x, Lbrack: lbrack, Index: typeparams.PackExpr(args), Rbrack: rbrack}
 }
 
 func (p *parser) parseFieldDecl() *ast.Field {
@@ -878,7 +883,7 @@ func (p *parser) parseParameters(acceptTParams bool) (tparams, params *ast.Field
 		defer un(trace(p, "Parameters"))
 	}
 
-	if p.mode&parseTypeParams != 0 && acceptTParams && p.tok == token.LBRACK {
+	if p.parseTypeParams() && acceptTParams && p.tok == token.LBRACK {
 		opening := p.pos
 		p.next()
 		// [T any](params) syntax
@@ -951,7 +956,7 @@ func (p *parser) parseMethodSpec() *ast.Field {
 	x := p.parseTypeName(nil)
 	if ident, _ := x.(*ast.Ident); ident != nil {
 		switch {
-		case p.tok == token.LBRACK && p.mode&parseTypeParams != 0:
+		case p.tok == token.LBRACK && p.parseTypeParams():
 			// generic method or embedded instantiated type
 			lbrack := p.pos
 			p.next()
@@ -967,7 +972,8 @@ func (p *parser) parseMethodSpec() *ast.Field {
 				_, params := p.parseParameters(false)
 				results := p.parseResult()
 				idents = []*ast.Ident{ident}
-				typ = &ast.FuncType{Func: token.NoPos, TParams: tparams, Params: params, Results: results}
+				typ = &ast.FuncType{Func: token.NoPos, Params: params, Results: results}
+				typeparams.Set(typ, tparams)
 			} else {
 				// embedded instantiated type
 				// TODO(rfindley) should resolve all identifiers in x.
@@ -984,7 +990,7 @@ func (p *parser) parseMethodSpec() *ast.Field {
 					p.exprLev--
 				}
 				rbrack := p.expectClosing(token.RBRACK, "type argument list")
-				typ = &ast.IndexExpr{X: ident, Lbrack: lbrack, Index: &ast.ListExpr{ElemList: list}, Rbrack: rbrack}
+				typ = &ast.IndexExpr{X: ident, Lbrack: lbrack, Index: typeparams.PackExpr(list), Rbrack: rbrack}
 			}
 		case p.tok == token.LPAREN:
 			// ordinary method
@@ -1000,7 +1006,7 @@ func (p *parser) parseMethodSpec() *ast.Field {
 	} else {
 		// embedded, possibly instantiated type
 		typ = x
-		if p.tok == token.LBRACK && p.mode&parseTypeParams != 0 {
+		if p.tok == token.LBRACK && p.parseTypeParams() {
 			// embedded instantiated interface
 			typ = p.parseTypeInstance(typ)
 		}
@@ -1020,7 +1026,7 @@ func (p *parser) parseInterfaceType() *ast.InterfaceType {
 	pos := p.expect(token.INTERFACE)
 	lbrace := p.expect(token.LBRACE)
 	var list []*ast.Field
-	for p.tok == token.IDENT || p.mode&parseTypeParams != 0 && p.tok == token.TYPE {
+	for p.tok == token.IDENT || p.parseTypeParams() && p.tok == token.TYPE {
 		if p.tok == token.IDENT {
 			list = append(list, p.parseMethodSpec())
 		} else {
@@ -1108,14 +1114,14 @@ func (p *parser) parseTypeInstance(typ ast.Expr) ast.Expr {
 
 	closing := p.expectClosing(token.RBRACK, "type argument list")
 
-	return &ast.IndexExpr{X: typ, Lbrack: opening, Index: &ast.ListExpr{ElemList: list}, Rbrack: closing}
+	return &ast.IndexExpr{X: typ, Lbrack: opening, Index: typeparams.PackExpr(list), Rbrack: closing}
 }
 
 func (p *parser) tryIdentOrType() ast.Expr {
 	switch p.tok {
 	case token.IDENT:
 		typ := p.parseTypeName(nil)
-		if p.tok == token.LBRACK && p.mode&parseTypeParams != 0 {
+		if p.tok == token.LBRACK && p.parseTypeParams() {
 			typ = p.parseTypeInstance(typ)
 		}
 		return typ
@@ -1360,13 +1366,13 @@ func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr {
 		return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: index[0], Rbrack: rbrack}
 	}
 
-	if p.mode&parseTypeParams == 0 {
+	if !p.parseTypeParams() {
 		p.error(firstComma, "expected ']' or ':', found ','")
 		return &ast.BadExpr{From: args[0].Pos(), To: args[len(args)-1].End()}
 	}
 
 	// instance expression
-	return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: &ast.ListExpr{ElemList: args}, Rbrack: rbrack}
+	return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: typeparams.PackExpr(args), Rbrack: rbrack}
 }
 
 func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
@@ -2406,7 +2412,7 @@ func (p *parser) parseValueSpec(doc *ast.CommentGroup, _ token.Pos, keyword toke
 func (p *parser) parseGenericType(spec *ast.TypeSpec, openPos token.Pos, name0 *ast.Ident, closeTok token.Token) {
 	list := p.parseParameterList(name0, closeTok, p.parseParamDecl, true)
 	closePos := p.expect(closeTok)
-	spec.TParams = &ast.FieldList{Opening: openPos, List: list, Closing: closePos}
+	typeparams.Set(spec, &ast.FieldList{Opening: openPos, List: list, Closing: closePos})
 	// Type alias cannot have type parameters. Accept them for robustness but complain.
 	if p.tok == token.ASSIGN {
 		p.error(p.pos, "generic type cannot be alias")
@@ -2432,7 +2438,7 @@ func (p *parser) parseTypeSpec(doc *ast.CommentGroup, _ token.Pos, _ token.Token
 			p.exprLev++
 			x := p.parseExpr()
 			p.exprLev--
-			if name0, _ := x.(*ast.Ident); p.mode&parseTypeParams != 0 && name0 != nil && p.tok != token.RBRACK {
+			if name0, _ := x.(*ast.Ident); p.parseTypeParams() && name0 != nil && p.tok != token.RBRACK {
 				// generic type [T any];
 				p.parseGenericType(spec, lbrack, name0, token.RBRACK)
 			} else {
@@ -2537,12 +2543,12 @@ func (p *parser) parseFuncDecl() *ast.FuncDecl {
 		Name: ident,
 		Type: &ast.FuncType{
 			Func:    pos,
-			TParams: tparams,
 			Params:  params,
 			Results: results,
 		},
 		Body: body,
 	}
+	typeparams.Set(decl.Type, tparams)
 	return decl
 }
 
diff --git a/src/go/parser/resolver.go b/src/go/parser/resolver.go
index dd77b685e39..1e357e26dfe 100644
--- a/src/go/parser/resolver.go
+++ b/src/go/parser/resolver.go
@@ -7,6 +7,7 @@ package parser
 import (
 	"fmt"
 	"go/ast"
+	"go/internal/typeparams"
 	"go/token"
 )
 
@@ -450,10 +451,10 @@ func (r *resolver) Visit(node ast.Node) ast.Visitor {
 				// at the identifier in the TypeSpec and ends at the end of the innermost
 				// containing block.
 				r.declare(spec, nil, r.topScope, ast.Typ, spec.Name)
-				if spec.TParams != nil {
+				if tparams := typeparams.Get(spec); tparams != nil {
 					r.openScope(spec.Pos())
 					defer r.closeScope()
-					r.walkFieldList(r.topScope, spec.TParams, ast.Typ)
+					r.walkFieldList(r.topScope, tparams, ast.Typ)
 				}
 				ast.Walk(r, spec.Type)
 			}
@@ -476,7 +477,6 @@ func (r *resolver) Visit(node ast.Node) ast.Visitor {
 }
 
 func (r *resolver) walkFuncType(scope *ast.Scope, typ *ast.FuncType) {
-	r.walkFieldList(scope, typ.TParams, ast.Typ)
 	r.walkFieldList(scope, typ.Params, ast.Var)
 	r.walkFieldList(scope, typ.Results, ast.Var)
 }
diff --git a/src/go/parser/resolver_test.go b/src/go/parser/resolver_test.go
index 9ae2844d730..80a6638210d 100644
--- a/src/go/parser/resolver_test.go
+++ b/src/go/parser/resolver_test.go
@@ -7,6 +7,7 @@ package parser
 import (
 	"fmt"
 	"go/ast"
+	"go/internal/typeparams"
 	"go/scanner"
 	"go/token"
 	"os"
@@ -41,7 +42,11 @@ func TestResolution(t *testing.T) {
 			src := readFile(path) // panics on failure
 			var mode Mode
 			if strings.HasSuffix(path, ".go2") {
-				mode = parseTypeParams
+				if !typeparams.Enabled {
+					t.Skip("type params are not enabled")
+				}
+			} else {
+				mode |= typeparams.DisallowParsing
 			}
 			file, err := ParseFile(fset, path, src, mode)
 			if err != nil {
diff --git a/src/go/parser/short_test.go b/src/go/parser/short_test.go
index b21dd0aa60f..67fef156655 100644
--- a/src/go/parser/short_test.go
+++ b/src/go/parser/short_test.go
@@ -6,7 +6,10 @@
 
 package parser
 
-import "testing"
+import (
+	"go/internal/typeparams"
+	"testing"
+)
 
 var valids = []string{
 	"package p\n",
@@ -130,19 +133,22 @@ func TestValid(t *testing.T) {
 		}
 	})
 	t.Run("tparams", func(t *testing.T) {
+		if !typeparams.Enabled {
+			t.Skip("type params are not enabled")
+		}
 		for _, src := range valids {
-			checkErrors(t, src, src, DeclarationErrors|AllErrors|parseTypeParams, false)
+			checkErrors(t, src, src, DeclarationErrors|AllErrors, false)
 		}
 		for _, src := range validWithTParamsOnly {
-			checkErrors(t, src, src, DeclarationErrors|AllErrors|parseTypeParams, false)
+			checkErrors(t, src, src, DeclarationErrors|AllErrors, false)
 		}
 	})
 }
 
 // TestSingle is useful to track down a problem with a single short test program.
 func TestSingle(t *testing.T) {
-	const src = `package p; var _ = T[P]{}`
-	checkErrors(t, src, src, DeclarationErrors|AllErrors|parseTypeParams, true)
+	const src = `package p; var _ = T{}`
+	checkErrors(t, src, src, DeclarationErrors|AllErrors, true)
 }
 
 var invalids = []string{
@@ -250,21 +256,24 @@ var invalidTParamErrs = []string{
 func TestInvalid(t *testing.T) {
 	t.Run("no tparams", func(t *testing.T) {
 		for _, src := range invalids {
-			checkErrors(t, src, src, DeclarationErrors|AllErrors, true)
+			checkErrors(t, src, src, DeclarationErrors|AllErrors|typeparams.DisallowParsing, true)
 		}
 		for _, src := range validWithTParamsOnly {
-			checkErrors(t, src, src, DeclarationErrors|AllErrors, true)
+			checkErrors(t, src, src, DeclarationErrors|AllErrors|typeparams.DisallowParsing, true)
 		}
 		for _, src := range invalidNoTParamErrs {
-			checkErrors(t, src, src, DeclarationErrors|AllErrors, true)
+			checkErrors(t, src, src, DeclarationErrors|AllErrors|typeparams.DisallowParsing, true)
 		}
 	})
 	t.Run("tparams", func(t *testing.T) {
+		if !typeparams.Enabled {
+			t.Skip("type params are not enabled")
+		}
 		for _, src := range invalids {
-			checkErrors(t, src, src, DeclarationErrors|AllErrors|parseTypeParams, true)
+			checkErrors(t, src, src, DeclarationErrors|AllErrors, true)
 		}
 		for _, src := range invalidTParamErrs {
-			checkErrors(t, src, src, DeclarationErrors|AllErrors|parseTypeParams, true)
+			checkErrors(t, src, src, DeclarationErrors|AllErrors, true)
 		}
 	})
 }
diff --git a/src/go/printer/nodes.go b/src/go/printer/nodes.go
index 1c0a14ec157..913281ea6c1 100644
--- a/src/go/printer/nodes.go
+++ b/src/go/printer/nodes.go
@@ -11,6 +11,7 @@ package printer
 import (
 	"bytes"
 	"go/ast"
+	"go/internal/typeparams"
 	"go/token"
 	"math"
 	"strconv"
@@ -382,8 +383,8 @@ func (p *printer) parameters(fields *ast.FieldList, isTypeParam bool) {
 }
 
 func (p *printer) signature(sig *ast.FuncType) {
-	if sig.TParams != nil {
-		p.parameters(sig.TParams, true)
+	if tparams := typeparams.Get(sig); tparams != nil {
+		p.parameters(tparams, true)
 	}
 	if sig.Params != nil {
 		p.parameters(sig.Params, false)
@@ -870,8 +871,14 @@ func (p *printer) expr1(expr ast.Expr, prec1, depth int) {
 		// TODO(gri): should treat[] like parentheses and undo one level of depth
 		p.expr1(x.X, token.HighestPrec, 1)
 		p.print(x.Lbrack, token.LBRACK)
-		if e, _ := x.Index.(*ast.ListExpr); e != nil {
-			p.exprList(x.Lbrack, e.ElemList, depth+1, commaTerm, x.Rbrack, false)
+		// Note: we're a bit defensive here to handle the case of a ListExpr of
+		// length 1.
+		if list := typeparams.UnpackExpr(x.Index); len(list) > 0 {
+			if len(list) > 1 {
+				p.exprList(x.Lbrack, list, depth+1, commaTerm, x.Rbrack, false)
+			} else {
+				p.expr0(list[0], depth+1)
+			}
 		} else {
 			p.expr0(x.Index, depth+1)
 		}
@@ -1628,8 +1635,8 @@ func (p *printer) spec(spec ast.Spec, n int, doIndent bool) {
 	case *ast.TypeSpec:
 		p.setComment(s.Doc)
 		p.expr(s.Name)
-		if s.TParams != nil {
-			p.parameters(s.TParams, true)
+		if tparams := typeparams.Get(s); tparams != nil {
+			p.parameters(tparams, true)
 		}
 		if n == 1 {
 			p.print(blank)
diff --git a/src/go/printer/printer_test.go b/src/go/printer/printer_test.go
index e03c2df0633..20c97b8c081 100644
--- a/src/go/printer/printer_test.go
+++ b/src/go/printer/printer_test.go
@@ -10,6 +10,7 @@ import (
 	"flag"
 	"fmt"
 	"go/ast"
+	"go/internal/typeparams"
 	"go/parser"
 	"go/token"
 	"io"
@@ -19,10 +20,6 @@ import (
 	"time"
 )
 
-// parseTypeParams tells go/parser to parse type parameters. Must be kept in
-// sync with go/parser/interface.go.
-const parseTypeParams parser.Mode = 1 << 30
-
 const (
 	dataDir  = "testdata"
 	tabwidth = 8
@@ -47,11 +44,7 @@ const (
 // if any.
 func format(src []byte, mode checkMode) ([]byte, error) {
 	// parse src
-	parseMode := parser.ParseComments
-	if mode&allowTypeParams != 0 {
-		parseMode |= parseTypeParams
-	}
-	f, err := parser.ParseFile(fset, "", src, parseMode)
+	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
 	if err != nil {
 		return nil, fmt.Errorf("parse: %s\n%s", err, src)
 	}
@@ -79,7 +72,7 @@ func format(src []byte, mode checkMode) ([]byte, error) {
 
 	// make sure formatted output is syntactically correct
 	res := buf.Bytes()
-	if _, err := parser.ParseFile(fset, "", res, parseTypeParams); err != nil {
+	if _, err := parser.ParseFile(fset, "", res, parser.ParseComments); err != nil {
 		return nil, fmt.Errorf("re-parse: %s\n%s", err, buf.Bytes())
 	}
 
@@ -210,7 +203,7 @@ var data = []entry{
 	{"linebreaks.input", "linebreaks.golden", idempotent},
 	{"expressions.input", "expressions.golden", idempotent},
 	{"expressions.input", "expressions.raw", rawFormat | idempotent},
-	{"declarations.input", "declarations.golden", allowTypeParams},
+	{"declarations.input", "declarations.golden", 0},
 	{"statements.input", "statements.golden", 0},
 	{"slow.input", "slow.golden", idempotent},
 	{"complit.input", "complit.x", export},
@@ -229,6 +222,9 @@ var data = []entry{
 func TestFiles(t *testing.T) {
 	t.Parallel()
 	for _, e := range data {
+		if !typeparams.Enabled && e.mode&allowTypeParams != 0 {
+			continue
+		}
 		source := filepath.Join(dataDir, e.source)
 		golden := filepath.Join(dataDir, e.golden)
 		mode := e.mode
diff --git a/src/go/printer/testdata/declarations.golden b/src/go/printer/testdata/declarations.golden
index 74ffce7d73f..fe0f7838de5 100644
--- a/src/go/printer/testdata/declarations.golden
+++ b/src/go/printer/testdata/declarations.golden
@@ -942,13 +942,6 @@ type _ interface {
 		x ...int)
 }
 
-// properly format one-line type lists
-type _ interface{ type a }
-
-type _ interface {
-	type a, b, c
-}
-
 // omit superfluous parentheses in parameter lists
 func _(int)
 func _(int)
@@ -999,10 +992,6 @@ func _(struct {
 	y	int
 })	// no extra comma between } and )
 
-// type parameters
-func _[A, B any](a A, b B) int	{}
-func _[T any](x, y T) T
-
 // alias declarations
 
 type c0 struct{}
diff --git a/src/go/printer/testdata/declarations.input b/src/go/printer/testdata/declarations.input
index ab2022142a6..f34395b505d 100644
--- a/src/go/printer/testdata/declarations.input
+++ b/src/go/printer/testdata/declarations.input
@@ -955,11 +955,6 @@ r string,
 		x ...int)
 }
 
-// properly format one-line type lists
-type _ interface { type a }
-
-type _ interface { type a,b,c }
-
 // omit superfluous parentheses in parameter lists
 func _((int))
 func _((((((int))))))
@@ -1010,10 +1005,6 @@ func _(struct {
 	y int
 }) // no extra comma between } and )
 
-// type parameters
-func _[A, B any](a A, b B) int {}
-func _[T any](x, y T) T
-
 // alias declarations
 
 type c0 struct{}
diff --git a/src/go/printer/testdata/generics.golden b/src/go/printer/testdata/generics.golden
index 88c461622ec..cc7fbbe1d83 100644
--- a/src/go/printer/testdata/generics.golden
+++ b/src/go/printer/testdata/generics.golden
@@ -4,6 +4,9 @@
 
 package generics
 
+func _[A, B any](a A, b B) int	{}
+func _[T any](x, y T) T
+
 type T[P any] struct{}
 type T[P1, P2, P3 any] struct{}
 
@@ -31,3 +34,10 @@ func _() {
 	var _ []T[P]
 	_ = []T[P]{}
 }
+
+// properly format one-line type lists
+type _ interface{ type a }
+
+type _ interface {
+	type a, b, c
+}
diff --git a/src/go/printer/testdata/generics.input b/src/go/printer/testdata/generics.input
index 5fdf8cdb871..f4571ad3369 100644
--- a/src/go/printer/testdata/generics.input
+++ b/src/go/printer/testdata/generics.input
@@ -4,6 +4,9 @@
 
 package generics
 
+func _[A, B any](a A, b B) int {}
+func _[T any](x, y T) T
+
 type T[P any] struct{}
 type T[P1, P2, P3 any] struct{}
 
@@ -28,3 +31,8 @@ func _() {
 	var _ []T[P]
 	_ = []T[P]{}
 }
+
+// properly format one-line type lists
+type _ interface { type a }
+
+type _ interface { type a,b,c }
diff --git a/src/go/types/api_test.go b/src/go/types/api_test.go
index 427aa04e47b..a8e29d3fdab 100644
--- a/src/go/types/api_test.go
+++ b/src/go/types/api_test.go
@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/importer"
+	"go/internal/typeparams"
 	"go/parser"
 	"go/token"
 	"internal/testenv"
@@ -48,8 +49,8 @@ func mustTypecheck(t *testing.T, path, source string, info *Info) string {
 const genericPkg = "package generic_"
 
 func modeForSource(src string) parser.Mode {
-	if strings.HasPrefix(src, genericPkg) {
-		return parseTypeParams
+	if !strings.HasPrefix(src, genericPkg) {
+		return typeparams.DisallowParsing
 	}
 	return 0
 }
@@ -347,6 +348,9 @@ func TestTypesInfo(t *testing.T) {
 	}
 
 	for _, test := range tests {
+		if strings.HasPrefix(test.src, genericPkg) && !typeparams.Enabled {
+			continue
+		}
 		info := Info{Types: make(map[ast.Expr]TypeAndValue)}
 		var name string
 		if strings.HasPrefix(test.src, broken) {
@@ -401,6 +405,9 @@ func TestDefsInfo(t *testing.T) {
 	}
 
 	for _, test := range tests {
+		if strings.HasPrefix(test.src, genericPkg) && !typeparams.Enabled {
+			continue
+		}
 		info := Info{
 			Defs: make(map[*ast.Ident]Object),
 		}
@@ -446,6 +453,9 @@ func TestUsesInfo(t *testing.T) {
 	}
 
 	for _, test := range tests {
+		if strings.HasPrefix(test.src, genericPkg) && !typeparams.Enabled {
+			continue
+		}
 		info := Info{
 			Uses: make(map[*ast.Ident]Object),
 		}
diff --git a/src/go/types/api_go1.18.go b/src/go/types/api_typeparams.go
similarity index 90%
rename from src/go/types/api_go1.18.go
rename to src/go/types/api_typeparams.go
index d98f4ef0dc1..108e526fbf5 100644
--- a/src/go/types/api_go1.18.go
+++ b/src/go/types/api_typeparams.go
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.18
-// +build go1.18
+//go:build typeparams
+// +build typeparams
 
 package types
 
diff --git a/src/go/types/api_go1.18_test.go b/src/go/types/api_typeparams_test.go
similarity index 98%
rename from src/go/types/api_go1.18_test.go
rename to src/go/types/api_typeparams_test.go
index e60fe232012..e6cccf8691a 100644
--- a/src/go/types/api_go1.18_test.go
+++ b/src/go/types/api_typeparams_test.go
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.18
-// +build go1.18
+//go:build typeparams
+// +build typeparams
 
 package types_test
 
diff --git a/src/go/types/assignments.go b/src/go/types/assignments.go
index f223cb75743..3aa06e8939f 100644
--- a/src/go/types/assignments.go
+++ b/src/go/types/assignments.go
@@ -303,20 +303,6 @@ func (check *Checker) assignVars(lhs, origRHS []ast.Expr) {
 	}
 }
 
-// unpack unpacks an *ast.ListExpr into a list of ast.Expr.
-// TODO(gri) Should find a more efficient solution that doesn't
-//           require introduction of a new slice for simple
-//           expressions.
-func unpackExpr(x ast.Expr) []ast.Expr {
-	if x, _ := x.(*ast.ListExpr); x != nil {
-		return x.ElemList
-	}
-	if x != nil {
-		return []ast.Expr{x}
-	}
-	return nil
-}
-
 func (check *Checker) shortVarDecl(pos positioner, lhs, rhs []ast.Expr) {
 	top := len(check.delayed)
 	scope := check.scope
diff --git a/src/go/types/call.go b/src/go/types/call.go
index ae0a245b2b7..642eb5e3915 100644
--- a/src/go/types/call.go
+++ b/src/go/types/call.go
@@ -8,6 +8,7 @@ package types
 
 import (
 	"go/ast"
+	"go/internal/typeparams"
 	"go/token"
 	"strings"
 	"unicode"
@@ -16,7 +17,8 @@ import (
 // funcInst type-checks a function instantiaton inst and returns the result in x.
 // The operand x must be the evaluation of inst.X and its type must be a signature.
 func (check *Checker) funcInst(x *operand, inst *ast.IndexExpr) {
-	args, ok := check.exprOrTypeList(unpackExpr(inst.Index))
+	exprs := typeparams.UnpackExpr(inst.Index)
+	args, ok := check.exprOrTypeList(exprs)
 	if !ok {
 		x.mode = invalid
 		x.expr = inst
diff --git a/src/go/types/check_test.go b/src/go/types/check_test.go
index 327fb4c5f19..8a15841e379 100644
--- a/src/go/types/check_test.go
+++ b/src/go/types/check_test.go
@@ -30,6 +30,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/importer"
+	"go/internal/typeparams"
 	"go/parser"
 	"go/scanner"
 	"go/token"
@@ -43,10 +44,6 @@ import (
 	. "go/types"
 )
 
-// parseTypeParams tells go/parser to parse type parameters. Must be kept in
-// sync with go/parser/interface.go.
-const parseTypeParams parser.Mode = 1 << 30
-
 var (
 	haltOnError = flag.Bool("halt", false, "halt on error")
 	listErrors  = flag.Bool("errlist", false, "list errors")
@@ -213,7 +210,11 @@ func checkFiles(t *testing.T, goVersion string, filenames []string, srcs [][]byt
 
 	mode := parser.AllErrors
 	if strings.HasSuffix(filenames[0], ".go2") {
-		mode |= parseTypeParams
+		if !typeparams.Enabled {
+			t.Skip("type params are not enabled")
+		}
+	} else {
+		mode |= typeparams.DisallowParsing
 	}
 
 	// parse files and collect parser errors
diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 2eb2c397459..b5b9d35b243 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/constant"
+	"go/internal/typeparams"
 	"go/token"
 )
 
@@ -645,7 +646,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 	})
 
 	alias := tdecl.Assign.IsValid()
-	if alias && tdecl.TParams != nil {
+	if alias && typeparams.Get(tdecl) != nil {
 		// The parser will ensure this but we may still get an invalid AST.
 		// Complain and continue as regular type definition.
 		check.error(atPos(tdecl.Assign), 0, "generic type cannot be alias")
@@ -668,10 +669,10 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 		def.setUnderlying(named)
 		obj.typ = named // make sure recursive type declarations terminate
 
-		if tdecl.TParams != nil {
+		if tparams := typeparams.Get(tdecl); tparams != nil {
 			check.openScope(tdecl, "type parameters")
 			defer check.closeScope()
-			named.tparams = check.collectTypeParams(tdecl.TParams)
+			named.tparams = check.collectTypeParams(tparams)
 		}
 
 		// determine underlying type of named
diff --git a/src/go/types/exprstring.go b/src/go/types/exprstring.go
index 9e073b1de02..f05e6424d44 100644
--- a/src/go/types/exprstring.go
+++ b/src/go/types/exprstring.go
@@ -10,6 +10,7 @@ import (
 	"bytes"
 	"fmt"
 	"go/ast"
+	"go/internal/typeparams"
 )
 
 // ExprString returns the (possibly shortened) string representation for x.
@@ -69,16 +70,14 @@ func WriteExpr(buf *bytes.Buffer, x ast.Expr) {
 	case *ast.IndexExpr:
 		WriteExpr(buf, x.X)
 		buf.WriteByte('[')
-		WriteExpr(buf, x.Index)
-		buf.WriteByte(']')
-
-	case *ast.ListExpr:
-		for i, e := range x.ElemList {
+		exprs := typeparams.UnpackExpr(x.Index)
+		for i, e := range exprs {
 			if i > 0 {
 				buf.WriteString(", ")
 			}
 			WriteExpr(buf, e)
 		}
+		buf.WriteByte(']')
 
 	case *ast.SliceExpr:
 		WriteExpr(buf, x.X)
diff --git a/src/go/types/resolver.go b/src/go/types/resolver.go
index 8e67237446b..43d2c739a55 100644
--- a/src/go/types/resolver.go
+++ b/src/go/types/resolver.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/constant"
+	"go/internal/typeparams"
 	"go/token"
 	"sort"
 	"strconv"
@@ -389,8 +390,8 @@ func (check *Checker) collectObjects() {
 						if name == "main" {
 							code = _InvalidMainDecl
 						}
-						if d.decl.Type.TParams != nil {
-							check.softErrorf(d.decl.Type.TParams, code, "func %s must have no type parameters", name)
+						if tparams := typeparams.Get(d.decl.Type); tparams != nil {
+							check.softErrorf(tparams, code, "func %s must have no type parameters", name)
 						}
 						if t := d.decl.Type; t.Params.NumFields() != 0 || t.Results != nil {
 							// TODO(rFindley) Should this be a hard error?
@@ -497,7 +498,7 @@ L: // unpack receiver type
 	if ptyp, _ := rtyp.(*ast.IndexExpr); ptyp != nil {
 		rtyp = ptyp.X
 		if unpackParams {
-			for _, arg := range unpackExpr(ptyp.Index) {
+			for _, arg := range typeparams.UnpackExpr(ptyp.Index) {
 				var par *ast.Ident
 				switch arg := arg.(type) {
 				case *ast.Ident:
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index 60a42b0426c..e6846545c63 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/constant"
+	"go/internal/typeparams"
 	"go/token"
 	"sort"
 	"strconv"
@@ -209,27 +210,22 @@ func isubst(x ast.Expr, smap map[*ast.Ident]*ast.Ident) ast.Expr {
 			return &new
 		}
 	case *ast.IndexExpr:
-		index := isubst(n.Index, smap)
-		if index != n.Index {
-			new := *n
-			new.Index = index
-			return &new
-		}
-	case *ast.ListExpr:
-		var elems []ast.Expr
-		for i, elem := range n.ElemList {
+		elems := typeparams.UnpackExpr(n.Index)
+		var newElems []ast.Expr
+		for i, elem := range elems {
 			new := isubst(elem, smap)
 			if new != elem {
-				if elems == nil {
-					elems = make([]ast.Expr, len(n.ElemList))
-					copy(elems, n.ElemList)
+				if newElems == nil {
+					newElems = make([]ast.Expr, len(elems))
+					copy(newElems, elems)
 				}
-				elems[i] = new
+				newElems[i] = new
 			}
 		}
-		if elems != nil {
+		if newElems != nil {
+			index := typeparams.PackExpr(newElems)
 			new := *n
-			new.ElemList = elems
+			new.Index = index
 			return &new
 		}
 	case *ast.ParenExpr:
@@ -316,13 +312,13 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast
 		}
 	}
 
-	if ftyp.TParams != nil {
-		sig.tparams = check.collectTypeParams(ftyp.TParams)
+	if tparams := typeparams.Get(ftyp); tparams != nil {
+		sig.tparams = check.collectTypeParams(tparams)
 		// Always type-check method type parameters but complain that they are not allowed.
 		// (A separate check is needed when type-checking interface method signatures because
 		// they don't have a receiver specification.)
 		if recvPar != nil {
-			check.errorf(ftyp.TParams, _Todo, "methods cannot have type parameters")
+			check.errorf(tparams, _Todo, "methods cannot have type parameters")
 		}
 	}
 
@@ -467,7 +463,8 @@ func (check *Checker) typInternal(e0 ast.Expr, def *Named) (T Type) {
 		}
 
 	case *ast.IndexExpr:
-		return check.instantiatedType(e.X, unpackExpr(e.Index), def)
+		exprs := typeparams.UnpackExpr(e.Index)
+		return check.instantiatedType(e.X, exprs, def)
 
 	case *ast.ParenExpr:
 		// Generic types must be instantiated before they can be used in any form.
@@ -801,7 +798,11 @@ func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, d
 			// (This extra check is needed here because interface method signatures don't have
 			// a receiver specification.)
 			if sig.tparams != nil {
-				check.errorf(f.Type.(*ast.FuncType).TParams, _Todo, "methods cannot have type parameters")
+				var at positioner = f.Type
+				if tparams := typeparams.Get(f.Type); tparams != nil {
+					at = tparams
+				}
+				check.errorf(at, _Todo, "methods cannot have type parameters")
 			}
 
 			// use named receiver type if available (for better error messages)