[Scons-users] scons checking targets actually built?

[robert zeigler]

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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>>

>>

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