How to force a reboot in post-install in Inno Setup

Question

In my setup I have to install an external driver.
In some rare cases the installation fails and I have to remove the old driver and reboot before I can try again.

I install the external driver in the ssPostInstall.

procedure CurStepChanged(CurStep: TSetupStep);
begin
  if CurStep = ssPostInstall then
  begin
    if Exec(ExpandConstant('{app}\external.exe'), '-install', '', SW_SHOW,
            ewWaitUntilTerminated, ResultCode) then
    begin
      { handle success if necessary; ResultCode contains the exit code }
    end
    else begin
      { handle failure if necessary; ResultCode contains the error code }
      bReboot := true;
    end;
  end;

function NeedRestart(): Boolean;
begin
  Result := bReboot;
end;

Unfortunately this does not work since NeedRestart is called before ssPostInstall.

Is there any other way to trigger a reboot?
I don't want to set AlwaysRestart = yes

I could let pop up a MsgBox to inform the user and tell them what to do. But it would be much nicer if it could be handled within of the setup automatically.

Answer 1

You can do the installation sooner. For example immediately after the external.exe is installed using AfterInstall:

[Files]
Source: "external.exe"; DestDir: "{app}"; AfterInstall: InstallDriver

[Code]
procedure InstallDriver;
begin
  if Exec(ExpandConstant('{app}\external.exe'), '-install', '', SW_SHOW,
          ewWaitUntilTerminated, ResultCode) then
  begin
    { handle success if necessary; ResultCode contains the exit code }
  end
    else
  begin
    { handle failure if necessary; ResultCode contains the error code }
    bReboot := true;
  end;
end;

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Another option is to use ssInstall step (or even PrepareToInstall event) and extract the file programmatically using ExtractTemporaryFile.

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Btw, if external.exe is only an installer, you may want to "install" it to {tmp} (to get it automatically deleted).