Using MSBuild 4.0, is it possible to “simplify” a property containing a path?

Question

Suppose that I have a property containing

c:\workdir\project\wonder\subproj\..\..\common

and I want to reduce/simplify it to

c:\workdir\project\common

---

Furthermore, I would also like to be able to get a relative path from the current directory or specified.

Using the same starting property and having the current working directory set to

c:\workdir\project\wonder

I want it reduced to

..\common

Answer 1

The first part (resolving '..' in path) is relatively simple, you can do this using just property functions:

<PropertyGroup>
  <Folder>c:\workdir\project\wonder\subproj\..\..\common</Folder>
</PropertyGroup>
<Message Text="Folder $(Folder)" />     
<Message Text="Shortened path $([System.IO.Path]::GetFullPath($(Folder)))" />

Output:

Folder c:\workdir\project\wonder\subproj\..\..\common
Shortened path c:\workdir\project\common

The second part - shortening one path relatively to another - requires the use of a magical function Uri.MakeRelativeUri() and wrapping it inside an inline task (or an external task library). Declare your task:

<UsingTask TaskName="RelativePath" TaskFactory="CodeTaskFactory"
  AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.v4.0.dll">
 <ParameterGroup>
    <Target Required="true" />
    <BaseDirectory Required="true" />
    <Result Output="true" />
  </ParameterGroup>
  <Task>
    <Code Type="Fragment" Language="cs"><![CDATA[
Uri fromUri = new Uri(new DirectoryInfo(BaseDirectory).FullName
  + Path.DirectorySeparatorChar);
Uri toUri = new Uri(new DirectoryInfo(Target).FullName);
Uri relativeUri = fromUri.MakeRelativeUri(toUri);
Result = relativeUri.ToString().Replace('/', Path.DirectorySeparatorChar);
]]></Code>
    </Task>
</UsingTask>

Then use it as follows:

<PropertyGroup>
  <Folder>c:\workdir\project\wonder\subproj\..\..\common</Folder>
  <WorkingDir>c:\workdir\project\wonder</WorkingDir>
</PropertyGroup>
<Message Text="Folder $(Folder)" />
<Message Text="Base directory $(WorkingDir)" />
<RelativePath Target="$(Folder)" BaseDirectory="$(WorkingDir)">
  <Output PropertyName="Relative" TaskParameter="Result"/>
</RelativePath>
<Message Text="Relative path $(Relative)" />

Output:

Folder c:\workdir\project\wonder\subproj\..\..\common
Base directory c:\workdir\project\wonder
Relative path ..\common