go.tools/go/types: make WriteType cycle-resistent

Also:
- expose WriteSignature
- s/identicalInternal/identical/g

LGTM=adonovan
R=adonovan
CC=golang-codereviews
https://golang.org/cl/57860043

go/types/objects.go

@@ -247,7 +247,7 @@ func writeObject(buf *bytes.Buffer, this *Package, obj Object) {
 		buf.WriteString("func ")
 		writeFuncName(buf, this, obj)
 		if typ != nil {
-			writeSignature(buf, this, typ.(*Signature))
+			WriteSignature(buf, this, typ.(*Signature))
 		}
 		return
 

go/types/predicates.go

@@ -110,7 +110,7 @@ func hasNil(typ Type) bool {
 
 // Identical reports whether x and y are identical.
 func Identical(x, y Type) bool {
-	return identicalInternal(x, y, nil)
+	return identical(x, y, nil)
 }
 
 // An ifacePair is a node in a stack of interface type pairs compared for identity.
@@ -123,7 +123,7 @@ func (p *ifacePair) identical(q *ifacePair) bool {
 	return p.x == q.x && p.y == q.y || p.x == q.y && p.y == q.x
 }
 
-func identicalInternal(x, y Type, p *ifacePair) bool {
+func identical(x, y Type, p *ifacePair) bool {
 	if x == y {
 		return true
 	}
@@ -141,13 +141,13 @@ func identicalInternal(x, y Type, p *ifacePair) bool {
 		// Two array types are identical if they have identical element types
 		// and the same array length.
 		if y, ok := y.(*Array); ok {
-			return x.len == y.len && identicalInternal(x.elem, y.elem, p)
+			return x.len == y.len && identical(x.elem, y.elem, p)
 		}
 
 	case *Slice:
 		// Two slice types are identical if they have identical element types.
 		if y, ok := y.(*Slice); ok {
-			return identicalInternal(x.elem, y.elem, p)
+			return identical(x.elem, y.elem, p)
 		}
 
 	case *Struct:
@@ -162,7 +162,7 @@ func identicalInternal(x, y Type, p *ifacePair) bool {
 					if f.anonymous != g.anonymous ||
 						x.Tag(i) != y.Tag(i) ||
 						!f.sameId(g.pkg, g.name) ||
-						!identicalInternal(f.typ, g.typ, p) {
+						!identical(f.typ, g.typ, p) {
 						return false
 					}
 				}
@@ -173,7 +173,7 @@ func identicalInternal(x, y Type, p *ifacePair) bool {
 	case *Pointer:
 		// Two pointer types are identical if they have identical base types.
 		if y, ok := y.(*Pointer); ok {
-			return identicalInternal(x.base, y.base, p)
+			return identical(x.base, y.base, p)
 		}
 
 	case *Tuple:
@@ -184,7 +184,7 @@ func identicalInternal(x, y Type, p *ifacePair) bool {
 				if x != nil {
 					for i, v := range x.vars {
 						w := y.vars[i]
-						if !identicalInternal(v.typ, w.typ, p) {
+						if !identical(v.typ, w.typ, p) {
 							return false
 						}
 					}
@@ -200,8 +200,8 @@ func identicalInternal(x, y Type, p *ifacePair) bool {
 		// names are not required to match.
 		if y, ok := y.(*Signature); ok {
 			return x.variadic == y.variadic &&
-				identicalInternal(x.params, y.params, p) &&
+				identical(x.params, y.params, p) &&
-				identicalInternal(x.results, y.results, p)
+				identical(x.results, y.results, p)
 		}
 
 	case *Interface:
@@ -247,7 +247,7 @@ func identicalInternal(x, y Type, p *ifacePair) bool {
 				}
 				for i, f := range a {
 					g := b[i]
-					if f.Id() != g.Id() || !identicalInternal(f.typ, g.typ, q) {
+					if f.Id() != g.Id() || !identical(f.typ, g.typ, q) {
 						return false
 					}
 				}
@@ -258,14 +258,14 @@ func identicalInternal(x, y Type, p *ifacePair) bool {
 	case *Map:
 		// Two map types are identical if they have identical key and value types.
 		if y, ok := y.(*Map); ok {
-			return identicalInternal(x.key, y.key, p) && identicalInternal(x.elem, y.elem, p)
+			return identical(x.key, y.key, p) && identical(x.elem, y.elem, p)
 		}
 
 	case *Chan:
 		// Two channel types are identical if they have identical value types
 		// and the same direction.
 		if y, ok := y.(*Chan); ok {
-			return x.dir == y.dir && identicalInternal(x.elem, y.elem, p)
+			return x.dir == y.dir && identical(x.elem, y.elem, p)
 		}
 
 	case *Named:

go/types/selection.go

@@ -141,6 +141,6 @@ func SelectionString(this *Package, s *Selection) string {
 	buf.WriteByte('(')
 	WriteType(&buf, this, s.Recv())
 	fmt.Fprintf(&buf, ") %s", s.obj.Name())
-	writeSignature(&buf, this, s.Type().(*Signature))
+	WriteSignature(&buf, this, s.Type().(*Signature))
 	return buf.String()
 }

go/types/typestring.go

@@ -40,6 +40,22 @@ func TypeString(this *Package, typ Type) string {
 // Named types are printed package-qualified if they
 // do not belong to this package.
 func WriteType(buf *bytes.Buffer, this *Package, typ Type) {
+	writeType(buf, this, typ, make([]Type, 8))
+}
+
+func writeType(buf *bytes.Buffer, this *Package, typ Type, visited []Type) {
+	// Theoretically, this is a quadratic lookup algorithm, but in
+	// practice deeply nested composite types with unnamed component
+	// types are uncommon. This code is likely more efficient than
+	// using a map.
+	for _, t := range visited {
+		if t == typ {
+			fmt.Fprintf(buf, "○%T", typ) // cycle to typ
+			return
+		}
+	}
+	visited = append(visited, typ)
+
 	switch t := typ.(type) {
 	case nil:
 		buf.WriteString("<nil>")
@@ -61,11 +77,11 @@ func WriteType(buf *bytes.Buffer, this *Package, typ Type) {
 
 	case *Array:
 		fmt.Fprintf(buf, "[%d]", t.len)
-		WriteType(buf, this, t.elem)
+		writeType(buf, this, t.elem, visited)
 
 	case *Slice:
 		buf.WriteString("[]")
-		WriteType(buf, this, t.elem)
+		writeType(buf, this, t.elem, visited)
 
 	case *Struct:
 		buf.WriteString("struct{")
@@ -77,7 +93,7 @@ func WriteType(buf *bytes.Buffer, this *Package, typ Type) {
 				buf.WriteString(f.name)
 				buf.WriteByte(' ')
 			}
-			WriteType(buf, this, f.typ)
+			writeType(buf, this, f.typ, visited)
 			if tag := t.Tag(i); tag != "" {
 				fmt.Fprintf(buf, " %q", tag)
 			}
@@ -86,14 +102,14 @@ func WriteType(buf *bytes.Buffer, this *Package, typ Type) {
 
 	case *Pointer:
 		buf.WriteByte('*')
-		WriteType(buf, this, t.base)
+		writeType(buf, this, t.base, visited)
 
 	case *Tuple:
-		writeTuple(buf, this, t, false)
+		writeTuple(buf, this, t, false, visited)
 
 	case *Signature:
 		buf.WriteString("func")
-		writeSignature(buf, this, t)
+		writeSignature(buf, this, t, visited)
 
 	case *Interface:
 		// We write the source-level methods and embedded types rather
@@ -116,7 +132,7 @@ func WriteType(buf *bytes.Buffer, this *Package, typ Type) {
 					buf.WriteString("; ")
 				}
 				buf.WriteString(m.name)
-				writeSignature(buf, this, m.typ.(*Signature))
+				writeSignature(buf, this, m.typ.(*Signature), visited)
 			}
 		} else {
 			// print explicit interface methods and embedded types
@@ -125,22 +141,22 @@ func WriteType(buf *bytes.Buffer, this *Package, typ Type) {
 					buf.WriteString("; ")
 				}
 				buf.WriteString(m.name)
-				writeSignature(buf, this, m.typ.(*Signature))
+				writeSignature(buf, this, m.typ.(*Signature), visited)
 			}
 			for i, typ := range t.embeddeds {
 				if i > 0 || len(t.methods) > 0 {
 					buf.WriteString("; ")
 				}
-				WriteType(buf, this, typ)
+				writeType(buf, this, typ, visited)
 			}
 		}
 		buf.WriteByte('}')
 
 	case *Map:
 		buf.WriteString("map[")
-		WriteType(buf, this, t.key)
+		writeType(buf, this, t.key, visited)
 		buf.WriteByte(']')
-		WriteType(buf, this, t.elem)
+		writeType(buf, this, t.elem, visited)
 
 	case *Chan:
 		var s string
@@ -163,7 +179,7 @@ func WriteType(buf *bytes.Buffer, this *Package, typ Type) {
 		if parens {
 			buf.WriteByte('(')
 		}
-		WriteType(buf, this, t.elem)
+		writeType(buf, this, t.elem, visited)
 		if parens {
 			buf.WriteByte(')')
 		}
@@ -190,7 +206,7 @@ func WriteType(buf *bytes.Buffer, this *Package, typ Type) {
 	}
 }
 
-func writeTuple(buf *bytes.Buffer, this *Package, tup *Tuple, variadic bool) {
+func writeTuple(buf *bytes.Buffer, this *Package, tup *Tuple, variadic bool, visited []Type) {
 	buf.WriteByte('(')
 	if tup != nil {
 		for i, v := range tup.vars {
@@ -206,14 +222,22 @@ func writeTuple(buf *bytes.Buffer, this *Package, tup *Tuple, variadic bool) {
 				buf.WriteString("...")
 				typ = typ.(*Slice).elem
 			}
-			WriteType(buf, this, typ)
+			writeType(buf, this, typ, visited)
 		}
 	}
 	buf.WriteByte(')')
 }
 
-func writeSignature(buf *bytes.Buffer, this *Package, sig *Signature) {
+// WriteSignature writes the representation of the signature sig to buf,
-	writeTuple(buf, this, sig.params, sig.variadic)
+// without a leading "func" keyword.
+// Named types are printed package-qualified if they
+// do not belong to this package.
+func WriteSignature(buf *bytes.Buffer, this *Package, sig *Signature) {
+	writeSignature(buf, this, sig, make([]Type, 8))
+}
+
+func writeSignature(buf *bytes.Buffer, this *Package, sig *Signature, visited []Type) {
+	writeTuple(buf, this, sig.params, sig.variadic, visited)
 
 	n := sig.results.Len()
 	if n == 0 {
@@ -224,10 +248,10 @@ func writeSignature(buf *bytes.Buffer, this *Package, sig *Signature) {
 	buf.WriteByte(' ')
 	if n == 1 && sig.results.vars[0].name == "" {
 		// single unnamed result
-		WriteType(buf, this, sig.results.vars[0].typ)
+		writeType(buf, this, sig.results.vars[0].typ, visited)
 		return
 	}
 
 	// multiple or named result(s)
-	writeTuple(buf, this, sig.results, false)
+	writeTuple(buf, this, sig.results, false, visited)
 }