hunter: support SuiteSparse-metis v7.5.1-1 without SuiteSparse::metis

Support the latest SuiteSparse-metis-for-windows `v7.5.1-1` release,
which doesn't provide the `SuiteSparse::metis` target anymore, as Metis
is now a private dependency of Cholmod.

Furthermore support finding `SuiteSparse-metis` with the non-Hunter
build, to use local dependencies with `-DSuiteSparse_DIR=...`.

Change-Id: I15dc9611efbd7ec7882773e92f4fa261c69bd669

CMakeLists.txt

@@ -314,11 +314,17 @@ if (SUITESPARSE)
   hunter_add_package(SuiteSparse)
   set(SuiteSparse_NO_CMAKE OFF) # don't install FindSuiteSparse and FindMetis
 
-  # Check for SuiteSparse and dependencies.
-  if (HUNTER_ENABLED)
-    find_package(SuiteSparse CONFIG)
+  # first try to find SuideSparse-metis config
+  find_package(SuiteSparse CONFIG)
+  if (SuiteSparse_FOUND AND TARGET SuiteSparse::cholmod)
+    set(SuiteSparse_metis ON)
     set(SuiteSparse_Partition_FOUND ON)
   else ()
+    set(SuiteSparse_metis OFF)
+    set(SuiteSparse_FOUND OFF) # try again with COMPONENTS
+  endif ()
+  # Check for SuiteSparse and dependencies.
+  if (NOT SuiteSparse_FOUND)
     find_package(SuiteSparse 4.5.6 COMPONENTS CHOLMOD SPQR
       OPTIONAL_COMPONENTS Partition)
   endif()

internal/ceres/CMakeLists.txt

@@ -100,7 +100,7 @@ endif (NOT MINIGLOG AND GLOG_FOUND)
 if (SUITESPARSE AND SuiteSparse_FOUND)
   # Define version information for use in Solver::FullReport.
   add_definitions(-DCERES_SUITESPARSE_VERSION="${SuiteSparse_VERSION}")
-  if (NOT HUNTER_ENABLED) # no indent to keep diffs small
+  if (NOT SuiteSparse_metis) # no indent to keep diffs small
   list(APPEND CERES_LIBRARY_PRIVATE_DEPENDENCIES SuiteSparse::CHOLMOD
     SuiteSparse::SPQR)
 
@@ -130,9 +130,16 @@ if (TARGET SuiteSparse::metis) # provided by SuiteSparse-metis-for-windows
   message(STATUS "Linking against 'SuiteSparse::metis' with version '${SuiteSparse_METIS_VERSION}'")
 else ()
 if (SuiteSparse_Partition_FOUND OR EIGENMETIS)
+  if ("${METIS_VERSION}" STREQUAL "")
+    # if none provided set a default version string
+    # this is the case for SuiteSparse-metis 7.5.1-1
+    set(METIS_VERSION "5.1.0")
+  endif()
   # Define version information for use in Solver::FullReport.
   add_definitions(-DCERES_METIS_VERSION="${METIS_VERSION}")
+  if (TARGET METIS::METIS) # no indent to keep changes small
   list(APPEND CERES_LIBRARY_PRIVATE_DEPENDENCIES METIS::METIS)
+  endif ()
 endif (SuiteSparse_Partition_FOUND OR EIGENMETIS)
 endif ()