[bdbaddog]

Fix Issue #2811

Reproducing this issue requires the following.

1. Generated source file which outputs 2 (or more) files
2. Action string gets scanned providing only compiler as part of implicit scan
3. Generated file gets built. Without the bugfix only the first target's .implicit list is cleared.
4. builder/executor/action gets tried again and implicits scanned. 2nd to Nth targets end up
   with the compiler at the beginning of the implicit list and the rest of the scanned files added to that list.
5. That bimplicit gets saved into sconsign
6. Second run loads sconsign, now with generated file present a regular implicit scan occurs. This yields 2nd through
   Nth target's implicit lists changing when compared to SConsign's which have been loaded.
7. This forces rebuild of source file and this propagates to massive recompile

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated master/src/CHANGES.txt directory (and read the README.txt in that directory)
• I have updated the appropriate documentation

[garyo]

This looks fine to me. I guess my only question would be why aren't the other targets already in waiting_parents so they get cleared above? (Just curious)

[bdbaddog]

It's a combination of the first target hit by the taskmaster walk and the fact that the N targets aren't linked. I'm going to continue looking at this, but this fix resolves a long standing issue so accepting the good enough, and then will continue working on the maybe better solution.