try_compile: Test that CMake re-runs on input change

With the Makefile and Ninja generators we expect that touching the input
source file for a try_compile will cause CMake to re-run on the next
build.  Extend the RunCMake.try_compile test with a case covering this.
Also check that CMake does not re-run if nothing has changed.

Tests/RunCMake/try_compile/RerunCMake-nowork-ninja-no-console-stdout.txt

@@ -0,0 +1 @@
+^ninja: no work to do\.$

Tests/RunCMake/try_compile/RerunCMake-rerun-ninja-no-console-stdout.txt

@@ -0,0 +1,5 @@
+Running CMake on RerunCMake
+FALSE
+-- Configuring done
+-- Generating done
+-- Build files have been written to: .*/Tests/RunCMake/try_compile/RerunCMake-build

Tests/RunCMake/try_compile/RerunCMake-rerun-stderr.txt

@@ -0,0 +1,2 @@
+^Running CMake on RerunCMake
+FALSE$

Tests/RunCMake/try_compile/RerunCMake-rerun-stdout.txt

@@ -0,0 +1,3 @@
+-- Configuring done
+-- Generating done
+-- Build files have been written to: .*/Tests/RunCMake/try_compile/RerunCMake-build

Tests/RunCMake/try_compile/RerunCMake-stderr.txt

@@ -0,0 +1,2 @@
+^Running CMake on RerunCMake
+TRUE$

Tests/RunCMake/try_compile/RerunCMake-stdout.txt

@@ -0,0 +1,3 @@
+-- Configuring done
+-- Generating done
+-- Build files have been written to: .*/Tests/RunCMake/try_compile/RerunCMake-build

Tests/RunCMake/try_compile/RerunCMake.cmake

@@ -0,0 +1,7 @@
+message("Running CMake on RerunCMake") # write to stderr if cmake reruns
+enable_language(C)
+try_compile(res
+  "${CMAKE_CURRENT_BINARY_DIR}"
+  SOURCES "${CMAKE_CURRENT_BINARY_DIR}/TryCompileInput.c"
+  )
+message("${res}")

Tests/RunCMake/try_compile/RunCMakeTest.cmake

@@ -17,3 +17,36 @@ run_cmake(NonSourceCopyFile)
 run_cmake(NonSourceCompileDefinitions)
 
 run_cmake(CMP0056)
+
+if(RunCMake_GENERATOR MATCHES "Make|Ninja")
+  # Use a single build tree for a few tests without cleaning.
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/RerunCMake-build)
+  set(RunCMake_TEST_NO_CLEAN 1)
+  file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+  file(MAKE_DIRECTORY "${RunCMake_TEST_BINARY_DIR}")
+  set(in_tc  "${RunCMake_TEST_BINARY_DIR}/TryCompileInput.c")
+  file(WRITE "${in_tc}" "int main(void) { return 0; }\n")
+
+  # Older Ninja keeps all rerun output on stdout
+  set(ninja "")
+  if(RunCMake_GENERATOR STREQUAL "Ninja")
+    execute_process(COMMAND ${RunCMake_MAKE_PROGRAM} --version
+      OUTPUT_VARIABLE ninja_version OUTPUT_STRIP_TRAILING_WHITESPACE)
+    if(ninja_version VERSION_LESS 1.5)
+      set(ninja -ninja-no-console)
+    endif()
+  endif()
+
+  message(STATUS "RerunCMake: first configuration...")
+  run_cmake(RerunCMake)
+  run_cmake_command(RerunCMake-nowork${ninja} ${CMAKE_COMMAND} --build .)
+
+  execute_process(COMMAND ${CMAKE_COMMAND} -E sleep 1) # handle 1s resolution
+  message(STATUS "RerunCMake: modify try_compile input...")
+  file(WRITE "${in_tc}" "does-not-compile\n")
+  run_cmake_command(RerunCMake-rerun${ninja} ${CMAKE_COMMAND} --build .)
+  run_cmake_command(RerunCMake-nowork${ninja} ${CMAKE_COMMAND} --build .)
+
+  unset(RunCMake_TEST_BINARY_DIR)
+  unset(RunCMake_TEST_NO_CLEAN)
+endif()