delta

[reuvenharrison]

This branch implements a new delta function for OpenAPI spec.
The delta function returns a numeric value between 0 and 1 representing the distance between base and revision specs.
For any spec, a: delta(a, a) = 0
For any two specs, a and b, with no common elements: delta(a, b) = 1

Delta is symmetric by default:
For any two specs, a and b: delta(a, b) = delta(b, a)

Delta can also be asymmetric so that it only considers elements of base that are deleted in revision but not elements of base that are added in revision.
For any two specs, a and b: asymmetricDelta(a, b) + asymmetricDelta(b, a) = 1

In order to implement delta, we need to traverse the diff tree.
We will implement this until all elements are covered.

Each diff element that is supported by delta must have a new Unchanged member that allows delta to know how many items were unchanged.
Note that the new Unchanged member will also appear in the oasdiff diff output when diff is not empty.
We will implement this gradually until all elements are covered.

To test delta:
oasdiff delta data/simple4.yaml data/simple3.yaml

To test asymmetric delta:
oasdiff delta data/simple4.yaml data/simple3.yaml --asymmetric

To see the new Unchanged fields:
oasdiff diff data/simple4.yaml data/simple3.yaml

[codecov-commenter]

Codecov Report

Attention: 20 lines in your changes are missing coverage. Please review.

Comparison is base (a8392c1) 83.75% compared to head (c7e9aaf) 83.85%.

Files	Patch %	Lines
delta/endpoints.go	79.31%	4 Missing and 2 partials ⚠️
delta/parameters.go	90.62%	2 Missing and 1 partial ⚠️
delta/schema.go	57.14%	2 Missing and 1 partial ⚠️
internal/delta.go	91.89%	2 Missing and 1 partial ⚠️
internal/changelog_flags.go	0.00%	2 Missing ⚠️
internal/diff_flags.go	0.00%	2 Missing ⚠️
delta/delta.go	95.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #473      +/-   ##
==========================================
+ Coverage   83.75%   83.85%   +0.10%     
==========================================
  Files         217      225       +8     
  Lines       12593    12799     +206     
==========================================
+ Hits        10547    10733     +186     
- Misses       1668     1683      +15     
- Partials      378      383       +5     

Flag	Coverage Δ
unittests	83.85% <90.99%> (+0.10%)	⬆️

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