go/gcimporter15: match https://golang.org/cl/22385

Don't export position info for now. Enabled/disabled with a flag.
The importer recognizes the chosen format automatically.

Change-Id: I055818eb9dba50cc97f40eb92220258a1ddbfbec
Reviewed-on: https://go-review.googlesource.com/22427
Reviewed-by: Alan Donovan <adonovan@google.com>

go/gcimporter15/bexport.go

@@ -37,6 +37,14 @@ import (
 // (suspected) format errors, and whenever a change is made to the format.
 const debugFormat = false // default: false
 
+// If posInfoFormat is set, position information (file, lineno) is written
+// for each exported object, including methods and struct fields. Currently
+// disabled because it may lead to different object files depending on which
+// directory they are built under, which causes tests checking for hermetic
+// builds to fail (e.g. TestCgoConsistentResults for cmd/go).
+// TODO(gri) determine what to do here.
+const posInfoFormat = false
+
 // If trace is set, debugging output is printed to std out.
 const trace = false // default: false
 
@@ -77,6 +85,9 @@ func BExportData(fset *token.FileSet, pkg *types.Package) []byte {
 	}
 	p.rawByte(format)
 
+	// posInfo exported or not?
+	p.bool(posInfoFormat)
+
 	// --- generic export data ---
 
 	if trace {
@@ -200,6 +211,10 @@ func (p *exporter) obj(obj types.Object) {
 }
 
 func (p *exporter) pos(obj types.Object) {
+	if !posInfoFormat {
+		return
+	}
+
 	var file string
 	var line int
 	if p.fset != nil {
@@ -563,6 +578,20 @@ func valueToRat(x constant.Value) *big.Rat {
 	return new(big.Rat).SetInt(new(big.Int).SetBytes(bytes))
 }
 
+func (p *exporter) bool(b bool) bool {
+	if trace {
+		p.tracef("[")
+		defer p.tracef("= %v] ", b)
+	}
+
+	x := 0
+	if b {
+		x = 1
+	}
+	p.int(x)
+	return b
+}
+
 // ----------------------------------------------------------------------------
 // Low-level encoders
 

go/gcimporter15/bimport.go

@@ -6,10 +6,6 @@
 
 // This file is a copy of $GOROOT/src/go/internal/gcimporter/bimport.go, tagged for go1.5.
 
-// Copyright 2015 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
 package gcimporter
 
 import (
@@ -35,8 +31,9 @@ type importer struct {
 	typList []types.Type     // in order of appearance
 
 	// position encoding
-	prevFile string
-	prevLine int
+	posInfoFormat bool
+	prevFile      string
+	prevLine      int
 
 	// debugging support
 	debugFormat bool
@@ -65,6 +62,8 @@ func BImportData(imports map[string]*types.Package, data []byte, path string) (i
 		return p.read, nil, fmt.Errorf("invalid encoding format in export data: got %q; want 'c' or 'd'", format)
 	}
 
+	p.posInfoFormat = p.int() != 0
+
 	// --- generic export data ---
 
 	if v := p.string(); v != "v0" {
@@ -202,6 +201,10 @@ func (p *importer) obj(tag int) {
 }
 
 func (p *importer) pos() {
+	if !p.posInfoFormat {
+		return
+	}
+
 	file := p.prevFile
 	line := p.prevLine