Set warnings with target_compile_options

The use of target_compile_options makes it easy to append warnings
to a target. The use of generator expressions also more succinctly
handles a few edge cases for compiler bugs and platform-specific
oddities.

This should be easy to read and maintain than the variable-based
solution it replaces.

cmake/CompilerWarnings.cmake

@@ -6,7 +6,9 @@
 function(set_target_warnings target)
     option(WARNINGS_AS_ERRORS "Treat compiler warnings as errors" TRUE)
 
-    set(MSVC_WARNINGS
+    if(SFML_COMPILER_MSVC)
+        target_compile_options(${target} PRIVATE
+            $<$<BOOL:${WARNINGS_AS_ERRORS}>:/WX>
             /W4 # Baseline reasonable warnings
             /w14242 # 'identifier': conversion from 'type1' to 'type1', possible loss of data
             /w14254 # 'operator': conversion from 'type1:field_bits' to 'type2:field_bits', possible loss of data
@@ -35,8 +37,11 @@ function(set_target_warnings target)
             /wd4505 # disable warnings about unused functions that might be platform-specific
             /wd4800 # disable warnings regarding implicit conversions to bool
         )
+    endif()
 
-    set(CLANG_AND_GCC_WARNINGS
+    if(SFML_COMPILER_GCC OR SFML_COMPILER_CLANG)
+        target_compile_options(${target} PRIVATE
+            $<$<BOOL:${WARNINGS_AS_ERRORS}>:-Werror>
             -Wall
             -Wextra # reasonable and standard
             -Wshadow # warn the user if a variable declaration shadows one from a parent context
@@ -53,48 +58,25 @@ function(set_target_warnings target)
             -Wnull-dereference # warn if a null dereference is detected
             -Wold-style-cast # warn for c-style casts
             -Wpedantic # warn if non-standard C++ is used
+            $<$<BOOL:${SFML_OS_ANDROID}>:-Wno-main> # allow main() to be called
         )
-
-    if(ANDROID)
-        set(CLANG_AND_GCC_WARNINGS ${CLANG_AND_GCC_WARNINGS} -Wno-main) # allow main() to be called
     endif()
 
-    if(WARNINGS_AS_ERRORS)
+    if(SFML_COMPILER_GCC)
-        set(CLANG_AND_GCC_WARNINGS ${CLANG_AND_GCC_WARNINGS} -Werror)
+        # Don't enable -Wduplicated-branches for GCC < 8.1 since it will lead to false positives
-        set(MSVC_WARNINGS ${MSVC_WARNINGS} /WX)
+        # https://github.com/gcc-mirror/gcc/commit/6bebae75035889a4844eb4d32a695bebf412bcd7
-    endif()
+        target_compile_options(${target} PRIVATE
-
-    set(CLANG_WARNINGS
-        ${CLANG_AND_GCC_WARNINGS}
-        -Wno-unknown-warning-option # do not warn on GCC-specific warning diagnostic pragmas
-    )
-
-    set(GCC_WARNINGS
-        ${CLANG_AND_GCC_WARNINGS}
             -Wmisleading-indentation # warn if indentation implies blocks where blocks do not exist
             -Wduplicated-cond # warn if if / else chain has duplicated conditions
             -Wlogical-op # warn about logical operations being used where bitwise were probably wanted
             # -Wuseless-cast # warn if you perform a cast to the same type (disabled because it is not portable as some type aliases might vary between platforms)
-    )
+            $<$<VERSION_GREATER_EQUAL:${CMAKE_CXX_COMPILER_VERSION},8.1>:-Wduplicated-branches> # warn if if / else branches have duplicated code
-
-    # Don't enable -Wduplicated-branches for GCC < 8.1 since it will lead to false positives
-    # https://github.com/gcc-mirror/gcc/commit/6bebae75035889a4844eb4d32a695bebf412bcd7
-    if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 8.1)
-        set(GCC_WARNINGS
-            ${GCC_WARNINGS}
-            -Wduplicated-branches # warn if if / else branches have duplicated code
         )
     endif()
 
-    if(MSVC)
+    if(SFML_COMPILER_CLANG)
-        set(FILE_WARNINGS ${MSVC_WARNINGS})
+        target_compile_options(${target} PRIVATE
-    elseif(CMAKE_CXX_COMPILER_ID MATCHES ".*Clang")
+            -Wno-unknown-warning-option # do not warn on GCC-specific warning diagnostic pragmas
-        set(FILE_WARNINGS ${CLANG_WARNINGS})
+        )
-    elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-        set(FILE_WARNINGS ${GCC_WARNINGS})
-    else()
-        message(AUTHOR_WARNING "No compiler warnings set for '${CMAKE_CXX_COMPILER_ID}' compiler.")
     endif()
-
-    target_compile_options(${target} PRIVATE ${FILE_WARNINGS})
 endfunction()