go/scanner, go/token: recognize => (ALIAS) token

For #16339.

Change-Id: I0f83e46f13b5c8801aacf48fc8b690049edbbbff
Reviewed-on: https://go-review.googlesource.com/30210
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/go/scanner/scanner.go

@@ -731,7 +731,7 @@ scanAgain:
 		case '>':
 			tok = s.switch4(token.GTR, token.GEQ, '>', token.SHR, token.SHR_ASSIGN)
 		case '=':
-			tok = s.switch2(token.ASSIGN, token.EQL)
+			tok = s.switch3(token.ASSIGN, token.EQL, '>', token.ALIAS)
 		case '!':
 			tok = s.switch2(token.NOT, token.NEQ)
 		case '&':

src/go/scanner/scanner_test.go

@@ -121,6 +121,7 @@ var tokens = [...]elt{
 	{token.LAND, "&&", operator},
 	{token.LOR, "||", operator},
 	{token.ARROW, "<-", operator},
+	{token.ALIAS, "=>", operator},
 	{token.INC, "++", operator},
 	{token.DEC, "--", operator},
 

src/go/token/token.go

@@ -121,6 +121,10 @@ const (
 	TYPE
 	VAR
 	keyword_end
+
+	// Alias support - must add at end to pass Go 1 compatibility test
+
+	ALIAS // =>
 )
 
 var tokens = [...]string{
@@ -221,6 +225,8 @@ var tokens = [...]string{
 	SWITCH: "switch",
 	TYPE:   "type",
 	VAR:    "var",
+
+	ALIAS: "=>",
 }
 
 // String returns the string corresponding to the token tok.
@@ -300,7 +306,7 @@ func (tok Token) IsLiteral() bool { return literal_beg < tok && tok < literal_en
 // IsOperator returns true for tokens corresponding to operators and
 // delimiters; it returns false otherwise.
 //
-func (tok Token) IsOperator() bool { return operator_beg < tok && tok < operator_end }
+func (tok Token) IsOperator() bool { return operator_beg < tok && tok < operator_end || tok == ALIAS }
 
 // IsKeyword returns true for tokens corresponding to keywords;
 // it returns false otherwise.