[Buildroot] [PATCH 1/2 v8] core: don't build host-cmake if it is available on the build host

[Luca Ceresoli <luca@lucaceresoli.net>]

Dear Arnout, Yann,

On 14/09/2016 00:45, Arnout Vandecappelle wrote:
> 
> 
> On 13-09-16 23:34, Yann E. MORIN wrote:
>> Luca, All,
>>
>> On 2016-09-13 23:05 +0200, Luca Ceresoli spake thusly:
>>> On 12/09/2016 23:59, 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/support/dependencies/check-host-cmake.sh b/support/dependencies/check-host-cmake.sh
>>>> new file mode 100755
>>>> index 0000000..9b63b06
>>>> --- /dev/null
>>>> +++ b/support/dependencies/check-host-cmake.sh
>>>> @@ -0,0 +1,39 @@
>>>> +#!/bin/sh
>>>> +
>>>> +candidate="${1}"
>>>> +version_min="${2}"
>>>> +
>>>> +major_min="${version_min%.*}"
>>>> +minor_min="${version_min#*.}"
>>>> +
>>>> +cmake=`which ${candidate}`
>>>> +if [ ! -x "${cmake}" ]; then
>>>> +    # echo nothing: no suitable cmake found
>>>> +    exit 1
>>>> +fi
>>>> +
>>>> +# Extract version X.Y from versions in the form X.Y or X.Y.Z
>>>> +# with X, Y and Z numbers with one or more digits each, e.g.
>>>> +#   3.2     -> 3.2
>>>> +#   3.2.3   -> 3.2
>>>> +#   3.2.42  -> 3.2
>>>> +#   3.10    -> 3.10
>>>> +#   3.10.4  -> 3.10
>>>> +#   3.10.42 -> 3.10
>>>> +version="$(${cmake} --version \
>>>> +           |sed -r -e '/.* ([[:digit:]]+\.[[:digit:]]+).*$/!d;' \
>>>> +                   -e 's//\1/'
>>>> +          )"
>>>> +major="${version%.*}"
>>>> +minor="${version#*.}"
>>>
>>> You removed the 'head -n1' in the pipe.
>>
>> Indeed, but look at the sed script (which is not that complicated): all
>> lines that do not match the pattern are ignored.
>>
>>         |sed -r -e '/.* ([[:digit:]]+\.[[:digit:]]+).*$/!d;' \
>>                                                Here ----^
>>
>> "!d" means "if no match, delete line".
>>
>> Then the next expression is only aplied on matching lines, and "\1"
>> refers to the ()-match, which is the version string.
> 
>  You snipped away Luca's example: if there are two lines that contain something
> that looks like a version number, then you get two versions out of this script.
> So repeating Luca's example:
> 
>   cmake version 3.5.1
> 
>   Linked against libfoobar 7.6.5
> 
> will give you
> 
> version="3.5
> 7.6"

You're right. Yann and I clarified this yesterday night on IRC.

OTOH we also agreed that:

 1. the script in v8 works with all cmake versions we are aware of,
    including 2.8.* and 3.5.1
 2. adding 'head -n1', or any other change to the script, can guard
    against any possible future change in the output of 'cmake
    --version' that we just can't predict.

Thus you can consider my comment as "if I wrote it, I'd have put a head
-n1", which is a matter of personal taste and not a request to Yann to
change the code. Should cmake change its output in the future, we'll
handle it when it happens.

-- 
Luca