[cmake-developers] Enabling more compiler warnings

[Stephen Kelly]

Hi there,

One common reason topcis warn on the dashboard and need to be updated and 
then rebased is that some machines have more warnings enabled by others.

If CMake enabled more warnings by default, developers would notice them 
locally too before even submitting to the dashboard. For example, many of my 
follow up commits have been related to unused parameters, or order of 
initialization in constructors.

I have a branch for enabling some warnings, but it would need to be upstream 
to be of any use:

 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index ea1c033..3eb1a43 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -586,6 +586,19 @@ option(CMAKE_STRICT
 mark_as_advanced(CMAKE_STRICT)
 
 
+if("${CMAKE_C_COMPILER_ID}" MATCHES "GNU")
+
+  set(CMAKE_C_FLAGS   "${CMAKE_C_FLAGS} -Wcast-align -Werror-implicit-
function-declaration -Wchar-subscripts -Wall -W")
+  set(CMAKE_C_FLAGS   "${CMAKE_C_FLAGS} -Wpointer-arith -Wwrite-strings -
Wformat-security -Wmissing-format-attribute -fno-common")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wnon-virtual-dtor -ansi -Wcast-
align -Wchar-subscripts -Wall -W -Wshadow")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wpointer-arith -Wformat-
security")
+
+  if (NOT APPLE)
+    set(CMAKE_SHARED_LINKER_FLAGS "-Wl,--fatal-warnings -Wl,--no-undefined 
${CMAKE_SHARED_LINKER_FLAGS}")
+    set(CMAKE_MODULE_LINKER_FLAGS "-Wl,--fatal-warnings -Wl,--no-undefined 
${CMAKE_MODULE_LINKER_FLAGS}")
+  endif ()
+endif()
+

I would prefer to also add -Wundef, but kwsys is not clean with that flag 
and creates many warnings, so it would have to be fixed there first.

I'm fairly sure it would work with GCC 4.2 or later (and I guess clang as 
well), which would probably cover many cmake developers. The GCC version 
check only becomes a lot easier with a recent version of CMake (I don't 
recall which), but I'm sure most people do cmake development using the 
development branch anyway, but we'd have to wrap it in a CMAKE_VERSION check 
anyway.

I'd prefer to just do it like this rather than with feature tests, because 
my experience with feature tests on the CMake dashboard (with the export 
header stuff a while back) indicates that it's not worth it in this case. It 
would take far too long to get right.

Any thoughts?

Thanks,

Steve.