WiX merge module dependencies - wix

Question

I have an issue with some existing installers which I have repeated in a simple test case as follows:
Installer1 installs App1 and LibraryA(v1).
Installer2 installs App2, LibraryA(v2) and LibraryB. LibraryA(v2) requires LibraryB, which is why LibraryB is now installed. LibraryA(v1) had no such dependency. LibraryA(v2) should overwrite LibraryA(v1).
If I run Installer1 then Installer2, then uninstall Installer2, LibraryB gets removed, but LibraryA remains at v2 (sensible - I wouldn't expect it to revert to a prior version).
Forgetting my existing problem and imagine I was starting from scratch, how would you suggest I construct my WiX project to cope with such a situation? In my case, all of the libraries are defined as merge modules - something I'm not in a position to change (wixlibs are out of the question).
I have tried, to no effect, to use a Dependency element to create a dependency between the LibraryA(v2) merge module and the LibraryB merge module - it just seems to issue a linker warning if I forget to reference LibraryB in the installer, rather than creating an actual dependency.
The .wxs scripts in my test case look something like this (they all install to the same folder for ease of testing):
LibraryA(v1).wxs:
<Directory Id="TARGETDIR" Name="SourceDir">
<Directory Id="MergeRedirectFolder">
<Component Id="LibraryAComponent" Guid="d98dd742-c3d3-4aee-8d84-87f2b3c837dc">
<File Source="v1\LibraryA.dll" />
</Component>
</Directory>
</Directory>
LibraryA(v2).wxs:
<Directory Id="TARGETDIR" Name="SourceDir">
<Directory Id="MergeRedirectFolder">
<Component Id="LibraryAComponent" Guid="d98dd742-c3d3-4aee-8d84-87f2b3c837dc">
<File Source="v2\LibraryA.dll" />
</Component>
</Directory>
</Directory>
<Dependency RequiredId="LibraryBMergeModule.DD524F28_EAE0_47B8_A895_3AF2F7A7361A" RequiredLanguage="1033"/>
LibraryB.wxs:
<Directory Id="TARGETDIR" Name="SourceDir">
<Directory Id="MergeRedirectFolder">
<Component Id="LibraryBComponent" Guid="46e6e0da-2a99-4f0d-bed2-e764e16b9eed">
<File Source="LibraryB.dll" />
</Component>
</Directory>
</Directory>
App1.wxs:
<Media Id="1" Cabinet="media1.cab" EmbedCab="yes" />
<Directory Id="TARGETDIR" DiskId="1" Name="SourceDir">
<Directory Id="ProgramFilesFolder">
<Directory Id="WiXTest" Name="WiXTest">
<Merge Id="LibraryAv1" Language="1033" SourceFile="LibraryAv1.msm" />
<Component Id="App1Component" Guid="93D11AFF-5307-4355-B261-0096775B6A89">
<File Source="App1.exe" />
</Component>
</Directory>
</Directory>
</Directory>
<Feature Id="Libraries" Title="Shared Files" Level="1">
<MergeRef Id="LibraryAv1" />
</Feature>
<Feature Id="App" Title="Application" Level="1">
<ComponentRef Id="App1Component" />
</Feature>
App2.wxs:
<Media Id="1" Cabinet="media1.cab" EmbedCab="yes" />
<Directory Id="TARGETDIR" DiskId="1" Name="SourceDir">
<Directory Id="ProgramFilesFolder">
<Directory Id="WiXTest" Name="WiXTest">
<Merge Id="LibraryB" Language="1033" SourceFile="LibraryB.msm" />
<Merge Id="LibraryAv2" Language="1033" SourceFile="LibraryAv2.msm" />
<Component Id="App2Component" Guid="173C71B6-E403-4AC1-894D-06799C6782A4">
<File Source="App2.exe" />
</Component>
</Directory>
</Directory>
</Directory>
<Feature Id="Libraries" Title="Shared Files" Level="1">
<MergeRef Id="LibraryB" />
<MergeRef Id="LibraryAv2" />
</Feature>
<Feature Id="App" Title="Application" Level="1">
<ComponentRef Id="App2Component" />
</Feature>
I'm guessing that this is entirely the wrong way to go about things and am looking for some pointers to bring me back on track. It feels like you need to have a PhD in Windows Installer in order to use WiX correctly.

Answer 1

I am no WIX expert but yes for MSI you need at least a PhD. At first you should know the rules about MSI components:
What Every Developer Should Know About MSI Components
From painful experience I do know that if several MSIs bring in the same components it is no good. If possible I would strive for the single source principle so that your libs are installed always by the same MSI (let it be a infrastructure MSI). Your application MSI´s then simply check if the infrastructure has been installed and that was it.
Coming back to your question what you should do with your merge modules. I would create for each merge module an extra msi (yes customers do not like crowed installed software catalogs) to be sure that if you are in need to service the libraries you have full freedom.
I do not know your software structure but it could be that you will need LibraryA v1 and v2 at the same time so you should think about deploying your libraries to the WinSxS cache or if they are managed the GAC. Or you come up with something similar in your folder structure or file name convention.