Re: [gentoo-dev] [RFC] Enable CMAKE_WARN_UNUSED_CLI by default in cmake-utils for EAPI>=6

[Maciej Mrozowski]

On Wednesday 18 of May 2016 09:22:53 Andrew Savchenko wrote:
> On Mon, 02 May 2016 18:06:44 +0200 Maciej Mrozowski wrote:
> > Hello,
> >
> > General advise: do not convert ebuilds inheriting cmake-utils to EAPI 6
> > unless you know what you are doing (you are fully aware of eclass
> > behaviour removed with https://bugs.gentoo.org/show_bug.cgi?id=514384).
> >
> > Background:
> >
> > Pre EAPI-6 cmake-utils.eclass contained certain feature to mitigate CMake
> > variable case changes done by upstream.
> > This feature was explicitly removed with
> > https://bugs.gentoo.org/show_bug.cgi?id=514384 and no alternative was
> > proposed.
> > It opened new area of possible ebuild regression bugs when switching to
> > EAPI-6 for ebuilds inheriting cmake-utils.eclass.
> >
> > Unfortunately there is common misconception, also among developers, that
> > it's sufficient to simply replace "${cmake-utils_use_with foo)" with
> > "-DWITH_foo=ON" etc.
> > This is MOST OF THE TIME not the case.
> > When converting cmake-utils ebuild to EAPI>=6, one needs to consult
> > CMakeLists.txt wrt case each variable is written with since CMake is case-
> > sensitive and WITH_FOO != WITH_foo != WITH_Foo.
> >
> > Proposal:
> >
> > CMake allows warning about unused CMake variables passed by CLI. Since
> > this is how Gentoo passes ebuild configuration options, it's proposed to
> > enable this feature.
> > Unfortunately it won't fail compilation but at least it gives a chance to
> > spot case mismatch when reading build output.
> >
> > Future thoughts:
> >
> > For better damage control it's technically possible to extend configure
> > phase of cmake-utuls eclass to check mycmakeargs against parsed package
> > buildsystem but this might not be very reliable.
>
> For me the real confusion was from this line:
>
>     die "${FUNCNAME[1]} is banned in EAPI 6 and later: use
> -D$1${arg}=\"\$(usex $2)\" instead"
>
> It recommends to use ${arg} without any warning about case, so when I just
> copied what it recommends: -DWITH_nls="$(usex nls)", I had a nice surprise
> and fun debugging.

Ah, there you go..

@kensington
Come on, man, you should have known better.

Invalid suggestion removed. Thanks for noticing.
I prefer to have developers figure out the right EAPI-6 migration path 
themselves rather than blindly relying on suggestions:

diff --git a/eclass/cmake-utils.eclass b/eclass/cmake-utils.eclass
index 427c13f..5958230 100644
--- a/eclass/cmake-utils.eclass
+++ b/eclass/cmake-utils.eclass
@@ -161,7 +161,7 @@ _cmake_use_me_now() {
        local arg=$2
        [[ ! -z $3 ]] && arg=$3
 
-       [[ ${EAPI} == [2345] ]] || die "${FUNCNAME[1]} is banned in EAPI 6 and 
later: use -D$1${arg}=\"\$(usex $2)\" instead"
+       [[ ${EAPI} == [2345] ]] || die "${FUNCNAME[1]} is banned in EAPI 6 and 
later"
 
        local uper capitalised x
        [[ -z $2 ]] && die "cmake-utils_use-$1 <USE flag> [<flag name>]"
@@ -184,7 +184,7 @@ _cmake_use_me_now_inverted() {
        [[ ! -z $3 ]] && arg=$3
 
        if [[ ${EAPI} != [2345] && "${FUNCNAME[1]}" != cmake-
utils_use_find_package ]] ; then
-               die "${FUNCNAME[1]} is banned in EAPI 6 and later: use -
D$1${arg}=\"\$(usex $2)\" instead"
+               die "${FUNCNAME[1]} is banned in EAPI 6 and later"
        fi
 
        local uper capitalised x

regards
MM