cmd/compile: don't export pos info in new export format for now

Exporting filenames as part of the position information can lead
to different object files which breaks tests.

Change-Id: Ia678ab64293ebf04bf83601e6ba72919d05762a4
Reviewed-on: https://go-review.googlesource.com/22385Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -112,6 +112,14 @@ 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
+
 // TODO(gri) remove eventually
 const forceNewExport = false // force new export format - DO NOT SUBMIT with this flag set
 
@@ -160,6 +168,9 @@ func export(out *bufio.Writer, trace bool) int {
 	}
 	p.rawByte(format)
 
+	// posInfo exported or not?
+	p.bool(posInfoFormat)
+
 	// --- generic export data ---
 
 	if p.trace {
@@ -493,6 +504,10 @@ func (p *exporter) obj(sym *Sym) {
 }
 
 func (p *exporter) pos(n *Node) {
+	if !posInfoFormat {
+		return
+	}
+
 	var file string
 	var line int
 	if n != nil {

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

@@ -30,8 +30,9 @@ type importer struct {
 	funcList []*Node // nil entry means already declared
 
 	// position encoding
-	prevFile string
-	prevLine int
+	posInfoFormat bool
+	prevFile      string
+	prevLine      int
 
 	// debugging support
 	debugFormat bool
@@ -55,6 +56,8 @@ func Import(in *bufio.Reader) {
 		Fatalf("importer: invalid encoding format in export data: got %q; want 'c' or 'd'", format)
 	}
 
+	p.posInfoFormat = p.bool()
+
 	// --- generic export data ---
 
 	if v := p.string(); v != exportVersion {
@@ -279,6 +282,10 @@ func (p *importer) obj(tag int) {
 }
 
 func (p *importer) pos() {
+	if !p.posInfoFormat {
+		return
+	}
+
 	file := p.prevFile
 	line := p.prevLine
 

src/go/internal/gcimporter/bimport.go

@@ -27,8 +27,9 @@ 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
@@ -57,6 +58,8 @@ 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" {
@@ -194,6 +197,10 @@ func (p *importer) obj(tag int) {
 }
 
 func (p *importer) pos() {
+	if !p.posInfoFormat {
+		return
+	}
+
 	file := p.prevFile
 	line := p.prevLine