[Scons-users] scons checking targets actually built?

[robert zeigler]

Perhaps it could be something configured on a per-environment basis?
I'm willing to do the work and submit the patch, but would appreciate some
guidance. I'm still really just getting my feet wet with scons.

Robert


On Fri, Apr 19, 2013 at 6:47 AM, Gary Oberbrunner <garyo at oberbrunner.com>wrote:


> If it were an option, off by default, why not? Patches accepted gratefully

> :-) But that said, you might get more false positives than you think.

> On Apr 19, 2013 7:06 AM, "Tom Tanner (BLOOMBERG/ LONDON)" <

> ttanner2 at bloomberg.net> wrote:

>

>> I must say I'd really like to see scons do this check (that the targets

>> actually exist at the end of the build rule).

>>

>> It would be a great help in tracking down broken build rules (and I've

>> had more than a few in my time). It's more difficult to get this wrong in

>> scons than in make, but it's still possible and it is a nightmare to track

>> down.

>>

>> And it presumably wouldn't be an expensive check to see if the file at

>> least exists.

>>

>> ----- Original Message -----

>> From: scons-users at scons.org

>> To: scons-users at scons.org

>> At: Apr 19 2013 02:00:59

>>

>>

>> Ah... makes sense, I suppose. I just figured that with scons computing

>> md5 hashes of sources to determine target freshness, it would have noticed

>> that the source was missing when attempting to build the dependent target,

>> but I suppose that's not going to be the case on the initial build because

>> the target has never been built, so there's no "freshness" to compute.

>>

>>

>> On Thu, Apr 18, 2013 at 7:49 PM, Gary Oberbrunner <garyo at oberbrunner.com>

>> wrote:

>>

>>

>> Hi Robert; some people make fake targets in SCons (like Make) so if SCons

>> complained about those people's builds would probably break.  I think it's

>> expected behavior at least in that case.

>> On Apr 18, 2013 7:13 PM, "robert zeigler" <robert.zeigler at gmail.com>

>> wrote:

>>

>> Hi,

>>

>> Fairly new to scons. I have been playing with it the last few days and

>> like what I see. However, I stumbled on behavior today that has me troubled.

>>

>> Consider a very simple build script:

>>

>> Command(['a.txt'],[],"echo hi > $TARGET")

>> Command(['b.txt'],['a.txt'],"cat $SOURCE > $TARGET && echo foo >>

>> $TARGET")

>>

>> This runs fine:

>>

>> scons: Reading SConscript files ...

>> scons: done reading SConscript files.

>> scons: Building targets ...

>> echo hi > a.txt

>> cat a.txt > b.txt && echo foo >> b.txt

>> scons: done building targets.

>>

>> Now consider an alternative command for building a:

>>

>> Command(['a.txt'],[],"echo hi > $TARGET && rm $TARGET")

>>

>> Then you get:

>>

>> scons: Reading SConscript files ...

>> scons: done reading SConscript files.

>> scons: Building targets ...

>> echo hi > a.txt && rm a.txt

>> cat a.txt > b.txt && echo humbug >> b.txt

>> cat: a.txt: No such file or directory

>> scons: *** [b.txt] Error 1

>> scons: building terminated because of errors.

>>

>> The build fails, of course, but what troubles me is that it doesn't fail

>> until we attempt to build b.txt. I would have expected scons to verify that

>> the target was actually build by the command; failing that, I'm surprised

>> that it attempted to build b.txt when a.txt was clearly not present for

>> b.txt to be built?

>>

>> Clarification on this is greatly appreciated. Although the case above is

>> trivial, I ran into this issue in a non-trivial case, as well.

>>

>> Robert

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