Deterministic judges: missing nested fields score Fail instead of erroring - #1709
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Deterministic judges: missing nested fields score Fail instead of erroring#1709chiang-daniel wants to merge 4 commits into
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extract() documents that missing keys return Undefined rather than raising, and every caller is built on that contract. It only held for a single lookup: one missing key does return Undefined, but any further operation on that Undefined -- an attribute access, an index, a filter, an operator -- raises jinja2's UndefinedError from inside the compiled expression. Nothing caught it. The deterministic v2 judges (exact match, contains, pattern match, set check) route extraction failures through JinjaExtractionError to score a Fail, and the eval API maps ValueError to a 400, so an UndefinedError escaped both and surfaced as an unexpected error that ended the whole run. Two of the canned example expressions in the Output to Check dialog hit this whenever the data was shaped differently than the expression assumed: (final_message | fromjson).user.status against JSON with no `user`, and trace[-1].tool_calls[0].function.name against an empty trace. Wrap the expression evaluation so UndefinedError becomes JinjaExtractionError, keeping jinja2's message because it names the field that wasn't there. The existing extraction-failure path then scores those inputs Fail, which is the right answer: the model didn't produce the structure the check asked for. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Included review availability: Your plan provides up to 8 included reviews per hour; 5 remain after this review. WalkthroughV2 value expressions now validate referenced evaluation-input roots. Jinja extraction converts missing-data failures, including deferred generator lookups, into ChangesV2 expression evaluation
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: ⚪ Minimal · up to This localized change is merge-ready after normal checks and review; no actionable merge-blocking risk remains. Sequence Diagram(s)sequenceDiagram
participant EvalConfig
participant JinjaEngine
participant EvalHelpers
participant StudioEvalAPI
EvalConfig->>JinjaEngine: Extract expression variables
JinjaEngine-->>EvalConfig: Return undeclared root variables
EvalHelpers->>JinjaEngine: Extract expression value
JinjaEngine-->>EvalHelpers: Raise JinjaExtractionError
EvalHelpers->>EvalHelpers: Create scored FAIL result
EvalHelpers->>StudioEvalAPI: Return score 0.0 without skip reason
Suggested reviewers: Poem
🚥 Pre-merge checks | ✅ 3 | ❌ 2❌ Failed checks (2 warnings)
✅ Passed checks (3 passed)
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📊 Coverage ReportOverall Coverage: 92% Diff: origin/sfierro/KIL-741...HEAD
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In `@libs/core/kiln_ai/utils/jinja_engine.py`:
- Line 114: Update the Jinja result evaluation flow so lazy results are
materialized with list(result) inside the existing UndefinedError handler,
ensuring deferred missing-attribute conversion is translated to
JinjaExtractionError. Add a regression test covering items |
map(attribute="missing") | map("int") and assert the raised exception type.
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The UndefinedError guard only wrapped `compiled(**data)`. Generators were materialized after it, outside the try. map/selectattr/groupby return lazy generators, so their per-item lookups don't run when the expression is called -- they run when list() drains them. A missing field there raised a raw UndefinedError straight past the guard, which is exactly the escape the guard was added to close, and it falsified the docstring line claiming extract() never raises UndefinedError. `trace | map(attribute='tool_calls.0.function.name')` over a trace where one message has no tool_calls is the shape a user hits: it escaped, while the same expression with `| list` appended was already converted, because the `list` filter materializes inside the compiled expression. Move the materialization inside the try so both routes land on JinjaExtractionError. Test hygiene alongside it. The extraction-error tests had picked up two cases that restate coverage already in TestExtract (a bare missing lookup returning Undefined, a valid nested expression extracting), and split one behavior across a "filter" test and an "operator" test when the actual dividing line is neither: merge them under a name that says what's true -- forcing the value raises -- with a note that join, `~` and `==` on Undefined don't. The API-level test for this path asserted 0.0 against an expected_value that could not have matched even on a successful extraction, so it passed for the wrong reason; pair it with a case where the field is present and matches, so the 0.0 is attributable. Also drop an inaccurate comment in the helpers test: the Fail path discards the detail string, so only the skip path renders Jinja's message. State what holds at this layer instead of describing an app surface. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Making extraction failures score Fail closed a crash, but it also made one authoring mistake silent. A typo'd root variable -- outpt.status, or messages[-1].content when the variable is trace -- resolves to Undefined, which the deterministic judges now read as "the model didn't produce this" and score 0.0 on every row. Before, it raised. An eval that reports a uniform zero because of a spelling mistake is worse than one that refuses to run. The expression can only ever see the fields of EvalTaskInput, because extract_value passes eval_input.model_dump() as the entire namespace: final_message, trace, task_input and reference_data. Anything else is unreachable by construction, so it can be rejected while the author still has the expression in front of them. The LLM judge template already does this shape of check, via find_undeclared_variables against the names it supplies. An expression needs one extra step first: parsed as a template, final_message.strip() is literal text with no variables at all, so it has to be wrapped in an output block before the AST walk. That belongs next to the environment it parses in, hence expression_variables() in jinja_engine. The allowed set is read off EvalTaskInput.model_fields rather than written out, so a field added to the bundle is accepted without a second edit here. Authoring-time only. A config saved before this check exists may name a variable it now rejects, and validators run on load as well as on write -- refusing to load would take down the whole eval, and every eval config beside it, rather than the one check that was already scoring zeros. It gates the write paths (config creation and the draft test endpoint, both of which build an EvalConfig) and steps aside when loading from file. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Several of the new tests overlapped: the same missing-field expression was asserted at the engine, helper, and API layers, and the materialized-generator case was strictly implied by the nested-attribute one. Fold the duplicates into the existing parametrize and drop the redundant helper-layer tests, keeping the lazy-generator test on its own since it is the only thing that catches materialization moving outside extract()'s try. Also make two coverage claims real instead of asserted in prose: the "every eval input field" parametrize now checks its roots against EvalTaskInput.model_fields, and the silent-Undefined behaviour the raising tests only described in a comment now has a case of its own. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Aug 20, 2026
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What does this PR do?
In the deterministic judges (Exact Match, Contains, Pattern Match, Set Check), an Output to Check expression that reaches into a missing nested field crashed the run instead of scoring Fail.
Before:
(final_message | fromjson).user.statusagainst JSON with no "user" shows "Unexpected error: 'dict object' has no attribute 'user'". Same fortrace[-1].tool_calls[0].function.nameon an empty trace. Both are canned examples in the dialog. A missing top-level field already scored Fail, so behavior depended on how deep the expression reached.After: those items score Fail — the model didn't produce the structure the check asked for. Runs with no trace still skip as missing_trace. And because missing fields now fail quietly, saving a judge validates the expression's variables (final_message, trace, task_input, reference_data), so a typo like
outpt.statusis rejected at save with a clear message instead of silently scoring 0% forever.How: the expression engine converts Jinja's UndefinedError into the extraction error the judges already score as Fail, including lazy map/selectattr results. Only the four deterministic judges are affected; the LLM judge and input transforms use different code paths.
Two judgment calls for review: an empty trace (as opposed to no trace) scores Fail — flip to skip is a two-line change if preferred. The variable check runs on save only; configs saved before it still load.
Out of scope, noted as follow-ups: Fail results don't say which field was missing; TypeError and ZeroDivisionError from typed expressions still escape raw; references_trace false-positives on a JSON field literally named "trace".
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