Autodetect gflags namespace.

- At version 2.1, gflags changed from using the google namespace, to
  using gflags by default.  However, it can be configured at build time
  to be something else (which would be google for legacy compatibility
  unless you were evil).
- Ceres previously assumed that gflags was in the google namespace.
- Now, FindGFlags.cmake extracts the namespace when gflags.h is found
  and saves it in GFLAGS_NAMESPACE.
- When building the tests and examples that require gflags,
  CERES_GFLAGS_NAMESPACE is defined to be the detected namespace, and
  all tests/examples now use CERES_GFLAGS_NAMESPACE:: instead of
  google:: when calling gflags functions.

Change-Id: Ia333df7a7e2f08ba9f26bbd339c3a785b88f04c4

CMakeLists.txt

@@ -378,7 +378,8 @@ IF (GFLAGS)
   # Don't search with REQUIRED as we can continue without gflags.
   FIND_PACKAGE(Gflags)
   IF (GFLAGS_FOUND)
-    MESSAGE("-- Found Google Flags header in: ${GFLAGS_INCLUDE_DIRS}")
+    MESSAGE("-- Found Google Flags header in: ${GFLAGS_INCLUDE_DIRS}, "
+      "in namespace: ${GFLAGS_NAMESPACE}")
   ELSE (GFLAGS_FOUND)
     MESSAGE("-- Did not find Google Flags (gflags), Building without gflags "
       "- no tests or tools will be built!")

cmake/FindGflags.cmake

@@ -36,6 +36,11 @@
 # 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:
 #
@@ -67,6 +72,7 @@ MACRO(GFLAGS_REPORT_NOT_FOUND REASON_MSG)
   UNSET(GFLAGS_FOUND)
   UNSET(GFLAGS_INCLUDE_DIRS)
   UNSET(GFLAGS_LIBRARIES)
+  UNSET(GFLAGS_NAMESPACE)
   # 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
@@ -128,6 +134,46 @@ ENDIF (NOT GFLAGS_LIBRARY OR
 # if called.
 SET(GFLAGS_FOUND TRUE)
 
+# Identify what namespace gflags was built with.
+IF (GFLAGS_INCLUDE_DIR)
+  # First try the (older) google namespace.
+  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})
+  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)
+  ELSE (GFLAGS_IN_GOOGLE_NAMESPACE)
+    # Try (newer) gflags namespace instead.
+    #
+    # 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})
+    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)
+    ENDIF (GFLAGS_IN_GFLAGS_NAMESPACE)
+  ENDIF (GFLAGS_IN_GOOGLE_NAMESPACE)
+
+  IF (NOT GFLAGS_NAMESPACE)
+    GFLAGS_REPORT_NOT_FOUND(
+      "Failed to determine gflags namespace, it is not google or gflags.")
+  ENDIF (NOT GFLAGS_NAMESPACE)
+ENDIF (GFLAGS_INCLUDE_DIR)
+
 # gflags does not seem to provide any record of the version in its
 # source tree, thus cannot extract version.
 
@@ -162,11 +208,12 @@ ENDIF (GFLAGS_FOUND)
 # Handle REQUIRED / QUIET optional arguments.
 INCLUDE(FindPackageHandleStandardArgs)
 FIND_PACKAGE_HANDLE_STANDARD_ARGS(Gflags DEFAULT_MSG
-  GFLAGS_INCLUDE_DIRS GFLAGS_LIBRARIES)
+  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_LIBRARY
+                         GFLAGS_NAMESPACE)
 ENDIF (GFLAGS_FOUND)

examples/CMakeLists.txt

@@ -70,6 +70,11 @@ ADD_EXECUTABLE(simple_bundle_adjuster
 TARGET_LINK_LIBRARIES(simple_bundle_adjuster ceres)
 
 IF (GFLAGS)
+  # The CERES_GFLAGS_NAMESPACE compile definition is NOT stored in
+  # CERES_COMPILE_OPTIONS (and thus config.h) as Ceres itself does not
+  # require gflags, only the tests and examples do.
+  ADD_DEFINITIONS(-DCERES_GFLAGS_NAMESPACE=${GFLAGS_NAMESPACE})
+
   ADD_EXECUTABLE(powell powell.cc)
   TARGET_LINK_LIBRARIES(powell ceres ${GFLAGS_LIBRARIES})
 

examples/bundle_adjuster.cc

@@ -333,7 +333,7 @@ void SolveProblem(const char* filename) {
 }  // namespace ceres
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
   if (FLAGS_input.empty()) {
     LOG(ERROR) << "Usage: bundle_adjustment_example --input=bal_problem";

examples/circle_fit.cc

@@ -107,7 +107,7 @@ class DistanceFromCircleCost {
 };
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   double x, y, r;

examples/denoising.cc

@@ -176,8 +176,8 @@ int main(int argc, char** argv) {
       usage("This program denoises an image using Ceres.  Sample usage:\n");
   usage += argv[0];
   usage += " --input=<noisy image PGM file> --foe_file=<FoE file name>";
-  google::SetUsageMessage(usage);
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::SetUsageMessage(usage);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   if (FLAGS_input.empty()) {

examples/libmv_bundle_adjuster.cc

@@ -779,7 +779,7 @@ void EuclideanBundleCommonIntrinsics(const vector<Marker> &all_markers,
 }  // namespace
 
 int main(int argc, char **argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   if (FLAGS_input.empty()) {

examples/more_garbow_hillstrom.cc

@@ -337,7 +337,7 @@ template<typename TestProblem> string UnconstrainedSolve() {
 }  // namespace ceres
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   using ceres::examples::UnconstrainedSolve;

examples/nist.cc

@@ -566,7 +566,7 @@ void SolveNISTProblems() {
 }  // namespace ceres
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
   ceres::examples::SolveNISTProblems();
   return 0;

examples/powell.cc

@@ -99,7 +99,7 @@ DEFINE_string(minimizer, "trust_region",
               "Minimizer type to use, choices are: line_search & trust_region");
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   double x1 =  3.0;

examples/robot_pose_mle.cc

@@ -271,7 +271,7 @@ void PrintState(const vector<double>& odometry_readings,
 
 int main(int argc, char** argv) {
   google::InitGoogleLogging(argv[0]);
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   // Make sure that the arguments parsed are all positive.
   CHECK_GT(FLAGS_corridor_length, 0.0);
   CHECK_GT(FLAGS_pose_separation, 0.0);

internal/ceres/CMakeLists.txt

@@ -205,6 +205,11 @@ INSTALL(TARGETS ceres
         ARCHIVE DESTINATION lib${LIB_SUFFIX})
 
 IF (BUILD_TESTING AND GFLAGS)
+  # The CERES_GFLAGS_NAMESPACE compile definition is NOT stored in
+  # CERES_COMPILE_OPTIONS (and thus config.h) as Ceres itself does not
+  # require gflags, only the tests and examples do.
+  ADD_DEFINITIONS(-DCERES_GFLAGS_NAMESPACE=${GFLAGS_NAMESPACE})
+
   ADD_LIBRARY(gtest gmock_gtest_all.cc gmock_main.cc)
   ADD_LIBRARY(test_util
               evaluator_test_utils.cc

internal/ceres/gmock_main.cc

@@ -63,6 +63,6 @@ int main(int argc, char** argv) {
   // gflags, InitGoogleTest() (called by InitGoogleMock()) must be called
   // before ParseCommandLineFlags() to handle & remove them before gflags
   // parses the remaining flags.
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   return RUN_ALL_TESTS();
 }