Make selfupdate maintain client version as well.

cipd/version/version.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 // Package version provides a way for CIPD packaged Go binaries to discover
 // their current package instance ID.
 //
 // It's safe to link this library into arbitrary executables. It is small and
 // doesn't pull in rest of CIPD client code.
 package version
@@ skipping 80 matching lines @@
                 return ""
         }
         // Must have at least ".cipd/pkgs/<name>/<id>/...".
         if len(chunks)-i <= 4 {
                 return ""
         }
         // Cut out .cipd/pkgs/<name>/<id> to get A/b/c/d.
         return strings.Join(append(chunks[:i], chunks[i+4:]...), string(filepath.Separator))
 }
 
+// GetVersionFile returns the path to the version file corresponding to the
+// provided exe. This isn't typically needed, but can be useful for debugging.
+func GetVersionFile(exePath string) string {
+        // <root>/.versions/exename.cipd_version
+        return filepath.Join(filepath.Dir(exePath), ".versions", filepath.Base(exePath)+".cipd_version")
+}
+
 func getCurrentVersion(exePath string) (Info, error) {
-        // <root>/.versions/exename.cipd_version
-        p := filepath.Join(filepath.Dir(exePath), ".versions", filepath.Base(exePath)+".cipd_version")
-        if vf, _ := readVersionFile(p); vf.InstanceID != "" {
+        if vf, _ := readVersionFile(GetVersionFile(exePath)); vf.InstanceID != "" {
                 return vf, nil
         }
         // <root>/exename.cipd_version
         return readVersionFile(exePath + ".cipd_version")

[Vadim Sh., 2016/11/27 01:25:55]

note that there's a fallback here. It's where version files were before I moved
them to ".versions"... I believe it's fine to ignore it.

[iannucci, 2016/11/29 01:46:20]

That's what I figured.

 }
 
 // readVersionFile returns parsed version file. Returns empty struct and nil if
 // it is missing, error if it can't be read.
 func readVersionFile(path string) (Info, error) {
         f, err := os.Open(path)
         if err != nil {
                 if os.IsNotExist(err) {
                         err = nil
                 }
@@ skipping 22 matching lines @@
         // Version file can also be changed. Remember the version of the started
         // executable.
         if initialExePathErr == nil {
                 // Don't use GetCurrentVersion since we specifically do not want to use
                 // the original symlink.
                 startupVersionFile, startupVersionFileErr = getCurrentVersion(initialExePath)
         } else {
                 startupVersionFileErr = initialExePathErr
         }
 }