Six refactors that looked behaviour-preserving. Each passed review and passed the tests.
Each one is run through equiv live. Five it catches. One it honestly cannot.
Every result here is reproducible with the files in this folder.
| # | Scenario | Domain | equiv verdict | Honest note |
|---|---|---|---|---|
| 1 | Stripe zero-decimal currency (amount * 100) |
payments | CAUGHT | Exact values. Real: Drupal commerce_stripe #2913605. |
| 2 | Tax personal-allowance floor dropped | tax/payroll | CAUGHT | Phantom negative tax below the allowance. |
| 3 | Gauss sum, negative clamp dropped | arithmetic | CAUGHT | Tests at 1, 5, 10 pass. Only negatives break. |
| 4 | Antimeridian guard added | geospatial | CAUGHT | Real: chrisveness/geodesy v1.1.2 #44. New code throws past +/-180. |
| 5 | Binary-search midpoint overflow | integer overflow | MISSED | Out of scope. Python ints are unbounded. |
| 6 | Average, empty-list guard dropped | edge guard | CAUGHT | New code divides by zero on []; old returns 0. |
equiv is value-accurate. For scenarios 1 to 4 and 6, equiv returns the exact
diverging input and the exact old and new outputs, matching real Python. That includes
the exception cases (scenarios 4 and 6): it shows the side that raised and the real
value the other side returned (-179, 0).
equiv says EQUIVALENT when it genuinely cannot see a bug. Scenario 5 is the famous
(low + high) / 2 overflow. That bug exists in C and Java, where ints are fixed-width.
Python ints are unbounded. The two functions really are equivalent in Python. equiv says so. It does not invent a bug that the language cannot have. A real scope limit,
stated plainly.
One scope limit (reproducible here):
No fixed-width overflow. See scenario 5. If your bug only exists under 32 or 64-bit integer wraparound, running the Python form will not surface it. Python ints do not wrap.
(An earlier version of this showcase noted a second issue: an exception on one side
printed the other side as None. That display bug is fixed in #7; the exception cases
now show the real value.)
This honesty is the point. equiv tells you what it checked and nothing more.
Build the CLI once (cargo build --release -p equiv-cli), then:
equiv review stripe-jpy/candidate.py stripe-jpy/reference.py to_minor_units int
equiv review tax-allowance-floor/candidate.py tax-allowance-floor/reference.py tax int
equiv review gauss-clamp/candidate.py gauss-clamp/reference.py total int
equiv review geodesy-antimeridian/candidate.py geodesy-antimeridian/reference.py normalize_lon int
equiv review binary-search-overflow/candidate.py binary-search-overflow/reference.py mid int,int
equiv review empty-collection-guard/candidate.py empty-collection-guard/reference.py average list[int]
Add --sign (with EQUIV_SIGNING_KEY set) for a signed receipt you can verify with
equiv verify-receipt.
- Stripe zero-decimal currencies: https://docs.stripe.com/currencies and https://www.drupal.org/project/commerce_stripe/issues/2913605
- geodesy antimeridian: chrisveness/geodesy#44
- binary-search overflow: https://research.google/blog/extra-extra-read-all-about-it-nearly-all-binary-searches-and-mergesorts-are-broken/