[Scons-users] Emitters vs. Scanners

Mon Mar 14 18:04:57 EDT 2016

Tom,

Does this previously reported issue look related (or exact):
http://scons.tigris.org/issues/show_bug.cgi?id=3022

On Mon, Mar 14, 2016 at 10:02 PM, Bill Deegan <bill at baddogconsulting.com>
wrote:

> I'd concur with what William said. If you're going to hack on this pull
> from the current default branch and work from there as there's been some
> non-trivial changes to how all this works in SCons which will be released
> with the next release.
> (Waiting on a couple pull requests to be ready before we publish that)
>
> I'm having a hard time understanding exactly what the issue is you're
> trying to solve.
> If you can make a toy build which demonstrates it, it would be better to
> have a concrete example.
>
> Thanks,
> Bill
>
> On Mon, Mar 14, 2016 at 5:26 PM, Plunket, Tom <
> tom.plunket at aristocrat-inc.com> wrote:
>
>> Thank you. I’ll pull the trunk to see how it works in my environment and
>> will start toying with tests.
>>
>>
>>
>> *From:* Scons-users [mailto:scons-users-bounces at scons.org] *On Behalf Of
>> *William Blevins
>> *Sent:* Monday, March 14, 2016 2:10 PM
>>
>> *To:* SCons users mailing list <scons-users at scons.org>
>> *Subject:* Re: [Scons-users] Emitters vs. Scanners
>>
>>
>>
>> I assume what you are asking for exists in
>> src/engine/SCons/Node/__init__.py in the Node class per the HG Trunk (not
>> yet released). In earlier versions of SCons, scanner execution happened in
>> the executor directly: src/engine/SCons/Executor.py.
>>
>>
>>
>> V/R,
>>
>> William
>>
>>
>>
>> On Mon, Mar 14, 2016 at 8:47 PM, Plunket, Tom <
>> tom.plunket at aristocrat-inc.com> wrote:
>>
>> Ok, so since I care about this I can spend energy working on it but
>> beyond browsing the sources I don’t have a great handle on where to start
>> on this.
>>
>>
>>
>> Is this an appropriate forum to ask where I should start poking, where I
>> can put an appropriate test for (or rather against) this behavior, so that
>> I can start the ball rolling on a fix? Should I join another forum for
>> development issues and questions?
>>
>>
>>
>> *From:* Scons-users [mailto:scons-users-bounces at scons.org] *On Behalf Of
>> *William Blevins
>> *Sent:* Monday, March 14, 2016 1:25 PM
>>
>>
>> *To:* SCons users mailing list <scons-users at scons.org>
>> *Subject:* Re: [Scons-users] Emitters vs. Scanners
>>
>>
>>
>> It is known, but it is not desired obviously.
>>
>>
>>
>> On Mon, Mar 14, 2016 at 7:13 PM, Plunket, Tom <
>> tom.plunket at aristocrat-inc.com> wrote:
>>
>> So it’s known (and desirable?) that scanners run on targets that are
>> scheduled for replacement?
>>
>>
>>
>> *From:* Scons-users [mailto:scons-users-bounces at scons.org] *On Behalf Of
>> *William Blevins
>> *Sent:* Friday, March 11, 2016 6:42 PM
>>
>>
>> *To:* SCons users mailing list <scons-users at scons.org>
>> *Subject:* Re: [Scons-users] Emitters vs. Scanners
>>
>>
>>
>> A TL;DR for scanners vs emitters. Emitters give explicit target nodes
>> (for the action being done) and scanners find implicit dependency nodes
>> (for the source being acted upon).
>>
>>
>>
>> V/R,
>>
>> William
>>
>>
>>
>> On Sat, Mar 12, 2016 at 2:13 AM, Plunket, Tom <
>> tom.plunket at aristocrat-inc.com> wrote:
>>
>> Ok cool, thanks for the example, I hadn’t thought of lex and yacc as
>> similar to what I’m doing. I see that they both use emitters and don’t have
>> scanners so maybe my understanding of emitter vs. scanner is … nonexistent.
>> J
>>
>>
>>
>> I see the CScanner is put in as a source_scanner. The mention of this
>> option in the documentation is sparse, I had previously put my scanner into
>> the environment with the file extension but it wasn’t attached to a
>> specific builder. Now that I have it attached to the builder I’d hoped it’d
>> fix things but… it doesn’t. L
>>
>>
>>
>> My Scene generate function is step A->B:
>>
>>     myAction = Action(sceneExport, 'Exporting ${SOURCES.file} to
>> ${TARGETS.file}.')
>>
>>     builder = Builder(action = myAction)
>>
>>     env.Append(BUILDERS = { 'Scene': builder })
>>
>>
>>
>> My Asset generate (step B->C) function sets it up like this (LAUNCH is a
>> command line hardcoded elsewhere):
>>
>>     message = "Packaging ${TARGETS.file}"
>>
>>     myAction = Action(LAUNCH, message)
>>
>>     assetScanner = Scanner(function=assetScan, skeys=['.xml'])
>>
>>     builder = Builder(action = myAction, source_scanner=assetScanner)
>>
>>     env.Append(BUILDERS = { 'Asset': builder })
>>
>>
>>
>> Print statements in the scanner (“Scanning blahblah.xml”) print before
>> the Scene command string (“Exporting blahblah.aep to blahblah.xml”).
>>
>>
>>
>> I’ll keep banging on this though and if I can get it going I’ll let
>> everyone know what I did wrong. If I can’t I’ll try to strip this down
>> (that is unfortunately more work than it should be at this point). The
>> SCons source is still a little opaque to me as it seems like components of
>> this process are spread around various folders somewhat wantonly still. J
>> (That’s not a criticism of anything beyond my own understanding!)
>>
>>
>>
>> -tom!
>>
>>
>>
>>
>>
>> *From:* Scons-users [mailto:scons-users-bounces at scons.org] *On Behalf Of
>> *Bill Deegan
>> *Sent:* Friday, March 11, 2016 3:22 PM
>> *To:* SCons users mailing list <scons-users at scons.org>
>> *Subject:* Re: [Scons-users] Emitters vs. Scanners
>>
>>
>>
>> Tom,
>>
>> Likely DynamicSourceGenerator is overkill for u.
>>
>> Can you create a small example to demonstrate your problem?
>>
>> If a->b is entirely predictable, then is there a:
>>
>> env.MyBuilder('b','a')
>>
>> env.otherBuilder('c','b')
>>
>> If SCons doesn't know that b is generated from a, then I can see the
>> issue you're running into.
>>
>> lex/yacc do similar and have no issues..
>>
>>
>>
>> -Bill
>>
>>
>>
>> On Fri, Mar 11, 2016 at 5:07 PM, Plunket, Tom <
>> tom.plunket at aristocrat-inc.com> wrote:
>>
>> I am struggling with an issue where an intermediate file is getting
>> scanned for targets even though it is about to get regenerated.  I’m
>> curious if I need to change my Scanner into an Emitter or if there’s
>> something else I should be considering?
>>
>>
>>
>> The flow is A->B->C, A is the input file which creates B. B is the
>> primary source for C but (B) also lists a bunch of other files that need to
>> go into C.  filename.a gets processed into filename.b and that, along with
>> the results of the scan get bundled up into filename.c. The closest
>> software construction analogy would be that A is like a “premake” or “
>> makefile.in” file, B would be the makefile and would list the source
>> files to be compiled, and C is the executable that results.
>>
>>
>>
>> If B exists, it gets scanned during dependency generation by the scanner,
>> even if A has changed. This is a problem if B refers to invalid or
>> otherwise broken dependencies that have been fixed by the changes to A,
>> since I will not be able to build nor clean these items without manually
>> deleting B.
>>
>>
>>
>> I’m looking at
>> https://bitbucket.org/scons/scons/wiki/DynamicSourceGenerator but I’m
>> not yet sure that it’ll fix my problem (or maybe it’s overkill) since B
>> exists, it just needs to get recreated before getting scanned.
>> (Could/should it be considered a deficiency to scan a file that’s scheduled
>> for replacement in the first place?)
>>
>>
>>
>> Thanks and sorry for the corporate junk that the email gateway sticks on
>> the end of this message.
>>
>>
>>
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