cmd/go/internal/syntax: reintroduce reverted comments

These comments were originally introduced together with the changes
for alias declarations, and then reverted when we backed out alias
support.

Reintroduce them.

Change-Id: I3ef2c4f4672d6af8a900f5d73df273edf28d1a14
Reviewed-on: https://go-review.googlesource.com/32826Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/syntax/nodes.go

@@ -33,6 +33,7 @@ func (n *node) init(p *parser) {
 // ----------------------------------------------------------------------------
 // Files
 
+// package PkgName; DeclList[0], DeclList[1], ...
 type File struct {
 	PkgName  *Name
 	DeclList []Decl
@@ -49,6 +50,8 @@ type (
 		aDecl()
 	}
 
+	//              Path
+	// LocalPkgName Path
 	ImportDecl struct {
 		LocalPkgName *Name // including "."; nil means no rename present
 		Path         *BasicLit
@@ -56,6 +59,9 @@ type (
 		decl
 	}
 
+	// NameList
+	// NameList      = Values
+	// NameList Type = Values
 	ConstDecl struct {
 		NameList []*Name
 		Type     Expr   // nil means no type
@@ -64,6 +70,7 @@ type (
 		decl
 	}
 
+	// Name Type
 	TypeDecl struct {
 		Name   *Name
 		Type   Expr
@@ -72,6 +79,9 @@ type (
 		decl
 	}
 
+	// NameList Type
+	// NameList Type = Values
+	// NameList      = Values
 	VarDecl struct {
 		NameList []*Name
 		Type     Expr   // nil means no type
@@ -80,6 +90,10 @@ type (
 		decl
 	}
 
+	// func          Name Type { Body }
+	// func          Name Type
+	// func Receiver Name Type { Body }
+	// func Receiver Name Type
 	FuncDecl struct {
 		Attr    map[string]bool // go:attr map
 		Recv    *Field          // nil means regular function
@@ -419,6 +433,8 @@ func (simpleStmt) aSimpleStmt() {}
 // ----------------------------------------------------------------------------
 // Comments
 
+// TODO(gri) Consider renaming to CommentPos, CommentPlacement, etc.
+//           Kind = Above doesn't make much sense.
 type CommentKind uint
 
 const (