Cannot make an update installer for an uninstallable app with Inno Setup

I want to make 2 installer, one to install and one to update an application.

Both installers uses the same AppId string, but only the install asks to user where install the application (DirName).
I expect that the update installer will get the same installation folder without selecting it.

Both installers should be not uninstallable.

Installer config:

[Setup]
AppId=MyApp
DefaultDirName={sd}\myapp
ChangesEnvironment=yes
PrivilegesRequired=admin
Uninstallable=no
ArchitecturesInstallIn64BitMode=x64
SignTool=signtool

And this is the Update config:

[Setup]
AppId=MyApp
DefaultDirName={sd}\myapp
CloseApplications=no
DisableProgramGroupPage=yes
UsePreviousAppDir=yes
ChangesEnvironment=yes
PrivilegesRequired=admin
Uninstallable=no
ArchitecturesInstallIn64BitMode=x64

When I use the installer and updater with the default DirName it works well. But if I change manually the installation folder at installation time, then the update will not find the folder of the application.

I checked in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall but I cannot find any registry about my installation. Is it possible the the option Uninstallable=no makes unavailable the previous dirname?

Solution

Yes, with the Uninstallable=no, no metadata are saved. You have to save/restore the path somewhere in your own code.

For example:

Save the path to registry in CurStepChanged(ssDone) using RegWriteStringValue.
Read it using a scripted constant in DefaultDirName directive using RegQueryStringValue

[Setup]
DefaultDirName={code:GetDefaultDirName}
Uninstallable=no

[Code]

const
  SubKeyName = 'Software\My Company\My Program';
  ValueName = 'InstallLocation';

procedure CurStepChanged(CurStep: TSetupStep);
begin
  if CurStep = ssDone then
  begin
    RegWriteStringValue(
      HKEY_AUTO, SubKeyName, ValueName, ExpandConstant('{app}'));
  end;
end;

function GetDefaultDirName(Param: string): string;
begin
  if not RegQueryStringValue(HKEY_AUTO, SubKeyName, ValueName, Result) then
    Result := ExpandConstant('{autopf}\My Program');
end;