/// <summary>
/// Returns the subst source and subst target under which the test is running.
/// </summary>
/// <param name="substSource">Subst source.</param>
/// <param name="substTarget">Subst target.</param>
/// <returns>True if the test is running under subst.</returns>
/// <remarks>
/// Unit tests are run during BuildXL selfhost. The latter most likely runs under subst, which
/// in turn, essentially, makes unit tests run under subst as well. If a unit test executes a pip that calls
/// a function like <code>GetFinalPathNameByHandle</code>, then, without directory translation,
/// instead of returning the substed path, the function returns the real path. This real path
/// can cause dependency access violation for the pip because the file access manifest for the pip may only
/// contain substed paths.
///
/// For example if <code>B:\</code> is the subst target and <code>E:\Repos\BuildXL</code> is the subst source. All paths,
/// based on <see cref="TemporaryDirectory"/>, that are specified for a pip executed by a unit test have <code>B:\</code> as the root.
/// If the pip calls <code>GetFinalPathNameByHandle</code> on <code>B:\file</code>, then the resulting path will be
/// <code>E:\Repos\BuildXL\file</code>. Further, if the pip reads <code>E:\Repos\BuildXL\file</code>, then there will be
/// read violation because the path <code>E:\Repos\BuildXL\file</code> is not present anywhere in the manifest.
///
/// This method calls <code>GetFinalPathNameByHandle</code> on <see cref="TemporaryDirectory"/> to infer
/// <paramref name="substSource"/> and <paramref name="substTarget"/>. Since <code>GetFinalPathNameByHandle</code>
/// is not implemented on non-Windows (and there is currently no subst on non-Windows), this method simply returns
/// false on non-Windows.
///
/// CAUTION:
/// This method only works if the unit test itself is called in undetoured environment. Or, in terms of
/// BuildXL Script for selfhost, the unit test itself is executed using <code>Sdk.Managed.Testing.XUnit.UnsafeUnDetoured</code> framework.
/// Recall that this method calls <code>GetFinalPathNameByHandle</code> internally. If it is called in a detoured environment,
/// then the detoured version of <code>GetFinalPathNameByHandle</code> will be called, and that detoured version takes into account
/// the subst specified by the selfhost via the directory translation. Thus, for the above example, calling the detoured version on
/// <code>B:\file</code> returns <code>B:\file</code> because the directory translation translated <code>E:\Repos\BuildXL\file</code>
/// to <code>B:\file</code>.
///
/// BuildXL unit tests that involve running Detours, e.g., integration tests and detours tests, are all run in undetoured environment.
/// </remarks>
protected bool TryGetSubstSourceAndTarget(out string substSource, out string substTarget)
{
substSource = null;
substTarget = null;
if (OperatingSystemHelper.IsUnixOS)
{
// There is currently no subst in non-Windows OS.
return(false);
}
OpenFileResult directoryOpenResult = FileUtilities.TryOpenDirectory(
TemporaryDirectory,
FileShare.Read | FileShare.Write | FileShare.Delete,
out SafeFileHandle directoryHandle);
XAssert.IsTrue(directoryOpenResult.Succeeded);
string directoryHandlePath = FileUtilities.GetFinalPathNameByHandle(directoryHandle, volumeGuidPath: false);
if (!string.Equals(TemporaryDirectory, directoryHandlePath, StringComparison.OrdinalIgnoreCase))
{
string commonPath = TemporaryDirectory.Substring(2); // Include '\' of '<Drive>:\' for searching.
substTarget = TemporaryDirectory.Substring(0, 3); // Include '\' of '<Drive>:\' in the substTarget.
int commonIndex = directoryHandlePath.IndexOf(commonPath, 0, StringComparison.OrdinalIgnoreCase);
if (commonIndex == -1)
{
substTarget = null;
}
else
{
substSource = directoryHandlePath.Substring(0, commonIndex + 1);
}
}
return(!string.IsNullOrWhiteSpace(substSource) && !string.IsNullOrWhiteSpace(substTarget));
}
