title: Why do my Conan packages appear to be getting corrupted?
body: <p><strong>Background</strong></p>
  
  <p>I have a project which was using <code>boost/1.71.0@conan/stable</code>, and was giving me a compile-time error.  I decided to try <code>boost/1.72.0</code> just on the off chance that it might fix it.  When I did, I got this:</p>
  
  <pre><code>1&gt; [CMake] ERROR: boost/1.72.0: Error in source() method, line 151
  1&gt; [CMake]  tools.get(**self.conan_data["sources"][self.version])
  1&gt; [CMake]  AttributeError: 'NoneType' object has no attribute 'token'
  1&gt; [CMake] CMake Error at out/build/x64-Debug/conan.cmake:402 (message):
  1&gt; [CMake]   Conan install failed='1'
  1&gt; [CMake] Call Stack (most recent call first):
  1&gt; [CMake]   out/build/x64-Debug/conan.cmake:497 (conan_cmake_install)
  1&gt; [CMake]   CMakeLists.txt:41 (conan_cmake_run)
  </code></pre>
  
  <p>which references the <code>conan_cmake_run()</code> call in my CMakeLists.txt:</p>
  
  <pre><code>if(CONAN_EXPORTED) # in conan local cache
      include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
      conan_basic_setup()
  else() # in user space
      include(${CMAKE_BINARY_DIR}/conan.cmake)
  
      conan_cmake_run(CONANFILE conanfile.txt
                      BASIC_SETUP
                      BUILD missing)
  endif()
  </code></pre>
  
  <p>and line 151 in the boost conanfile.py:</p>
  
  <pre><code>        if tools.os_info.is_windows:
              sha256 = "85a94ac71c28e59cf97a96714e4c58a18550c227ac8b0388c260d6c717e47a69"
              extension = ".zip"
          else:
              sha256 = "d73a8da01e8bf8c7eda40b4c84915071a8c8a0df4a6734537ddde4a8580524ee"
              extension = ".tar.bz2"
  
          zip_name = "%s%s" % (self.folder_name, extension)
          url = "https://dl.bintray.com/boostorg/release/%s/source/%s" % (self.version, zip_name)
  151:    tools.get(url, sha256=sha256)
  
          ...
  </code></pre>
  
  <p>My conanfile.txt:</p>
  
  <pre><code>[requires]
  boost/1.72.0
  ...some of my own packages...
  
  [generators]
  cmake
  
  [options]
  boost:shared=True
  </code></pre>
  
  <p><strong>What I've Tried</strong></p>
  
  <ul>
  <li>Upgrading Conan from 1.21 to 1.23.  That gave me a different error ("Forbidden" something or other), so after trying to get rid of that for a while, I reverted.  I also updated Pip somewhere in here.</li>
  <li>Removing boost packages using <code>conan remove boost/*</code></li>
  <li>Other boost versions... I've tried <code>boost/1.71.0</code>, <code>boost/1.72.0</code>, and <code>boost/1.71.0@conan/stable</code>.  The latter, which worked initially, no longer works after removing all boost packages.  Related to that, when I generate the CMake cache for a second time (i.e. the boost package is already in the local cache), I get these warnings:</li>
  </ul>
  
  <pre><code>1&gt; [CMake] boost/1.72.0: Configuring sources in C:\.conan\133b85\1
  1&gt; [CMake] boost/1.72.0: WARN: Package is corrupted, removing folder: C:\.conan\854baa\1
  1&gt; [CMake] boost/1.72.0: WARN: Build folder is dirty, removing it: C:\.conan\34c708\1
  1&gt; [CMake] boost/1.72.0: WARN: Trying to remove corrupted source folder
  1&gt; [CMake] boost/1.72.0: WARN: This can take a while for big packages
  1&gt; [CMake] ERROR: boost/1.72.0: Error in source() method, line 151]
  ... snip: the additional errors already copied at the beginning of the post ...
  </code></pre>
  
  <p>So, my suspicion is that even the formerly working <code>boost/1.71.0@conan/stable</code> is being corrupted upon a fresh pull.</p>
  
  <p><em>Note: This happens when instructing Visual Studio to generate the CMake cache.</em></p>