[dev.typeparams] cmd/compile: move to new export version, keep reading previous version

I added constants for the previous export versions, and for the final
generics export version. I also added a const for the current export
version. We can increment the current export version for unstable
changes in dev.typeparams, and eventally set it back to the generics
version (2) before release. Added the same constants in
typecheck/iexport.go, importer/iimport.go, and gcimporter/iimport.go,
must be kept in sync.

Put in the needed conditionals to be able to read old versions.

Added new export/import test listimp.dir.

Change-Id: I166d17d943e07951aa752562e952b067704aeeca
Reviewed-on: https://go-review.googlesource.com/c/go/+/319931
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 37 insertions, 10 deletions

diff --git a/src/cmd/compile/internal/importer/iimport.go b/src/cmd/compile/internal/importer/iimport.go
index a4637ec34f..37e5113435 100644
--- a/src/cmd/compile/internal/importer/iimport.go
+++ b/src/cmd/compile/internal/importer/iimport.go
@@ -1,4 +1,3 @@
-// UNREVIEWED
 // Copyright 2018 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.
@@ -42,6 +41,16 @@ func (r *intReader) uint64() uint64 {
 	return i
 }
 
+// Keep this in sync with constants in iexport.go.
+const (
+	iexportVersionGo1_11   = 0
+	iexportVersionPosCol   = 1
+	iexportVersionGenerics = 2
+
+	// Start of the unstable series of versions, remove "+ n" before release.
+	iexportVersionCurrent = iexportVersionGenerics + 1
+)
+
 const predeclReserved = 32
 
 type itag uint64
@@ -68,7 +77,7 @@ const io_SeekCurrent = 1 // io.SeekCurrent (not defined in Go 1.4)
 // If the export data version is not recognized or the format is otherwise
 // compromised, an error is returned.
 func iImportData(imports map[string]*types2.Package, data []byte, path string) (_ int, pkg *types2.Package, err error) {
-	const currentVersion = 1
+	const currentVersion = iexportVersionCurrent
 	version := int64(-1)
 	defer func() {
 		if e := recover(); e != nil {
@@ -84,9 +93,13 @@ func iImportData(imports map[string]*types2.Package, data []byte, path string) (
 
 	version = int64(r.uint64())
 	switch version {
-	case currentVersion, 0:
+	case currentVersion, iexportVersionPosCol, iexportVersionGo1_11:
 	default:
-		errorf("unknown iexport format version %d", version)
+		if version > iexportVersionGenerics {
+			errorf("unstable iexport format version %d, just rebuild compiler and std library", version)
+		} else {
+			errorf("unknown iexport format version %d", version)
+		}
 	}
 
 	sLen := int64(r.uint64())
@@ -98,8 +111,9 @@ func iImportData(imports map[string]*types2.Package, data []byte, path string) (
 	r.Seek(sLen+dLen, io_SeekCurrent)
 
 	p := iimporter{
-		ipath:   path,
-		version: int(version),
+		exportVersion: version,
+		ipath:         path,
+		version:       int(version),
 
 		stringData:   stringData,
 		stringCache:  make(map[uint64]string),
@@ -178,8 +192,9 @@ func iImportData(imports map[string]*types2.Package, data []byte, path string) (
 }
 
 type iimporter struct {
-	ipath   string
-	version int
+	exportVersion int64
+	ipath         string
+	version       int
 
 	stringData   []byte
 	stringCache  map[uint64]string
@@ -294,14 +309,20 @@ func (r *importReader) obj(name string) {
 		r.declare(types2.NewConst(pos, r.currPkg, name, typ, val))
 
 	case 'F':
-		tparams := r.tparamList()
+		var tparams []*types2.TypeName
+		if r.p.exportVersion >= iexportVersionGenerics {
+			tparams = r.tparamList()
+		}
 		sig := r.signature(nil)
 		sig.SetTParams(tparams)
 
 		r.declare(types2.NewFunc(pos, r.currPkg, name, sig))
 
 	case 'T':
-		tparams := r.tparamList()
+		var tparams []*types2.TypeName
+		if r.p.exportVersion >= iexportVersionGenerics {
+			tparams = r.tparamList()
+		}
 
 		// Types can be recursive. We need to setup a stub
 		// declaration before recursing.
@@ -592,6 +613,9 @@ func (r *importReader) doType(base *types2.Named) types2.Type {
 		return typ
 
 	case typeParamType:
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected type param type")
+		}
 		r.currPkg = r.pkg()
 		pos := r.pos()
 		name := r.string()
@@ -622,6 +646,9 @@ func (r *importReader) doType(base *types2.Named) types2.Type {
 		return t
 
 	case instType:
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected instantiation type")
+		}
 		pos := r.pos()
 		len := r.uint64()
 		targs := make([]types2.Type, len)