go/types: return typeHash value without blanks

This is an adjusted port of CL 349990 from types2 to go/types:
typeHash remains unexported but is adjusted to not contain blanks.

Change-Id: I37fa826b8a185e3c275ae9bea29a3b0ed386d2c9
Reviewed-on: https://go-review.googlesource.com/c/go/+/351171
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/go/types/environment.go

@@ -6,6 +6,7 @@ package types
 
 import (
 	"bytes"
+	"strings"
 	"sync"
 )
 
@@ -32,7 +33,7 @@ func NewEnvironment() *Environment {
 // typeHash returns a string representation of typ, which can be used as an exact
 // type hash: types that are identical produce identical string representations.
 // If typ is a *Named type and targs is not empty, typ is printed as if it were
-// instantiated with targs.
+// instantiated with targs. The result is guaranteed to not contain blanks (" ").
 func (env *Environment) typeHash(typ Type, targs []Type) string {
 	assert(env != nil)
 	assert(typ != nil)
@@ -50,7 +51,7 @@ func (env *Environment) typeHash(typ Type, targs []Type) string {
 		h.typ(typ)
 	}
 
-	return buf.String()
+	return strings.Replace(buf.String(), " ", "#", -1) // ReplaceAll is not available in Go1.4
 }
 
 // typeForHash returns the recorded type for the type hash h, if it exists.

src/go/types/typestring.go

@@ -8,7 +8,6 @@ package types
 
 import (
 	"bytes"
-	"fmt"
 	"go/token"
 	"strconv"
 	"unicode/utf8"
@@ -81,14 +80,29 @@ func newTypeHasher(buf *bytes.Buffer, env *Environment) *typeWriter {
 	return &typeWriter{buf, make(map[Type]bool), nil, env}
 }
 
-func (w *typeWriter) byte(b byte)                               { w.buf.WriteByte(b) }
-func (w *typeWriter) string(s string)                           { w.buf.WriteString(s) }
-func (w *typeWriter) writef(format string, args ...interface{}) { fmt.Fprintf(w.buf, format, args...) }
+func (w *typeWriter) byte(b byte) {
+	if w.env != nil {
+		if b == ' ' {
+			b = '#'
+		}
+		w.buf.WriteByte(b)
+		return
+	}
+	w.buf.WriteByte(b)
+	if b == ',' || b == ';' {
+		w.buf.WriteByte(' ')
+	}
+}
+
+func (w *typeWriter) string(s string) {
+	w.buf.WriteString(s)
+}
+
 func (w *typeWriter) error(msg string) {
 	if w.env != nil {
 		panic(msg)
 	}
-	w.string("<" + msg + ">")
+	w.buf.WriteString("<" + msg + ">")
 }
 
 func (w *typeWriter) typ(typ Type) {
@@ -115,7 +129,9 @@ func (w *typeWriter) typ(typ Type) {
 		w.string(t.name)
 
 	case *Array:
-		w.writef("[%d]", t.len)
+		w.byte('[')
+		w.string(strconv.FormatInt(t.len, 10))
+		w.byte(']')
 		w.typ(t.elem)
 
 	case *Slice:
@@ -126,7 +142,7 @@ func (w *typeWriter) typ(typ Type) {
 		w.string("struct{")
 		for i, f := range t.fields {
 			if i > 0 {
-				w.string("; ")
+				w.byte(';')
 			}
 			// This doesn't do the right thing for embedded type
 			// aliases where we should print the alias name, not
@@ -137,7 +153,11 @@ func (w *typeWriter) typ(typ Type) {
 			}
 			w.typ(f.typ)
 			if tag := t.Tag(i); tag != "" {
-				w.writef(" %q", tag)
+				w.byte(' ')
+				// TODO(rfindley) If tag contains blanks, replacing them with '#'
+				//                in Environment.TypeHash may produce another tag
+				//                accidentally.
+				w.string(strconv.Quote(tag))
 			}
 		}
 		w.byte('}')
@@ -175,7 +195,7 @@ func (w *typeWriter) typ(typ Type) {
 		first := true
 		for _, m := range t.methods {
 			if !first {
-				w.string("; ")
+				w.byte(';')
 			}
 			first = false
 			w.string(m.name)
@@ -183,7 +203,7 @@ func (w *typeWriter) typ(typ Type) {
 		}
 		for _, typ := range t.embeddeds {
 			if !first {
-				w.string("; ")
+				w.byte(';')
 			}
 			first = false
 			w.typ(typ)
@@ -270,7 +290,7 @@ func (w *typeWriter) typeList(list []Type) {
 	w.byte('[')
 	for i, typ := range list {
 		if i > 0 {
-			w.string(", ")
+			w.byte(',')
 		}
 		w.typ(typ)
 	}
@@ -294,7 +314,7 @@ func (w *typeWriter) tParamList(list []*TypeParam) {
 				w.byte(' ')
 				w.typ(prev)
 			}
-			w.string(", ")
+			w.byte(',')
 		}
 		prev = tpar.bound
 		w.typ(tpar)
@@ -318,7 +338,7 @@ func (w *typeWriter) tuple(tup *Tuple, variadic bool) {
 	if tup != nil {
 		for i, v := range tup.vars {
 			if i > 0 {
-				w.string(", ")
+				w.byte(',')
 			}
 			// parameter names are ignored for type identity and thus type hashes
 			if w.env == nil && v.name != "" {