clang-tidy: Clarify comment explaining purpose of CLANG_TIDY_SHA1

Suggested-by: Bill Hoffman <bill.hoffman@kitware.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index f14f62f..72ad7f5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -251,7 +251,12 @@ if(CMake_RUN_CLANG_TIDY)
   endif()
   set(CMAKE_CXX_CLANG_TIDY "${CLANG_TIDY_COMMAND}")
 
-  # provide definitions for targets that require a rebuild once .clang-tidy changes
+  # Create a preprocessor definition that depends on .clang-tidy content so
+  # the compile command will change when .clang-tidy changes.  This ensures
+  # that a subsequent build re-runs clang-tidy on all sources even if they
+  # do not otherwise need to be recompiled.  Nothing actually uses this
+  # definition.  We add it to targets on which we run clang-tidy just to
+  # get the build dependency on the .clang-tidy file.
   file(SHA1 ${CMAKE_CURRENT_SOURCE_DIR}/.clang-tidy clang_tidy_sha1)
   set(CLANG_TIDY_DEFINITIONS "CLANG_TIDY_SHA1=${clang_tidy_sha1}")
   unset(clang_tidy_sha1)