Re: [Boost-build] Generated header files.

Subject: Re: [Boost-build] Generated header files.
From: Mathias Lorente (mathias.lorente_at_[hidden])
Date: 2008-12-04 06:34:22

Vladimir Prus wrote:
> On Thursday 04 December 2008 11:34:42 Mathias Lorente wrote:
>   
>> Vladimir Prus wrote:
>>     
>>> On Wednesday 03 December 2008 19:09:16 Mathias Lorente wrote:
>>>   
>>>       
>>>> Vladimir Prus wrote:
>>>>     
>>>>         
>>>>> On Wednesday 03 December 2008 17:36:05 Mathias Lorente wrote:
>>>>>   
>>>>>       
>>>>>           
>>>>>> Dear list,
>>>>>>
>>>>>> I use bjam to build a library which relies on some generated header files.
>>>>>> These files are generated by a specific application which is also built 
>>>>>> using bjam.
>>>>>> I added a dependency for my library so that the application is built 
>>>>>> before the library.
>>>>>> But:
>>>>>> - I didn't manage to launch the application in order to generate the 
>>>>>> necessary header files before the library is being built.
>>>>>>     
>>>>>>         
>>>>>>             
>>>>> Hi Mathias,
>>>>>
>>>>> it's generally best to show what approaches you've tried, so that you
>>>>> get help about your specific issue, not some approximation. Generally,
>>>>> something like this should work:
>>>>>
>>>>>
>>>>> 	exe header_generator : header_generator.cpp ;
>>>>> 	make header.h : header_generator : @generate-header ;
>>>>> 	actions generate-header 
>>>>> 	{
>>>>> 		$(>) > $(<)
>>>>> 	}
>>>>> 	lib header_user : header_user.cpp : <implicit-dependency>header.h ;
>>>>>
>>>>> - Volodya
>>>>>   
>>>>>       
>>>>>           
>>>> Hello Volodya,
>>>>
>>>> Thanks for your reply.
>>>> In fact my 'header generator' uses input files (let's say .txt) which 
>>>> are parsed/modified/... to make the corresponding .h files.
>>>> Until now, I was launching the generator by hand and it was working on 
>>>> all files in the specified directory (as command line parameter).
>>>> I suppose I would have to modify it in order to make it take one file at 
>>>> a time. 
>>>>     
>>>>         
>>> For dependency tracking, it's best if each invocation takes specific input
>>> and produces a single file. Otherwise, Boost.Build or you would have to run
>>> your tool on all files. Here's how to modify my code to make it accept a source:
>>>
>>>  	make header.h : header_generator input.txt : @generate-header ;
>>>  	actions generate-header 
>>> 	{
>>>  		$(>[1]) $(>[2]) > $(<)
>>>  	}
>>>   
>>>       
>> I have modified my header generator which takes one input file and 
>> writes the corresponding header file in the same directory as the input 
>> file. So I have the following bjam script:
>>
>>     make header.h
>>       : ../utils//gen header.txt
>>       : @generate-header
>>       ;
>>
>>     actions generate-header
>>     {
>>       $(>[1]) $(>[2])
>>     }
>>
>> But this solution does not meet some requirements:
>> - Each time I launch bjam, the header generator is launched even if 
>> header.txt has not been modified.
>>     
>
> This means that your tool generates header not where Boost.Build wants
> it to be -- which I've mentioned in the previous email.
> Add 
>
> 	echo $(<)
>
> to your actions. This will print the location where the header *should* be generated.
> And then check if that location actually has the file. If you want the file to
> be located somewhere else, use:
>
>      make header.h
>        : ../utils//gen header.txt
>        : @generate-header
>        : <location>somewhere
>        ;
>
>   
>> - My library (which relies on generated header) is rebuilt only the 
>> second time I launch bjam: first time, headers are generated, second 
>> time, headers are generated and the library is rebuilt. I suspect that 
>> bjam checks the timestamp of the header files before they are generated 
>> again...
>> Here is the definition to build my library:
>>
>>     lib my_lib
>>       : [ glob-tree *.cpp : .svn ]
>>       : <link>static
>>         <define>BUILDING_LIBRARY
>>         <variant>debug:<define>ENABLE_DEBUG_LOG
>>       ;
>>     
>
> This lacks <implicit-dependency> -- which I've mentioned previously as well.
> You can read about that in the docs:
>
> 	http://www.boost.org/boost-build2/doc/html/bbv2/reference/generated_headers.html
>
> - Volodya
Thank you for all your efforts!

I added the <location> and the <implicit-dependency>.
Now header files are no more generated unless input files are modified.
But there is still the second behavior I've described: when one 
header.txt is updated, the first time I run bjam, new header file is 
generated. I need to launch again bjam in order to generate updated 
version of my library (the second time header files are not generated 
again).
So to test whether actions are performed in right order, I did the 
following:

    $ touch header.h
    $ touch header.txt  (so header.h need to be regenerated)
    $ bjam

First the header files are generated, then my library is built.
New definition to build my library:

    lib my_lib
        : [ glob-tree *.cpp : .svn ]
        : <implicit-dependency>../utils//gen
          <link>static
          <define>BUILDING_LIBRARY
          <variant>debug:<define>ENABLE_DEBUG_LOG
        ;

Do you have any other suggestion?
Mathias