diff reachability: only use start locations present and active in both snapshots

[anothermattbrown]

No description provided.

[batfish-bot]

This change is 

[codecov]

Codecov Report

Merging #5236 into master will decrease coverage by <.01%.
The diff coverage is 91.3%.

@@             Coverage Diff              @@
##             master    #5236      +/-   ##
============================================
- Coverage     73.33%   73.33%   -0.01%     
+ Complexity    31834    31829       -5     
============================================
  Files          2610     2610              
  Lines        128396   128411      +15     
  Branches      15423    15424       +1     
============================================
+ Hits          94163    94168       +5     
- Misses        26794    26804      +10     
  Partials       7439     7439

Impacted Files	Coverage Δ	Complexity Δ
...reachability/DifferentialReachabilityAnswerer.java	93.54% <91.3%> (-2.2%)	3 <1> (ø)
.../src/main/java/org/batfish/datamodel/flow/Hop.java	53.33% <0%> (-6.67%)	5% <0%> (-1%)
...org/batfish/datamodel/flow/BidirectionalTrace.java	79.54% <0%> (-2.28%)	13% <0%> (-1%)
...col/src/main/java/org/batfish/role/InferRoles.java	89.54% <0%> (-1.37%)	50% <0%> (-1%)
...tfish/representation/cisco/CiscoConfiguration.java	85.48% <0%> (-0.13%)	519% <0%> (-1%)

[progwriter]

Reviewed 2 of 3 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @anothermattbrown)

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projects/question/src/main/java/org/batfish/question/differentialreachability/DifferentialReachabilityAnswerer.java, line 74 at r2 (raw file):

    // requiredTransitNodes can be different in each snapshot. flow must transit any one
    Set<String> requiredTransitNodes =
        Sets.union(

I would have assumed this has to be intersection. must transit same node(s) in both snapshots?

[anothermattbrown]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @progwriter)

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projects/question/src/main/java/org/batfish/question/differentialreachability/DifferentialReachabilityAnswerer.java, line 74 at r2 (raw file):

Previously, progwriter (Victor Heorhiadi) wrote…

I would have assumed this has to be intersection. must transit same node(s) in both snapshots?

semantics of required transit nodes is that any (i.e. one) of the specified nodes must be transited. we do not enforce that the transited node (can) be the same in both snapshots

[progwriter]

Reviewable status: complete! all files reviewed, all discussions resolved

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projects/question/src/main/java/org/batfish/question/differentialreachability/DifferentialReachabilityAnswerer.java, line 74 at r2 (raw file):

Previously, anothermattbrown (Matt Brown) wrote…

semantics of required transit nodes is that any (i.e. one) of the specified nodes must be transited. we do not enforce that the transited node (can) be the same in both snapshots

seem counterintuitive but ok

[anothermattbrown]

Reviewable status: complete! all files reviewed, all discussions resolved

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projects/question/src/main/java/org/batfish/question/differentialreachability/DifferentialReachabilityAnswerer.java, line 74 at r2 (raw file):

Previously, progwriter (Victor Heorhiadi) wrote…

seem counterintuitive but ok

yeah we could do much more powerful waypointing. probably will some day 😉