Refresh P4C's ccache setup.

CMakeLists.txt

@@ -16,12 +16,6 @@
 # This is the CMake version supplied by Ubuntu 20.04.
 cmake_minimum_required (VERSION 3.16.3 FATAL_ERROR)
 
-find_program(CCACHE_PROGRAM ccache)
-if(CCACHE_PROGRAM)
-    MESSAGE(STATUS "Enabling ccache")
-    set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE "${CCACHE_PROGRAM}")
-endif()
-
 project (P4C)
 
 include(CMakeDependentOption)
@@ -31,6 +25,7 @@ set (CMAKE_CXX_STANDARD 20)
 set (CMAKE_CXX_STANDARD_REQUIRED ON)
 
 set (CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake)
+include(ccache)
 set (P4C_RUNTIME_OUTPUT_DIRECTORY bin)
 set (P4C_LIBRARY_OUTPUT_DIRECTORY lib)
 set (P4C_ARTIFACTS_OUTPUT_DIRECTORY share/p4c)

backends/p4tools/cmake/common.cmake

@@ -1,15 +1,7 @@
 # Common configuration across all P4Tools projects.
 
-# Use ccache if available.
-find_program(CCACHE_PROGRAM ccache)
-if(CCACHE_PROGRAM)
-  message(STATUS "Enabling ccache")
-  set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE "${CCACHE_PROGRAM}")
-endif()
-
 # Helper for defining a p4tools executable target.
 function(add_p4tools_executable target source)
   add_executable(${target} ${source} ${ARGN})
   install(TARGETS ${target} RUNTIME DESTINATION ${P4C_RUNTIME_OUTPUT_DIRECTORY})
 endfunction(add_p4tools_executable)
-

cmake/ccache.cmake

@@ -0,0 +1,22 @@
+# ccache integration for p4c builds.
+
+include_guard(GLOBAL)
+
+option(ENABLE_CCACHE "Enable ccache compiler launcher when available" ON)
+
+if(NOT ENABLE_CCACHE)
+  return()
+endif()
+
+find_program(CCACHE_PROGRAM ccache)
+if(NOT CCACHE_PROGRAM)
+  return()
+endif()
+
+message(STATUS "Enabling ccache: ${CCACHE_PROGRAM}")
+
+foreach(LANG C CXX)
+  if(NOT CMAKE_${LANG}_COMPILER_LAUNCHER)
+    set(CMAKE_${LANG}_COMPILER_LAUNCHER "${CCACHE_PROGRAM}")
+  endif()
+endforeach()