cmd/compile/internal/syntax: support for alias declarations

Permits parsing of alias declarations with -newparser

	const/type/var/func T => p.T

but the compiler will reject it with an error. For now this
also accepts

	type T = p.T

so we can experiment with a type-alias only scenario.

- renamed _Arrow token to _Larrow (<-)
- introduced _Rarrow token (=>)
- introduced AliasDecl node
- extended scanner to accept _Rarrow
- extended parser and printer to handle alias declarations

Change-Id: I0170d10a87df8255db9186d466b6fd405228c38e
Reviewed-on: https://go-review.googlesource.com/29355
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 10 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/syntax/tokens.go b/src/cmd/compile/internal/syntax/tokens.go
index bd0118a141..4a02c0ce3b 100644
--- a/src/cmd/compile/internal/syntax/tokens.go
+++ b/src/cmd/compile/internal/syntax/tokens.go
@@ -22,7 +22,8 @@ const (
 	_IncOp
 	_Assign
 	_Define
-	_Arrow
+	_Larrow
+	_Rarrow
 	_Star
 
 	// delimitors
@@ -69,6 +70,12 @@ const (
 )
 
 const (
+	// for AliasDecl
+	Const = _Const
+	Type  = _Type
+	Var   = _Var
+	Func  = _Func
+
 	// for BranchStmt
 	Break       = _Break
 	Continue    = _Continue
@@ -94,7 +101,8 @@ var tokstrings = [...]string{
 	_IncOp:    "opop",
 	_Assign:   "=",
 	_Define:   ":=",
-	_Arrow:    "<-",
+	_Larrow:   "<-",
+	_Rarrow:   "=>",
 	_Star:     "*",
 
 	// delimitors