(BBv1 and BBv2) Unnecessary compiles due to header/directory name conflict

From: c_andy_martin (c_andy_martin_at_[hidden])
Date: 2004-11-12 14:36:53

This seems to be a problem with bjam. If you have a directory named
the same as an include file in your project, when the directory's
timestamp is changed bjam interprets the include file as being out of
date. This is a problem, when for instance, you have a directory
called `utility' that you include files from, and you also make use of
the STL <utility> header (either directly, or indirectly). See the
original email below for a detailed example.

Does anyone familiar with the bjam source no why this is occuring and
if there are any workarounds? I'm not familiar enough with the bjam
source to track down where the timestamping is done and why it
confuses a directory name in one directory with an include file in
another.

I have tried this with both BBv1 and BBv2 with the exact same results.

Thank you for any response!

-Andy

--- In jamboost_at_[hidden], "c_andy_martin" <c_andy_martin_at_y...>
wrote:
> 
> In my programming project, I have discovered an interesting "feature"
> of bjam. I have created a sample project which demonstrates this
> feature. Here is the output of `tree':
> .
> |-- Jamfile
> |-- Jamrules
> |-- boost-build.jam
> |-- common
> | |-- Jamfile
> | |-- exception
> | | |-- Exception.cpp
> | | `-- Exception.h
> | |-- test
> | | |-- test.cpp
> | | `-- test.h
> | `-- xml
> | |-- xml_a.cpp
> | |-- xml_a.h
> | |-- xml_b.cpp
> | `-- xml_b.h
> `-- main
> |-- Jamfile
> `-- main.cpp
> 
> Now, I have added <include>common to the Jamfiles, so that I can write:
> #include "test/test.h"
> from main.cpp and from test.cpp, etc.
> 
> The project builds normally. Everything works. Now we do something
> that should normally have no effect on rebuilding:
> cd project_root; touch common/exception/
> 
> However, because common/exception/Exception.h has this line:
> #include <exception>
> bjam thinks that the standard include <exception> was updated, so all
> of its dependencies must be updated (since it confused the directory
> `exception' with the standard include file <exception>!).
> 
> This is really frustrating because using commands like `vi
> common/exception/Exception.h' causes the timestamp on the directory
> `common/exception' to be udpated (because of swap file creation) so
> bjam interprets this as the standard include <exception> being out of
> date, forcing to rebuild almost the entire project which makes
> programming very difficult.
> 
> My actual project is much, much larger than this and moving files
> around and renaming things at this point to get around the conflict
> would be inconvinient. Note that parts of the boost distribution would
> have had this problem if instead of <include>$(BOOST_ROOT) was used,
> <include>$(BOOST_ROOT)/boost and code used #include
> <utility/result_of.hpp> in place of #include
> <boost/utility/result_of.hpp> and the standard header #include
> <utility> was used as well. I suppose I could go through all my code
> and translate include files like <exception/Exception.h> into
> <common/exception/Exception.h> and that would fix things.
> 
> Is there any easy way to work around this other than renaming
> directories which match standard include files (such as <exception>,
> <string>, <utility>, <algorithm>, etc.)? I guess one way might be to
> somehow modify the search path so that bjam finds the standard
> exception include before the directory common/exception.
> 
> Thanks for any help,
> -Andy