[Scons-users] Emitters vs. Scanners

[William Blevins]

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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