Make using clang-tidy actively opt-in

.github/workflows/.key4hep-build-env

@@ -0,0 +1 @@
+export K4_EXTRA_CMAKE_ARGS=-DFCALCLUSTERER_USE_CLANG_TIDY=ON

.github/workflows/key4hep.yml

@@ -0,0 +1,28 @@
+name: Key4hep build
+
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+  workflow_dispatch:
+  schedule:
+    - cron: 16 4 * * 1
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        build_type: ["release", "nightly"]
+        image: ["alma9"]
+        include:
+          - build_type: "nightly"
+            image: ubuntu24
+    steps:
+    - uses: actions/checkout@v5
+    - uses: key4hep/key4hep-actions/key4hep-build@main
+      with:
+        build_type: ${{ matrix.build_type }}
+        image: ${{ matrix.image }}

CMakeLists.txt

@@ -37,10 +37,15 @@ IF(${FCAL_USE_DD4hep})
   FIND_PACKAGE(DD4hep COMPONENTS DDRec)
 ENDIF()
 
-FIND_PROGRAM(CLANG_TIDY "clang-tidy")
-IF(CLANG_TIDY)
-  MESSAGE(STATUS "FOUND clang-tidy: ${CLANG_TIDY}")
-  SET(CMAKE_CXX_CLANG_TIDY ${CLANG_TIDY})
+OPTION(FCALCLUSTERER_USE_CLANG_TIDY "Build with clang-tidy (if available)" OFF)
+IF(FCALCLUSTERER_USE_CLANG_TIDY)
+  FIND_PROGRAM(CLANG_TIDY "clang-tidy")
+  IF(CLANG_TIDY)
+    MESSAGE(STATUS "FOUND clang-tidy: ${CLANG_TIDY}")
+    SET(CMAKE_CXX_CLANG_TIDY ${CLANG_TIDY})
+  ELSE()
+    MESSAGE(STATUS "Did not find clang-tidy. Will not build with clang-tidy")
+  ENDIF()
 ENDIF()
 
 ADD_SUBDIRECTORY(source/)