visual_studio generator variables

[memsharded]

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[lasote]

/home/travis/build/conan-io/docs/reference/generators/visualstudio.rst:16:Could not lex literal_block as "xml". Highlighting skipped.

[adaviding]

The usage of ConanVariables is a fine idea, but it threw me for a curveball. I was thinking about asking you to update your documentation, but I'm not sure if there is an easy way to describe the curveball I received. I will describe it here and maybe you will find an easy way to describe it (if possible).

I have one VisualStudio project that imports a conanbuildinfo.props. Then on the same project, I have an export.props file which looks kind of like this (notice how it includes the conanbuildinfo.props):

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <ImportGroup Label="PropertySheets">
    <Import Project="conanbuildinfo.props" />
  </ImportGroup>

  <!-- some other stuff -->

</Project>

Then I have a second Visual Studio project (a GTest project) which consumes the first project via its export.props. The second project pulls in its own conanbuildinfo.props (which adds a conan package for GTest).

Now in the *.vcxproj file for the second project, I was pulling in the conanbuildinfo.props before the export.props like this, and I had a build error was that gtest/gtest.h could not be found.

  <ImportGroup Label="PropertySheets">
    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
    <Import Project="conanbuildinfo.props" />
    <Import Project="..\..\Panopto.Native.Media.Lib\export.props" />    
  </ImportGroup>

I eventually fixed the build error by switching the order of the XML fields so that export.props came before conanbuildinfo.props:

  <ImportGroup Label="PropertySheets">
    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
    <Import Project="..\..\Panopto.Native.Media.Lib\export.props" />
    <!--This needs to come after all of the `export.props` imports because of something odd about how intermediate variables are defined and then can be redefined before they are evaluated.-->
    <Import Project="conanbuildinfo.props" />
  </ImportGroup>

Apparently, the intermediate ConanVariables were being redefined in the export.props prior to being evaluated in the conanbuildinfo.props file. It took me a day to solve this one.