[CMake] Check for required ccache config.

CMakeLists.txt

@@ -34,6 +34,7 @@ include(scripts/cmake/Functions.cmake)
 include(scripts/cmake/CMakeSetup.cmake)
 include(scripts/cmake/CompilerSetup.cmake)
 include(scripts/cmake/Find.cmake)
+include(scripts/cmake/CCacheSetup.cmake)
 include(scripts/cmake/SubmoduleSetup.cmake)
 include(scripts/cmake/ProjectSetup.cmake)
 include(scripts/cmake/DocumentationSetup.cmake)

scripts/cmake/CCacheSetup.cmake

+if(NOT CCACHE_TOOL_PATH)
+    return()
+endif()
+
+# Set ccache as the compiler launcher
+set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache)
+set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK ccache)
+
+if(COMPILER_IS_CLANG)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Qunused-arguments")
+endif()
+
+# Check ccache pre-compiled headers config
+execute_process(COMMAND ${CCACHE_TOOL_PATH} --print-config
+    OUTPUT_VARIABLE CCACHE_CONFIG
+    ERROR_VARIABLE CCACHE_CONFIG
+)
+
+# Regex should be "sloppiness.*time_macros.*pch_defines.*" but due to bug fixed
+# in https://ccache.samba.org/releasenotes.html#_ccache_3_2_5 we have to leave
+# out pch_defines. Ubuntu 16.04 comes with ccache 3.2.4 ...
+string(REGEX MATCH "sloppiness.*time_macros.*"
+    COTIRE_CCACHE_CONFIG ${CCACHE_CONFIG}
+)
+
+if(NOT COTIRE_CCACHE_CONFIG)
+    message(FATAL_ERROR "CCache not configured! You must set sloppiness to pch_defines,time_macros. See https://docs.opengeosys.org/docs/devguide/advanced/using-ccache")
+endif()

scripts/cmake/Find.cmake

@@ -54,15 +54,7 @@ find_program(CURL_TOOL_PATH curl DOC "The curl-tool")
 
 find_program(S3CMD_TOOL_PATH s3cmd DOC "S3cmd tool for uploading to Amazon S3")
 
-## CCache
-find_program(CCACHE_FOUND ccache)
-if(CCACHE_FOUND)
-    set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache)
-    set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK ccache)
-    if(COMPILER_IS_CLANG)
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Qunused-arguments")
-    endif()
-endif(CCACHE_FOUND)
+find_program(CCACHE_TOOL_PATH ccache)
 
 # Tools for web
 find_program(VTKJS_CONVERTER vtkDataConverter