Remove hand-written assumed.TFormula (it shadows the file's own StreamerInfo) and fix TStreamerLoop of TString* #72

🤖 AI generated content

Line item of #9: TFormula.update_members is not implemented (uproot-issue-181.root). Also found independently by the bootstrap review (#66).

Problem 1 — self-inflicted shadowing. src/rootfilespec/bootstrap/assumed.py:102-142 defines a hand-written TFormula that is exported in bootstrap.__all__, so src/rootfilespec/dynamic.py:27-30 skips the file's own info ("already declared") and reading hits the deliberate NotImplementedError. Spec, TFormula and TF1: "Every version of both classes that a released ROOT ever wrote is streamer-info driven … no hand-written layout is needed." uproot-issue-181.root carries complete TFormula v8 and TF1 v7 infos; uproot-issue-607.root (TFormula v10) and the spec fixture data/classes/formula.root are unreadable for the same reason.

Problem 2 — exposed once (1) is removed. With TFormula dropped from BOOTSTRAP_TYPES at runtime, the generated class fails in fOper. The cause is the preceding member fExpr, a TStreamerLoop (501) of TString*: TStreamerLoop.member_definition (src/rootfilespec/bootstrap/TStreamerInfo.py:448-478) generates list[Ref[TString]], i.e. object slots. Element types §8: the form is chosen by a strstr for ** in fTypeName — one * is c plain objects, ** is c object slots, and "a TString* loop is c bare counted strings". Bytes in the file agree: 40 00 00 07 00 09 | 04 70 6f 6c 35 = frame, then the bare counted string "pol5", then 01 (the is-present flag of fOper).

Suggested fix: delete TFormula from assumed.py and bootstrap/__init__.py; in TStreamerLoop.member_definition use the pointee type directly unless fTypeName contains **.

Note for #67 / #22: TFormula ≤ 8 and ≥ 9 are two unrelated C++ classes under one name (Formula.md intro and §1.1: "TFormula at version ≤ 8 is the old class, ≥ 9 is the new one"), likewise TF1 ≤ 7 / ≥ 8.

Severity / size: medium (any file with a TF1/TFormula fails), S–M. Clears 1 xfail.

Assisted-by: claude-code:claude-fable-5-1