no-ad-hoc-jsonl-parser: isLineSource doesn't traverse ConditionalExpression, missing live ad-hoc parse in conclusion_admission.c #71028

Summary

no-ad-hoc-jsonl-parser's isLineSource() helper (eslint-factory/src/rules/no-ad-hoc-jsonl-parser.ts:76-98) only resolves a variable's "line-ness" through one hop of identifier-to-initializer resolution (Identifier → initializer()) and through a small whitelist of chained CallExpression methods (split, filter, slice, reverse, toReversed). It never unwraps a ConditionalExpression (ternary) to check whether either branch is itself a line source. Any line array built behind a ternary — a very ordinary "empty vs. split" guard — escapes detection entirely, including when it is subsequently JSON.parse'd per-element, which is exactly the ad-hoc-parsing idiom this rule exists to catch.

Live, grounded false negative

actions/setup/js/conclusion_admission.cjs:50-54:

const lines = compact.session === "" ? [] : compact.session.split("\n");
if (lines.at(-1) === "") lines.pop();
if ((!compact.session.endsWith("\n") && compact.session !== "") || lines.length !== compact.included_events) throw new AdmissionError();
try {
  const projected = compactUnifiedSession(lines.map(line => JSON.parse(line)));

This is a manual split-by-newline followed by .map(line => JSON.parse(line)) — the canonical pattern the rule is designed to flag (compare to the rule's own invalid test case const lines = text.split((r/redacted)?\n/); ... JSON.parse(line)). It is not wrapped by iterateJsonl/iterateJsonlEvents/JsonlParser from jsonl_helpers.cjs, yet the rule produces zero diagnostic here.

Root cause

Tracing lines in isLineSource():

1. lines is an Identifier → initializer(node) returns its VariableDeclarator init, which is the ConditionalExpression compact.session === "" ? [] : compact.session.split("\n").
2. isLineSource(conditionalExpr) hits if (node.type !== "CallExpression") return false; (line 83) immediately, since ConditionalExpression is neither Identifier nor CallExpression.
3. Because isLineSource(lines) is false, the CallExpression visitor's lineArray check for lines.map(...) (arrayCallbacks.has("map") && isLineSource(node.callee.object)) never marks line as a line binding, so the later JSON.parse(line) inside the map callback is never reported.

The same gap applies to fromLine() (used for the Program:exit cross-call propagation pass), which also only descends through Identifier/ArrayExpression/MemberExpression(computed)/a small CallExpression method whitelist — no ConditionalExpression handling there either.

Proposed fix

In isLineSource() (and ideally the equivalent place in fromLine()), add a branch: if (node.type === "ConditionalExpression") return isLineSource(node.consequent, seen) || isLineSource(node.alternate, seen);. This directly fixes the cond ? [] : x.split("\n") idiom; an empty-array consequent is harmless since an empty array can't ever actually be the source of a flagged JSON.parse call.

Acceptance criteria

• isLineSource() recognizes a ConditionalExpression as a line source when at least one branch resolves to a line source (via recursive isLineSource on consequent/alternate).
• New invalid test case reproducing the live shape: const lines = cond ? [] : text.split("\n"); lines.map(line => JSON.parse(line)); must report adHoc.
• A valid-case test confirms a ConditionalExpression where neither branch is a line source (e.g. cond ? documents : otherDocuments) is still not flagged.
• conclusion_admission.cjs:54 is verified to now be caught after the fix (run against the real file, not just the synthetic test).
• No existing passing test in no-ad-hoc-jsonl-parser.test.ts regresses.

Scope note

Out of scope for this issue: fixing conclusion_admission.cjs itself (app code, not rule code) — this is purely about closing the detection gap in the ESLint rule so a future regression or similar idiom elsewhere is caught.

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Work 6b99120dce1d760d9b16b2c32e2b3939143961ca50ff5820849e9da583d8e97f · Claim c_2d1370e23519794ff88ba3c5ce7e17ee202e9a6904e679f8ad827e073d503dae_3

• expires on Oct 28, 2026, 8:03 PM UTC-08:00