[dev.go2go] go/printer: don't write "type" keyword in type parameter …

…lists if brackets are used

When the printer mode UseBrackets is set, use the new unified parameter
list syntax: use []'s for type parameters without the "type" keyword.
This will also change gofmt behavior accordingly.

Fixes #41053.

Change-Id: Ibaf490ea9ed178684bea34da5b57afa823a6829f
Reviewed-on: https://go-review.googlesource.com/c/go/+/250998
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/printer/nodes.go

@@ -325,7 +325,7 @@ func (p *printer) parameters(isTypeParam bool, fields *ast.FieldList) {
 		openTok, closeTok = token.LBRACK, token.RBRACK
 	}
 	p.print(fields.Opening, openTok)
-	if isTypeParam {
+	if isTypeParam && p.Mode&UseBrackets == 0 {
 		p.print(token.TYPE)
 	}
 	if len(fields.List) > 0 {
@@ -352,7 +352,7 @@ func (p *printer) parameters(isTypeParam bool, fields *ast.FieldList) {
 			if needsLinebreak && p.linebreak(parLineBeg, 0, ws, true) > 0 {
 				// break line if the opening "(" or previous parameter ended on a different line
 				ws = ignore
-			} else if isTypeParam && len(par.Names) > 0 || i > 0 {
+			} else if isTypeParam && len(par.Names) > 0 && p.Mode&UseBrackets == 0 || i > 0 {
 				p.print(blank)
 			}
 			// parameter names

src/go/printer/printer.go

@@ -1277,7 +1277,7 @@ const (
 	UseSpaces                    // use spaces instead of tabs for alignment
 	SourcePos                    // emit //line directives to preserve original source positions
 	StdFormat                    // apply standard formatting changes (exact byte output may change between versions of Go)
-	UseBrackets                  // use square brackets instead of parentheses for type parameters
+	UseBrackets                  // use square brackets instead of parentheses for type parameters (implies unified parameter syntax)
 )
 
 // A Config node controls the output of Fprint.

src/go/printer/testdata/genericsB.golden

@@ -4,27 +4,24 @@
 
 package generics
 
-type T[type] struct{}
-type T[type P] struct{}
-type T[type P1, P2, P3] struct{}
+type T[P any] struct{}
+type T[P1, P2, P3 any] struct{}
 
-type T[type P C] struct{}
-type T[type P1, P2, P3, C] struct{}
+type T[P C] struct{}
+type T[P1, P2, P3, C] struct{}
 
-type T[type P C[P]] struct{}
-type T[type P1, P2, P3 C[P1, P2, P3]] struct{}
+type T[P C[P]] struct{}
+type T[P1, P2, P3 C[P1, P2, P3]] struct{}
 
-func f[type]()
-func f[type P](x P)
-func f[type P1, P2, P3](x1 P1, x2 P2, x3 P3) struct{}
+func f[P any](x P)
+func f[P1, P2, P3 any](x1 P1, x2 P2, x3 P3) struct{}
 
-func f[type]()
-func f[type P interface{}](x P)
-func f[type P1, P2, P3 interface {
+func f[P interface{}](x P)
+func f[P1, P2, P3 interface {
 	m1(P1)
 	type P2, P3
 }](x1 P1, x2 P2, x3 P3) struct{}
-func f[type P](T1[P], T2[P]) T3[P]
+func f[P any](T1[P], T2[P]) T3[P]
 
 func (x T[P]) m()
 func (T[P]) m(x T[P]) P

src/go/printer/testdata/genericsB.input

@@ -4,24 +4,21 @@
 
 package generics
 
-type T[type] struct{}
-type T[type P] struct{}
-type T[type P1, P2, P3] struct{}
+type T[P any] struct{}
+type T[P1, P2, P3 any] struct{}
 
-type T[type P C] struct{}
-type T[type P1, P2, P3, C] struct{}
+type T[P C] struct{}
+type T[P1, P2, P3, C] struct{}
 
-type T[type P C[P]] struct{}
-type T[type P1, P2, P3 C[P1, P2, P3]] struct{}
+type T[P C[P]] struct{}
+type T[P1, P2, P3 C[P1, P2, P3]] struct{}
 
-func f[type]()
-func f[type P](x P)
-func f[type P1, P2, P3](x1 P1, x2 P2, x3 P3) struct{}
+func f[P any](x P)
+func f[P1, P2, P3 any](x1 P1, x2 P2, x3 P3) struct{}
 
-func f[type]()
-func f[type P interface{}](x P)
-func f[type P1, P2, P3 interface{ m1(P1); type P2, P3 }](x1 P1, x2 P2, x3 P3) struct{}
-func f[type P](T1[P], T2[P]) T3[P]
+func f[P interface{}](x P)
+func f[P1, P2, P3 interface{ m1(P1); type P2, P3 }](x1 P1, x2 P2, x3 P3) struct{}
+func f[P any](T1[P], T2[P]) T3[P]
 
 func (x T[P]) m()
 func ((T[P])) m(x T[P]) P