In Inno Setup is it possible to add conditional statements to what in the [Run] section gets executed?

Question

Alternatively is it possible to manually update the built in progress bar? Basically I have 2 MSIs included and using Inno Setup as a bootstrapper, and depending on user input one or both of the MSIs are to be installed. I have something working using Exec statements in CurStepChanged but it doesn't update the progress bar as the files are extracted and it looks like the installer is stalled. I guess the end result is I want some progress bar updates while the files are extracted to the temp folder. The following is my current code:

procedure CurStepChanged(CurStep: TSetupStep);
var
    ResultCode: Integer;
begin
    if(CurStep = ssInstall) then begin
     if(InstallServer) then begin
      ExtractTemporaryFile('ServerSetup.msi');
      Exec('msiexec',ExpandConstant('/i "{tmp}\ServerSetup.msi" /qb INSTALLDIR="{code:GetInstallPath}\Server\" ALLUSERS=2'),'', SW_SHOW, ewWaitUntilTerminated, ResultCode);
     end;
     if(InstallClient) then begin
      ExtractTemporaryFile('ClientSetup.msi');
      Exec('msiexec',ExpandConstant('/i "{tmp}\ClientSetup.msi" /qb INSTALLDIR="{code:GetInstallPath}\Client\" ALLUSERS=2'),'', SW_SHOW, ewWaitUntilTerminated, ResultCode);
     end;
    end;
end;

Answer 1

Why not simply try something like this:

[Files]
Source: ClientSetup.msi; DestDir: {tmp}; Flags: deleteafterinstall; Components: Client
Source: ServerSetup.msi; DestDir: {tmp}; Flags: deleteafterinstall; Components: Server

[Run]
Filename: msiexec.exe; Parameters: /i "{tmp}\ClientSetup.msi" /qb INSTALLDIR="{code:GetInstallPath}\Client\" ALLUSERS=2; WorkingDir: {tmp}; StatusMsg: Installing client; Components: Client
Filename: msiexec.exe; Parameters: /i "{tmp}\ServerSetup.msi" /qb INSTALLDIR="{code:GetInstallPath}\Server\" ALLUSERS=2; WorkingDir: {tmp}; StatusMsg: Installing server; Components: Server

[Components]
Name: Client; Description: Client Installation
Name: Server; Description: Server Installation

Of course you don't necessarily have to use Components. You did not write how you decide which installer to run. If you need more complex logic you could also use Check functions as in:

[Files]
Source: ClientSetup.msi; DestDir: {tmp}; Flags: deleteafterinstall; Check: CheckClient
Source: ServerSetup.msi; DestDir: {tmp}; Flags: deleteafterinstall; Check: CheckServer

[Run]
Filename: msiexec.exe; Parameters: /i "{tmp}\ClientSetup.msi" /qb INSTALLDIR="{code:GetInstallPath}\Client\" ALLUSERS=2; WorkingDir: {tmp}; StatusMsg: Installing client; Check: CheckClient
Filename: msiexec.exe; Parameters: /i "{tmp}\ServerSetup.msi" /qb INSTALLDIR="{code:GetInstallPath}\Server\" ALLUSERS=2; WorkingDir: {tmp}; StatusMsg: Installing server; Check: CheckServer

[Code]
function CheckClient: Boolean;
begin
  Result := WhateverCondition;
end;

function CheckServer: Boolean;
begin
  Result := WhateverOtherCondition;
end;

Answer 2

And if in 'WhateverCondition' I'd like to check if a specific component was chosen to be installed, what would I do?