[Scons-users] Build Order

[Russell, J.J.]

I’ll try to cut this example down to the minimum.  In the meantime, I’ve narrowed the issue to the symbolic links that are links, not to files, but to directories that I am having trouble with.  Even though I pass the stem of that include path to the C code, if the symbolic has not been created, the C scanner wouldn’t be able to locate the include file as a dependency.  That is the scanner will try all the include paths and none will locate the file. 

Here is a rough outline.  In the C file is something that looks like

   #include “test-pkg/platform/atomic_ops.h”

The CPPPATH includes a reference to a directory that looks like

      <platform-specific-stem>/inc/test-pkg/platform

where platform is a symbolic link, that dependent on the target platform, points to one of a number of directories that contain platform dependent code, for example

     <platform-specific-stem>/inc/test-pkg/platform ->  <project-stem>/test-pkg/inc/linux-x86_64  ..or..
                                                                                    <project-stem>/test-pkg/inc/rtems-armCA9 … etc…

(The platform selection is done when the user invokes scons.  The motivation for this is to keep the platform selection out of the C code avoiding the usual #ifdef preprocessor method, but instead using the include paths to do the steering and to keep the number of include paths to as few as possible. I think ‘boost’ attempts a similar tactic.)
 

 So in this case, a CPPPATH that looks like
       CPPPATH = <platform-specifiic-stem/inc>

The problem is the that the symbolic link <platform-specific-stem/inc/test-pkg/platform sometimes does not exist yet when the code is compiled.

I do not want to make every C file dependent on every included file, but I am wondering if what you are suggesting is just make it dependent on the existence of the CPPPATHs and the symbolically linked directories. That seems promising and I will try it.  Still not quite what I want, since at the SConscript level, I don’t know which of these symbolically linked directories any given piece of code uses.  Note that there are other symbolically linked directories in addition to ‘platform’.

As you may have surmised, I am a minimalist.  Having worked in medical and other safety conscious fieids, I grew to distrust search paths. They create unstable builds. It is not that they didn’t find a target (what I call fatal, but not serious; the build failed, just fix it), it is that they sometimes find the wrong target ( serious but not fatal, i.e. it built, but unless you look carefully, it is not what you wanted).

JJ



On Jul 12, 2014, at 10:48 PM, <scons-users-request at scons.org> <scons-users-request at scons.org> wrote:

> Date: Sat, 12 Jul 2014 23:33:57 +0200
> From: Dirk B?chle <tshortik at gmx.de>
> To: scons-users at scons.org
> Subject: Re: [Scons-users] Build Order
> Message-ID: <53C1A9C5.9010101 at gmx.de>
> Content-Type: text/plain; charset=windows-1252; format=flowed
> 
> Hello Jim,
> 
> On 12.07.2014 20:29, Russell, J.J. wrote:
>> Before compiling some C code, an include directory which that code uses needs to be populated.  I?ve written a builder to do this populating, but, because SCons controls the build order, there is no guarantee that the include directory will be populated when needed by the Object builder.
> 
> it should just work...if your Builder correctly returns the list of 
> copied targets in the include directory (you might need an Emitter for 
> this), and the CPPPATH variable points to your includes, such that they 
> get detected as implicit dependencies by SCons.
> Then it *is* guaranteed that the required headers get copied before a 
> target's build.
> 
> So I'm wondering why you think you need additional methods like Requires 
> or Depends. But maybe I'm missing something. Do you have something like 
> a simple example (SConstruct + Builder) that you can post?
> 
> Best regards,
> 
> Dirk