Add clang-tidy support to cmake

Also, enables it in CI.

.clang-tidy

@@ -0,0 +1,4 @@
+---
+Checks:          '-*,modernize-use-nullptr'
+WarningsAsErrors: true
+...

.github/workflows/ci-main.yml

@@ -104,7 +104,7 @@ jobs:
                 cmake "$@" -DCMAKE_BUILD_TYPE="$CFG" -DCXX_STD="$CXX_STD" \
                   -DEXTRA_FLAGS_CONFIG="-pipe" -DENABLE_MYSQL=true \
                   -DENABLE_NLS=false -DENABLE_LTO="$LTO" -DFORCE_COLOR_OUTPUT=true -DLTO_JOBS=2 \
-                  -DENABLE_SYSTEM_LUA="$SYS_LUA" .
+                  -DENABLE_SYSTEM_LUA="$SYS_LUA -DCLANG_TIDY=true" .
               }
               rm -R /usr/local/lib/cmake
               rm /usr/local/lib/libboost*

CMakeLists.txt

@@ -171,6 +171,7 @@ option(GLIBCXX_ASSERTIONS "Whether to define _GLIBCXX_ASSERTIONS" OFF)
 option(GLIBCXX_DEBUG "Whether to define _GLIBCXX_DEBUG and _GLIBCXX_DEBUG_PEDANTIC. Requires a version of Boost's program_options that's compiled with __GLIBCXX_DEBUG too." OFF)
 option(ENABLE_POT_UPDATE_TARGET "Enables the tools to update the pot files and manuals. This target has extra dependencies." OFF)
 option(FORCE_COLOR_OUTPUT "Always produce ANSI-colored output (GNU/Clang only)." FALSE)
+option(CLANG_TIDY "Enable clang-tidy linter checks." OFF)
 
 if(UNIX AND NOT APPLE AND NOT CYGWIN)
 	option(ENABLE_NOTIFICATIONS "Enable Window manager notification messages" ON)
@@ -255,6 +256,11 @@ if(NOT MSVC)
 		endif()
 	endif()
 
+### Enable clang-tidy linting
+	if (CLANG_TIDY)
+		set(CMAKE_CXX_CLANG_TIDY "clang-tidy -Wno-unknown-warning-option")
+	endif()
+
 ### Set the final compiler flags.
 
 	set(COMPILER_FLAGS "${COMPILER_FLAGS} ${CXX_FLAGS_USER}")

src/crypt_blowfish/.clang-tidy

@@ -0,0 +1,4 @@
+---
+Checks:          '-*,bugprone-use-after-move'
+WarningsAsErrors: true
+...