title: CMake & "PATH" Variables
body: <p>In CMake, how do I define a PATH-type cache variable that (in Windows,  <code>cmake-gui.exe</code>) gives me the little &quot;...&quot; button to get the Popup dialog?  Right now, I'm using syntax like:</p>
  <pre><code>SET(LIBRARY_INCLUDE_DIR &quot;something&quot; CACHE PATH &quot;Location of libraries&quot;)
  </code></pre>
  <p>But it seems to treat it as a String.</p>
  <p>Update:</p>
  <p>Here's an explicit example:</p>
  <pre><code>IF(EIGEN_DIR)
      SET(EIGEN_INCLUDE_DIRS ${EIGEN_DIR} CACHE PATH &quot;Location of the Eigen include files&quot;)
  ELSE()
      SET(EIGEN_INCLUDE_DIRS &quot;&quot; CACHE path &quot;Location of the Eigen include files&quot;)
  ENDIF(EIGEN_DIR)
  </code></pre>
  <p>And <code>EIGEN_INCLUDE_DIRS</code> winds up as a String, even upon a fresh first-time run of CMake.</p>