[dev.typeparams] import go2go changes to parse type parameters

This CL imports changes on the go2go branch to support parsing type
params, as well as the unsubmitted changes from CL 269300 to remove
support for parenthesize type parameter syntax.

Change-Id: I27ab942ce69eab62c2a1800f8f9661c4dcb233fe
Reviewed-on: https://go-review.googlesource.com/c/go/+/270857
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Robert Griesemer <gri@golang.org>
Trust: Robert Findley <rfindley@google.com>

12 files changed, 1063 insertions, 243 deletions

diff --git a/src/go/parser/error_test.go b/src/go/parser/error_test.go
index 9b79097acf..ed9e9473da 100644
--- a/src/go/parser/error_test.go
+++ b/src/go/parser/error_test.go
@@ -114,6 +114,7 @@ func expectedErrors(fset *token.FileSet, filename string, src []byte) map[token.
 // of found errors and reports discrepancies.
 //
 func compareErrors(t *testing.T, fset *token.FileSet, expected map[token.Pos]string, found scanner.ErrorList) {
+	t.Helper()
 	for _, error := range found {
 		// error.Pos is a token.Position, but we want
 		// a token.Pos so we can do a map lookup
@@ -149,7 +150,8 @@ func compareErrors(t *testing.T, fset *token.FileSet, expected map[token.Pos]str
 	}
 }
 
-func checkErrors(t *testing.T, filename string, input interface{}) {
+func checkErrors(t *testing.T, filename string, input interface{}, mode Mode) {
+	t.Helper()
 	src, err := readSource(filename, input)
 	if err != nil {
 		t.Error(err)
@@ -157,7 +159,7 @@ func checkErrors(t *testing.T, filename string, input interface{}) {
 	}
 
 	fset := token.NewFileSet()
-	_, err = ParseFile(fset, filename, src, DeclarationErrors|AllErrors)
+	_, err = ParseFile(fset, filename, src, mode)
 	found, ok := err.(scanner.ErrorList)
 	if err != nil && !ok {
 		t.Error(err)
@@ -180,8 +182,12 @@ func TestErrors(t *testing.T) {
 	}
 	for _, fi := range list {
 		name := fi.Name()
-		if !fi.IsDir() && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".src") {
-			checkErrors(t, filepath.Join(testdata, name), nil)
+		if !fi.IsDir() && !strings.HasPrefix(name, ".") && (strings.HasSuffix(name, ".src") || strings.HasSuffix(name, ".go2")) {
+			mode := DeclarationErrors | AllErrors
+			if strings.HasSuffix(name, ".go2") {
+				mode |= ParseTypeParams
+			}
+			checkErrors(t, filepath.Join(testdata, name), nil, mode)
 		}
 	}
 }
diff --git a/src/go/parser/interface.go b/src/go/parser/interface.go
index cc7e455c4d..1c9a1acd66 100644
--- a/src/go/parser/interface.go
+++ b/src/go/parser/interface.go
@@ -55,6 +55,7 @@ const (
 	Trace                                          // print a trace of parsed productions
 	DeclarationErrors                              // report declaration errors
 	SpuriousErrors                                 // same as AllErrors, for backward-compatibility
+	ParseTypeParams                                // Placeholder. Will control the parsing of type parameters.
 	AllErrors         = SpuriousErrors             // report all errors (not just the first 10 on different lines)
 )
 
diff --git a/src/go/parser/parser.go b/src/go/parser/parser.go
index 31a73985bf..6d92373c33 100644
--- a/src/go/parser/parser.go
+++ b/src/go/parser/parser.go
@@ -34,7 +34,7 @@ type parser struct {
 
 	// Tracing/debugging
 	mode   Mode // parsing mode
-	trace  bool // == (mode & Trace != 0)
+	trace  bool // == (mode&Trace != 0)
 	indent int  // indentation used for tracing output
 
 	// Comments
@@ -181,7 +181,7 @@ func (p *parser) tryResolve(x ast.Expr, collectUnresolved bool) {
 	if ident == nil {
 		return
 	}
-	assert(ident.Obj == nil, "identifier already declared or resolved")
+	assert(ident.Obj == nil, fmt.Sprintf("identifier %s already declared or resolved", ident.Name))
 	if ident.Name == "_" {
 		return
 	}
@@ -352,6 +352,10 @@ func (p *parser) next() {
 type bailout struct{}
 
 func (p *parser) error(pos token.Pos, msg string) {
+	if p.trace {
+		defer un(trace(p, "error: "+msg))
+	}
+
 	epos := p.file.Position(pos)
 
 	// If AllErrors is not set, discard errors reported on the same line
@@ -594,9 +598,7 @@ func (p *parser) parseLhsList() []ast.Expr {
 	switch p.tok {
 	case token.DEFINE:
 		// lhs of a short variable declaration
-		// but doesn't enter scope until later:
-		// caller must call p.shortVarDecl(p.makeIdentList(list))
-		// at appropriate time.
+		// but doesn't enter scope until later.
 	case token.COLON:
 		// lhs of a label declaration or a communication clause of a select
 		// statement (parseLhsList is not called when parsing the case clause
@@ -643,14 +645,29 @@ func (p *parser) parseType() ast.Expr {
 	return typ
 }
 
+func (p *parser) parseQualifiedIdent(ident *ast.Ident) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "QualifiedIdent"))
+	}
+
+	typ := p.parseTypeName(ident)
+	if p.tok == token.LBRACK {
+		typ = p.parseTypeInstance(typ)
+	}
+
+	return typ
+}
+
 // If the result is an identifier, it is not resolved.
-func (p *parser) parseTypeName() ast.Expr {
+func (p *parser) parseTypeName(ident *ast.Ident) ast.Expr {
 	if p.trace {
 		defer un(trace(p, "TypeName"))
 	}
 
-	ident := p.parseIdent()
-	// don't resolve ident yet - it may be a parameter or field name
+	if ident == nil {
+		ident = p.parseIdent()
+		// don't resolve ident yet - it may be a parameter or field name
+	}
 
 	if p.tok == token.PERIOD {
 		// ident is a package name
@@ -663,12 +680,11 @@ func (p *parser) parseTypeName() ast.Expr {
 	return ident
 }
 
-func (p *parser) parseArrayType() ast.Expr {
+func (p *parser) parseArrayLen() ast.Expr {
 	if p.trace {
-		defer un(trace(p, "ArrayType"))
+		defer un(trace(p, "ArrayLen"))
 	}
 
-	lbrack := p.expect(token.LBRACK)
 	p.exprLev++
 	var len ast.Expr
 	// always permit ellipsis for more fault-tolerant parsing
@@ -679,26 +695,47 @@ func (p *parser) parseArrayType() ast.Expr {
 		len = p.parseRhs()
 	}
 	p.exprLev--
-	p.expect(token.RBRACK)
-	elt := p.parseType()
 
-	return &ast.ArrayType{Lbrack: lbrack, Len: len, Elt: elt}
+	return len
 }
 
-func (p *parser) makeIdentList(list []ast.Expr) []*ast.Ident {
-	idents := make([]*ast.Ident, len(list))
-	for i, x := range list {
-		ident, isIdent := x.(*ast.Ident)
-		if !isIdent {
-			if _, isBad := x.(*ast.BadExpr); !isBad {
-				// only report error if it's a new one
-				p.errorExpected(x.Pos(), "identifier")
-			}
-			ident = &ast.Ident{NamePos: x.Pos(), Name: "_"}
+func (p *parser) parseArrayFieldOrTypeInstance(x *ast.Ident) (*ast.Ident, ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ArrayFieldOrTypeInstance"))
+	}
+
+	// TODO(gri) Should we allow a trailing comma in a type argument
+	//           list such as T[P,]? (We do in parseTypeInstance).
+	lbrack := p.expect(token.LBRACK)
+	var args []ast.Expr
+	if p.tok != token.RBRACK {
+		p.exprLev++
+		args = append(args, p.parseRhsOrType())
+		for p.tok == token.COMMA {
+			p.next()
+			args = append(args, p.parseRhsOrType())
 		}
-		idents[i] = ident
+		p.exprLev--
+	}
+	rbrack := p.expect(token.RBRACK)
+
+	if len(args) == 0 {
+		// x []E
+		elt := p.parseType()
+		return x, &ast.ArrayType{Lbrack: lbrack, Elt: elt}
 	}
-	return idents
+
+	// x [P]E or x[P]
+	if len(args) == 1 {
+		elt := p.tryType()
+		if elt != nil {
+			// x [P]E
+			return x, &ast.ArrayType{Lbrack: lbrack, Len: args[0], Elt: elt}
+		}
+	}
+
+	// x[P], x[P1, P2], ...
+	return nil, &ast.CallExpr{Fun: x, Lparen: lbrack, Args: args, Rparen: rbrack, Brackets: true}
 }
 
 func (p *parser) parseFieldDecl(scope *ast.Scope) *ast.Field {
@@ -708,37 +745,44 @@ func (p *parser) parseFieldDecl(scope *ast.Scope) *ast.Field {
 
 	doc := p.leadComment
 
-	// 1st FieldDecl
-	// A type name used as an anonymous field looks like a field identifier.
-	var list []ast.Expr
-	for {
-		list = append(list, p.parseVarType(false))
-		if p.tok != token.COMMA {
-			break
+	var names []*ast.Ident
+	var typ ast.Expr
+	if p.tok == token.IDENT {
+		name := p.parseIdent()
+		if p.tok == token.PERIOD || p.tok == token.STRING || p.tok == token.SEMICOLON || p.tok == token.RBRACE {
+			// embedded type
+			typ = name
+			if p.tok == token.PERIOD {
+				typ = p.parseQualifiedIdent(name)
+			} else {
+				p.resolve(typ)
+			}
+		} else {
+			// name1, name2, ... T
+			names = []*ast.Ident{name}
+			for p.tok == token.COMMA {
+				p.next()
+				names = append(names, p.parseIdent())
+			}
+			// Careful dance: We don't know if we have an embedded instantiated
+			// type T[P1, P2, ...] or a field T of array type []E or [P]E.
+			if len(names) == 1 && p.tok == token.LBRACK {
+				name, typ = p.parseArrayFieldOrTypeInstance(name)
+				if name == nil {
+					names = nil
+				}
+			} else {
+				// T P
+				typ = p.parseType()
+			}
 		}
-		p.next()
-	}
-
-	typ := p.tryVarType(false)
-
-	// analyze case
-	var idents []*ast.Ident
-	if typ != nil {
-		// IdentifierList Type
-		idents = p.makeIdentList(list)
 	} else {
-		// ["*"] TypeName (AnonymousField)
-		typ = list[0] // we always have at least one element
-		if n := len(list); n > 1 {
-			p.errorExpected(p.pos, "type")
-			typ = &ast.BadExpr{From: p.pos, To: p.pos}
-		} else if !isTypeName(deref(typ)) {
-			p.errorExpected(typ.Pos(), "anonymous field")
-			typ = &ast.BadExpr{From: typ.Pos(), To: p.safePos(typ.End())}
-		}
+		// embedded, possibly generic type
+		// (using the enclosing parentheses to distinguish it from a named field declaration)
+		// TODO(gri) confirm that this doesn't allow parenthesized embedded type
+		typ = p.parseType()
 	}
 
-	// Tag
 	var tag *ast.BasicLit
 	if p.tok == token.STRING {
 		tag = &ast.BasicLit{ValuePos: p.pos, Kind: p.tok, Value: p.lit}
@@ -747,10 +791,8 @@ func (p *parser) parseFieldDecl(scope *ast.Scope) *ast.Field {
 
 	p.expectSemi() // call before accessing p.linecomment
 
-	field := &ast.Field{Doc: doc, Names: idents, Type: typ, Tag: tag, Comment: p.lineComment}
-	p.declare(field, nil, scope, ast.Var, idents...)
-	p.resolve(typ)
-
+	field := &ast.Field{Doc: doc, Names: names, Type: typ, Tag: tag, Comment: p.lineComment}
+	p.declare(field, nil, scope, ast.Var, names...)
 	return field
 }
 
@@ -792,107 +834,222 @@ func (p *parser) parsePointerType() *ast.StarExpr {
 	return &ast.StarExpr{Star: star, X: base}
 }
 
-// If the result is an identifier, it is not resolved.
-func (p *parser) tryVarType(isParam bool) ast.Expr {
-	if isParam && p.tok == token.ELLIPSIS {
-		pos := p.pos
-		p.next()
-		typ := p.tryIdentOrType() // don't use parseType so we can provide better error message
-		if typ != nil {
-			p.resolve(typ)
-		} else {
-			p.error(pos, "'...' parameter is missing type")
-			typ = &ast.BadExpr{From: pos, To: p.pos}
-		}
-		return &ast.Ellipsis{Ellipsis: pos, Elt: typ}
+func (p *parser) parseDotsType() *ast.Ellipsis {
+	if p.trace {
+		defer un(trace(p, "DotsType"))
 	}
-	return p.tryIdentOrType()
+
+	pos := p.expect(token.ELLIPSIS)
+	elt := p.parseType()
+
+	return &ast.Ellipsis{Ellipsis: pos, Elt: elt}
 }
 
-// If the result is an identifier, it is not resolved.
-func (p *parser) parseVarType(isParam bool) ast.Expr {
-	typ := p.tryVarType(isParam)
-	if typ == nil {
-		pos := p.pos
-		p.errorExpected(pos, "type")
-		p.next() // make progress
-		typ = &ast.BadExpr{From: pos, To: p.pos}
+type field struct {
+	name *ast.Ident
+	typ  ast.Expr
+}
+
+func (p *parser) parseParamDecl(name *ast.Ident) (f field) {
+	if p.trace {
+		defer un(trace(p, "ParamDeclOrNil"))
 	}
-	return typ
+
+	ptok := p.tok
+	if name != nil {
+		p.tok = token.IDENT // force token.IDENT case in switch below
+	}
+
+	switch p.tok {
+	case token.IDENT:
+		if name != nil {
+			f.name = name
+			p.tok = ptok
+		} else {
+			f.name = p.parseIdent()
+		}
+		switch p.tok {
+		case token.IDENT, token.MUL, token.ARROW, token.FUNC, token.CHAN, token.MAP, token.STRUCT, token.INTERFACE, token.LPAREN:
+			// name type
+			f.typ = p.parseType()
+
+		case token.LBRACK:
+			// name[type1, type2, ...] or name []type or name [len]type
+			f.name, f.typ = p.parseArrayFieldOrTypeInstance(f.name)
+
+		case token.ELLIPSIS:
+			// name ...type
+			f.typ = p.parseDotsType()
+
+		case token.PERIOD:
+			// qualified.typename
+			f.typ = p.parseQualifiedIdent(f.name)
+			f.name = nil
+		}
+
+	case token.MUL, token.ARROW, token.FUNC, token.LBRACK, token.CHAN, token.MAP, token.STRUCT, token.INTERFACE, token.LPAREN:
+		// type
+		f.typ = p.parseType()
+
+	case token.ELLIPSIS:
+		// ...type
+		// (always accepted)
+		f.typ = p.parseDotsType()
+
+	default:
+		p.errorExpected(p.pos, ")")
+		p.advance(exprEnd)
+	}
+
+	return
 }
 
-func (p *parser) parseParameterList(scope *ast.Scope, ellipsisOk bool) (params []*ast.Field) {
+func (p *parser) parseParameterList(scope *ast.Scope, name0 *ast.Ident, closing token.Token, parseParamDecl func(*ast.Ident) field, tparams bool) (params []*ast.Field) {
 	if p.trace {
 		defer un(trace(p, "ParameterList"))
 	}
 
-	// 1st ParameterDecl
-	// A list of identifiers looks like a list of type names.
-	var list []ast.Expr
-	for {
-		list = append(list, p.parseVarType(ellipsisOk))
-		if p.tok != token.COMMA {
-			break
+	pos := p.pos
+	if name0 != nil {
+		pos = name0.Pos()
+	}
+
+	var list []field
+	var named int // number of parameters that have an explicit name and type
+
+	for name0 != nil || p.tok != closing && p.tok != token.EOF {
+		par := parseParamDecl(name0)
+		name0 = nil // 1st name was consumed if present
+		if par.name != nil || par.typ != nil {
+			list = append(list, par)
+			if par.name != nil && par.typ != nil {
+				named++
+			}
 		}
-		p.next()
-		if p.tok == token.RPAREN {
+		if !p.atComma("parameter list", closing) {
 			break
 		}
+		p.next()
 	}
 
-	// analyze case
-	if typ := p.tryVarType(ellipsisOk); typ != nil {
-		// IdentifierList Type
-		idents := p.makeIdentList(list)
-		field := &ast.Field{Names: idents, Type: typ}
-		params = append(params, field)
-		// Go spec: The scope of an identifier denoting a function
-		// parameter or result variable is the function body.
-		p.declare(field, nil, scope, ast.Var, idents...)
-		p.resolve(typ)
-		if !p.atComma("parameter list", token.RPAREN) {
-			return
+	if len(list) == 0 {
+		return // not uncommon
+	}
+
+	// TODO(gri) parameter distribution and conversion to []*ast.Field
+	//           can be combined and made more efficient
+
+	// distribute parameter types
+	if named == 0 {
+		// all unnamed => found names are type names
+		for i := 0; i < len(list); i++ {
+			par := &list[i]
+			if typ := par.name; typ != nil {
+				p.resolve(typ)
+				par.typ = typ
+				par.name = nil
+			}
 		}
-		p.next()
-		for p.tok != token.RPAREN && p.tok != token.EOF {
-			idents := p.parseIdentList()
-			typ := p.parseVarType(ellipsisOk)
-			field := &ast.Field{Names: idents, Type: typ}
-			params = append(params, field)
-			// Go spec: The scope of an identifier denoting a function
-			// parameter or result variable is the function body.
-			p.declare(field, nil, scope, ast.Var, idents...)
-			p.resolve(typ)
-			if !p.atComma("parameter list", token.RPAREN) {
-				break
+		if tparams {
+			p.error(pos, "all type parameters must be named")
+		}
+	} else if named != len(list) {
+		// some named => all must be named
+		ok := true
+		var typ ast.Expr
+		for i := len(list) - 1; i >= 0; i-- {
+			if par := &list[i]; par.typ != nil {
+				typ = par.typ
+				if par.name == nil {
+					ok = false
+					n := ast.NewIdent("_")
+					n.NamePos = typ.Pos() // correct position
+					par.name = n
+				}
+			} else if typ != nil {
+				par.typ = typ
+			} else {
+				// par.typ == nil && typ == nil => we only have a par.name
+				ok = false
+				par.typ = &ast.BadExpr{From: par.name.Pos(), To: p.pos}
+			}
+		}
+		if !ok {
+			if tparams {
+				p.error(pos, "all type parameters must be named")
+			} else {
+				p.error(pos, "mixed named and unnamed parameters")
 			}
-			p.next()
+		}
+	}
+
+	// convert list []*ast.Field
+	if named == 0 {
+		// parameter list consists of types only
+		for _, par := range list {
+			assert(par.typ != nil, "nil type in unnamed parameter list")
+			params = append(params, &ast.Field{Type: par.typ})
 		}
 		return
 	}
 
-	// Type { "," Type } (anonymous parameters)
-	params = make([]*ast.Field, len(list))
-	for i, typ := range list {
-		p.resolve(typ)
-		params[i] = &ast.Field{Type: typ}
+	// parameter list consists of named parameters with types
+	var names []*ast.Ident
+	var typ ast.Expr
+	addParams := func() {
+		assert(typ != nil, "nil type in named parameter list")
+		field := &ast.Field{Names: names, Type: typ}
+		// Go spec: The scope of an identifier denoting a function
+		// parameter or result variable is the function body.
+		p.declare(field, nil, scope, ast.Var, names...)
+		params = append(params, field)
+		names = nil
+	}
+	for _, par := range list {
+		if par.typ != typ {
+			if len(names) > 0 {
+				addParams()
+			}
+			typ = par.typ
+		}
+		names = append(names, par.name)
+	}
+	if len(names) > 0 {
+		addParams()
 	}
 	return
 }
 
-func (p *parser) parseParameters(scope *ast.Scope, ellipsisOk bool) *ast.FieldList {
+func (p *parser) parseParameters(scope *ast.Scope, acceptTParams bool) (tparams, params *ast.FieldList) {
 	if p.trace {
 		defer un(trace(p, "Parameters"))
 	}
 
-	var params []*ast.Field
-	lparen := p.expect(token.LPAREN)
+	if acceptTParams && p.tok == token.LBRACK {
+		opening := p.pos
+		p.next()
+		// [T any](params) syntax
+		list := p.parseParameterList(scope, nil, token.RBRACK, p.parseParamDecl, true)
+		rbrack := p.expect(token.RBRACK)
+		tparams = &ast.FieldList{Opening: opening, List: list, Closing: rbrack}
+		// Type parameter lists must not be empty.
+		if tparams != nil && tparams.NumFields() == 0 {
+			p.error(tparams.Closing, "empty type parameter list")
+			tparams = nil // avoid follow-on errors
+		}
+	}
+
+	opening := p.expect(token.LPAREN)
+
+	var fields []*ast.Field
 	if p.tok != token.RPAREN {
-		params = p.parseParameterList(scope, ellipsisOk)
+		fields = p.parseParameterList(scope, nil, token.RPAREN, p.parseParamDecl, false)
 	}
+
 	rparen := p.expect(token.RPAREN)
+	params = &ast.FieldList{Opening: opening, List: fields, Closing: rparen}
 
-	return &ast.FieldList{Opening: lparen, List: params, Closing: rparen}
+	return
 }
 
 func (p *parser) parseResult(scope *ast.Scope) *ast.FieldList {
@@ -901,7 +1058,8 @@ func (p *parser) parseResult(scope *ast.Scope) *ast.FieldList {
 	}
 
 	if p.tok == token.LPAREN {
-		return p.parseParameters(scope, false)
+		_, results := p.parseParameters(scope, false)
+		return results
 	}
 
 	typ := p.tryType()
@@ -914,17 +1072,6 @@ func (p *parser) parseResult(scope *ast.Scope) *ast.FieldList {
 	return nil
 }
 
-func (p *parser) parseSignature(scope *ast.Scope) (params, results *ast.FieldList) {
-	if p.trace {
-		defer un(trace(p, "Signature"))
-	}
-
-	params = p.parseParameters(scope, true)
-	results = p.parseResult(scope)
-
-	return
-}
-
 func (p *parser) parseFuncType() (*ast.FuncType, *ast.Scope) {
 	if p.trace {
 		defer un(trace(p, "FuncType"))
@@ -932,7 +1079,11 @@ func (p *parser) parseFuncType() (*ast.FuncType, *ast.Scope) {
 
 	pos := p.expect(token.FUNC)
 	scope := ast.NewScope(p.topScope) // function scope
-	params, results := p.parseSignature(scope)
+	tparams, params := p.parseParameters(scope, true)
+	if tparams != nil {
+		p.error(tparams.Pos(), "function type cannot have type parameters")
+	}
+	results := p.parseResult(scope)
 
 	return &ast.FuncType{Func: pos, Params: params, Results: results}, scope
 }
@@ -945,17 +1096,65 @@ func (p *parser) parseMethodSpec(scope *ast.Scope) *ast.Field {
 	doc := p.leadComment
 	var idents []*ast.Ident
 	var typ ast.Expr
-	x := p.parseTypeName()
-	if ident, isIdent := x.(*ast.Ident); isIdent && p.tok == token.LPAREN {
-		// method
-		idents = []*ast.Ident{ident}
-		scope := ast.NewScope(nil) // method scope
-		params, results := p.parseSignature(scope)
-		typ = &ast.FuncType{Func: token.NoPos, Params: params, Results: results}
+	x := p.parseTypeName(nil)
+	if ident, _ := x.(*ast.Ident); ident != nil {
+		switch p.tok {
+		case token.LBRACK:
+			// generic method or embedded instantiated type
+			lbrack := p.pos
+			p.next()
+			p.exprLev++
+			x := p.parseExpr(true) // we don't know yet if we're a lhs or rhs expr
+			p.exprLev--
+			if name0, _ := x.(*ast.Ident); name0 != nil && p.tok != token.COMMA && p.tok != token.RBRACK {
+				// generic method m[T any]
+				scope := ast.NewScope(nil) // method scope
+				list := p.parseParameterList(scope, name0, token.RBRACK, p.parseParamDecl, true)
+				rbrack := p.expect(token.RBRACK)
+				tparams := &ast.FieldList{Opening: lbrack, List: list, Closing: rbrack}
+				// TODO(rfindley) refactor to share code with parseFuncType.
+				_, params := p.parseParameters(scope, false)
+				results := p.parseResult(scope)
+				idents = []*ast.Ident{ident}
+				typ = &ast.FuncType{Func: token.NoPos, TParams: tparams, Params: params, Results: results}
+			} else {
+				// embedded instantiated type
+				// TODO(rfindley) should resolve all identifiers in x.
+				list := []ast.Expr{x}
+				if p.atComma("type argument list", token.RBRACK) {
+					p.exprLev++
+					for p.tok != token.RBRACK && p.tok != token.EOF {
+						list = append(list, p.parseType())
+						if !p.atComma("type argument list", token.RBRACK) {
+							break
+						}
+						p.next()
+					}
+					p.exprLev--
+				}
+				rbrack := p.expectClosing(token.RBRACK, "type argument list")
+				typ = &ast.CallExpr{Fun: ident, Lparen: lbrack, Args: list, Rparen: rbrack, Brackets: true}
+			}
+		case token.LPAREN:
+			// ordinary method
+			// TODO(rfindley) refactor to share code with parseFuncType.
+			scope := ast.NewScope(nil) // method scope
+			_, params := p.parseParameters(scope, false)
+			results := p.parseResult(scope)
+			idents = []*ast.Ident{ident}
+			typ = &ast.FuncType{Func: token.NoPos, Params: params, Results: results}
+		default:
+			// embedded type
+			typ = x
+			p.resolve(typ)
+		}
 	} else {
-		// embedded interface
+		// embedded, possibly instantiated type
 		typ = x
-		p.resolve(typ)
+		if p.tok == token.LBRACK {
+			// embedded instantiated interface
+			typ = p.parseTypeInstance(typ)
+		}
 	}
 	p.expectSemi() // call before accessing p.linecomment
 
@@ -974,8 +1173,24 @@ func (p *parser) parseInterfaceType() *ast.InterfaceType {
 	lbrace := p.expect(token.LBRACE)
 	scope := ast.NewScope(nil) // interface scope
 	var list []*ast.Field
-	for p.tok == token.IDENT {
-		list = append(list, p.parseMethodSpec(scope))
+L:
+	for {
+		switch p.tok {
+		case token.IDENT, token.LPAREN:
+			list = append(list, p.parseMethodSpec(scope))
+		case token.TYPE:
+			// all types in a type list share the same field name "type"
+			// (since type is a keyword, a Go program cannot have that field name)
+			name := []*ast.Ident{{NamePos: p.pos, Name: "type"}}
+			p.next()
+			// add each type as a field named "type"
+			for _, typ := range p.parseTypeList() {
+				list = append(list, &ast.Field{Names: name, Type: typ})
+			}
+			p.expectSemi()
+		default:
+			break L
+		}
 	}
 	rbrace := p.expect(token.RBRACE)
 
@@ -1028,13 +1243,44 @@ func (p *parser) parseChanType() *ast.ChanType {
 	return &ast.ChanType{Begin: pos, Arrow: arrow, Dir: dir, Value: value}
 }
 
+func (p *parser) parseTypeInstance(typ ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeInstance"))
+	}
+
+	opening := p.expect(token.LBRACK)
+
+	p.exprLev++
+	var list []ast.Expr
+	for p.tok != token.RBRACK && p.tok != token.EOF {
+		list = append(list, p.parseType())
+		if !p.atComma("type argument list", token.RBRACK) {
+			break
+		}
+		p.next()
+	}
+	p.exprLev--
+
+	closing := p.expectClosing(token.RBRACK, "type argument list")
+
+	return &ast.CallExpr{Fun: typ, Lparen: opening, Args: list, Rparen: closing, Brackets: true}
+}
+
 // If the result is an identifier, it is not resolved.
 func (p *parser) tryIdentOrType() ast.Expr {
 	switch p.tok {
 	case token.IDENT:
-		return p.parseTypeName()
+		typ := p.parseTypeName(nil)
+		if p.tok == token.LBRACK {
+			typ = p.parseTypeInstance(typ)
+		}
+		return typ
 	case token.LBRACK:
-		return p.parseArrayType()
+		lbrack := p.expect(token.LBRACK)
+		alen := p.parseArrayLen()
+		p.expect(token.RBRACK)
+		elt := p.parseType()
+		return &ast.ArrayType{Lbrack: lbrack, Len: alen, Elt: elt}
 	case token.STRUCT:
 		return p.parseStructType()
 	case token.MUL:
@@ -1169,7 +1415,7 @@ func (p *parser) parseOperand(lhs bool) ast.Expr {
 		return p.parseFuncTypeOrLit()
 	}
 
-	if typ := p.tryIdentOrType(); typ != nil {
+	if typ := p.tryIdentOrType(); typ != nil { // do not consume trailing type parameters
 		// could be type for composite literal or conversion
 		_, isIdent := typ.(*ast.Ident)
 		assert(!isIdent, "type cannot be identifier")
@@ -1211,28 +1457,53 @@ func (p *parser) parseTypeAssertion(x ast.Expr) ast.Expr {
 	return &ast.TypeAssertExpr{X: x, Type: typ, Lparen: lparen, Rparen: rparen}
 }
 
-func (p *parser) parseIndexOrSlice(x ast.Expr) ast.Expr {
+func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr {
 	if p.trace {
-		defer un(trace(p, "IndexOrSlice"))
+		defer un(trace(p, "parseIndexOrSliceOrInstance"))
 	}
 
-	const N = 3 // change the 3 to 2 to disable 3-index slices
 	lbrack := p.expect(token.LBRACK)
+	if p.tok == token.RBRACK {
+		// empty index, slice or index expressions are not permitted;
+		// accept them for parsing tolerance, but complain
+		p.errorExpected(p.pos, "operand")
+		p.next()
+		return x
+	}
 	p.exprLev++
+
+	const N = 3 // change the 3 to 2 to disable 3-index slices
+	var args []ast.Expr
 	var index [N]ast.Expr
 	var colons [N - 1]token.Pos
 	if p.tok != token.COLON {
-		index[0] = p.parseRhs()
+		// We can't know if we have an index expression or a type instantiation;
+		// so even if we see a (named) type we are not going to be in type context.
+		index[0] = p.parseRhsOrType()
 	}
 	ncolons := 0
-	for p.tok == token.COLON && ncolons < len(colons) {
-		colons[ncolons] = p.pos
-		ncolons++
-		p.next()
-		if p.tok != token.COLON && p.tok != token.RBRACK && p.tok != token.EOF {
-			index[ncolons] = p.parseRhs()
+	switch p.tok {
+	case token.COLON:
+		// slice expression
+		for p.tok == token.COLON && ncolons < len(colons) {
+			colons[ncolons] = p.pos
+			ncolons++
+			p.next()
+			if p.tok != token.COLON && p.tok != token.RBRACK && p.tok != token.EOF {
+				index[ncolons] = p.parseRhs()
+			}
+		}
+	case token.COMMA:
+		// instance expression
+		args = append(args, index[0])
+		for p.tok == token.COMMA {
+			p.next()
+			if p.tok != token.RBRACK && p.tok != token.EOF {
+				args = append(args, p.parseType())
+			}
 		}
 	}
+
 	p.exprLev--
 	rbrack := p.expect(token.RBRACK)
 
@@ -1255,7 +1526,13 @@ func (p *parser) parseIndexOrSlice(x ast.Expr) ast.Expr {
 		return &ast.SliceExpr{X: x, Lbrack: lbrack, Low: index[0], High: index[1], Max: index[2], Slice3: slice3, Rbrack: rbrack}
 	}
 
-	return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: index[0], Rbrack: rbrack}
+	if len(args) == 0 {
+		// index expression
+		return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: index[0], Rbrack: rbrack}
+	}
+
+	// instance expression
+	return &ast.CallExpr{Fun: x, Lparen: lbrack, Args: args, Rparen: rbrack, Brackets: true}
 }
 
 func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
@@ -1404,45 +1681,6 @@ func (p *parser) checkExpr(x ast.Expr) ast.Expr {
 	return x
 }
 
-// isTypeName reports whether x is a (qualified) TypeName.
-func isTypeName(x ast.Expr) bool {
-	switch t := x.(type) {
-	case *ast.BadExpr:
-	case *ast.Ident:
-	case *ast.SelectorExpr:
-		_, isIdent := t.X.(*ast.Ident)
-		return isIdent
-	default:
-		return false // all other nodes are not type names
-	}
-	return true
-}
-
-// isLiteralType reports whether x is a legal composite literal type.
-func isLiteralType(x ast.Expr) bool {
-	switch t := x.(type) {
-	case *ast.BadExpr:
-	case *ast.Ident:
-	case *ast.SelectorExpr:
-		_, isIdent := t.X.(*ast.Ident)
-		return isIdent
-	case *ast.ArrayType:
-	case *ast.StructType:
-	case *ast.MapType:
-	default:
-		return false // all other nodes are not legal composite literal types
-	}
-	return true
-}
-
-// If x is of the form *T, deref returns T, otherwise it returns x.
-func deref(x ast.Expr) ast.Expr {
-	if p, isPtr := x.(*ast.StarExpr); isPtr {
-		x = p.X
-	}
-	return x
-}
-
 // If x is of the form (T), unparen returns unparen(T), otherwise it returns x.
 func unparen(x ast.Expr) ast.Expr {
 	if p, isParen := x.(*ast.ParenExpr); isParen {
@@ -1470,13 +1708,12 @@ func (p *parser) checkExprOrType(x ast.Expr) ast.Expr {
 }
 
 // If lhs is set and the result is an identifier, it is not resolved.
-func (p *parser) parsePrimaryExpr(lhs bool) ast.Expr {
+func (p *parser) parsePrimaryExpr(lhs bool) (x ast.Expr) {
 	if p.trace {
 		defer un(trace(p, "PrimaryExpr"))
 	}
 
-	x := p.parseOperand(lhs)
-L:
+	x = p.parseOperand(lhs)
 	for {
 		switch p.tok {
 		case token.PERIOD:
@@ -1500,28 +1737,48 @@ L:
 			if lhs {
 				p.resolve(x)
 			}
-			x = p.parseIndexOrSlice(p.checkExpr(x))
+			x = p.parseIndexOrSliceOrInstance(p.checkExpr(x))
 		case token.LPAREN:
 			if lhs {
 				p.resolve(x)
 			}
 			x = p.parseCallOrConversion(p.checkExprOrType(x))
 		case token.LBRACE:
-			if isLiteralType(x) && (p.exprLev >= 0 || !isTypeName(x)) {
-				if lhs {
-					p.resolve(x)
+			// operand may have returned a parenthesized complit
+			// type; accept it but complain if we have a complit
+			t := unparen(x)
+			// determine if '{' belongs to a composite literal or a block statement
+			switch t := t.(type) {
+			case *ast.BadExpr, *ast.Ident, *ast.SelectorExpr:
+				if p.exprLev < 0 {
+					return
 				}
-				x = p.parseLiteralValue(x)
-			} else {
-				break L
+				// x is possibly a composite literal type
+			case *ast.CallExpr:
+				if !t.Brackets || p.exprLev < 0 {
+					return
+				}
+				// x is possibly a composite literal type
+			case *ast.IndexExpr:
+				if p.exprLev < 0 {
+					return
+				}
+				// x is possibly a composite literal type
+			case *ast.ArrayType, *ast.StructType, *ast.MapType:
+				// x is a composite literal type
+			default:
+				return
+			}
+			if t != x {
+				p.error(t.Pos(), "cannot parenthesize type in composite literal")
+				// already progressed, no need to advance
 			}
+			x = p.parseLiteralValue(x)
 		default:
-			break L
+			return
 		}
 		lhs = false // no need to try to resolve again
 	}
-
-	return x
 }
 
 // If lhs is set and the result is an identifier, it is not resolved.
@@ -1846,14 +2103,14 @@ func (p *parser) parseIfHeader() (init ast.Stmt, cond ast.Expr) {
 	}
 	// p.tok != token.LBRACE
 
-	outer := p.exprLev
+	prevLev := p.exprLev
 	p.exprLev = -1
 
 	if p.tok != token.SEMICOLON {
 		// accept potential variable declaration but complain
 		if p.tok == token.VAR {
 			p.next()
-			p.error(p.pos, fmt.Sprintf("var declaration not allowed in 'IF' initializer"))
+			p.error(p.pos, "var declaration not allowed in 'IF' initializer")
 		}
 		init, _ = p.parseSimpleStmt(basic)
 	}
@@ -1894,7 +2151,7 @@ func (p *parser) parseIfHeader() (init ast.Stmt, cond ast.Expr) {
 		cond = &ast.BadExpr{From: p.pos, To: p.pos}
 	}
 
-	p.exprLev = outer
+	p.exprLev = prevLev
 	return
 }
 
@@ -2275,7 +2532,7 @@ func (p *parser) parseStmt() (s ast.Stmt) {
 // ----------------------------------------------------------------------------
 // Declarations
 
-type parseSpecFunction func(doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec
+type parseSpecFunction func(doc *ast.CommentGroup, pos token.Pos, keyword token.Token, iota int) ast.Spec
 
 func isValidImport(lit string) bool {
 	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
@@ -2288,7 +2545,7 @@ func isValidImport(lit string) bool {
 	return s != ""
 }
 
-func (p *parser) parseImportSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
+func (p *parser) parseImportSpec(doc *ast.CommentGroup, _ token.Pos, _ token.Token, _ int) ast.Spec {
 	if p.trace {
 		defer un(trace(p, "ImportSpec"))
 	}
@@ -2327,7 +2584,7 @@ func (p *parser) parseImportSpec(doc *ast.CommentGroup, _ token.Token, _ int) as
 	return spec
 }
 
-func (p *parser) parseValueSpec(doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec {
+func (p *parser) parseValueSpec(doc *ast.CommentGroup, _ token.Pos, keyword token.Token, iota int) ast.Spec {
 	if p.trace {
 		defer un(trace(p, keyword.String()+"Spec"))
 	}
@@ -2374,7 +2631,21 @@ func (p *parser) parseValueSpec(doc *ast.CommentGroup, keyword token.Token, iota
 	return spec
 }
 
-func (p *parser) parseTypeSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
+func (p *parser) parseGenericType(spec *ast.TypeSpec, openPos token.Pos, name0 *ast.Ident, closeTok token.Token) {
+	p.openScope()
+	list := p.parseParameterList(p.topScope, name0, closeTok, p.parseParamDecl, true)
+	closePos := p.expect(closeTok)
+	spec.TParams = &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")
+		p.next()
+	}
+	spec.Type = p.parseType()
+	p.closeScope()
+}
+
+func (p *parser) parseTypeSpec(doc *ast.CommentGroup, _ token.Pos, _ token.Token, _ int) ast.Spec {
 	if p.trace {
 		defer un(trace(p, "TypeSpec"))
 	}
@@ -2387,11 +2658,44 @@ func (p *parser) parseTypeSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.
 	// (Global identifiers are resolved in a separate phase after parsing.)
 	spec := &ast.TypeSpec{Doc: doc, Name: ident}
 	p.declare(spec, nil, p.topScope, ast.Typ, ident)
-	if p.tok == token.ASSIGN {
-		spec.Assign = p.pos
+
+	switch p.tok {
+	case token.LBRACK:
+		lbrack := p.pos
 		p.next()
+		if p.tok == token.IDENT {
+			// array type or generic type [T any]
+			p.exprLev++
+			x := p.parseExpr(true) // we don't know yet if we're a lhs or rhs expr
+			p.exprLev--
+			if name0, _ := x.(*ast.Ident); name0 != nil && p.tok != token.RBRACK {
+				// generic type [T any];
+				p.parseGenericType(spec, lbrack, name0, token.RBRACK)
+			} else {
+				// array type
+				// TODO(rfindley) should resolve all identifiers in x.
+				p.expect(token.RBRACK)
+				elt := p.parseType()
+				spec.Type = &ast.ArrayType{Lbrack: lbrack, Len: x, Elt: elt}
+			}
+		} else {
+			// array type
+			alen := p.parseArrayLen()
+			p.expect(token.RBRACK)
+			elt := p.parseType()
+			spec.Type = &ast.ArrayType{Lbrack: lbrack, Len: alen, Elt: elt}
+		}
+
+	default:
+		// no type parameters
+		if p.tok == token.ASSIGN {
+			// type alias
+			spec.Assign = p.pos
+			p.next()
+		}
+		spec.Type = p.parseType()
 	}
-	spec.Type = p.parseType()
+
 	p.expectSemi() // call before accessing p.linecomment
 	spec.Comment = p.lineComment
 
@@ -2411,12 +2715,12 @@ func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.Gen
 		lparen = p.pos
 		p.next()
 		for iota := 0; p.tok != token.RPAREN && p.tok != token.EOF; iota++ {
-			list = append(list, f(p.leadComment, keyword, iota))
+			list = append(list, f(p.leadComment, pos, keyword, iota))
 		}
 		rparen = p.expect(token.RPAREN)
 		p.expectSemi()
 	} else {
-		list = append(list, f(nil, keyword, 0))
+		list = append(list, f(nil, pos, keyword, 0))
 	}
 
 	return &ast.GenDecl{
@@ -2440,12 +2744,13 @@ func (p *parser) parseFuncDecl() *ast.FuncDecl {
 
 	var recv *ast.FieldList
 	if p.tok == token.LPAREN {
-		recv = p.parseParameters(scope, false)
+		_, recv = p.parseParameters(scope, false)
 	}
 
 	ident := p.parseIdent()
 
-	params, results := p.parseSignature(scope)
+	tparams, params := p.parseParameters(scope, true)
+	results := p.parseResult(scope)
 
 	var body *ast.BlockStmt
 	if p.tok == token.LBRACE {
@@ -2469,6 +2774,7 @@ func (p *parser) parseFuncDecl() *ast.FuncDecl {
 		Name: ident,
 		Type: &ast.FuncType{
 			Func:    pos,
+			TParams: tparams,
 			Params:  params,
 			Results: results,
 		},
diff --git a/src/go/parser/short_test.go b/src/go/parser/short_test.go
index 49bb681e09..46fa764466 100644
--- a/src/go/parser/short_test.go
+++ b/src/go/parser/short_test.go
@@ -48,14 +48,106 @@ var valids = []string{
 	`package p; var _ = map[*P]int{&P{}:0, {}:1}`,
 	`package p; type T = int`,
 	`package p; type (T = p.T; _ = struct{}; x = *T)`,
+	`package p; type T (*int)`,
+
+	// structs with parameterized embedded fields (for symmetry with interfaces)
+	`package p; type _ struct{ ((int)) }`,
+	`package p; type _ struct{ (*(int)) }`,
+	`package p; type _ struct{ ([]byte) }`, // disallowed by type-checker
+
+	// type parameters
+	`package p; type T[P any] struct { P }`,
+	`package p; type T[P comparable] struct { P }`,
+	`package p; type T[P comparable[P]] struct { P }`,
+	`package p; type T[P1, P2 any] struct { P1; f []P2 }`,
+	`package p; type _ []T[int]`,
+
+	`package p; var _ = func()T(nil)`,
+	`package p; func _[T any]()`,
+	`package p; func _[T any]()()`,
+	`package p; func _(T (P))`,
+	`package p; func _(T []E)`,
+	`package p; func _(T [P]E)`,
+	`package p; func _(x T[P1, P2, P3])`,
+	`package p; func _(x p.T[Q])`,
+	`package p; func _(p.T[Q])`,
+
+	`package p; var _ T[chan int]`,
+	`package p; func f[A, B any](); func _() { _ = f[int, int] }`,
+
+	`package p; type _[A interface{},] struct{}`,
+	`package p; type _[A interface{}] struct{}`,
+	`package p; type _[A, B any,] struct{}`,
+	`package p; type _[A, B any] struct{}`,
+	`package p; type _[A any,] struct{}`,
+	`package p; type _ [A+B]struct{}`, // this is an array!
+	`package p; type _[A any]struct{}`,
+	`package p; type _[A any] struct{ A }`, // this is not an array!
+
+	`package p; func _[T any]()`,
+	`package p; func _[T any](x T)`,
+	`package p; func _[T1, T2 any](x T)`,
+
+	`package p; func (R) _()`,
+	`package p; func (R[P]) _[T any]()`,
+	`package p; func (_ R[P]) _[T any](x T)`,
+	`package p; func (_ R[P, Q]) _[T1, T2 any](x T)`,
+
+	`package p; var _ = []T[int]{}`,
+	`package p; var _ = [10]T[int]{}`,
+	`package p; var _ = func()T[int]{}`,
+	`package p; var _ = map[T[int]]T[int]{}`,
+	`package p; var _ = chan T[int](x)`,
+	`package p; func _(T[P])`,
+	`package p; func _(T[P1, P2, P3])`,
+	`package p; func _(T[P]) T[P]`,
+	`package p; func _(_ T[P], T P) T[P]`,
+
+	`package p; func _[A, B any](a A) B`,
+	`package p; func _[A, B C](a A) B`,
+	`package p; func _[A, B C[A, B]](a A) B`,
+
+	// method type parameters (if methodTypeParamsOk)
+	`package p; func (T) _[A, B any](a A) B`,
+	`package p; func (T) _[A, B C](a A) B`,
+	`package p; func (T) _[A, B C[A, B]](a A) B`,
+
+	// method type parameters are not permitted in interfaces.
+	`package p; type _[A, B any] interface { _(a A) B }`,
+	`package p; type _[A, B C[A, B]] interface { _(a A) B }`,
+
+	// type bounds
+	`package p; func _[T1, T2 interface{}](x T1) T2`,
+	`package p; func _[T1 interface{ m() }, T2, T3 interface{}](x T1, y T3) T2`,
+
+	// struct embedding
+	`package p; type _ struct{ T[P] }`,
+	`package p; type _ struct{ T[struct{a, b, c int}] }`,
+	`package p; type _ struct{ f [n]E }`,
+	`package p; type _ struct{ f [a+b+c+d]E }`,
+
+	// interfaces with type lists
+	`package p; type _ interface{type int}`,
+	`package p; type _ interface{type int, float32; type bool; m(); type string;}`,
+
+	// interface embedding
+	`package p; type I1 interface{}; type I2 interface{ I1 }`,
+	`package p; type I1[T any] interface{}; type I2 interface{ I1[int] }`,
+	`package p; type I1[T any] interface{}; type I2[T any] interface{ I1[T] }`,
 }
 
 func TestValid(t *testing.T) {
 	for _, src := range valids {
-		checkErrors(t, src, src)
+		checkErrors(t, src, src, DeclarationErrors|AllErrors)
 	}
 }
 
+// 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)
+}
+
 var invalids = []string{
 	`foo /* ERROR "expected 'package'" */ !`,
 	`package p; func f() { if { /* ERROR "missing condition" */ } };`,
@@ -79,7 +171,6 @@ var invalids = []string{
 	`package p; var a = chan /* ERROR "expected expression" */ int;`,
 	`package p; var a = []int{[ /* ERROR "expected expression" */ ]int};`,
 	`package p; var a = ( /* ERROR "expected expression" */ []int);`,
-	`package p; var a = a[[ /* ERROR "expected expression" */ ]int:[]int];`,
 	`package p; var a = <- /* ERROR "expected expression" */ chan int;`,
 	`package p; func f() { select { case _ <- chan /* ERROR "expected expression" */ int: } };`,
 	`package p; func f() { _ = (<-<- /* ERROR "expected 'chan'" */ chan int)(nil) };`,
@@ -102,7 +193,22 @@ var invalids = []string{
 	`package p; func f() { go f /* ERROR HERE "function must be invoked" */ }`,
 	`package p; func f() { defer func() {} /* ERROR HERE "function must be invoked" */ }`,
 	`package p; func f() { go func() { func() { f(x func /* ERROR "missing ','" */ (){}) } } }`,
-	`package p; func f(x func(), u v func /* ERROR "missing ','" */ ()){}`,
+	//`package p; func f(x func(), u v func /* ERROR "missing ','" */ ()){}`,
+
+	// type parameters
+	`package p; var _ func[ /* ERROR "cannot have type parameters" */ T any](T)`,
+	`package p; func _() (type /* ERROR "found 'type'" */ T)(T)`,
+	`package p; func (type /* ERROR "found 'type'" */ T)(T) _()`,
+	`package p; type _[A+B, /* ERROR "expected ']'" */ ] int`,
+	`package p; type _[_ any] int; var _ = T[] /* ERROR "expected operand" */ {}`,
+	`package p; type T[P any] = /* ERROR "cannot be alias" */ T0`,
+	`package p; func _[]/* ERROR "empty type parameter list" */()`,
+
+	// errors that could be improved
+	`package p; var a = a[[]int:[ /* ERROR "expected expression" */ ]int];`,                      // TODO: should this be on the ':'?
+	`package p; type _[A/* ERROR "all type parameters must be named" */,] struct{ A }`,           // TODO: a better location would be after the ']'
+	`package p; func _[type /* ERROR "all type parameters must be named" */P, *Q interface{}]()`, // TODO: this is confusing.
+	`package p; type I1 interface{}; type I2 interface{ (/* ERROR "expected 'IDENT'" */I1) }`,    // TODO: compiler error is 'syntax error: cannot parenthesize embedded type'
 
 	// issue 8656
 	`package p; func f() (a b string /* ERROR "missing ','" */ , ok bool)`,
@@ -118,11 +224,11 @@ var invalids = []string{
 	`package p; var _ = struct { x int, /* ERROR "expected ';', found ','" */ y float }{};`,
 
 	// issue 11611
-	`package p; type _ struct { int, } /* ERROR "expected type, found '}'" */ ;`,
+	`package p; type _ struct { int, } /* ERROR "expected 'IDENT', found '}'" */ ;`,
 	`package p; type _ struct { int, float } /* ERROR "expected type, found '}'" */ ;`,
-	`package p; type _ struct { ( /* ERROR "expected anonymous field" */ int) };`,
-	`package p; func _()(x, y, z ... /* ERROR "expected '\)', found '...'" */ int){}`,
-	`package p; func _()(... /* ERROR "expected type, found '...'" */ int){}`,
+	//`package p; type _ struct { ( /* ERROR "cannot parenthesize embedded type" */ int) };`,
+	//`package p; func _()(x, y, z ... /* ERROR "expected '\)', found '...'" */ int){}`,
+	//`package p; func _()(... /* ERROR "expected type, found '...'" */ int){}`,
 
 	// issue 13475
 	`package p; func f() { if true {} else ; /* ERROR "expected if statement or block" */ }`,
@@ -131,6 +237,6 @@ var invalids = []string{
 
 func TestInvalid(t *testing.T) {
 	for _, src := range invalids {
-		checkErrors(t, src, src)
+		checkErrors(t, src, src, DeclarationErrors|AllErrors)
 	}
 }
diff --git a/src/go/parser/testdata/chans.go2 b/src/go/parser/testdata/chans.go2
new file mode 100644
index 0000000000..fad2bcec9d
--- /dev/null
+++ b/src/go/parser/testdata/chans.go2
@@ -0,0 +1,62 @@
+package chans
+
+import "runtime"
+
+// Ranger returns a Sender and a Receiver. The Receiver provides a
+// Next method to retrieve values. The Sender provides a Send method
+// to send values and a Close method to stop sending values. The Next
+// method indicates when the Sender has been closed, and the Send
+// method indicates when the Receiver has been freed.
+//
+// This is a convenient way to exit a goroutine sending values when
+// the receiver stops reading them.
+func Ranger[T any]() (*Sender[T], *Receiver[T]) {
+	c := make(chan T)
+	d := make(chan bool)
+	s := &Sender[T]{values: c, done: d}
+	r := &Receiver[T]{values: c, done: d}
+	runtime.SetFinalizer(r, r.finalize)
+	return s, r
+}
+
+// A sender is used to send values to a Receiver.
+type Sender[T any] struct {
+	values chan<- T
+	done <-chan bool
+}
+
+// Send sends a value to the receiver. It returns whether any more
+// values may be sent; if it returns false the value was not sent.
+func (s *Sender[T]) Send(v T) bool {
+	select {
+	case s.values <- v:
+		return true
+	case <-s.done:
+		return false
+	}
+}
+
+// Close tells the receiver that no more values will arrive.
+// After Close is called, the Sender may no longer be used.
+func (s *Sender[T]) Close() {
+	close(s.values)
+}
+
+// A Receiver receives values from a Sender.
+type Receiver[T any] struct {
+	values <-chan T
+	done chan<- bool
+}
+
+// Next returns the next value from the channel. The bool result
+// indicates whether the value is valid, or whether the Sender has
+// been closed and no more values will be received.
+func (r *Receiver[T]) Next() (T, bool) {
+	v, ok := <-r.values
+	return v, ok
+}
+
+// finalize is a finalizer for the receiver.
+func (r *Receiver[T]) finalize() {
+	close(r.done)
+}
diff --git a/src/go/parser/testdata/linalg.go2 b/src/go/parser/testdata/linalg.go2
new file mode 100644
index 0000000000..fba0d02eb2
--- /dev/null
+++ b/src/go/parser/testdata/linalg.go2
@@ -0,0 +1,83 @@
+// Copyright 2019 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 linalg
+
+import "math"
+
+// Numeric is type bound that matches any numeric type.
+// It would likely be in a constraints package in the standard library.
+type Numeric interface {
+	type int, int8, int16, int32, int64,
+		uint, uint8, uint16, uint32, uint64, uintptr,
+		float32, float64,
+		complex64, complex128
+}
+
+func DotProduct[T Numeric](s1, s2 []T) T {
+	if len(s1) != len(s2) {
+		panic("DotProduct: slices of unequal length")
+	}
+	var r T
+	for i := range s1 {
+		r += s1[i] * s2[i]
+	}
+	return r
+}
+
+// NumericAbs matches numeric types with an Abs method.
+type NumericAbs[T any] interface {
+	Numeric
+
+	Abs() T
+}
+
+// AbsDifference computes the absolute value of the difference of
+// a and b, where the absolute value is determined by the Abs method.
+func AbsDifference[T NumericAbs](a, b T) T {
+	d := a - b
+	return d.Abs()
+}
+
+// OrderedNumeric is a type bound that matches numeric types that support the < operator.
+type OrderedNumeric interface {
+	type int, int8, int16, int32, int64,
+		uint, uint8, uint16, uint32, uint64, uintptr,
+		float32, float64
+}
+
+// Complex is a type bound that matches the two complex types, which do not have a < operator.
+type Complex interface {
+	type complex64, complex128
+}
+
+// OrderedAbs is a helper type that defines an Abs method for
+// ordered numeric types.
+type OrderedAbs[T OrderedNumeric] T
+
+func (a OrderedAbs[T]) Abs() OrderedAbs[T] {
+	if a < 0 {
+		return -a
+	}
+	return a
+}
+
+// ComplexAbs is a helper type that defines an Abs method for
+// complex types.
+type ComplexAbs[T Complex] T
+
+func (a ComplexAbs[T]) Abs() ComplexAbs[T] {
+	r := float64(real(a))
+	i := float64(imag(a))
+	d := math.Sqrt(r * r + i * i)
+	return ComplexAbs[T](complex(d, 0))
+}
+
+func OrderedAbsDifference[T OrderedNumeric](a, b T) T {
+	return T(AbsDifference(OrderedAbs[T](a), OrderedAbs[T](b)))
+}
+
+func ComplexAbsDifference[T Complex](a, b T) T {
+	return T(AbsDifference(ComplexAbs[T](a), ComplexAbs[T](b)))
+}
diff --git a/src/go/parser/testdata/map.go2 b/src/go/parser/testdata/map.go2
new file mode 100644
index 0000000000..74c79ae44f
--- /dev/null
+++ b/src/go/parser/testdata/map.go2
@@ -0,0 +1,109 @@
+// Package orderedmap provides an ordered map, implemented as a binary tree.
+package orderedmap
+
+import "chans"
+
+// Map is an ordered map.
+type Map[K, V any] struct {
+	root    *node[K, V]
+	compare func(K, K) int
+}
+
+// node is the type of a node in the binary tree.
+type node[K, V any] struct {
+	key         K
+	val         V
+	left, right *node[K, V]
+}
+
+// New returns a new map.
+func New[K, V any](compare func(K, K) int) *Map[K, V] {
+        return &Map[K, V]{compare: compare}
+}
+
+// find looks up key in the map, and returns either a pointer
+// to the node holding key, or a pointer to the location where
+// such a node would go.
+func (m *Map[K, V]) find(key K) **node[K, V] {
+	pn := &m.root
+	for *pn != nil {
+		switch cmp := m.compare(key, (*pn).key); {
+		case cmp < 0:
+			pn = &(*pn).left
+		case cmp > 0:
+			pn = &(*pn).right
+		default:
+			return pn
+		}
+	}
+	return pn
+}
+
+// Insert inserts a new key/value into the map.
+// If the key is already present, the value is replaced.
+// Returns true if this is a new key, false if already present.
+func (m *Map[K, V]) Insert(key K, val V) bool {
+	pn := m.find(key)
+	if *pn != nil {
+		(*pn).val = val
+		return false
+	}
+        *pn = &node[K, V]{key: key, val: val}
+	return true
+}
+
+// Find returns the value associated with a key, or zero if not present.
+// The found result reports whether the key was found.
+func (m *Map[K, V]) Find(key K) (V, bool) {
+	pn := m.find(key)
+	if *pn == nil {
+		var zero V // see the discussion of zero values, above
+		return zero, false
+	}
+	return (*pn).val, true
+}
+
+// keyValue is a pair of key and value used when iterating.
+type keyValue[K, V any] struct {
+	key K
+	val V
+}
+
+// InOrder returns an iterator that does an in-order traversal of the map.
+func (m *Map[K, V]) InOrder() *Iterator[K, V] {
+	sender, receiver := chans.Ranger[keyValue[K, V]]()
+	var f func(*node[K, V]) bool
+	f = func(n *node[K, V]) bool {
+		if n == nil {
+			return true
+		}
+		// Stop sending values if sender.Send returns false,
+		// meaning that nothing is listening at the receiver end.
+		return f(n.left) &&
+                        // TODO
+			// sender.Send(keyValue[K, V]{n.key, n.val}) &&
+			f(n.right)
+	}
+	go func() {
+		f(m.root)
+		sender.Close()
+	}()
+	return &Iterator{receiver}
+}
+
+// Iterator is used to iterate over the map.
+type Iterator[K, V any] struct {
+	r *chans.Receiver[keyValue[K, V]]
+}
+
+// Next returns the next key and value pair, and a boolean indicating
+// whether they are valid or whether we have reached the end.
+func (it *Iterator[K, V]) Next() (K, V, bool) {
+	keyval, ok := it.r.Next()
+	if !ok {
+		var zerok K
+		var zerov V
+		return zerok, zerov, false
+	}
+	return keyval.key, keyval.val, true
+}
diff --git a/src/go/parser/testdata/metrics.go2 b/src/go/parser/testdata/metrics.go2
new file mode 100644
index 0000000000..ef1c66b241
--- /dev/null
+++ b/src/go/parser/testdata/metrics.go2
@@ -0,0 +1,58 @@
+package metrics
+
+import "sync"
+
+type Metric1[T comparable] struct {
+	mu sync.Mutex
+	m  map[T]int
+}
+
+func (m *Metric1[T]) Add(v T) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.m == nil {
+		m.m = make(map[T]int)
+	}
+	m[v]++
+}
+
+type key2[T1, T2 comparable] struct {
+	f1 T1
+	f2 T2
+}
+
+type Metric2[T1, T2 cmp2] struct {
+	mu sync.Mutex
+	m  map[key2[T1, T2]]int
+}
+
+func (m *Metric2[T1, T2]) Add(v1 T1, v2 T2) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.m == nil {
+		m.m = make(map[key2[T1, T2]]int)
+	}
+	m[key[T1, T2]{v1, v2}]++
+}
+
+type key3[T1, T2, T3 comparable] struct {
+	f1 T1
+	f2 T2
+	f3 T3
+}
+
+type Metric3[T1, T2, T3 comparable] struct {
+	mu sync.Mutex
+	m  map[key3[T1, T2, T3]]int
+}
+
+func (m *Metric3[T1, T2, T3]) Add(v1 T1, v2 T2, v3 T3) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.m == nil {
+		m.m = make(map[key3]int)
+	}
+	m[key[T1, T2, T3]{v1, v2, v3}]++
+}
+
+// Repeat for the maximum number of permitted arguments.
diff --git a/src/go/parser/testdata/set.go2 b/src/go/parser/testdata/set.go2
new file mode 100644
index 0000000000..0da6377cbd
--- /dev/null
+++ b/src/go/parser/testdata/set.go2
@@ -0,0 +1,31 @@
+// Package set implements sets of any type.
+package set
+
+type Set[Elem comparable] map[Elem]struct{}
+
+func Make[Elem comparable]() Set[Elem] {
+	return make(Set(Elem))
+}
+
+func (s Set[Elem]) Add(v Elem) {
+	s[v] = struct{}{}
+}
+
+func (s Set[Elem]) Delete(v Elem) {
+	delete(s, v)
+}
+
+func (s Set[Elem]) Contains(v Elem) bool {
+	_, ok := s[v]
+	return ok
+}
+
+func (s Set[Elem]) Len() int {
+	return len(s)
+}
+
+func (s Set[Elem]) Iterate(f func(Elem)) {
+	for v := range s {
+		f(v)
+	}
+}
diff --git a/src/go/parser/testdata/slices.go2 b/src/go/parser/testdata/slices.go2
new file mode 100644
index 0000000000..e060212f29
--- /dev/null
+++ b/src/go/parser/testdata/slices.go2
@@ -0,0 +1,31 @@
+// Package slices implements various slice algorithms.
+package slices
+
+// Map turns a []T1 to a []T2 using a mapping function.
+func Map[T1, T2 any](s []T1, f func(T1) T2) []T2 {
+	r := make([]T2, len(s))
+	for i, v := range s {
+		r[i] = f(v)
+	}
+	return r
+}
+
+// Reduce reduces a []T1 to a single value using a reduction function.
+func Reduce[T1, T2 any](s []T1, initializer T2, f func(T2, T1) T2) T2 {
+	r := initializer
+	for _, v := range s {
+		r = f(r, v)
+	}
+	return r
+}
+
+// Filter filters values from a slice using a filter function.
+func Filter[T any](s []T, f func(T) bool) []T {
+	var r []T
+	for _, v := range s {
+		if f(v) {
+			r = append(r, v)
+		}
+	}
+	return r
+}
diff --git a/src/go/parser/testdata/sort.go2 b/src/go/parser/testdata/sort.go2
new file mode 100644
index 0000000000..88be79f966
--- /dev/null
+++ b/src/go/parser/testdata/sort.go2
@@ -0,0 +1,27 @@
+package sort
+
+type orderedSlice[Elem comparable] []Elem
+
+func (s orderedSlice[Elem]) Len() int           { return len(s) }
+func (s orderedSlice[Elem]) Less(i, j int) bool { return s[i] < s[j] }
+func (s orderedSlice[Elem]) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+
+// OrderedSlice sorts the slice s in ascending order.
+// The elements of s must be ordered using the < operator.
+func OrderedSlice[Elem comparable](s []Elem) {
+	sort.Sort(orderedSlice[Elem](s))
+}
+
+type sliceFn[Elem any] struct {
+	s []Elem
+	f func(Elem, Elem) bool
+}
+
+func (s sliceFn[Elem]) Len() int           { return len(s.s) }
+func (s sliceFn[Elem]) Less(i, j int) bool { return s.f(s.s[i], s.s[j]) }
+func (s sliceFn[Elem]) Swap(i, j int)      { s.s[i], s.s[j] = s.s[j], s.s[i] }
+
+// SliceFn sorts the slice s according to the function f.
+func SliceFn[Elem any](s []Elem, f func(Elem, Elem) bool) {
+	Sort(sliceFn[Elem]{s, f})
+}
diff --git a/src/go/types/testdata/issues.src b/src/go/types/testdata/issues.src
index e0c5d7a37c..db415eadfb 100644
--- a/src/go/types/testdata/issues.src
+++ b/src/go/types/testdata/issues.src
@@ -325,8 +325,8 @@ func issue28281c(a, b, c ... /* ERROR can only use ... with final parameter */ i
 func issue28281d(... /* ERROR can only use ... with final parameter */ int, int)
 func issue28281e(a, b, c  ... /* ERROR can only use ... with final parameter */ int, d int)
 func issue28281f(... /* ERROR can only use ... with final parameter */ int, ... /* ERROR can only use ... with final parameter */ int, int)
-func (... /* ERROR expected type */ TT) f()
-func issue28281g() (... /* ERROR expected type */ TT)
+func (... /* ERROR can only use ... with final parameter */ TT) f()
+func issue28281g() (... /* ERROR can only use ... with final parameter */ TT)
 
 // Issue #26234: Make various field/method lookup errors easier to read by matching cmd/compile's output
 func issue26234a(f *syn.File) {