cmd/api: support type parameters

Fixes #48706

Change-Id: If0f8d0b49300027e3b2b46f6870302acf2e00f4e
Reviewed-on: https://go-review.googlesource.com/c/go/+/354612
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

src/cmd/api/goapi.go

@@ -706,6 +706,36 @@ func sortedMethodNames(typ *types.Interface) []string {
 	return list
 }
 
+// sortedEmbeddeds returns constraint types embedded in an
+// interface. It does not include embedded interface types or methods.
+func (w *Walker) sortedEmbeddeds(typ *types.Interface) []string {
+	n := typ.NumEmbeddeds()
+	list := make([]string, 0, n)
+	for i := 0; i < n; i++ {
+		emb := typ.EmbeddedType(i)
+		switch emb := emb.(type) {
+		case *types.Interface:
+			list = append(list, w.sortedEmbeddeds(emb)...)
+		case *types.Union:
+			var buf bytes.Buffer
+			nu := emb.Len()
+			for i := 0; i < nu; i++ {
+				if i > 0 {
+					buf.WriteString(" | ")
+				}
+				term := emb.Term(i)
+				if term.Tilde() {
+					buf.WriteByte('~')
+				}
+				w.writeType(&buf, term.Type())
+			}
+			list = append(list, buf.String())
+		}
+	}
+	sort.Strings(list)
+	return list
+}
+
 func (w *Walker) writeType(buf *bytes.Buffer, typ types.Type) {
 	switch typ := typ.(type) {
 	case *types.Basic:
@@ -763,9 +793,16 @@ func (w *Walker) writeType(buf *bytes.Buffer, typ types.Type) {
 
 	case *types.Interface:
 		buf.WriteString("interface{")
-		if typ.NumMethods() > 0 {
+		if typ.NumMethods() > 0 || typ.NumEmbeddeds() > 0 {
 			buf.WriteByte(' ')
+		}
+		if typ.NumMethods() > 0 {
 			buf.WriteString(strings.Join(sortedMethodNames(typ), ", "))
+		}
+		if typ.NumEmbeddeds() > 0 {
+			buf.WriteString(strings.Join(w.sortedEmbeddeds(typ), ", "))
+		}
+		if typ.NumMethods() > 0 || typ.NumEmbeddeds() > 0 {
 			buf.WriteByte(' ')
 		}
 		buf.WriteString("}")
@@ -800,12 +837,18 @@ func (w *Walker) writeType(buf *bytes.Buffer, typ types.Type) {
 		}
 		buf.WriteString(typ.Obj().Name())
 
+	case *types.TypeParam:
+		buf.WriteString(typ.Obj().Name())
+
 	default:
 		panic(fmt.Sprintf("unknown type %T", typ))
 	}
 }
 
 func (w *Walker) writeSignature(buf *bytes.Buffer, sig *types.Signature) {
+	if tparams := sig.TypeParams(); tparams != nil {
+		w.writeTypeParams(buf, tparams, true)
+	}
 	w.writeParams(buf, sig.Params(), sig.Variadic())
 	switch res := sig.Results(); res.Len() {
 	case 0:
@@ -819,6 +862,23 @@ func (w *Walker) writeSignature(buf *bytes.Buffer, sig *types.Signature) {
 	}
 }
 
+func (w *Walker) writeTypeParams(buf *bytes.Buffer, tparams *types.TypeParamList, withConstraints bool) {
+	buf.WriteByte('[')
+	c := tparams.Len()
+	for i := 0; i < c; i++ {
+		if i > 0 {
+			buf.WriteString(", ")
+		}
+		tp := tparams.At(i)
+		buf.WriteString(tp.Obj().Name())
+		if withConstraints {
+			buf.WriteByte(' ')
+			w.writeType(buf, tp.Constraint())
+		}
+	}
+	buf.WriteByte(']')
+}
+
 func (w *Walker) writeParams(buf *bytes.Buffer, t *types.Tuple, variadic bool) {
 	buf.WriteByte('(')
 	for i, n := 0, t.Len(); i < n; i++ {
@@ -872,6 +932,12 @@ func (w *Walker) emitObj(obj types.Object) {
 
 func (w *Walker) emitType(obj *types.TypeName) {
 	name := obj.Name()
+	if tparams := obj.Type().(*types.Named).TypeParams(); tparams != nil {
+		var buf bytes.Buffer
+		buf.WriteString(name)
+		w.writeTypeParams(&buf, tparams, true)
+		name = buf.String()
+	}
 	typ := obj.Type()
 	if obj.IsAlias() {
 		w.emitf("type %s = %s", name, w.typeString(typ))
@@ -995,7 +1061,13 @@ func (w *Walker) emitMethod(m *types.Selection) {
 			log.Fatalf("exported method with unexported receiver base type: %s", m)
 		}
 	}
-	w.emitf("method (%s) %s%s", w.typeString(recv), m.Obj().Name(), w.signatureString(sig))
+	tps := ""
+	if rtp := sig.RecvTypeParams(); rtp != nil {
+		var buf bytes.Buffer
+		w.writeTypeParams(&buf, rtp, false)
+		tps = buf.String()
+	}
+	w.emitf("method (%s%s) %s%s", w.typeString(recv), tps, m.Obj().Name(), w.signatureString(sig))
 }
 
 func (w *Walker) emitf(format string, args ...interface{}) {

src/cmd/api/testdata/src/pkg/p4/golden.txt

@@ -0,0 +1,4 @@
+pkg p4, func NewPair[T1 interface{ M }, T2 interface{ ~int }](T1, T2) Pair
+pkg p4, method (Pair[_, X2]) Second() X2
+pkg p4, method (Pair[X1, _]) First() X1
+pkg p4, type Pair[T1 interface{ M }, T2 interface{ ~int }] struct

src/cmd/api/testdata/src/pkg/p4/p4.go

@@ -0,0 +1,22 @@
+// 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 p4
+
+type Pair[T1 interface { M() }, T2 ~int] struct {
+	f1 T1
+	f2 T2
+}
+
+func NewPair[T1 interface { M() }, T2 ~int](v1 T1, v2 T2) Pair[T1, T2] {
+	return Pair[T1, T2]{f1: v1, f2: v2}
+}
+
+func (p Pair[X1, _]) First() X1 {
+	return p.f1
+}
+
+func (p Pair[_, X2]) Second() X2 {
+	return p.f2
+}