Revert unchanged file.

cmake/FindGflags.cmake

+# Ceres Solver - A fast non-linear least squares minimizer
+# Copyright 2015 Google Inc. All rights reserved.
+# http://ceres-solver.org/
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# * Redistributions of source code must retain the above copyright notice,
+#   this list of conditions and the following disclaimer.
+# * Redistributions in binary form must reproduce the above copyright notice,
+#   this list of conditions and the following disclaimer in the documentation
+#   and/or other materials provided with the distribution.
+# * Neither the name of Google Inc. nor the names of its contributors may be
+#   used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+# Author: alexs.mac@gmail.com (Alex Stewart)
+#
+
+# FindGflags.cmake - Find Google gflags logging library.
+#
+# This module will attempt to find gflags, either via an exported CMake
+# configuration (generated by gflags >= 2.1 which are built with CMake), or
+# by performing a standard search for all gflags components.  The order of
+# precedence for these two methods of finding gflags is controlled by:
+# GFLAGS_PREFER_EXPORTED_GFLAGS_CMAKE_CONFIGURATION.
+#
+# This module defines the following variables:
+#
+# GFLAGS_FOUND: TRUE iff gflags is found.
+# GFLAGS_INCLUDE_DIRS: Include directories for gflags.
+# GFLAGS_LIBRARIES: Libraries required to link gflags.
+# GFLAGS_NAMESPACE: The namespace in which gflags is defined.  In versions of
+#                   gflags < 2.1, this was google, for versions >= 2.1 it is
+#                   by default gflags, although can be configured when building
+#                   gflags to be something else (i.e. google for legacy
+#                   compatibility).
+#
+# The following variables control the behaviour of this module when an exported
+# gflags CMake configuration is not found.
+#
+# GFLAGS_PREFER_EXPORTED_GFLAGS_CMAKE_CONFIGURATION: TRUE/FALSE, iff TRUE then
+#                           then prefer using an exported CMake configuration
+#                           generated by gflags >= 2.1 over searching for the
+#                           gflags components manually.  Otherwise (FALSE)
+#                           ignore any exported gflags CMake configurations and
+#                           always perform a manual search for the components.
+#                           Default: TRUE iff user does not define this variable
+#                           before we are called, and does NOT specify either
+#                           GFLAGS_INCLUDE_DIR_HINTS or GFLAGS_LIBRARY_DIR_HINTS
+#                           otherwise FALSE.
+# GFLAGS_INCLUDE_DIR_HINTS: List of additional directories in which to
+#                           search for gflags includes, e.g: /timbuktu/include.
+# GFLAGS_LIBRARY_DIR_HINTS: List of additional directories in which to
+#                           search for gflags libraries, e.g: /timbuktu/lib.
+#
+# The following variables are also defined by this module, but in line with
+# CMake recommended FindPackage() module style should NOT be referenced directly
+# by callers (use the plural variables detailed above instead).  These variables
+# do however affect the behaviour of the module via FIND_[PATH/LIBRARY]() which
+# are NOT re-called (i.e. search for library is not repeated) if these variables
+# are set with valid values _in the CMake cache_. This means that if these
+# variables are set directly in the cache, either by the user in the CMake GUI,
+# or by the user passing -DVAR=VALUE directives to CMake when called (which
+# explicitly defines a cache variable), then they will be used verbatim,
+# bypassing the HINTS variables and other hard-coded search locations.
+#
+# GFLAGS_INCLUDE_DIR: Include directory for gflags, not including the
+#                     include directory of any dependencies.
+# GFLAGS_LIBRARY: gflags library, not including the libraries of any
+#                 dependencies.
+
+# Reset CALLERS_CMAKE_FIND_LIBRARY_PREFIXES to its value when FindGflags was
+# invoked, necessary for MSVC.
+macro(GFLAGS_RESET_FIND_LIBRARY_PREFIX)
+  if (MSVC)
+    set(CMAKE_FIND_LIBRARY_PREFIXES "${CALLERS_CMAKE_FIND_LIBRARY_PREFIXES}")
+  endif (MSVC)
+endmacro(GFLAGS_RESET_FIND_LIBRARY_PREFIX)
+
+# Called if we failed to find gflags or any of it's required dependencies,
+# unsets all public (designed to be used externally) variables and reports
+# error message at priority depending upon [REQUIRED/QUIET/<NONE>] argument.
+macro(GFLAGS_REPORT_NOT_FOUND REASON_MSG)
+  unset(GFLAGS_FOUND)
+  unset(GFLAGS_INCLUDE_DIRS)
+  unset(GFLAGS_LIBRARIES)
+  # Do not use unset, as we want to keep GFLAGS_NAMESPACE in the cache,
+  # but simply clear its value.
+  set(GFLAGS_NAMESPACE "" CACHE STRING
+    "gflags namespace (google or gflags)" FORCE)
+
+  # Make results of search visible in the CMake GUI if gflags has not
+  # been found so that user does not have to toggle to advanced view.
+  mark_as_advanced(CLEAR GFLAGS_INCLUDE_DIR
+                         GFLAGS_LIBRARY
+                         GFLAGS_NAMESPACE)
+
+  gflags_reset_find_library_prefix()
+
+  # Note <package>_FIND_[REQUIRED/QUIETLY] variables defined by FindPackage()
+  # use the camelcase library name, not uppercase.
+  if (Gflags_FIND_QUIETLY)
+    message(STATUS "Failed to find gflags - " ${REASON_MSG} ${ARGN})
+  elseif (Gflags_FIND_REQUIRED)
+    message(FATAL_ERROR "Failed to find gflags - " ${REASON_MSG} ${ARGN})
+  else()
+    # Neither QUIETLY nor REQUIRED, use no priority which emits a message
+    # but continues configuration and allows generation.
+    message("-- Failed to find gflags - " ${REASON_MSG} ${ARGN})
+  endif ()
+  return()
+endmacro(GFLAGS_REPORT_NOT_FOUND)
+
+# Verify that all variable names passed as arguments are defined (can be empty
+# but must be defined) or raise a fatal error.
+macro(GFLAGS_CHECK_VARS_DEFINED)
+  foreach(CHECK_VAR ${ARGN})
+    if (NOT DEFINED ${CHECK_VAR})
+      message(FATAL_ERROR "Ceres Bug: ${CHECK_VAR} is not defined.")
+    endif()
+  endforeach()
+endmacro(GFLAGS_CHECK_VARS_DEFINED)
+
+# Use check_cxx_source_compiles() to compile trivial test programs to determine
+# the gflags namespace.  This works on all OSs except Windows.  If using Visual
+# Studio, it fails because msbuild forces check_cxx_source_compiles() to use
+# CMAKE_BUILD_TYPE=Debug for the test project, which usually breaks detection
+# because MSVC requires that the test project use the same build type as gflags,
+# which would normally be built in Release.
+#
+# Defines: GFLAGS_NAMESPACE in the caller's scope with the detected namespace,
+#          which is blank (empty string, will test FALSE is CMake conditionals)
+#          if detection failed.
+function(GFLAGS_CHECK_GFLAGS_NAMESPACE_USING_TRY_COMPILE)
+  # Verify that all required variables are defined.
+  gflags_check_vars_defined(
+    GFLAGS_INCLUDE_DIR GFLAGS_LIBRARY)
+  # Ensure that GFLAGS_NAMESPACE is always unset on completion unless
+  # we explicitly set if after having the correct namespace.
+  set(GFLAGS_NAMESPACE "" PARENT_SCOPE)
+
+  include(CheckCXXSourceCompiles)
+  # Setup include path & link library for gflags for CHECK_CXX_SOURCE_COMPILES.
+  set(CMAKE_REQUIRED_INCLUDES ${GFLAGS_INCLUDE_DIR})
+  set(CMAKE_REQUIRED_LIBRARIES ${GFLAGS_LIBRARY} ${GFLAGS_LINK_LIBRARIES})
+  # First try the (older) google namespace.  Note that the output variable
+  # MUST be unique to the build type as otherwise the test is not repeated as
+  # it is assumed to have already been performed.
+  check_cxx_source_compiles(
+    "#include <gflags/gflags.h>
+     int main(int argc, char * argv[]) {
+       google::ParseCommandLineFlags(&argc, &argv, true);
+       return 0;
+     }"
+     GFLAGS_IN_GOOGLE_NAMESPACE)
+  if (GFLAGS_IN_GOOGLE_NAMESPACE)
+    set(GFLAGS_NAMESPACE google PARENT_SCOPE)
+    return()
+  endif()
+
+  # Try (newer) gflags namespace instead.  Note that the output variable
+  # MUST be unique to the build type as otherwise the test is not repeated as
+  # it is assumed to have already been performed.
+  set(CMAKE_REQUIRED_INCLUDES ${GFLAGS_INCLUDE_DIR})
+  set(CMAKE_REQUIRED_LIBRARIES ${GFLAGS_LIBRARY} ${GFLAGS_LINK_LIBRARIES})
+  check_cxx_source_compiles(
+    "#include <gflags/gflags.h>
+     int main(int argc, char * argv[]) {
+        gflags::ParseCommandLineFlags(&argc, &argv, true);
+        return 0;
+     }"
+     GFLAGS_IN_GFLAGS_NAMESPACE)
+  if (GFLAGS_IN_GFLAGS_NAMESPACE)
+    set(GFLAGS_NAMESPACE gflags PARENT_SCOPE)
+    return()
+  endif (GFLAGS_IN_GFLAGS_NAMESPACE)
+endfunction(GFLAGS_CHECK_GFLAGS_NAMESPACE_USING_TRY_COMPILE)
+
+# Use regex on the gflags headers to attempt to determine the gflags namespace.
+# Checks both gflags.h (contained namespace on versions < 2.1.2) and
+# gflags_declare.h, which contains the namespace on versions >= 2.1.2.
+# In general, this method should only be used when
+# GFLAGS_CHECK_GFLAGS_NAMESPACE_USING_TRY_COMPILE() cannot be used, or has
+# failed.
+#
+# Defines: GFLAGS_NAMESPACE in the caller's scope with the detected namespace,
+#          which is blank (empty string, will test FALSE is CMake conditionals)
+#          if detection failed.
+function(GFLAGS_CHECK_GFLAGS_NAMESPACE_USING_REGEX)
+  # Verify that all required variables are defined.
+  gflags_check_vars_defined(GFLAGS_INCLUDE_DIR)
+  # Ensure that GFLAGS_NAMESPACE is always undefined on completion unless
+  # we explicitly set if after having the correct namespace.
+  set(GFLAGS_NAMESPACE "" PARENT_SCOPE)
+
+  # Scan gflags.h to identify what namespace gflags was built with.  On
+  # versions of gflags < 2.1.2, gflags.h was configured with the namespace
+  # directly, on >= 2.1.2, gflags.h uses the GFLAGS_NAMESPACE #define which
+  # is defined in gflags_declare.h, we try each location in turn.
+  set(GFLAGS_HEADER_FILE ${GFLAGS_INCLUDE_DIR}/gflags/gflags.h)
+  if (NOT EXISTS ${GFLAGS_HEADER_FILE})
+    gflags_report_not_found(
+      "Could not find file: ${GFLAGS_HEADER_FILE} "
+      "containing namespace information in gflags install located at: "
+      "${GFLAGS_INCLUDE_DIR}.")
+  endif()
+  file(READ ${GFLAGS_HEADER_FILE} GFLAGS_HEADER_FILE_CONTENTS)
+
+  string(REGEX MATCH "namespace [A-Za-z]+"
+    GFLAGS_NAMESPACE "${GFLAGS_HEADER_FILE_CONTENTS}")
+  string(REGEX REPLACE "namespace ([A-Za-z]+)" "\\1"
+    GFLAGS_NAMESPACE "${GFLAGS_NAMESPACE}")
+
+  if (NOT GFLAGS_NAMESPACE)
+    gflags_report_not_found(
+      "Failed to extract gflags namespace from header file: "
+      "${GFLAGS_HEADER_FILE}.")
+  endif (NOT GFLAGS_NAMESPACE)
+
+  if (GFLAGS_NAMESPACE STREQUAL "google" OR
+      GFLAGS_NAMESPACE STREQUAL "gflags")
+    # Found valid gflags namespace from gflags.h.
+    set(GFLAGS_NAMESPACE "${GFLAGS_NAMESPACE}" PARENT_SCOPE)
+    return()
+  endif()
+
+  # Failed to find gflags namespace from gflags.h, gflags is likely a new
+  # version, check gflags_declare.h, which in newer versions (>= 2.1.2) contains
+  # the GFLAGS_NAMESPACE #define, which is then referenced in gflags.h.
+  set(GFLAGS_DECLARE_FILE ${GFLAGS_INCLUDE_DIR}/gflags/gflags_declare.h)
+  if (NOT EXISTS ${GFLAGS_DECLARE_FILE})
+    gflags_report_not_found(
+      "Could not find file: ${GFLAGS_DECLARE_FILE} "
+      "containing namespace information in gflags install located at: "
+      "${GFLAGS_INCLUDE_DIR}.")
+  endif()
+  file(READ ${GFLAGS_DECLARE_FILE} GFLAGS_DECLARE_FILE_CONTENTS)
+
+  string(REGEX MATCH "#define GFLAGS_NAMESPACE [A-Za-z]+"
+    GFLAGS_NAMESPACE "${GFLAGS_DECLARE_FILE_CONTENTS}")
+  string(REGEX REPLACE "#define GFLAGS_NAMESPACE ([A-Za-z]+)" "\\1"
+    GFLAGS_NAMESPACE "${GFLAGS_NAMESPACE}")
+
+  if (NOT GFLAGS_NAMESPACE)
+    gflags_report_not_found(
+      "Failed to extract gflags namespace from declare file: "
+      "${GFLAGS_DECLARE_FILE}.")
+  endif (NOT GFLAGS_NAMESPACE)
+
+  if (GFLAGS_NAMESPACE STREQUAL "google" OR
+      GFLAGS_NAMESPACE STREQUAL "gflags")
+    # Found valid gflags namespace from gflags.h.
+    set(GFLAGS_NAMESPACE "${GFLAGS_NAMESPACE}" PARENT_SCOPE)
+    return()
+  endif()
+endfunction(GFLAGS_CHECK_GFLAGS_NAMESPACE_USING_REGEX)
+
+# -----------------------------------------------------------------
+# By default, if the user has expressed no preference for using an exported
+# gflags CMake configuration over performing a search for the installed
+# components, and has not specified any hints for the search locations, then
+# prefer a gflags exported configuration if available.
+if (NOT DEFINED GFLAGS_PREFER_EXPORTED_GFLAGS_CMAKE_CONFIGURATION
+    AND NOT GFLAGS_INCLUDE_DIR_HINTS
+    AND NOT GFLAGS_LIBRARY_DIR_HINTS)
+  message(STATUS "No preference for use of exported gflags CMake configuration "
+    "set, and no hints for include/library directories provided. "
+    "Defaulting to preferring an installed/exported gflags CMake configuration "
+    "if available.")
+  set(GFLAGS_PREFER_EXPORTED_GFLAGS_CMAKE_CONFIGURATION TRUE)
+endif()
+
+if (GFLAGS_PREFER_EXPORTED_GFLAGS_CMAKE_CONFIGURATION)
+  # Try to find an exported CMake configuration for gflags, as generated by
+  # gflags versions >= 2.1.
+  #
+  # We search twice, s/t we can invert the ordering of precedence used by
+  # find_package() for exported package build directories, and installed
+  # packages (found via CMAKE_SYSTEM_PREFIX_PATH), listed as items 6) and 7)
+  # respectively in [1].
+  #
+  # By default, exported build directories are (in theory) detected first, and
+  # this is usually the case on Windows.  However, on OS X & Linux, the install
+  # path (/usr/local) is typically present in the PATH environment variable
+  # which is checked in item 4) in [1] (i.e. before both of the above, unless
+  # NO_SYSTEM_ENVIRONMENT_PATH is passed).  As such on those OSs installed
+  # packages are usually detected in preference to exported package build
+  # directories.
+  #
+  # To ensure a more consistent response across all OSs, and as users usually
+  # want to prefer an installed version of a package over a locally built one
+  # where both exist (esp. as the exported build directory might be removed
+  # after installation), we first search with NO_CMAKE_PACKAGE_REGISTRY which
+  # means any build directories exported by the user are ignored, and thus
+  # installed directories are preferred.  If this fails to find the package
+  # we then research again, but without NO_CMAKE_PACKAGE_REGISTRY, so any
+  # exported build directories will now be detected.
+  #
+  # To prevent confusion on Windows, we also pass NO_CMAKE_BUILDS_PATH (which
+  # is item 5) in [1]), to not preferentially use projects that were built
+  # recently with the CMake GUI to ensure that we always prefer an installed
+  # version if available.
+  #
+  # [1] http://www.cmake.org/cmake/help/v2.8.11/cmake.html#command:find_package
+  find_package(gflags QUIET
+                      NO_MODULE
+                      NO_CMAKE_PACKAGE_REGISTRY
+                      NO_CMAKE_BUILDS_PATH)
+  if (gflags_FOUND)
+    message(STATUS "Found installed version of gflags: ${gflags_DIR}")
+  else(gflags_FOUND)
+    # Failed to find an installed version of gflags, repeat search allowing
+    # exported build directories.
+    message(STATUS "Failed to find installed gflags CMake configuration, "
+      "searching for gflags build directories exported with CMake.")
+    # Again pass NO_CMAKE_BUILDS_PATH, as we know that gflags is exported and
+    # do not want to treat projects built with the CMake GUI preferentially.
+    find_package(gflags QUIET
+                        NO_MODULE
+                        NO_CMAKE_BUILDS_PATH)
+    if (gflags_FOUND)
+      message(STATUS "Found exported gflags build directory: ${gflags_DIR}")
+    endif(gflags_FOUND)
+  endif(gflags_FOUND)
+
+  set(FOUND_INSTALLED_GFLAGS_CMAKE_CONFIGURATION ${gflags_FOUND})
+
+  # gflags v2.1 - 2.1.2 shipped with a bug in their gflags-config.cmake [1]
+  # whereby gflags_LIBRARIES = "gflags", but there was no imported target
+  # called "gflags", they were called: gflags[_nothreads]-[static/shared].
+  # As this causes linker errors when gflags is not installed in a location
+  # on the current library paths, detect if this problem is present and
+  # fix it.
+  #
+  # [1] https://github.com/gflags/gflags/issues/110
+  if (gflags_FOUND)
+    # NOTE: This is not written as additional conditions in the outer
+    #       if (gflags_FOUND) as the NOT TARGET "${gflags_LIBRARIES}"
+    #       condition causes problems if gflags is not found.
+    if (${gflags_VERSION} VERSION_LESS 2.1.3 AND
+        NOT TARGET "${gflags_LIBRARIES}")
+      message(STATUS "Detected broken gflags install in: ${gflags_DIR}, "
+        "version: ${gflags_VERSION} <= 2.1.2 which defines gflags_LIBRARIES = "
+        "${gflags_LIBRARIES} which is not an imported CMake target, see: "
+        "https://github.com/gflags/gflags/issues/110.  Attempting to fix by "
+        "detecting correct gflags target.")
+      # Ordering here expresses preference for detection, specifically we do not
+      # want to use the _nothreads variants if the full library is available.
+      list(APPEND CHECK_GFLAGS_IMPORTED_TARGET_NAMES
+        gflags-shared gflags-static
+        gflags_nothreads-shared gflags_nothreads-static)
+      foreach(CHECK_GFLAGS_TARGET ${CHECK_GFLAGS_IMPORTED_TARGET_NAMES})
+        if (TARGET ${CHECK_GFLAGS_TARGET})
+          message(STATUS "Found valid gflags target: ${CHECK_GFLAGS_TARGET}, "
+            "updating gflags_LIBRARIES.")
+          set(gflags_LIBRARIES ${CHECK_GFLAGS_TARGET})
+          break()
+        endif()
+      endforeach()
+      if (NOT TARGET ${gflags_LIBRARIES})
+        message(STATUS "Failed to fix detected broken gflags install in: "
+          "${gflags_DIR}, version: ${gflags_VERSION} <= 2.1.2, none of the "
+          "imported targets for gflags: ${CHECK_GFLAGS_IMPORTED_TARGET_NAMES} "
+          "are defined.  Will continue with a manual search for gflags "
+          "components.  We recommend you build/install a version of gflags > "
+          "2.1.2 (or master).")
+        set(FOUND_INSTALLED_GFLAGS_CMAKE_CONFIGURATION FALSE)
+      endif()
+    endif()
+  endif()
+
+  if (FOUND_INSTALLED_GFLAGS_CMAKE_CONFIGURATION)
+    message(STATUS "Detected gflags version: ${gflags_VERSION}")
+    set(GFLAGS_FOUND ${gflags_FOUND})
+    set(GFLAGS_INCLUDE_DIR ${gflags_INCLUDE_DIR})
+    set(GFLAGS_LIBRARY ${gflags_LIBRARIES})
+
+    # gflags does not export the namespace in their CMake configuration, so
+    # use our function to determine what it should be, as it can be either
+    # gflags or google dependent upon version & configuration.
+    #
+    # NOTE: We use the regex method to determine the namespace here, as
+    #       check_cxx_source_compiles() will not use imported targets, which
+    #       is what gflags will be in this case.
+    gflags_check_gflags_namespace_using_regex()
+
+    if (NOT GFLAGS_NAMESPACE)
+      gflags_report_not_found(
+        "Failed to determine gflags namespace using regex for gflags "
+        "version: ${gflags_VERSION} exported here: ${gflags_DIR} using CMake.")
+    endif (NOT GFLAGS_NAMESPACE)
+  else (FOUND_INSTALLED_GFLAGS_CMAKE_CONFIGURATION)
+    message(STATUS "Failed to find an installed/exported CMake configuration "
+      "for gflags, will perform search for installed gflags components.")
+  endif (FOUND_INSTALLED_GFLAGS_CMAKE_CONFIGURATION)
+endif(GFLAGS_PREFER_EXPORTED_GFLAGS_CMAKE_CONFIGURATION)
+
+if (NOT GFLAGS_FOUND)
+  # Either failed to find an exported gflags CMake configuration, or user
+  # told us not to use one.  Perform a manual search for all gflags components.
+
+  # Handle possible presence of lib prefix for libraries on MSVC, see
+  # also GFLAGS_RESET_FIND_LIBRARY_PREFIX().
+  if (MSVC)
+    # Preserve the caller's original values for CMAKE_FIND_LIBRARY_PREFIXES
+    # s/t we can set it back before returning.
+    set(CALLERS_CMAKE_FIND_LIBRARY_PREFIXES "${CMAKE_FIND_LIBRARY_PREFIXES}")
+    # The empty string in this list is important, it represents the case when
+    # the libraries have no prefix (shared libraries / DLLs).
+    set(CMAKE_FIND_LIBRARY_PREFIXES "lib" "" "${CMAKE_FIND_LIBRARY_PREFIXES}")
+  endif (MSVC)
+
+  # Search user-installed locations first, so that we prefer user installs
+  # to system installs where both exist.
+  list(APPEND GFLAGS_CHECK_INCLUDE_DIRS
+    /usr/local/include
+    /usr/local/homebrew/include # Mac OS X
+    /opt/local/var/macports/software # Mac OS X.
+    /opt/local/include
+    /usr/include)
+  list(APPEND GFLAGS_CHECK_PATH_SUFFIXES
+    gflags/include # Windows (for C:/Program Files prefix).
+    gflags/Include ) # Windows (for C:/Program Files prefix).
+
+  list(APPEND GFLAGS_CHECK_LIBRARY_DIRS
+    /usr/local/lib
+    /usr/local/homebrew/lib # Mac OS X.
+    /opt/local/lib
+    /usr/lib)
+  list(APPEND GFLAGS_CHECK_LIBRARY_SUFFIXES
+    gflags/lib # Windows (for C:/Program Files prefix).
+    gflags/Lib ) # Windows (for C:/Program Files prefix).
+
+  # Search supplied hint directories first if supplied.
+  find_path(GFLAGS_INCLUDE_DIR
+    NAMES gflags/gflags.h
+    PATHS ${GFLAGS_INCLUDE_DIR_HINTS}
+    ${GFLAGS_CHECK_INCLUDE_DIRS}
+    PATH_SUFFIXES ${GFLAGS_CHECK_PATH_SUFFIXES})
+  if (NOT GFLAGS_INCLUDE_DIR OR
+      NOT EXISTS ${GFLAGS_INCLUDE_DIR})
+    gflags_report_not_found(
+      "Could not find gflags include directory, set GFLAGS_INCLUDE_DIR "
+      "to directory containing gflags/gflags.h")
+  endif (NOT GFLAGS_INCLUDE_DIR OR
+    NOT EXISTS ${GFLAGS_INCLUDE_DIR})
+
+  find_library(GFLAGS_LIBRARY NAMES gflags
+    PATHS ${GFLAGS_LIBRARY_DIR_HINTS}
+    ${GFLAGS_CHECK_LIBRARY_DIRS}
+    PATH_SUFFIXES ${GFLAGS_CHECK_LIBRARY_SUFFIXES})
+  if (NOT GFLAGS_LIBRARY OR
+      NOT EXISTS ${GFLAGS_LIBRARY})
+    gflags_report_not_found(
+      "Could not find gflags library, set GFLAGS_LIBRARY "
+      "to full path to libgflags.")
+  endif (NOT GFLAGS_LIBRARY OR
+    NOT EXISTS ${GFLAGS_LIBRARY})
+
+  # gflags typically requires a threading library (which is OS dependent), note
+  # that this defines the CMAKE_THREAD_LIBS_INIT variable.  If we are able to
+  # detect threads, we assume that gflags requires it.
+  find_package(Threads QUIET)
+  set(GFLAGS_LINK_LIBRARIES ${CMAKE_THREAD_LIBS_INIT})
+  # On Windows (including MinGW), the Shlwapi library is used by gflags if
+  # available.
+  if (WIN32)
+    include(CheckIncludeFileCXX)
+    check_include_file_cxx("shlwapi.h" HAVE_SHLWAPI)
+    if (HAVE_SHLWAPI)
+      list(APPEND GFLAGS_LINK_LIBRARIES shlwapi.lib)
+    endif(HAVE_SHLWAPI)
+  endif (WIN32)
+
+  # Mark internally as found, then verify. GFLAGS_REPORT_NOT_FOUND() unsets
+  # if called.
+  set(GFLAGS_FOUND TRUE)
+
+  # Identify what namespace gflags was built with.
+  if (GFLAGS_INCLUDE_DIR AND NOT GFLAGS_NAMESPACE)
+    # To handle Windows peculiarities / CMake bugs on MSVC we try two approaches
+    # to detect the gflags namespace:
+    #
+    # 1) Try to use check_cxx_source_compiles() to compile a trivial program
+    #    with the two choices for the gflags namespace.
+    #
+    # 2) [In the event 1) fails] Use regex on the gflags headers to try to
+    #    determine the gflags namespace.  Whilst this is less robust than 1),
+    #    it does avoid any interaction with msbuild.
+    gflags_check_gflags_namespace_using_try_compile()
+
+    if (NOT GFLAGS_NAMESPACE)
+      # Failed to determine gflags namespace using check_cxx_source_compiles()
+      # method, try and obtain it using regex on the gflags headers instead.
+      message(STATUS "Failed to find gflags namespace using using "
+        "check_cxx_source_compiles(), trying namespace regex instead, "
+        "this is expected on Windows.")
+      gflags_check_gflags_namespace_using_regex()
+
+      if (NOT GFLAGS_NAMESPACE)
+        gflags_report_not_found(
+          "Failed to determine gflags namespace either by "
+          "check_cxx_source_compiles(), or namespace regex.")
+      endif (NOT GFLAGS_NAMESPACE)
+    endif (NOT GFLAGS_NAMESPACE)
+  endif (GFLAGS_INCLUDE_DIR AND NOT GFLAGS_NAMESPACE)
+
+  # Make the GFLAGS_NAMESPACE a cache variable s/t the user can view it, and could
+  # overwrite it in the CMake GUI.
+  set(GFLAGS_NAMESPACE "${GFLAGS_NAMESPACE}" CACHE STRING
+    "gflags namespace (google or gflags)" FORCE)
+
+  # gflags does not seem to provide any record of the version in its
+  # source tree, thus cannot extract version.
+
+  # Catch case when caller has set GFLAGS_NAMESPACE in the cache / GUI
+  # with an invalid value.
+  if (GFLAGS_NAMESPACE AND
+      NOT GFLAGS_NAMESPACE STREQUAL "google" AND
+      NOT GFLAGS_NAMESPACE STREQUAL "gflags")
+    gflags_report_not_found(
+      "Caller defined GFLAGS_NAMESPACE:"
+      " ${GFLAGS_NAMESPACE} is not valid, not google or gflags.")
+  endif ()
+  # Catch case when caller has set GFLAGS_INCLUDE_DIR in the cache / GUI and
+  # thus FIND_[PATH/LIBRARY] are not called, but specified locations are
+  # invalid, otherwise we would report the library as found.
+  if (GFLAGS_INCLUDE_DIR AND
+      NOT EXISTS ${GFLAGS_INCLUDE_DIR}/gflags/gflags.h)
+    gflags_report_not_found(
+      "Caller defined GFLAGS_INCLUDE_DIR:"
+      " ${GFLAGS_INCLUDE_DIR} does not contain gflags/gflags.h header.")
+  endif (GFLAGS_INCLUDE_DIR AND
+    NOT EXISTS ${GFLAGS_INCLUDE_DIR}/gflags/gflags.h)
+  # TODO: This regex for gflags library is pretty primitive, we use lowercase
+  #       for comparison to handle Windows using CamelCase library names, could
+  #       this check be better?
+  string(TOLOWER "${GFLAGS_LIBRARY}" LOWERCASE_GFLAGS_LIBRARY)
+  if (GFLAGS_LIBRARY AND
+      NOT "${LOWERCASE_GFLAGS_LIBRARY}" MATCHES ".*gflags[^/]*")
+    gflags_report_not_found(
+      "Caller defined GFLAGS_LIBRARY: "
+      "${GFLAGS_LIBRARY} does not match gflags.")
+  endif (GFLAGS_LIBRARY AND
+    NOT "${LOWERCASE_GFLAGS_LIBRARY}" MATCHES ".*gflags[^/]*")
+
+  gflags_reset_find_library_prefix()
+
+endif(NOT GFLAGS_FOUND)
+
+# Set standard CMake FindPackage variables if found.
+if (GFLAGS_FOUND)
+  set(GFLAGS_INCLUDE_DIRS ${GFLAGS_INCLUDE_DIR})
+  set(GFLAGS_LIBRARIES ${GFLAGS_LIBRARY} ${GFLAGS_LINK_LIBRARIES})
+endif (GFLAGS_FOUND)
+
+# Handle REQUIRED / QUIET optional arguments.
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(Gflags DEFAULT_MSG
+  GFLAGS_INCLUDE_DIRS GFLAGS_LIBRARIES GFLAGS_NAMESPACE)
+
+# Only mark internal variables as advanced if we found gflags, otherwise
+# leave them visible in the standard GUI for the user to set manually.
+if (GFLAGS_FOUND)
+  mark_as_advanced(FORCE GFLAGS_INCLUDE_DIR
+    GFLAGS_LIBRARY
+    GFLAGS_NAMESPACE
+    gflags_DIR) # Autogenerated by find_package(gflags)
+endif (GFLAGS_FOUND)