cmd/compile: move Io state into lexer and remove Io type

Pass lexer around so state is accessible and dependency is explicit.
In the process remove EOF -> '\n' conversion that has to be corrected
for when reporting errors.

Change-Id: If95564b70e7484dedc1f5348e585cd19acbc1243
Reviewed-on: https://go-review.googlesource.com/19819
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/parser.go

@@ -21,24 +21,14 @@ import (
 
 const trace = false // if set, parse tracing can be enabled with -x
 
+// parse_import parses the export data of a package that is imported.
 func parse_import(bin *obj.Biobuf, indent []byte) {
-	pushedio := curio
-	curio = Io{bin: bin}
-
-	importparser := parser{indent: indent} // preserve indentation
-	importparser.next()
-	importparser.import_package()
-
-	curio = pushedio
+	newparser(bin, indent).import_package()
 }
 
-// parse_file sets up a new parser and parses a single Go source file.
+// parse_file parses a single Go source file.
 func parse_file(bin *obj.Biobuf) {
-	curio = Io{bin: bin}
-
-	fileparser := parser{}
-	fileparser.next()
-	fileparser.file()
+	newparser(bin, nil).file()
 }
 
 type parser struct {
@@ -48,6 +38,16 @@ type parser struct {
 	indent []byte // tracing support
 }
 
+// newparser returns a new parser ready to parse from src.
+// indent is the initial indentation for tracing output.
+func newparser(src *obj.Biobuf, indent []byte) *parser {
+	var p parser
+	p.bin = src
+	p.indent = indent
+	p.next()
+	return &p
+}
+
 func (p *parser) got(tok int32) bool {
 	if p.tok == tok {
 		p.next()