Use ExePayloadRef for PrimaryPayloadId and SecondaryPayloadId

[drolevar]

This is a fix when using a custom BootstrapperApplication Id. This property can be anything, for example, "MyBootstrapper", but it's later assigned to PrimaryPayloadId, which is matched against Payload Id here:

    // Find the primary and secondary bootstrapper application payloads.
    for (DWORD i = 0; i < pUserExperience->payloads.cPayloads; ++i)
    {
        BURN_PAYLOAD* pPayload = pUserExperience->payloads.rgPayloads + i;

        if (!pUserExperience->pPrimaryExePayload && CSTR_EQUAL == ::CompareStringOrdinal(pPayload->sczKey, -1, sczPrimaryId, -1, FALSE))
        {
            pUserExperience->pPrimaryExePayload = pPayload;
        }
        else if (fFoundSecondary && !pUserExperience->pSecondaryExePayload && CSTR_EQUAL == ::CompareStringOrdinal(pPayload->sczKey, -1, sczSecondaryId, -1, FALSE))
        {
            pUserExperience->pSecondaryExePayload = pPayload;
        }
    }

While ExePayloadRef is exactly the reference to the exe payload.

Fixes wixtoolset/issues#8673

[drolevar]

@robmen Please, tell if more stuff has to be done, like unit tests, etc.

[robmen]

Yeah, need the following:

1. Reference an open issue, it'll need to be approved by triage
2. Add a test (unit or integration, whichever is most appropriate... this one should be a unit test) - especially for an issue like this which is a very subtle change

[drolevar]

@robmen Ready. Created the issue and added the test.

[drolevar]

@robmen Anything else missing in the PR?

[robmen]

Nothing missing but time. I'm currently focused on customer work. This PR, in particular, I need time to dig into and make sure I understand the root cause. So, it takes more than a cursory look. The added test case is very much appreciated as it will highlight the broken code path.

[drolevar]

@robmen To facilitate your root cause analysis a little bit.

This issue was introduced in #496.

Prior to that, the application was loaded in burn/engine/userexperience.cpp, in UserExperienceLoad(...) like this:

    LPCWSTR wzPath = pUserExperience->payloads.rgPayloads[0].sczLocalFilePath;
    ...
    // Load BA DLL.
    pUserExperience->hUXModule = ::LoadLibraryExW(wzPath, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);

So it was the first Payload child of the UX element.

With #496 the UX element got a PrimaryPayloadId element, which is now parsed and then matched to the Id of the Payload in BootstrapperApplicationParseFromXml(...) in burn/engine/bootstrapperapplication.cpp:

    // @PrimaryPayloadId
    hr = XmlGetAttributeEx(pixnUserExperienceNode, L"PrimaryPayloadId", &sczPrimaryId);
    ExitOnRequiredXmlQueryFailure(hr, "Failed to get @PrimaryPayloadId.");

    // @SecondaryPayloadId
    hr = XmlGetAttributeEx(pixnUserExperienceNode, L"SecondaryPayloadId", &sczSecondaryId);
    ExitOnOptionalXmlQueryFailure(hr, fFoundSecondary, "Failed to get @SecondaryPayloadId.");

    ...

    // Find the primary and secondary bootstrapper application payloads.
    for (DWORD i = 0; i < pUserExperience->payloads.cPayloads; ++i)
    {
        BURN_PAYLOAD* pPayload = pUserExperience->payloads.rgPayloads + i;

        if (!pUserExperience->pPrimaryExePayload && CSTR_EQUAL == ::CompareStringOrdinal(pPayload->sczKey, -1, sczPrimaryId, -1, FALSE))
        {
            pUserExperience->pPrimaryExePayload = pPayload;
        }
        else if (fFoundSecondary && !pUserExperience->pSecondaryExePayload && CSTR_EQUAL == ::CompareStringOrdinal(pPayload->sczKey, -1, sczSecondaryId, -1, FALSE))
        {
            pUserExperience->pSecondaryExePayload = pPayload;
        }
    }

So currently if one sets a custom Id to the BootstrapperApplication, it's set used as an Id in the Payload element, but not used in the PrimaryPayloadId attribute, so matching in BootstrapperApplicationParseFromXml(...) fails.