ExternalProject: add support for just downloading a file

Some projects only ship self-extracting installers rather than
compressed archives. Add a flag so that these files may be used in
ExternalProject.

Help/release/dev/external-project-no-extract.rst

@@ -0,0 +1,6 @@
+external-project-no-extract
+---------------------------
+
+* The :module:`ExternalProject` module leared the ``DOWNLOAD_NO_EXTRACT 1``
+  argument to skip extracting the file that is downloaded (e.g., for
+  self-extracting shell installers or ``.msi`` files).

Modules/ExternalProject.cmake

@@ -77,6 +77,9 @@ Create custom targets to build projects in external trees
     Path to a certificate authority file
   ``TIMEOUT <seconds>``
     Time allowed for file download operations
+  ``DOWNLOAD_NO_EXTRACT 1``
+    Just download the file and do not extract it; the full path to the
+    downloaded file is available as ``<DOWNLOADED_FILE>``.
 
   Update/Patch step options are:
 
@@ -1107,7 +1110,7 @@ macro(_ep_replace_location_tags target_name)
   set(vars ${ARGN})
   foreach(var ${vars})
     if(${var})
-      foreach(dir SOURCE_DIR BINARY_DIR INSTALL_DIR TMP_DIR)
+      foreach(dir SOURCE_DIR BINARY_DIR INSTALL_DIR TMP_DIR DOWNLOADED_FILE)
         get_property(val TARGET ${target_name} PROPERTY _EP_${dir})
         string(REPLACE "<${dir}>" "${val}" ${var} "${${var}}")
       endforeach()
@@ -1875,6 +1878,7 @@ function(_ep_add_download_command name)
       set(cmd   ${CMAKE_COMMAND} -E remove_directory ${source_dir}
         COMMAND ${CMAKE_COMMAND} -E copy_directory ${abs_dir} ${source_dir})
     else()
+      get_property(no_extract TARGET "${name}" PROPERTY _EP_DOWNLOAD_NO_EXTRACT SET)
       if("${url}" MATCHES "^[a-z]+://")
         # TODO: Should download and extraction be different steps?
         if("x${fname}" STREQUAL "x")
@@ -1884,7 +1888,9 @@ function(_ep_add_download_command name)
           string(REGEX MATCH "([^/\\?]+(\\.|=)(7z|tar|tar\\.bz2|tar\\.gz|tar\\.xz|tbz2|tgz|txz|zip))/.*$" match_result "${url}")
           set(fname "${CMAKE_MATCH_1}")
         endif()
-        if(NOT "${fname}" MATCHES "(\\.|=)(7z|tar|tar\\.bz2|tar\\.gz|tar\\.xz|tbz2|tgz|txz|zip)$")
+        if (no_extract)
+          get_filename_component(fname "${url}" NAME)
+        elseif(NOT "${fname}" MATCHES "(\\.|=)(7z|tar|tar\\.bz2|tar\\.gz|tar\\.xz|tbz2|tgz|txz|zip)$")
           message(FATAL_ERROR "Could not extract tarball filename from url:\n  ${url}")
         endif()
         string(REPLACE ";" "-" fname "${fname}")
@@ -1898,16 +1904,30 @@ function(_ep_add_download_command name)
         set(cmd ${CMAKE_COMMAND} -P "${download_script}"
           COMMAND)
         set(retries 3)
-        set(comment "Performing download step (download, verify and extract) for '${name}'")
+        if (no_extract)
+          set(steps "download and verify")
+        else ()
+          set(steps "download, verify and extract")
+        endif ()
+        set(comment "Performing download step (${steps}) for '${name}'")
       else()
         set(file "${url}")
-        set(comment "Performing download step (verify and extract) for '${name}'")
+        if (no_extract)
+          set(steps "verify")
+        else ()
+          set(steps "verify and extract")
+        endif ()
+        set(comment "Performing download step (${steps}) for '${name}'")
       endif()
       _ep_write_verifyfile_script("${stamp_dir}/verify-${name}.cmake" "${file}" "${hash}" "${retries}" "${download_script}")
       list(APPEND cmd ${CMAKE_COMMAND} -P ${stamp_dir}/verify-${name}.cmake
         COMMAND)
-      _ep_write_extractfile_script("${stamp_dir}/extract-${name}.cmake" "${name}" "${file}" "${source_dir}")
+      if (NOT no_extract)
-      list(APPEND cmd ${CMAKE_COMMAND} -P ${stamp_dir}/extract-${name}.cmake)
+        _ep_write_extractfile_script("${stamp_dir}/extract-${name}.cmake" "${name}" "${file}" "${source_dir}")
+        list(APPEND cmd ${CMAKE_COMMAND} -P ${stamp_dir}/extract-${name}.cmake)
+      else ()
+        set_property(TARGET ${name} PROPERTY _EP_DOWNLOADED_FILE ${file})
+      endif ()
     endif()
   else()
     _ep_is_dir_empty("${source_dir}" empty)