[Scons-users] Bug in up_to_date for directory targets

[Manish Vachharajani]

If you look at my original message, the problem is that in my real use
case, I have no idea what the file targets will be.  The only target I know
will be built by the builder is a set of directories.  Your example simply
causes scons to have a file target in the second Command builder which
works around the bug as I describe in my original email.  In real life, my
builder looks something like this;

env.Command(['node_modules/minimist', 'node_modules/@types/node, ...],
#these are directories
            ['package.json'],
            ['npm install --global-style'],
            chdir=Dir('.')) #chdir because npm doesn't have a way to
install elsewhere

In this case, I have no idea what files npm install will create.  The
targets array is actually created by reading package.json and looking at
the dependencies and devDependencies fields of the main object, so those
aren't even hard-coded in the SConstruct/SConscript.

Again, if I fake out scons by have a 'node_modules/.built' File target in
the list and add a 'touch node_modules/.built' command to the builder after
'npm install', all will work as expected because there is a File target.
In your example, things work because the second builder has a file target
and SCons will only run the first builder in your example when foo does not
exist, regardless of the state of foo-contents.txt in relation to what is
in .sconsign.  That is the essence of the bug, if the target directory
exists and it is the only target, the builder will not run regardless of
the state of the sources.

Manish


On Mon, Mar 20, 2017 at 9:09 PM, William Blevins <wblevins001 at gmail.com>
wrote:

> Manish,
>
> * Why does my example not work?
>
> SCons Comand Builder parameters are target(s), source(s), command(s):
> http://scons.org/doc/HTML/scons-user.html#chap-builders-commands
>
> Foo is the target parameter, and foo-contents.txt is the source parameter.
> Targets explicitly depend on sources. In your example, directory foo
> depends on source file foo-contents.txt; target file copy does not depend
> on source file.
>
> * How do I fix this issue?
>
> 1. Call Command Builder correctly: Command('foo', 'foo-contents', 'mkdir
> $TARGET') which creates file dependency on directory, and then
> Command('foo/foo-contents.txt', 'foo-contents.txt', 'cp $SOURCE $TARGET')
> which creates file target dependency on file source.
>
> 2: [PREFERRED] Use the SCons FileSystem factory http://scons.org/doc/HTML/
> scons-user.html#chap-factories
>
> V/R,
> William
>
>
> On Mon, Mar 20, 2017 at 1:47 PM, Manish Vachharajani <
> manishv at unbounded.systems> wrote:
>
>> I believe there is a bug in how up to date is computed for file nodes and
>> directory targets.  Below is a SConstruct and run output illustrating the
>> bug.
>>
>> ##############
>> # SConstruct
>> env = Environment()
>> targets = env.Command('foo',
>>                       'foo-contents.txt',
>>                       ['mkdir foo',
>>                        'cp foo-contents.txt foo'])
>> env.Default(targets)
>>
>> ##############
>> # Shell log
>>
>> # Create the file that will be installed into foo/foo-contents.txt
>> $ echo "Hello, " >> foo-contents.txt
>> # All is well, scons runs the command builder as expected
>> $ scons
>>
>> scons: Reading SConscript files ...
>> scons: done reading SConscript files.
>> scons: Building targets ...
>> mkdir foo
>> cp foo-contents.txt foo
>> scons: done building targets.
>>
>> # All is well, the target is up to date as expected
>> $ scons
>>
>> scons: Reading SConscript files ...
>> scons: done reading SConscript files.
>> scons: Building targets ...
>> scons: `foo' is up to date.
>> scons: done building targets.
>>
>> # Uh-oh, source is updated but the target is considered up to date!
>> $ echo "World!" >> foo-contents.txt
>> $ scons
>>
>> scons: Reading SConscript files ...
>> scons: done reading SConscript files.
>> scons: Building targets ...
>> scons: `foo' is up to date.
>> scons: done building targets.
>>
>> For the bug to trigger, all targets for a builder must be directories.
>> The target directory must exist and the source file must exist and be out
>> of date due to a content update (resulting in a signature mismatch).
>>
>> I think the problem is that is_up_to_date for File nodes only checks the
>> signatures of its children, which avoids this bug as long as one of the
>> builder targets is a File and not a Directory.  However, I haven't done
>> enough analysis to be sure that this is the issue.
>>
>> A work around is to make sure that you have a file (or create a dummy
>> .built file) and include it as a target.
>>
>> This is showing up specifically for us when trying to calculate
>> dependencies for a package manager (npm) where we have no insight into the
>> contents of the resulting directory.
>>
>> Manish
>>
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>>
>>
>
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