Re: [boost] [build] Running b2 with particular toolset invokes other toolsets in user-config.jam

Subject: Re: [boost] [build] Running b2 with particular toolset invokes other toolsets in user-config.jam
From: Edward Diener (eldiener_at_[hidden])
Date: 2014-08-26 21:14:41

On 8/26/2014 5:43 PM, Steven Watanabe wrote:
> AMDG
>
> On 08/26/2014 03:23 PM, Edward Diener wrote:
>>
>> I did not mean to imply that it was building with some other toolset but
>> that it is executing some other executables mentioned in my
>> user-config.jam, for what reason I do not understand. I posted the
>> result of:
>>
>> b2 --debug-configuration toolset=gcc-4.8.1
>>
>> on the Boost Build forum after asked to do so but never heard anything
>> further. The output shows that clang is being executed for some reason
>> or other.
>>
>
> I see.  That's the expected behavior.  It's
> running clang in order to get the version number
> from the compiler.  using clang ... ; is a function
> call which configures the clang toolset and it
> does so immediately.

I think it is wrong to do so immediately. If I am using the clang 
toolset I would understand it, but if I am not using the clang toolset I 
do not understand what purpose configuring the clang toolset could serve.

I do understand that as far as Boost Build is concerned user-config.jam 
is probably just another jamfile, which follows the rules of how jam 
files are processed, and that this may make programming Boost Build 
easier. But I think an exception should be made for user-config.jam ( 
and probably site-config.jam also ) in that the end-user may place jam 
statements in it which are totally irrelevant for the particular jam 
file(s) being invoked and the toolset used, but which will of course be 
relevant in another situation. Therefore completely configuring toolsets 
which appear in user-config.jam, before the toolsets are specified 
anywhere in the jam file(s) being invoked, every time b2 is run against 
jam file(s) and a toolset is specified, does not seem the right way of 
doing things to me.

Besides the local problem I encountered, described in my OP, which 
admittedly is very probably a rare situation, Boost Build is doing all 
sorts of extra processing it probably doesn't need to do the majority of 
the time when b2 is run, when it auomatically configures every toolset 
in user-config.jam which has the 'using toolset ... ' statement.

I will file this as a suggestion on Trac and I hope it will be 
considered in Boost Build.