clang-tidy: allow target to be disabled

ClangTidy.cmake

@@ -13,31 +13,60 @@
 #
 # A module to create custom targets to lint source files using clang-tidy
 #
-# Call swift_create_clang_tidy_targets at the end of the top level CMakeLists.txt to create targets for running clang-tidy
+# Call swift_create_clang_tidy_targets at the end of the top level
+# CMakeLists.txt to create targets for running clang-tidy
 #
-# clang-tidy version 6 must be available on the system for this module to work properly. If an appropriate clang-tidy can't be found no targets will be created and a warning will
-# be logged
+# clang-tidy version 6 must be available on the system for this module to work
+# properly. If an appropriate clang-tidy can't be found no targets will be
+# created and a warning will be logged
 #
-# swift_create_clang_tidy_targets will only have an effect for top level projects. If called within a subproject it will return without taking any action
+# swift_create_clang_tidy_targets will only have an effect for top level
+# projects. If called within a subproject it will return without taking any
+# action
 #
-# For every compilable target defined within the calling repository two targets will be created.
+# For every compilable target defined within the calling repository two targets
+# will be created.
 #
-# The first target 'clang-tidy-${target}' will invoke clang-tidy for all source files which make up the given target. It will export fixes to a file called 'fixes-${target}.yaml'
-# in the top level project source directory.
+# The first target 'clang-tidy-${target}' will invoke clang-tidy for all source
+# files which make up the given target. It will export fixes to a file called
+# 'fixes-${target}.yaml' in the top level project source directory.
 #
-# The second target 'clang-tidy-${target}-check' will run clang-tidy as the target described above and then return an error code if any warning/errors were generated
+# The second target 'clang-tidy-${target}-check' will run clang-tidy as the
+# target described above and then return an error code if any warning/errors
+# were generated
 #
-# In addition there are two other targets created which lint multiple targets at the same time
+# In addition there are two other targets created which lint multiple targets
+# at the same time
 #
-# clang-tidy-all runs clang-tidy on all "core" targets in the repository (targets which were added with swift_add_executable or swift_add_library)
+# clang-tidy-all runs clang-tidy on all "core" targets in the repository
+# (targets which were added with swift_add_executable or swift_add_library)
 #
-# clang-tidy-world runs clang-tidy on all compilable targets in the repository including all test suites
+# clang-tidy-world runs clang-tidy on all compilable targets in the repository
+# including all test suites
 #
-# clang-tidy-all and clang-tidy-world each have a "check" variant which returns an error code should any warning/errors be generated
+# clang-tidy-all and clang-tidy-world each have a "check" variant which returns
+# an error code should any warning/errors be generated
 #
-# swift_create_clang_tidy_targets will generate a .clang-tidy file in the project source directory which contains the Swift master config for clang-tidy. There is no need for
-# repositories to maintain their own version of .clang-tidy, it should be added to .gitignore in each repository to prevent being checked in. Pass the option
-# DONT_GENERATE_CLANG_TIDY_CONFIG to disable the autogenerated config
+# swift_create_clang_tidy_targets will generate a .clang-tidy file in the
+# project source directory which contains the Swift master config for
+# clang-tidy. There is no need for repositories to maintain their own version
+# of .clang-tidy, it should be added to .gitignore in each repository to
+# prevent being checked in. Pass the option DONT_GENERATE_CLANG_TIDY_CONFIG to
+# disable the autogenerated config
+#
+# In addition this function sets up a cmake option which can be used to control
+# whether the targets are created either on the command line or by a super project.
+# The option has the name
+#
+# ${PROJECT_NAME}_ENABLE_CLANG_TIDY
+#
+# The default value is ON for top level projects, and OFF for any others.
+#
+# Running
+#
+# cmake -D<project>_ENABLE_CLANG_TIDY=OFF ..
+#
+# will explicitly disable these targets from the command line at configure time
 #
 
 # Helper function to actually create the targets, not to be used outside this file
@@ -54,6 +83,11 @@ function(create_clang_tidy_targets key fixes)
     WORKING_DIRECTORY ${CMAKE_BINARY_DIR})
 endfunction()
 
+macro(early_exit level msg)
+  message(${level} "${msg}")
+  return()
+endmacro()
+
 function(swift_create_clang_tidy_targets)
   if(NOT ${CMAKE_PROJECT_NAME} STREQUAL ${PROJECT_NAME})
     return()
@@ -68,6 +102,19 @@ function(swift_create_clang_tidy_targets)
     message(FATAL_ERROR "Unparsed arguments to swift_create_clang_tidy_targets ${ARGN}")
   endif()
 
+  # Global clang-tidy enable option, influences the default project specific enable option
+  option(ENABLE_CLANG_TIDY "Enable auto-linting of code using clang-tidy globally" ON)
+  if(NOT ENABLE_CLANG_TIDY)
+    early_exit(STATUS "clang-tidy is disabled globally")
+  endif()
+
+  # Create a cmake option to enable linting of this specific project
+  option(${PROJECT_NAME}_ENABLE_CLANG_TIDY "Enable auto-linting of code using clang-tidy for project" ON)
+
+  if(NOT ${PROJECT_NAME}_ENABLE_CLANG_TIDY)
+    early_exit(STATUS "${PROJECT_NAME} clang-tidy support is DISABLED")
+  endif()
+
   # This is required so that clang-tidy can work out what compiler options to use for each file
   set(CMAKE_EXPORT_COMPILE_COMMANDS
       ON