cmd/compile: remove conditional code dealing with two export formats

This removes some scaffolding introduced pre-1.7, introduced to
fix an export format bug, and to minimize conflicts with older
formats. The currently deployed and recognized format is "v1",
so don't worry about other versions. This is a step towards a
better scheme for internal export format versioning.

For #16244.

Change-Id: Ic7cf99dd2a24ad5484cc54aed44fa09332c2cf72
Reviewed-on: https://go-review.googlesource.com/27205Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Robert Griesemer <gri@golang.org>

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

@@ -153,13 +153,9 @@ const debugFormat = false // default: false
 // TODO(gri) disable and remove once there is only one export format again
 const forceObjFileStability = true
 
-// Supported export format versions.
+// Current export format version.
 // TODO(gri) Make this more systematic (issue #16244).
-const (
-	exportVersion0 = "v0"
-	exportVersion1 = "v1"
-	exportVersion  = exportVersion1
-)
+const exportVersion = "v1"
 
 // exportInlined enables the export of inlined function bodies and related
 // dependencies. The compiler should work w/o any loss of functionality with
@@ -734,14 +730,7 @@ func (p *exporter) typ(t *Type) {
 			p.paramList(sig.Recvs(), inlineable)
 			p.paramList(sig.Params(), inlineable)
 			p.paramList(sig.Results(), inlineable)
-
-			// for issue #16243
-			// We make this conditional for 1.7 to avoid consistency problems
-			// with installed packages compiled with an older version.
-			// TODO(gri) Clean up after 1.7 is out (issue #16244)
-			if exportVersion == exportVersion1 {
-				p.bool(m.Nointerface)
-			}
+			p.bool(m.Nointerface) // record go:nointerface pragma value (see also #16243)
 
 			var f *Func
 			if inlineable {

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

@@ -21,9 +21,8 @@ import (
 // changes to bimport.go and bexport.go.
 
 type importer struct {
-	in      *bufio.Reader
-	buf     []byte // reused for reading strings
-	version string
+	in  *bufio.Reader
+	buf []byte // reused for reading strings
 
 	// object lists, in order of deserialization
 	strList       []string
@@ -68,9 +67,8 @@ func Import(in *bufio.Reader) {
 
 	// --- generic export data ---
 
-	p.version = p.string()
-	if p.version != exportVersion0 && p.version != exportVersion1 {
-		Fatalf("importer: unknown export data version: %s", p.version)
+	if v := p.string(); v != exportVersion {
+		Fatalf("importer: unknown export data version: %s", v)
 	}
 
 	// populate typList with predeclared "known" types
@@ -429,11 +427,7 @@ func (p *importer) typ() *Type {
 			recv := p.paramList() // TODO(gri) do we need a full param list for the receiver?
 			params := p.paramList()
 			result := p.paramList()
-
-			nointerface := false
-			if p.version == exportVersion1 {
-				nointerface = p.bool()
-			}
+			nointerface := p.bool()
 
 			n := methodname1(newname(sym), recv[0].Right)
 			n.Type = functype(recv[0], params, result)

src/go/internal/gcimporter/bimport.go

@@ -21,7 +21,6 @@ type importer struct {
 	data    []byte
 	path    string
 	buf     []byte // for reading strings
-	version string
 
 	// object lists
 	strList       []string         // in order of appearance
@@ -67,9 +66,8 @@ func BImportData(imports map[string]*types.Package, data []byte, path string) (i
 
 	// --- generic export data ---
 
-	p.version = p.string()
-	if p.version != "v0" && p.version != "v1" {
-		return p.read, nil, fmt.Errorf("unknown export data version: %s", p.version)
+	if v := p.string(); v != "v1" {
+		return p.read, nil, fmt.Errorf("unknown export data version: %s", v)
 	}
 
 	// populate typList with predeclared "known" types
@@ -305,10 +303,7 @@ func (p *importer) typ(parent *types.Package) types.Type {
 			recv, _ := p.paramList() // TODO(gri) do we need a full param list for the receiver?
 			params, isddd := p.paramList()
 			result, _ := p.paramList()
-
-			if p.version == "v1" {
-				p.int() // nointerface flag - discarded
-			}
+			p.int() // go:nointerface pragma - discarded
 
 			sig := types.NewSignature(recv.At(0), params, result, isddd)
 			t0.AddMethod(types.NewFunc(token.NoPos, parent, name, sig))