Pascal OOP corpus — real libraries that hammer classes/interfaces/generics

• Type: feature (umbrella — Pascal frontend validation)
• Track: P — tag: compat (FPC-parity on real OO code; see parallel-tracks.md)
• Status: backlog
• Owner: claude-P1
• Unblocks: the whole OO surface's credibility (RTTI, streaming, generics×classes)

Why

The self-host gate compiles the compiler, and the compiler is written in a thin, deliberately procedural Pascal subset — records, arrays, plain procedures. It exercises almost zero OOP: no deep inheritance chains, no virtual/abstract dispatch storms, no interfaces, no generic classes, no RTTI, no TPersistent/streaming. So the class system (pinned features from v175's class-system batch onward) is currently guarded only by our own small tests. A real, non-GUI, OOP-dense corpus is the missing gate.

Requirements for a candidate: non-GUI, self-contained (no DB/X11/network), OOP-dense, and ideally ships its own test suite so the oracle is built in (the duktape/tcc shape — see [[feature-c-corpus-duktape]]).

Sizing rule (user call 2026-07-12)

Climb the ladder by size, smallest first. A 60k-LOC library hits a dozen unrelated walls in the same build and you cannot tell a metaclass bug from a refcount bug from an RTL gap. Small library = walls arrive one at a time = clean bisect signal. Depth comes last, once the OOP surface is already shaken out.

Candidates (sizes MEASURED 2026-07-12 against the local FPC checkout)

Rung 1 — fpcunit (5k). Test framework = OOP by construction: TTestCase inheritance, TTestSuite composite, ITestListener interfaces, exception classes, and RTTI method enumeration to discover Test* methods. It is also the harness every other FPC library's suite is written against → landing it unlocks every rung above it. Cheapest, highest leverage.

Rung 2 — fpjson (10k src / 12k tests). Abstract base + polymorphic descendants (TJSONData → number/string/bool/null/array/object), class of factory dispatch, owned-child lifetimes — plus fpjsonrtti.pp, object ⇄ JSON streaming through RTTI, which is the same machinery [[project RTTI→streaming→LFM]] needs. Byte-exact roundtrip oracle.

Rung 3 — reassess. Likely rtl-generics (Generics.Collections: generic classes + IComparer<T>/IEqualityComparer<T> + class constraints — the generics × classes × interfaces intersection nothing else touches) or fcl-xml DOM (22k, TDOMNode tree, roundtrip oracle). Also on the shelf: TPersistent/TCollection/TStream from classes + contnrs.

Rung 4 (endgame) — fcl-passrc. The deep structural workout: ~200-class TPasElement hierarchy, abstract/virtual dispatch on every node, manual refcounted object graph, visitors, metaclass construction; paswrite gives a source-roundtrip oracle. Only after 1–3 are green.

Not now:

• BESEN (ECMAScript engine, Object Pascal, non-GUI): enormous class/interface use, a GC, virtual dispatch in hot loops, Delphi-ish dialect. Real prize, but same too-many-walls problem as passrc — revisit after the ladder.
• DWScript core: huge OOP + generics + interfaces, has a suite. Later.
• mORMot 2: enormous OOP/RTTI but asm-laden and Delphi-first → high pain, low signal.
• Spring4D: DI container, extreme interfaces/generics/attributes; Delphi-only idioms — likely a wall, not a test.

Plan

Climb rungs 1 → 4 in order, one at a time. Each library follows the corpus loop: vendor pinned source (PROVENANCE.md), compile with $(PXX_STABLE), run its own suite, reduce each failure to a minimal repro vs FPC, fix ONE in the owning lane, add a bXXX regression, land green. Re-rate the next rung's prio: upward when the current one goes green.

Gate

Per sub-ticket. Frontend/IR changed → make test + self-host byte-identical → make stabilize && make pin.

Log

• 2026-07-12 — opened. Candidate survey done; passrc + fpcunit picked as the first landing.