How to keep a config file when major upgrade in wix v3.8?

This solved it for me... config file is preserved with minor/major upgrade, and completely removed on uninstall.

Ref: http://blogs.msdn.com/b/astebner/archive/2008/10/19/9006538.aspx

EDIT: Summarized info from the linked page...

1. Each config file shall have it's own component, where the config file is marked as the keypath of the component. Unversioned file replacement logic will be used by the Windows Installer.
2. Add "RemoveExistingProducts" action after the "InstallFiles" action. New versions of all components are installed before removing the old MSI. When it's done in this sequence, the components will have their reference count incremented to 2, but the config files will not be replaced unless they are unmodified (because of unversioned file replacement logic). When the old MSI is removed, the reference count will be decremented back to 1, but the files will not be removed because the reference count are not 0.

You have 3 options when upgrading:

1. Make the config file component permanent. This will not un-install it, and you will be able to upgrade it, but removing it will be very difficult.
2. Use the Remember property pattern to store the config settings for the IP and PORT in the registry.
3. As part of the install, write the config file to a temporary filename and then use a CopyFile command to create the destination file. On upgrade check for the file using a FileSearch, and if it exists then don't copy. Only issue here is if the config file has changed you won't get the updated sections.

The best option is the remember me property as this has the least problems.

It took me a while, but here is how I solved it myself. It's probably a variation of caveman_dick's third option.

1) Add new action into UISequence to back up your current config file. You can do it with the magic of custom action and ComponentSearch to actually locate the file.

2) Restore the file later in ExecuteSequence.

<Binary Id="CustomActions.CA.dll" SourceFile="..\CustomActions\bin\$(var.Configuration)\CustomActions.CA.dll" />
<CustomAction Id="BackupConfigFile"
         Return="check"
         BinaryKey="CustomActions.CA.dll"
         DllEntry="BackupFile" />

<CustomAction Id="RestoreConfigFile"
     Return="check"
     Execute="deferred"
     Impersonate="no"
     BinaryKey="CustomActions.CA.dll"
     DllEntry="RestoreFile" />

<CustomAction Id="PropertyDelegator" 
              Property="RestoreConfigFile" 
              Value="MYTARGET=[MYTARGET];FILENAME_TO_BACKUP=[FILENAME_TO_BACKUP]" />

<Property Id="FILENAME_TO_BACKUP" Value="test.exe.config" />

<Property Id="PREVIOUS_PATH">
  <ComponentSearch Id="evSearch" Guid="{010447A6-3330-41BB-8A7A-70D08ADB35E4}" />
</Property>

and here is quick CustomAction.cs I wrote:

[CustomAction]
public static ActionResult BackupFile(Session session)
{
    try
    {
        // check out if the previous installation has our file included
        // and if it does,
        // then make copy of it.
        var previousInstallationPath = session["PREVIOUS_PATH"];
        var fileToBackup = session["FILENAME_TO_BACKUP"];

        if (!string.IsNullOrEmpty(previousInstallationPath) && !string.IsNullOrEmpty(fileToBackup))
        {
            var absolutePath = Path.Combine(previousInstallationPath, fileToBackup);
            if (File.Exists(absolutePath))
            {
                var destinationPath = Path.Combine(Path.GetTempPath(),
                    string.Concat(fileToBackup, _MODIFIER));

                File.Copy(absolutePath, destinationPath);
            }
        }
    }
    catch (Exception e)
    {
        session.Log("Couldn't backup previous file: {0}", e);
    }
    return ActionResult.Success;
}

[CustomAction]
public static ActionResult RestoreFile(Session session)
{
    try
    {
        // check if our CustomAction made backup of file,
        // and if it indeed exists in temp path, then
        // we basically copy it back.
        var currentInstallationPath = session.CustomActionData["MYTARGET"];
        var fileToRestore = session.CustomActionData["FILENAME_TO_BACKUP"];
        var fileOriginalContentPath = Path.Combine(Path.GetTempPath(),
            string.Concat(fileToRestore, _MODIFIER));

        if (File.Exists(fileOriginalContentPath))
        {
            var destinationFile = Path.Combine(currentInstallationPath, fileToRestore);
            if (File.Exists(destinationFile))
                File.Delete(destinationFile);

            File.Move(fileOriginalContentPath, destinationFile);
        }
    }
    catch (Exception e)
    {
        session.Log("Couldn't restore previous file: {0}", e);
    }
    return ActionResult.Success;
}

to actually define sequences:

<InstallUISequence>
  <Custom Action="BackupConfigFile" After="AppSearch"></Custom>
</InstallUISequence>

<InstallExecuteSequence>
  <Custom Action="PropertyDelegator" Before="RestoreConfigFile" />
  <Custom Action="RestoreConfigFile" After="InstallFiles"></Custom>
</InstallExecuteSequence>

haven't tested it thoroughly, but seems to do the job for now. Caveat: Temp folder might change?!

Alternatively there is this one that I found from Internet, but haven't tested it.

            <!-- Support Upgrading the Product -->

            <Upgrade Id="{B0FB80ED-249E-4946-87A2-08A5BCA36E7E}">

                  <UpgradeVersion Minimum="$(var.Version)"
OnlyDetect="yes" Property="NEWERVERSIONDETECTED" />

                  <UpgradeVersion Minimum="0.0.0"
Maximum="$(var.Version)" IncludeMinimum="yes" 

                                          IncludeMaximum="no"
Property="OLDERVERSIONBEINGUPGRADED" />

            </Upgrade>

            <Property Id="OLDERVERSIONBEINGUPGRADED" Secure="yes" />



            <!-- Action to save and Restore the Config-File on reinstall
-->

            <!-- We're using CAQuietExec to prevent DOS-Boxes from
popping up -->

            <CustomAction Id="SetQtCmdLineCopy" Property="QtExecCmdLine"
Value="&quot;[SystemFolder]cmd.exe&quot; /c copy
&quot;[INSTALLDIR]MyApp.exe.config&quot;
&quot;[INSTALLDIR]config.bak&quot;" />

            <CustomAction Id="QtCmdCopy" BinaryKey="WixCA"
DllEntry="CAQuietExec" Execute="immediate" />

            <CustomAction Id="SetQtCmdLineRestore"
Property="QtCmdRestore" Value="&quot;[SystemFolder]cmd.exe&quot; /c move
/Y &quot;[INSTALLDIR]config.bak&quot;
&quot;[INSTALLDIR]MyApp.exe.config&quot;" />

            <CustomAction Id="QtCmdRestore" Execute="commit"
BinaryKey="WixCA" DllEntry="CAQuietExec" />



            <!-- These actions will run only for a major upgrade -->

            <InstallExecuteSequence>

                  <Custom Action="SetQtCmdLineCopy"
After="InstallInitialize"> NOT (OLDERVERSIONBEINGUPGRADED = "")</Custom>

                  <Custom Action="QtCmdCopy"
After="SetQtCmdLineCopy">NOT (OLDERVERSIONBEINGUPGRADED = "")</Custom>

                  <Custom Action="SetQtCmdLineRestore"
Before="InstallFinalize">NOT (OLDERVERSIONBEINGUPGRADED = "")</Custom>

                  <Custom Action="QtCmdRestore"
After="SetQtCmdLineRestore">NOT (OLDERVERSIONBEINGUPGRADED =
"")</Custom>

            </InstallExecuteSequence>