[dev.go2go] cmd/go2go: switch to unified parameter syntax

Type and ordinary parameter lists use the same syntax except
for the square brackets or parentheses, respectively.

Change-Id: I6fb93e93bbfc649a2c1ef195d130e0dcee212c79
Reviewed-on: https://go-review.googlesource.com/c/go/+/250717
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go2go/go2go_test.go

@@ -198,7 +198,7 @@ package main
 
 import "fmt"
 
-func PrintSlice(type Elem)(s []Elem) {
+func PrintSlice[Elem any](s []Elem) {
 	for _, v := range s {
 		fmt.Println(v)
 	}
@@ -295,7 +295,7 @@ func TestTransitiveGo1(t *testing.T) {
 	testFiles{
 		{
 			"a/a.go2",
-			`package a; func ident(type T)(v T) T { return v }; func F1(v int) int { return ident(v) }`,
+			`package a; func ident[T any](v T) T { return v }; func F1(v int) int { return ident(v) }`,
 		},
 		{
 			"b/b.go",

src/go/go2go/go2go.go

@@ -126,7 +126,7 @@ func rewriteFilesInPath(importer *Importer, importPath, dir string, go2files []s
 // for error messages.
 func RewriteBuffer(importer *Importer, filename string, file []byte) ([]byte, error) {
 	fset := token.NewFileSet()
-	pf, err := parser.ParseFile(fset, filename, file, 0)
+	pf, err := parser.ParseFile(fset, filename, file, parser.UnifiedParamLists)
 	if err != nil {
 		return nil, err
 	}
@@ -222,7 +222,7 @@ func checkGoFile(dir, f string) error {
 func parseFiles(importer *Importer, dir string, go2files []string, fset *token.FileSet) ([]*ast.Package, error) {
 	pkgs := make(map[string]*ast.Package)
 	for _, go2f := range go2files {
-		var mode parser.Mode
+		mode := parser.UnifiedParamLists // overrides UseBrackets
 		if importer.UseBrackets {
 			mode = parser.UseBrackets
 		}

test/gen/g011.go2

@@ -11,16 +11,19 @@ import (
 	"strconv"
 )
 
-type Setter interface {
+type Setter[B any] interface {
 	Set(string)
+	type *B
 }
 
-func FromStrings[*T Setter](s []string) []T {
+func FromStrings[T any, PT Setter[T]](s []string) []T {
 	result := make([]T, len(s))
 	for i, v := range s {
-		// result[i] is an addressable value of type T,
-		// so it's OK to call Set.
-		result[i].Set(v)
+		// The type of &result[i] is *T which is in the type list
+		// of Setter, so we can convert it to PT.
+		p := PT(&result[i])
+		// PT has a Set method.
+		p.Set(v)
 	}
 	return result
 }
@@ -36,7 +39,7 @@ func (p *Settable) Set(s string) {
 }
 
 func main() {
-	s := FromStrings[Settable]([]string{"1"})
+	s := FromStrings[Settable, *Settable]([]string{"1"})
 	if len(s) != 1 || s[0] != 1 {
 		log.Fatalf("got %v, want %v", s, []int{1})
 	}

test/gen/g041.go2

@@ -7,6 +7,6 @@
 // Issue 40015.
 package p
 
-func F1[type](s []int) {}
+func F1[](s []int) {}
 
 func F2() { F1([]int{1, 2}) }

test/gen/g043.go2

@@ -17,11 +17,11 @@ type Number interface {
 
 type MySlice []int
 
-type SC[type E] interface {
+type SC[E any] interface {
 	type []E
 }
 
-func DoubleDefined[type S SC[E], E Number](s S) S {
+func DoubleDefined[S SC[E], E Number](s S) S {
 	r := make(S, len(s))
 	for i, v := range s {
 		r[i] = v + v