[Scons-dev] SCons missing dependencies (not rebuilding files when they need to be)

[Krzysztof Trzciński]

Below is fully self contained SConstruct showing (I think) a bug
(interesting bits at the end):

    env = Environment(tools=['default', 'textfile'])

    # That bit is not that important.
    # It just creates to programs, one of which
    # prints "1" and the other prints "2".
    # It just emulates having i.e. two versions of compiler
    # (in different directories).
    prints = []
    for num in (1,2):
        printcc = env.Textfile(
            '{0}/print.cc'.format(num),
            [(
                '#include <iostream>\n'
                'int main()\n'
                '{{\n'
                '    std::cout << "Printing " << {0} << std::endl;\n'
                '    return 0;\n'
                '}}\n'
            ).format(num),],
        )

        prints.extend(env.Program(
            '{0}/print'.format(num),
            printcc
        ))

    for p in prints:
        print p.path


    # Here starts the important bit.
    # This is not actual use case, actual use case for me was
    # changing compiler version (by changing base directory
    # of all my tools to newer version).
    # For ease of use this takes `use_task` argument to select
    # which "compiler version" to use.

    env['PRINT_TASK'] = prints[int(ARGUMENTS['use_task'])]

    # And now the build command dependent on
    # on "compiler".

    result = env.Command(
        'result.txt',
        [],
        '$PRINT_TASK > $TARGET'
    )

    Default(prints+result)

Now let's see how it works:

# Let's use "older compiler":

$ scons use_task=0
scons: Reading SConscript files ...
1/print
2/print
scons: done reading SConscript files.
scons: Building targets ...
Creating '1/print.cc'
g++ -o 1/print.o -c 1/print.cc
g++ -o 1/print 1/print.o
Creating '2/print.cc'
g++ -o 2/print.o -c 2/print.cc
g++ -o 2/print 2/print.o
1/print > result.txt
scons: done building targets.

$ cat result.txt
Printing 1

# All built fine and looking good.

# Now let's use "newer compiler".
# This one should produce "2" in result.txt

$ scons use_task=1
scons: Reading SConscript files ...
1/print
2/print
scons: done reading SConscript files.
scons: Building targets ...
scons: `1/print' is up to date.
scons: `2/print' is up to date.
scons: `result.txt' is up to date.
scons: done building targets.

$ cat result.txt
Printing 1

# Yet it doesn't! It says it is already up to date!
# HERE it went wrong.

# Some sanity checks to verify it is incorrectly
# reporting state.
# Let's just check if building that file first with
# use_task=1 gives us "2" in file.
# First remove result.txt to force build.

$ rm result.txt

# Then build with "new compiler".

$ scons use_task=1
scons: Reading SConscript files ...
1/print
2/print
scons: done reading SConscript files.
scons: Building targets ...
scons: `1/print' is up to date.
scons: `2/print' is up to date.
2/print > result.txt
scons: done building targets.

$ cat result.txt
Printing 2

# And this time it executed new compiler
# which gave expected result of "2".

# If I switch back to old one it again reports
# result to up to date incorrectly:

$ scons use_task=0
scons: Reading SConscript files ...
1/print
2/print
scons: done reading SConscript files.
scons: Building targets ...
scons: `1/print' is up to date.
scons: `2/print' is up to date.
scons: `result.txt' is up to date.
scons: done building targets.

So bottom line seems to be that SCons is missing out on dependencies.
When a substition value is a file node it seems to only look at `node.name`,
not whole `node.path`, causing incorrect rebuilds.

I have checked and it seems to behave that way on 2.5.0 version (everyday
we got stuck on 2.1.0).

Is this a bug? If not what is the explanation of this behaviour?

On 5 May 2016 at 21:41, <scons-dev-request at scons.org> wrote:
Welcome to the Scons-dev at scons.org mailing list!

To post to this list, send your message to:

  scons-dev at scons.org

General information about the mailing list is at:

  https://pairlist2.pair.net/mailman/listinfo/scons-dev

If you ever want to unsubscribe or change your options (eg, switch to
or from digest mode, change your password, etc.), visit your
subscription page at:


https://pairlist2.pair.net/mailman/options/scons-dev/christopher.trzcinski%2Bscons%40gmail.com


You can also make such adjustments via email by sending a message to:

  Scons-dev-request at scons.org

with the word `help' in the subject or body (don't include the
quotes), and you will get back a message with instructions.

You must know your password to change your options (including changing
the password, itself) or to unsubscribe without confirmation.  It is:

  MJwKL3hoS2sc

Normally, Mailman will remind you of your scons.org mailing list
passwords once every month, although you can disable this if you
prefer.  This reminder will also include instructions on how to
unsubscribe or change your account options.  There is also a button on
your options page that will email your current password to you.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://pairlist2.pair.net/pipermail/scons-dev/attachments/20160506/690e5140/attachment.html>