Including files with directory specified separately in MSBuild - msbuild

Question

This seems like it should be simple but I can't work it out from the reference and my google-fu is apparently weak.
I just want to specify the file names and base folder separately in the build file...
<?xml version="1.0" encoding="utf-8"?>
<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<TestFilesWithFolder>
B:\Root\Test1.*;
B:\Root\Test2.*
</TestFilesWithFolder>
<TestFiles>Test1.*;Test2.*</TestFiles>
<TestFileRoot>B:\Root</TestFileRoot>
</PropertyGroup>
<Target Name="Build">
<ItemGroup>
<TestFilesGroupWithFolder Include="$(TestFilesWithFolder)" />
<TestFilesGroup Include="$(TestFileRoot)\$(TestFiles)" />
</ItemGroup>
<Warning Text="Source files with folder: #(TestFilesGroupWithFolder)" />
<Warning Text="Source files: #(TestFilesGroup)" />
</Target>
</Project>
When I run this, the first warning shows both files as expected, but the second warning only shows the first file (since the straight string concat put the folder name on the first but not second).
How would I get the ItemGroup "TestFilesGroup" to include both the files given the "TestFiles" and "TestFileRoot" properties?

Answer 1

It is possible to convert a semicolon delimited list of things into an item, which would make this possible, except that the items in your property contain wildcards, so if you want to have MSBuild treat them as items in a list, at the moment MSBuild first sees it the path must be valid. There may be a way to do that but I can't think of one. In other words...
<ItemGroup>
<TestFiles Include="$(TestFiles)" />
</ItemGroup>
...only works if $(TestFiles) contains a delimited list of either things with no wildcards, or qualified paths that actually exist.
Further, MSBuild can't compose a path with a wildcard inside the Include attribute and evaluate it at the same time, so you need a trick to first compose the full path separately, then feed it into the Include attribute. The following will work, but it requires changing your delimited property into a set of items. It batches a dependent target on this item list, with each batched target execution calculating a meta value for one item, which is stored off in a new meta value. When the original target executes, it is able to use that meta value in a subsequent Include.
<PropertyGroup>
<TestFilesWithFolder>
D:\Code\Test1.*;
D:\Code\Test2.*
</TestFilesWithFolder>
<TestFileRoot>D:\Code</TestFileRoot>
</PropertyGroup>
<ItemGroup>
<TestFilePattern Include="TestFilePattern">
<Pattern>Test1.*</Pattern>
</TestFilePattern>
<TestFilePattern Include="TestFilePattern">
<Pattern>Test2.*</Pattern>
</TestFilePattern>
</ItemGroup>
<Target Name="Compose" Outputs="%(TestFilePattern.Pattern)">
<ItemGroup>
<TestFilePattern Include="TestFilePattern">
<ComposedPath>#(TestFilePattern->'$(TestFileRoot)\%(Pattern)')</ComposedPath>
</TestFilePattern>
</ItemGroup>
</Target>
<Target Name="Build" DependsOnTargets="Compose">
<ItemGroup>
<TestFilesGroupWithFolder Include="$(TestFilesWithFolder)" />
</ItemGroup>
<Warning Text="Source files with folder: #(TestFilesGroupWithFolder)" />
<ItemGroup>
<ComposedTestFiles Include="%(TestFilePattern.ComposedPath)" />
</ItemGroup>
<Warning Text="Source files: #(ComposedTestFiles)" />
</Target>
Which produces the following output:
(Build target) ->
d:\Code\My.proj(80,5): warning : Source files with folder:
D:\Code\Test1.txt;D:\Code\Test2.txt
d:\Code\My.proj(84,5): warning : Source files:
D:\Code\Test1.txt;D:\Code\Test2.txt