2.1.0: coverage gate, charset/bytes/enum/unique/interval/recursive generators, shrink debugging

[rasuvaeff]

Wave 3 (ROADMAP): consumer-driven additions — 2.1.0, no BC breaks

Everything is additive: the ArbitraryInterface contract and seed sequences of existing generators are untouched. roave/backward-compatibility-check --from=v2.0.0: no backwards-incompatible changes detected.

Guarantees

• Classify::cover($condition, $label, $minPercent) — the headline: an under-covered label now FAILS the property with the new CoverageViolationException instead of only printing a distribution line. Discarded runs are excluded from the denominator; all-discarded runs with requirements fail outright. Requirements are drained per property (no leakage after a falsified run).

Generators

• Gen::stringFrom($alphabet, $min, $max) (CharsetStringArbitrary) — identifiers/hex/slugs, multibyte alphabets, shrink toward the first alphabet character.
• Gen::bytes($min, $max) (BytesArbitrary) — raw bytes for parsers/codecs, shrink toward "\x00".
• Gen::enum(SomeEnum::class) — shrinks toward earlier-declared cases.
• Gen::uniqueArrayOf($el, $min, $max) (UniqueArrayArbitrary) — pairwise-distinct lists; element shrink candidates that would collide are pruned.
• Gen::intRange($min, $max) — ordered [lo, hi] pairs on top of flatMap; both bounds shrink, order always holds.
• Gen::floatSpecial() — opt-in NaN/±INF/-0.0/representation edges (default floats stay finite; no seed shift).
• Gen::recursive($leaf, $wrap, $maxDepth) — bounded recursive structures, 50/50 leaf-vs-branch per level.
• Optional size bounds on arrayOf/nonEmptyArrayOf/dictOf.

DX

• Gen::sampleShrinks($arb, $seed, $limit) — value + first shrink candidates, for authors of custom arbitraries.
• PROPERTY_VERBOSE env — log every run's generated arguments.
• README: recipes section (dependent sizes, intervals, bounded recursion) + coverage docs.

Verification

• composer build green: 364 tests
• Mutation: 802 mutants, 761 test-killed + 22 timeout, 19 escaped (the documented 2.0.0 equivalents; nothing new) — MSI ≈ 97.6% vs minMsi 90
• bc-check --from=v2.0.0 clean; examples executed; zizmor clean
• Psalm note: Gen::floatSpecial() builds NaN/INF via fdiv() — Psalm crashes on the NAN constant