go/importer: better error message when importer is out of date

Separated out panic handling for bimporter and importer so that
the handler can consider the current version and report a better
error.

Added new export data test for export data version 999 (created
by changing the compiler temporarily) and verifying expected
error message.

Fixes #25856.

Change-Id: Iaafec07b79499154ef7c007341783fa07c57f24d
Reviewed-on: https://go-review.googlesource.com/118496
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/go/internal/gcimporter/bimport.go

@@ -50,24 +50,24 @@ type importer struct {
 // compromised, an error is returned.
 func BImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (_ int, pkg *types.Package, err error) {
 	// catch panics and return them as errors
+	const currentVersion = 6
+	version := -1 // unknown version
 	defer func() {
 		if e := recover(); e != nil {
-			// The package (filename) causing the problem is added to this
-			// error by a wrapper in the caller (Import in gcimporter.go).
 			// Return a (possibly nil or incomplete) package unchanged (see #16088).
-			err = fmt.Errorf("cannot import, possibly version skew (%v) - reinstall package", e)
+			if version > currentVersion {
+				err = fmt.Errorf("cannot import %q (%v), export data is newer version - update tool", path, e)
+			} else {
+				err = fmt.Errorf("cannot import %q (%v), possibly version skew - reinstall package", path, e)
 			}
-	}()
-
-	if len(data) > 0 && data[0] == 'i' {
-		return iImportData(fset, imports, data[1:], path)
 		}
+	}()
 
 	p := importer{
 		imports:    imports,
 		data:       data,
 		importpath: path,
-		version:    -1,           // unknown version
+		version:    version,
 		strList:    []string{""}, // empty string is mapped to 0
 		pathList:   []string{""}, // empty string is mapped to 0
 		fake: fakeFileSet{
@@ -92,7 +92,7 @@ func BImportData(fset *token.FileSet, imports map[string]*types.Package, data []
 		p.posInfoFormat = p.int() != 0
 		versionstr = p.string()
 		if versionstr == "v1" {
-			p.version = 0
+			version = 0
 		}
 	} else {
 		// Go1.8 extensible encoding
@@ -100,24 +100,25 @@ func BImportData(fset *token.FileSet, imports map[string]*types.Package, data []
 		versionstr = p.rawStringln(b)
 		if s := strings.SplitN(versionstr, " ", 3); len(s) >= 2 && s[0] == "version" {
 			if v, err := strconv.Atoi(s[1]); err == nil && v > 0 {
-				p.version = v
+				version = v
 			}
 		}
 	}
+	p.version = version
 
 	// read version specific flags - extend as necessary
 	switch p.version {
-	// case 7:
+	// case currentVersion:
 	// 	...
 	//	fallthrough
-	case 6, 5, 4, 3, 2, 1:
+	case currentVersion, 5, 4, 3, 2, 1:
 		p.debugFormat = p.rawStringln(p.rawByte()) == "debug"
 		p.trackAllTypes = p.int() != 0
 		p.posInfoFormat = p.int() != 0
 	case 0:
 		// Go1.7 encoding format - nothing to do here
 	default:
-		errorf("unknown export format version %d (%q)", p.version, versionstr)
+		errorf("unknown bexport format version %d (%q)", p.version, versionstr)
 	}
 
 	// --- generic export data ---

src/go/internal/gcimporter/gcimporter.go

@@ -144,16 +144,27 @@ func Import(packages map[string]*types.Package, path, srcDir string, lookup func
 	switch hdr {
 	case "$$\n":
 		err = fmt.Errorf("import %q: old export format no longer supported (recompile library)", path)
+
 	case "$$B\n":
 		var data []byte
 		data, err = ioutil.ReadAll(buf)
-		if err == nil {
+		if err != nil {
+			break
+		}
+
 		// TODO(gri): allow clients of go/importer to provide a FileSet.
 		// Or, define a new standard go/types/gcexportdata package.
 		fset := token.NewFileSet()
+
+		// The indexed export format starts with an 'i'; the older
+		// binary export format starts with a 'c', 'd', or 'v'
+		// (from "version"). Select appropriate importer.
+		if len(data) > 0 && data[0] == 'i' {
+			_, pkg, err = iImportData(fset, packages, data[1:], id)
+		} else {
 			_, pkg, err = BImportData(fset, packages, data, id)
-			return
 		}
+
 	default:
 		err = fmt.Errorf("unknown export data header: %q", hdr)
 	}

src/go/internal/gcimporter/gcimporter_test.go

@@ -141,9 +141,21 @@ func TestVersionHandling(t *testing.T) {
 		}
 		pkgpath := "./" + name[:len(name)-2]
 
+		if testing.Verbose() {
+			t.Logf("importing %s", name)
+		}
+
 		// test that export data can be imported
 		_, err := Import(make(map[string]*types.Package), pkgpath, dir, nil)
 		if err != nil {
+			// ok to fail if it fails with a newer version error for select files
+			if strings.Contains(err.Error(), "newer version") {
+				switch name {
+				case "test_go1.11_999b.a", "test_go1.11_999i.a":
+					continue
+				}
+				// fall through
+			}
 			t.Errorf("import %q failed: %v", pkgpath, err)
 			continue
 		}

src/go/internal/gcimporter/iimport.go

@@ -10,6 +10,7 @@ package gcimporter
 import (
 	"bytes"
 	"encoding/binary"
+	"fmt"
 	"go/constant"
 	"go/token"
 	"go/types"
@@ -60,13 +61,25 @@ const (
 // If the export data version is not recognized or the format is otherwise
 // compromised, an error is returned.
 func iImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (_ int, pkg *types.Package, err error) {
+	const currentVersion = 0
+	version := -1
+	defer func() {
+		if e := recover(); e != nil {
+			if version > currentVersion {
+				err = fmt.Errorf("cannot import %q (%v), export data is newer version - update tool", path, e)
+			} else {
+				err = fmt.Errorf("cannot import %q (%v), possibly version skew - reinstall package", path, e)
+			}
+		}
+	}()
+
 	r := &intReader{bytes.NewReader(data), path}
 
-	version := r.uint64()
+	version = int(r.uint64())
 	switch version {
-	case 0:
+	case currentVersion:
 	default:
-		errorf("cannot import %q: unknown iexport format version %d", path, version)
+		errorf("unknown iexport format version %d", version)
 	}
 
 	sLen := int64(r.uint64())

src/go/internal/gcimporter/testdata/versions/test.go

@@ -11,7 +11,10 @@
 //
 // go build -o test_go1.$X_$Y.a test.go
 //
-// with $X = Go version and $Y = export format version.
+// with $X = Go version and $Y = export format version
+// (add 'b' or 'i' to distinguish between binary and
+// indexed format starting with 1.11 as long as both
+// formats are supported).
 //
 // Make sure this source is extended such that it exercises
 // whatever export format change has taken place.