[PATCHv6] core: don't build host-cmake if it is available on the build host

From: Luca Ceresoli <luca@lucaceresoli.net>

Currently all cmake packages depend on host-cmake. Unfortunately
host-cmake takes a long time to configure and build: almost 7 minutes
on a dual-core i5 with SSD. The time does not change even with ccache
enabled.

Indeed, building host-cmake is avoidable if it is already installed on
the build host: CMake is supposed to be quite portable, and the only
patch in Buildroot for the CMake package seems to only affect
target-cmake.

Thus we automatically skip building host-cmake and use the one on the
system if:
 - cmake is available on the system and
 - it is recent enough.

First, we leverage the existing infrastructure in
support/dependencies/dependencies.mk to find out whether there's a
suitable cmake executable on the system. Its path can be passed in the
BR2_CMAKE environment variable, otherwise it defaults to "cmake". If
it is enabled, found and suitable then we set BR2_CMAKE_HOST_DEPENDENCY
to empty; otherwise we set BR2_CMAKE_HOST_DEPENDENCY to 'host-cmake' and
override BR2_CMAKE with "$(HOST_DIR)/usr/bin/cmake" to revert to using
our own cmake (the old behaviour).

Then in pkg-cmake.mk we replace the hard-coded dependency on host-cmake
to using the BR2_CMAKE_HOST_DEPENDENCY variable, and we use $(BR2_CMAKE)
instead of $(HOST_DIR)/usr/bin/cmake.

Unlike what we do for host-tar and host-xzcat, for host-cmake we do
not add host-cmake to DEPENDENCIES_HOST_PREREQ. If we did, host-cmake
would be a dependency for _any_ package when it's not installed on the
host, even when no cmake package is selected.

Cmake versions older than 3.0 are affected by the bug described and
fixed in Buildroot in ef2c1970e4bf ("cmake: add patch to fix Qt mkspecs
detection"). The bug was fixed in upstream CMake in version 3.0 [0].

Amongst all the cmake packages currently in Buildroot, the currently
highest version mentioned in cmake_minimum_required() is 3.1 (grantlee
and opencv3).

Thus we use 3.1 as the lowest required cmake for now, until a package is
bumped, or a new package added, with a higher required version.

We then ensure, as a post-patch hook in the cmake infra, that no
package requires a cmake version higher than what we do in Buildroot.
If that's not the case, this is considered an error and the build is
aborted. We use a post-patch hook rather a more obvious pre-configure
hook because it is then easier to check the requirements of a package
without having to build all its dependencies first.

However, the target cmake requires up to cmake 3.4 for running its
tests; and they do not get built in our case. Bumping the required host
cmake minimum version for the whole of Buildroot would almost always
defeat the purpose of this change. So we just exclude the target cmake
from the version check.

[0] https://cmake.org/gitweb?p=cmake.git;h=e8b8b37ef6fef094940d3384df5a1d421b9fa568

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Samuel Martin <s.martin49@gmail.com>
Cc: Davide Viti <zinosat@tiscali.it>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
Tested-by: Romain Naour <romain.naour@gmail.com>
[yann.morin.1998@free.fr:
  - simplify logic in check-host-cmake.mk;
  - set and use BR2_CMAKE_HOST_DEPENDENCY, drop USE_SYSTEM_CMAKE;
  - bump to cmake 3.1 for grantlee and opencv;
  - add the post-patch hook; exclude target cmake from the check.
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

---
Results (by Luca, before Yann's changes):

On my build server, this patch reduced the build time for a batch of
16 Buildroot configurations (all building cmake-based packages) from
2h44m to 1h54m. Woah, it's a 30% saving!

Tested on:
 - Ubuntu 14.04 without CMake, with official CMake (2.8), PPA CMake
   (3.2)
 - Ubuntu 15.10 without CMake, with official CMake (3.2)
 - Ubuntu 16.04 without CMake, with official CMake (3.5)

Results (by Yann):

On my machine, this gains about 5min 30s per build, which is far from
negligible.

Tested, by artificially bumping/lowering the minimum required version,
on:
 - Ubuntu 16.04 without CMake, with official CMake (3.5)

---
Changes v5 -> v6:
  - rename variables in the version check in pkg-cmake  (Luca)
  - fix commit log  (Luca)

Changes v4 -> v5:
 - adopted by Yann;
 - drop USE_SYSTEM_CMAKE in favour of BR2_CMAKE_HOST_DEPENDENCY which
   directly contains 'host-cmake' if it is needed;
 - unconditionally add $(BR2_CMAKE_HOST_DEPENDENCY) to dependencies: it
   is empty if host-cmake is not needed;
 - check our minimum version is enough in a post-patch hook.

Changes v3 -> v4:
 - rename USE_SYSTEM_HOST_CMAKE -> USE_SYSTEM_CMAKE (Arnout)
 - ditch BR2_TRY_SYSTEM_CMAKE and use system-cmake unconditionally
   if it is found and >= 3.0 (Arnout)
 - rename BR2_HOST_CMAKE -> BR2_CMAKE since it can be either a
   host-cmake (built by Buildroot) or a system-cmake

Changes v2 -> v3:
 - make this feature optional via the BR2_TRY_SYSTEM_CMAKE kconfig
   variable
 - rename the CMAKE variable to BR2_HOST_CMAKE, so it's coherent
   with the naming of other variables overridable by the
   environment, e.g. BR2_DL_DIR
 - invert the logic of the variable triggering the host-cmake
   dependency: USE_SYSTEM_CMAKE instead of BUILD_HOST_CMAKE;
   needed to implement BR2_TRY_SYSTEM_CMAKE

Changes v1 -> v2:
 - Require cmake >= 3.0. Fixes qjson failure (Luca, Samuel, Thomas)
 - In check-host-cmake.sh only search $1, not "cmake" (Arnout)
 - typo: host-ccache -> host-cmake (Arnout)
---
 package/pkg-cmake.mk                     | 45 +++++++++++++++++++++++++++++---
 support/dependencies/check-host-cmake.mk | 19 ++++++++++++++
 support/dependencies/check-host-cmake.sh | 26 ++++++++++++++++++
 3 files changed, 87 insertions(+), 3 deletions(-)
 create mode 100644 support/dependencies/check-host-cmake.mk
 create mode 100755 support/dependencies/check-host-cmake.sh

Dear Yann,

On 07/09/2016 00:32, Yann E. MORIN wrote:
> From: Luca Ceresoli <luca@lucaceresoli.net>
> 
> Currently all cmake packages depend on host-cmake. Unfortunately
> host-cmake takes a long time to configure and build: almost 7 minutes
> on a dual-core i5 with SSD. The time does not change even with ccache
> enabled.
> 
> Indeed, building host-cmake is avoidable if it is already installed on
> the build host: CMake is supposed to be quite portable, and the only
> patch in Buildroot for the CMake package seems to only affect
> target-cmake.
> 
> Thus we automatically skip building host-cmake and use the one on the
> system if:
>  - cmake is available on the system and
>  - it is recent enough.
> 
> First, we leverage the existing infrastructure in
> support/dependencies/dependencies.mk to find out whether there's a
> suitable cmake executable on the system. Its path can be passed in the
> BR2_CMAKE environment variable, otherwise it defaults to "cmake". If
> it is enabled, found and suitable then we set BR2_CMAKE_HOST_DEPENDENCY
> to empty; otherwise we set BR2_CMAKE_HOST_DEPENDENCY to 'host-cmake' and
> override BR2_CMAKE with "$(HOST_DIR)/usr/bin/cmake" to revert to using
> our own cmake (the old behaviour).
> 
> Then in pkg-cmake.mk we replace the hard-coded dependency on host-cmake
> to using the BR2_CMAKE_HOST_DEPENDENCY variable, and we use $(BR2_CMAKE)
> instead of $(HOST_DIR)/usr/bin/cmake.
> 
> Unlike what we do for host-tar and host-xzcat, for host-cmake we do
> not add host-cmake to DEPENDENCIES_HOST_PREREQ. If we did, host-cmake
> would be a dependency for _any_ package when it's not installed on the
> host, even when no cmake package is selected.
> 
> Cmake versions older than 3.0 are affected by the bug described and
> fixed in Buildroot in ef2c1970e4bf ("cmake: add patch to fix Qt mkspecs
> detection"). The bug was fixed in upstream CMake in version 3.0 [0].
> 
> Amongst all the cmake packages currently in Buildroot, the currently
> highest version mentioned in cmake_minimum_required() is 3.1 (grantlee
> and opencv3).
> 
> Thus we use 3.1 as the lowest required cmake for now, until a package is
> bumped, or a new package added, with a higher required version.
> 
> We then ensure, as a post-patch hook in the cmake infra, that no
> package requires a cmake version higher than what we do in Buildroot.
> If that's not the case, this is considered an error and the build is
> aborted. We use a post-patch hook rather a more obvious pre-configure
> hook because it is then easier to check the requirements of a package
> without having to build all its dependencies first.
> 
> However, the target cmake requires up to cmake 3.4 for running its
> tests; and they do not get built in our case. Bumping the required host
> cmake minimum version for the whole of Buildroot would almost always
> defeat the purpose of this change. So we just exclude the target cmake
> from the version check.
> 
> [0] https://cmake.org/gitweb?p=cmake.git;h=e8b8b37ef6fef094940d3384df5a1d421b9fa568
> 
> Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
> Cc: Samuel Martin <s.martin49@gmail.com>
> Cc: Davide Viti <zinosat@tiscali.it>
> Cc: Arnout Vandecappelle <arnout@mind.be>
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Reviewed-by: Romain Naour <romain.naour@gmail.com>
> Tested-by: Romain Naour <romain.naour@gmail.com>
> [yann.morin.1998@free.fr:
>   - simplify logic in check-host-cmake.mk;
>   - set and use BR2_CMAKE_HOST_DEPENDENCY, drop USE_SYSTEM_CMAKE;
>   - bump to cmake 3.1 for grantlee and opencv;
>   - add the post-patch hook; exclude target cmake from the check.
> ]
> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>

On 07-09-16 00:32, Yann E. MORIN wrote:
> From: Luca Ceresoli <luca@lucaceresoli.net>
> 
> Currently all cmake packages depend on host-cmake. Unfortunately
> host-cmake takes a long time to configure and build: almost 7 minutes
> on a dual-core i5 with SSD. The time does not change even with ccache
> enabled.
> 
> Indeed, building host-cmake is avoidable if it is already installed on
> the build host: CMake is supposed to be quite portable, and the only
> patch in Buildroot for the CMake package seems to only affect
> target-cmake.
> 
> Thus we automatically skip building host-cmake and use the one on the
> system if:
>  - cmake is available on the system and
>  - it is recent enough.
> 
> First, we leverage the existing infrastructure in
> support/dependencies/dependencies.mk to find out whether there's a
> suitable cmake executable on the system. Its path can be passed in the
> BR2_CMAKE environment variable, otherwise it defaults to "cmake". If
> it is enabled, found and suitable then we set BR2_CMAKE_HOST_DEPENDENCY
> to empty; otherwise we set BR2_CMAKE_HOST_DEPENDENCY to 'host-cmake' and
> override BR2_CMAKE with "$(HOST_DIR)/usr/bin/cmake" to revert to using
> our own cmake (the old behaviour).
> 
> Then in pkg-cmake.mk we replace the hard-coded dependency on host-cmake
> to using the BR2_CMAKE_HOST_DEPENDENCY variable, and we use $(BR2_CMAKE)
> instead of $(HOST_DIR)/usr/bin/cmake.
> 
> Unlike what we do for host-tar and host-xzcat, for host-cmake we do
> not add host-cmake to DEPENDENCIES_HOST_PREREQ. If we did, host-cmake
> would be a dependency for _any_ package when it's not installed on the
> host, even when no cmake package is selected.
> 
> Cmake versions older than 3.0 are affected by the bug described and
> fixed in Buildroot in ef2c1970e4bf ("cmake: add patch to fix Qt mkspecs
> detection"). The bug was fixed in upstream CMake in version 3.0 [0].
> 
> Amongst all the cmake packages currently in Buildroot, the currently
                                                             ^^^^^^^^^dupe

> highest version mentioned in cmake_minimum_required() is 3.1 (grantlee
> and opencv3).
> 
> Thus we use 3.1 as the lowest required cmake for now, until a package is
> bumped, or a new package added, with a higher required version.
> 
> We then ensure, as a post-patch hook in the cmake infra, that no
> package requires a cmake version higher than what we do in Buildroot.
> If that's not the case, this is considered an error and the build is
> aborted. We use a post-patch hook rather a more obvious pre-configure
> hook because it is then easier to check the requirements of a package
> without having to build all its dependencies first.

 I still have some comments about this minimum version check. Perhaps it's
better to split that into a separate patch so the core functionality can already
be committed.

> 
> However, the target cmake requires up to cmake 3.4 for running its
> tests; and they do not get built in our case. Bumping the required host
> cmake minimum version for the whole of Buildroot would almost always
> defeat the purpose of this change. So we just exclude the target cmake
> from the version check.
> 
> [0] https://cmake.org/gitweb?p=cmake.git;h=e8b8b37ef6fef094940d3384df5a1d421b9fa568
[snip]
> diff --git a/package/pkg-cmake.mk b/package/pkg-cmake.mk
> index 4c6dc62..759b3e6 100644
> --- a/package/pkg-cmake.mk
> +++ b/package/pkg-cmake.mk
> @@ -35,6 +35,38 @@ ifneq ($(QUIET),)
>  CMAKE_QUIET = -DCMAKE_RULE_MESSAGES=OFF -DCMAKE_INSTALL_MESSAGE=NEVER
>  endif
>  
> +#
> +# Check the package does not require a cmake version more recent than we do.
> +#
> +# Some packages may use a variable to set the minimum required version. In
> +# this case, there is not much we can do, so we just accept it; the configure
> +# would fail later anyway in this case.
> +#
> +define CMAKE_CHECK_MIN_VERSION

 This would be perfect to do with a script instead - no make support is needed,
except for passing $(@D) $($(PKG)_NAME) and BR2_CMAKE_MIN_VERSION.

> +	$(Q)v=$$( grep -hr -i 'cmake_minimum_required.*version' $(@D) \

 Shouldn't we search just in CMakeLists.txt files? Do you think it's likely that
a package declares the minimum required version in and included file? That said,
the extra time spent on grepping through everything doesn't amount to much
unless it's a large package, and in that case it's anyway going to be dominated
by package build time.

> +		|tr '[:upper:]' '[:lower:]' \
> +		|sed -r -e '/.*\(version ([[:digit:]]+\.[[:digit:]]+).+/!d; s//\1/' \

 Not exactly an easy to understand sed script...

> +		|sort -t. -k 1,1nr -k2,2nr \

 Since you're anyway doing the version sort here already, you could just add
$(BR2_CMAKE_MIN_VERSION_MAJOR).$(BR2_CMAKE_MIN_VERSION_MINOR) into the mix and
verify that the first line is equal to
$(BR2_CMAKE_MIN_VERSION_MAJOR).$(BR2_CMAKE_MIN_VERSION_MINOR)
We already use that trick for checking the make version, for instance.

(and then you don't need to split anymore, just $(BR2_CMAKE_MIN_VERSION)).

> +		|head -n 1 \
> +	 ); \
> +	MAJOR=$${v%.*}; minor=$${v#*.}; \
> +	if [ -z "$${v}" ]; then \
> +		: Unknown, not much we can do, OK; \
> +	elif [ $(BR2_CMAKE_MIN_VERSION_MAJOR) -gt $${MAJOR} ]; then \
> +		: OK; \
> +	elif [    $(BR2_CMAKE_MIN_VERSION_MAJOR) -eq $${MAJOR} \
> +	       -a $(BR2_CMAKE_MIN_VERSION_MINOR) -ge $${minor} ]; then \
> +		: OK; \

 Which removes the need for all these conditions.

> +	else \
> +		printf "*** Error: incorrect minimum cmake version:\n"; \
> +		printf "*** Error: Buildroot requires %s.%s\n" \
> +			$(BR2_CMAKE_MIN_VERSION_MAJOR) $(BR2_CMAKE_MIN_VERSION_MINOR); \
> +		printf "*** Error: %s needs at least %s.%s\n" \
> +			$($(PKG)_NAME) $${MAJOR} $${minor}; \

 I don't think this error message is very clear. How about:

*** Error: package %s needs cmake version %s.%s\n
***        Buildroot's minimum version BR2_CMAKE_MIN_VERSION\n
***        should be set to at least that version. Currently\n
***        it is set to %s.\n

> +		exit 1; \
> +	fi
> +endef
> +
>  ################################################################################
>  # inner-cmake-package -- defines how the configuration, compilation and
>  # installation of a CMake package should be done, implements a few hooks to
> @@ -71,6 +103,13 @@ else
>  $(2)_BUILDDIR			= $$($(2)_SRCDIR)/buildroot-build
>  endif
>  
> +# Special exception for cmake, which requires cmake up to 3.4, but
> +# only to run its tests; all other equirements are on at most 3.0.
> +# Just skip the version check for cmake, and only for cmake.
> +ifneq ($(1),cmake)
> +$(2)_POST_PATCH_HOOKS += CMAKE_CHECK_MIN_VERSION
> +endif
> +
>  #
>  # Configure step. Only define it if not already defined by the package
>  # .mk file. And take care of the differences between host and target
> @@ -85,7 +124,7 @@ define $(2)_CONFIGURE_CMDS
>  	cd $$($$(PKG)_BUILDDIR) && \
>  	rm -f CMakeCache.txt && \
>  	PATH=$$(BR_PATH) \
> -	$$($$(PKG)_CONF_ENV) $$(HOST_DIR)/usr/bin/cmake $$($$(PKG)_SRCDIR) \
> +	$$($$(PKG)_CONF_ENV) $$(BR2_CMAKE) $$($$(PKG)_SRCDIR) \
>  		-DCMAKE_TOOLCHAIN_FILE="$$(HOST_DIR)/usr/share/buildroot/toolchainfile.cmake" \
>  		-DCMAKE_BUILD_TYPE=$$(if $$(BR2_ENABLE_DEBUG),RelWithDebInfo,Release) \
>  		-DCMAKE_INSTALL_PREFIX="/usr" \
> @@ -110,7 +149,7 @@ define $(2)_CONFIGURE_CMDS
>  	cd $$($$(PKG)_BUILDDIR) && \
>  	rm -f CMakeCache.txt && \
>  	PATH=$$(BR_PATH) \
> -	$$(HOST_DIR)/usr/bin/cmake $$($$(PKG)_SRCDIR) \
> +	$$(BR2_CMAKE) $$($$(PKG)_SRCDIR) \
>  		-DCMAKE_INSTALL_SO_NO_EXE=0 \
>  		-DCMAKE_FIND_ROOT_PATH="$$(HOST_DIR)" \
>  		-DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM="BOTH" \
> @@ -146,7 +185,7 @@ endif
>  # primitives to find {C,LD}FLAGS, add it to the dependency list.
>  $(2)_DEPENDENCIES += host-pkgconf
>  
> -$(2)_DEPENDENCIES += host-cmake
> +$(2)_DEPENDENCIES += $(BR2_CMAKE_HOST_DEPENDENCY)
>  
>  #
>  # Build step. Only define it if not already defined by the package .mk
> diff --git a/support/dependencies/check-host-cmake.mk b/support/dependencies/check-host-cmake.mk
> new file mode 100644
> index 0000000..8680ec9
> --- /dev/null
> +++ b/support/dependencies/check-host-cmake.mk
> @@ -0,0 +1,19 @@
> +# Versions before 3.0 are affected by the bug described in
> +# https://git.busybox.net/buildroot/commit/?id=ef2c1970e4bff3be3992014070392b0e6bc28bd2
> +# and fixed in upstream CMake in version 3.0:
> +# https://cmake.org/gitweb?p=cmake.git;h=e8b8b37ef6fef094940d3384df5a1d421b9fa568
> +#
> +# Set this to either 3.0 or higher, depending on the highest minimum
> +# version required by any of the packages bundled in Buildroot. If a
> +# package is bumped or a new one added, and it requires a higher
> +# version, our cmake infra will catch it and whine.
> +#
> +BR2_CMAKE_MIN_VERSION_MAJOR = 3
> +BR2_CMAKE_MIN_VERSION_MINOR = 1

 It's just a personal preference, but I'd rather see a single
BR2_CMAKE_MIN_VERSION = 3.1, and where you need the major or minor use ${v%.*}.

> +
> +BR2_CMAKE ?= cmake
> +ifeq ($(call suitable-host-package,cmake,\
> +	$(BR2_CMAKE) $(BR2_CMAKE_MIN_VERSION_MAJOR) $(BR2_CMAKE_MIN_VERSION_MINOR)),)
> +BR2_CMAKE = $(HOST_DIR)/usr/bin/cmake
> +BR2_CMAKE_HOST_DEPENDENCY = host-cmake
> +endif
> diff --git a/support/dependencies/check-host-cmake.sh b/support/dependencies/check-host-cmake.sh
> new file mode 100755
> index 0000000..4951a05
> --- /dev/null
> +++ b/support/dependencies/check-host-cmake.sh
> @@ -0,0 +1,26 @@
> +#!/bin/sh
> +
> +candidate="${1}"
> +major_min="${2}"
> +minor_min="${3}"
> +
> +cmake=`which ${candidate}`
> +if [ ! -x "${cmake}" ]; then
> +	# echo nothing: no suitable cmake found
> +	exit 1
> +fi
> +
> +version=`${cmake} --version | head -n1 | cut -d\  -f3`

 Again minor nit, but I think -d' ' is easier to understand than -d\ .

> +major=`echo "${version}" | cut -d. -f1`
> +minor=`echo "${version}" | cut -d. -f2`

 I know this is just copy-paste from the other scripts, but ${version%.*} really
is better.


 Regards,
 Arnout

> +
> +if [ ${major} -gt ${major_min} ]; then
> +	echo "${cmake}"
> +else
> +	if [ ${major} -eq ${major_min} -a ${minor} -ge ${minor_min} ]; then
> +		echo "${cmake}"
> +	else
> +		# echo nothing: no suitable cmake found
> +		exit 1
> +	fi
> +fi
>

Arnout, All,

On 2016-09-10 00:26 +0200, Arnout Vandecappelle spake thusly:
> On 07-09-16 00:32, Yann E. MORIN wrote:
> > From: Luca Ceresoli <luca@lucaceresoli.net>
> > 
> > Currently all cmake packages depend on host-cmake. Unfortunately
> > host-cmake takes a long time to configure and build: almost 7 minutes
> > on a dual-core i5 with SSD. The time does not change even with ccache
> > enabled.
[--SNIP--]
> > diff --git a/package/pkg-cmake.mk b/package/pkg-cmake.mk
> > index 4c6dc62..759b3e6 100644
> > --- a/package/pkg-cmake.mk
> > +++ b/package/pkg-cmake.mk
> > @@ -35,6 +35,38 @@ ifneq ($(QUIET),)
> >  CMAKE_QUIET = -DCMAKE_RULE_MESSAGES=OFF -DCMAKE_INSTALL_MESSAGE=NEVER
> >  endif
> >  
> > +#
> > +# Check the package does not require a cmake version more recent than we do.
> > +#
> > +# Some packages may use a variable to set the minimum required version. In
> > +# this case, there is not much we can do, so we just accept it; the configure
> > +# would fail later anyway in this case.
> > +#
> > +define CMAKE_CHECK_MIN_VERSION
> 
>  This would be perfect to do with a script instead - no make support is needed,
> except for passing $(@D) $($(PKG)_NAME) and BR2_CMAKE_MIN_VERSION.
> 
> > +	$(Q)v=$$( grep -hr -i 'cmake_minimum_required.*version' $(@D) \
> 
>  Shouldn't we search just in CMakeLists.txt files? Do you think it's likely that
> a package declares the minimum required version in and included file? That said,
> the extra time spent on grepping through everything doesn't amount to much
> unless it's a large package, and in that case it's anyway going to be dominated
> by package build time.

Well, grepping in a source tree that has been freshly extracted (i.e. it
would be cache-hot) would not be very costly...

> > +		|tr '[:upper:]' '[:lower:]' \
> > +		|sed -r -e '/.*\(version ([[:digit:]]+\.[[:digit:]]+).+/!d; s//\1/' \
> 
>  Not exactly an easy to understand sed script...

I must be very weird, then, as I can read it pretty easily:
  - any number of any character,
  - followed by an opening paranthesis,
  - followed by the literal string 'version' and then a space,
  - start a matching group
    - followed by one or more digits,
    - followed by a literal dot
    - followed by one or more digits,
  - end the matching group
  - followed by one or more of any character (implied: up to the end of
    the line),
  - delete lines that don't match the above,
  - on a line that matches, replace it with the matching group.

;-)

> > +		|sort -t. -k 1,1nr -k2,2nr \
> 
>  Since you're anyway doing the version sort here already, you could just add
> $(BR2_CMAKE_MIN_VERSION_MAJOR).$(BR2_CMAKE_MIN_VERSION_MINOR) into the mix and
> verify that the first line is equal to
> $(BR2_CMAKE_MIN_VERSION_MAJOR).$(BR2_CMAKE_MIN_VERSION_MINOR)

orry, I'm not sure I understand what you meant. Something like:

    (echo 3.1; grep blabla) |blabla

and then check that we get 3.1, right?

> We already use that trick for checking the make version, for instance.

I've looked at support/dependencies/dependencies.sh and we're not using
that "trick" to check the make version;

   85 MAKE_MAJOR=$(echo $MAKE_VERSION | sed -e "s/\..*//g")
   86 MAKE_MINOR=$(echo $MAKE_VERSION | sed -e "s/^$MAKE_MAJOR\.//g" -e "s/\..*//g" -e "s/[a-zA-Z].*//g")
   87 if [ $MAKE_MAJOR -lt 3 ] || [ $MAKE_MAJOR -eq 3 -a $MAKE_MINOR -lt 81 ] ; then
   88 »   echo
   89 »   echo "You have make '$MAKE_VERSION' installed.  GNU make >=3.81 is required"
   90 »   exit 1;
   91 fi;

> > +	else \
> > +		printf "*** Error: incorrect minimum cmake version:\n"; \
> > +		printf "*** Error: Buildroot requires %s.%s\n" \
> > +			$(BR2_CMAKE_MIN_VERSION_MAJOR) $(BR2_CMAKE_MIN_VERSION_MINOR); \
> > +		printf "*** Error: %s needs at least %s.%s\n" \
> > +			$($(PKG)_NAME) $${MAJOR} $${minor}; \
> 
>  I don't think this error message is very clear. How about:
> 
> *** Error: package %s needs cmake version %s.%s\n
> ***        Buildroot's minimum version BR2_CMAKE_MIN_VERSION\n
> ***        should be set to at least that version. Currently\n
> ***        it is set to %s.\n

If you want...

[--SNIP--]
> > diff --git a/support/dependencies/check-host-cmake.mk b/support/dependencies/check-host-cmake.mk
> > new file mode 100644
> > index 0000000..8680ec9
> > --- /dev/null
> > +++ b/support/dependencies/check-host-cmake.mk
> > @@ -0,0 +1,19 @@
> > +# Versions before 3.0 are affected by the bug described in
> > +# https://git.busybox.net/buildroot/commit/?id=ef2c1970e4bff3be3992014070392b0e6bc28bd2
> > +# and fixed in upstream CMake in version 3.0:
> > +# https://cmake.org/gitweb?p=cmake.git;h=e8b8b37ef6fef094940d3384df5a1d421b9fa568
> > +#
> > +# Set this to either 3.0 or higher, depending on the highest minimum
> > +# version required by any of the packages bundled in Buildroot. If a
> > +# package is bumped or a new one added, and it requires a higher
> > +# version, our cmake infra will catch it and whine.
> > +#
> > +BR2_CMAKE_MIN_VERSION_MAJOR = 3
> > +BR2_CMAKE_MIN_VERSION_MINOR = 1
> 
>  It's just a personal preference, but I'd rather see a single
> BR2_CMAKE_MIN_VERSION = 3.1, and where you need the major or minor use ${v%.*}.

OK...

> > +BR2_CMAKE ?= cmake
> > +ifeq ($(call suitable-host-package,cmake,\
> > +	$(BR2_CMAKE) $(BR2_CMAKE_MIN_VERSION_MAJOR) $(BR2_CMAKE_MIN_VERSION_MINOR)),)
> > +BR2_CMAKE = $(HOST_DIR)/usr/bin/cmake
> > +BR2_CMAKE_HOST_DEPENDENCY = host-cmake
> > +endif
> > diff --git a/support/dependencies/check-host-cmake.sh b/support/dependencies/check-host-cmake.sh
> > new file mode 100755
> > index 0000000..4951a05
> > --- /dev/null
> > +++ b/support/dependencies/check-host-cmake.sh
> > @@ -0,0 +1,26 @@
> > +#!/bin/sh
> > +
> > +candidate="${1}"
> > +major_min="${2}"
> > +minor_min="${3}"
> > +
> > +cmake=`which ${candidate}`
> > +if [ ! -x "${cmake}" ]; then
> > +	# echo nothing: no suitable cmake found
> > +	exit 1
> > +fi
> > +
> > +version=`${cmake} --version | head -n1 | cut -d\  -f3`
> 
>  Again minor nit, but I think -d' ' is easier to understand than -d\ .

OK...

> > +major=`echo "${version}" | cut -d. -f1`
> > +minor=`echo "${version}" | cut -d. -f2`
> 
>  I know this is just copy-paste from the other scripts, but ${version%.*} really
> is better.

Yep, I missed changing it...

Thanks!

Regards,
Yann E. MORIN.

On 11-09-16 15:35, Yann E. MORIN wrote:
> Arnout, All,
> 
> On 2016-09-10 00:26 +0200, Arnout Vandecappelle spake thusly:
>> On 07-09-16 00:32, Yann E. MORIN wrote:
[snip]
>>> +		|sort -t. -k 1,1nr -k2,2nr \
>>
>>  Since you're anyway doing the version sort here already, you could just add
>> $(BR2_CMAKE_MIN_VERSION_MAJOR).$(BR2_CMAKE_MIN_VERSION_MINOR) into the mix and
>> verify that the first line is equal to
>> $(BR2_CMAKE_MIN_VERSION_MAJOR).$(BR2_CMAKE_MIN_VERSION_MINOR)
> 
> orry, I'm not sure I understand what you meant. Something like:
> 
>     (echo 3.1; grep blabla) |blabla
> 
> and then check that we get 3.1, right?

 Yep.

> 
>> We already use that trick for checking the make version, for instance.
> 
> I've looked at support/dependencies/dependencies.sh and we're not using
> that "trick" to check the make version;
> 
>    85 MAKE_MAJOR=$(echo $MAKE_VERSION | sed -e "s/\..*//g")
>    86 MAKE_MINOR=$(echo $MAKE_VERSION | sed -e "s/^$MAKE_MAJOR\.//g" -e "s/\..*//g" -e "s/[a-zA-Z].*//g")
>    87 if [ $MAKE_MAJOR -lt 3 ] || [ $MAKE_MAJOR -eq 3 -a $MAKE_MINOR -lt 81 ] ; then
>    88 »   echo
>    89 »   echo "You have make '$MAKE_VERSION' installed.  GNU make >=3.81 is required"
>    90 »   exit 1;
>    91 fi;

 Ha, so we check for the make version twice then...

Top-level Makefile, line 51-59:
# Save running make version since it's clobbered by the make package
RUNNING_MAKE_VERSION := $(MAKE_VERSION)

# Check for minimal make version (note: this check will break at make 10.x)
MIN_MAKE_VERSION = 3.81
ifneq ($(firstword $(sort $(RUNNING_MAKE_VERSION)
$(MIN_MAKE_VERSION))),$(MIN_MAKE_VERSION))
$(error You have make '$(RUNNING_MAKE_VERSION)' installed. GNU make >=
$(MIN_MAKE_VERSION) is required)
endif


 Regards,
 Arnout

[snip]