🐛 fix: handle PEP 604 union syntax in list type detection (#139)

[vawsgit]

Fields declared with PEP 604 syntax (list[X] | None) produce a types.UnionType at runtime, which has no __origin__ and is not recognized by get_origin(...) is Union. As a result, the type-detection methods failed to identify these as list fields, routing empty-list comparisons ([] vs []) through the primitive comparator and yielding match=False, score=0.0 instead of a true negative.

✨ Add types.UnionType handling to 5 type-detection methods:

• _is_list_field (structured_model.py)
• _is_list_of_structured_model_type (structured_model.py)
• is_structured_field_type (configuration_helper.py)
• _is_list_structured_model (configuration_helper.py)
• _extract_structured_class_from_list (configuration_helper.py)

✅ Add test_pep604_union_type_handling.py with 24 tests covering type detection, empty/non-empty nested list comparison, primitive lists, and a parametrized validation suite guarding both PEP 604 and typing.Optional.

🧪 Full suite: 1100 passed, 2 skipped, 0 failures.

Issue #, if available:

#139

Description of changes:

🔍 Root Cause

Python 3.10+ PEP 604 syntax (X | Y) produces a types.UnionType at runtime, which behaves differently from typing.Union:

import types
from typing import get_origin

t = list[int] | None
type(t)                    # → types.UnionType
get_origin(t)              # → types.UnionType  (NOT typing.Union!)
hasattr(t, '__origin__')   # → False

The type-detection methods only checked get_origin(...) is Union and hasattr(field_type, "__origin__"), so PEP 604 unions silently fell through to return False. The comparison logic itself was correct — the bug was purely in type detection.

✨ Changes

Added types.UnionType handling to 5 type-detection methods:

File	Method
structured_model.py	_is_list_field
structured_model.py	_is_list_of_structured_model_type
configuration_helper.py	is_structured_field_type
configuration_helper.py	_is_list_structured_model
configuration_helper.py	_extract_structured_class_from_list

Each method now unwraps types.UnionType args (skipping NoneType) using the same logic already applied to typing.Union.

✅ Tests

New file test_pep604_union_type_handling.py — 24 tests:

• 🔬 Unit tests — verify all 5 type-detection methods recognize PEP 604 syntax (structured lists, primitive lists, root-level)
• 🔗 Integration tests — empty list → score 1.0, mismatched list → penalty, non-empty structured dispatch
• 🛡️ Regression guard — typing.Optional[List[X]] behavior unchanged
• 🎯 Parametrized validation (TestIssue139Validation) — runs every assertion against both PEP 604 and typing.Optional styles in one command:

uv run pytest tests/structured_object_evaluator/test_pep604_union_type_handling.py::TestIssue139Validation -v

🧪 Test Results

1100 passed, 2 skipped, 0 failures

No regressions — all existing tests continue to pass because they use typing.Union / typing.Optional syntax.

📌 Notes

• No public API or ComparableField interface changes
• No new dependencies (types is stdlib; project requires Python >=3.12 where types.UnionType is guaranteed)
• Orthogonal to PR Feat/universal aggregate metrics #115 (aggregate metrics) — this fix is a prerequisite that ensures type detection works for either PR's paths

Closes #139

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

---

🔄 Update (addressing review #146)

Per @adiadd's review, the five duplicated union branches were collapsed to a single get_origin(annotation) in (Union, types.UnionType) check across all five type-detection methods. This fixes the blocking issue by construction: is_structured_field_type no longer has a divergent direct-Model | None arm, so Model | None keeps parity with Optional[Model] (both route through LevenshteinComparator), and behavior no longer reverts on Python 3.14.

⚠️ Behavior change on upgrade

Fields spelled list[Model] | None = ComparableField(threshold=...) (PEP 604) now raise ValueError at class-definition time — the same guard that has always applied to Optional[List[Model]]. Hungarian matching uses each element class's match_threshold, so a per-field threshold on a list-of-models field is rejected. Previously the PEP 604 spelling silently bypassed this validation.

📌 Supported annotation syntax

List/optional detection now handles list[X], List[X], Optional[List[X]], and PEP 604 list[X] | None uniformly.

🔭 Tracked follow-ups (out of scope)

_is_optional_structured_model, _extract_structured_class_from_optional, _unwrap_optional, data_extractors.py:205, and the dead field_helper.py:48 duplicate remain PEP-604-blind — to be filed as separate issues.

[github-actions]

Security Scan Results

ASH Security Scan Report

• Report generated: 2026-07-16T22:11:52+00:00
• Time since scan: 2 minutes

Scan Metadata

• Project: ASH
• Scan executed: 2026-07-16T22:09:22+00:00
• ASH version: 3.1.2

Summary

Scanner Results

The table below shows findings by scanner, with status based on severity thresholds and dependencies:

• Severity levels:
  • Suppressed (S): Findings that have been explicitly suppressed and don't affect scanner status
  • Critical (C): Highest severity findings that require immediate attention
  • High (H): Serious findings that should be addressed soon
  • Medium (M): Moderate risk findings
  • Low (L): Lower risk findings
  • Info (I): Informational findings with minimal risk
• Duration (Time): Time taken by the scanner to complete its execution
• Actionable: Number of findings at or above the threshold severity level that require attention
• Result:
  • PASSED = No findings at or above threshold
  • FAILED = Findings at or above threshold
  • MISSING = Required dependencies not available
  • SKIPPED = Scanner explicitly disabled
  • ERROR = Scanner execution error
• Threshold: The minimum severity level that will cause a scanner to fail
  • Thresholds: ALL, LOW, MEDIUM, HIGH, CRITICAL
  • Source: Values in parentheses indicate where the threshold is set:
    • global (global_settings section in the ASH_CONFIG used)
    • config (scanner config section in the ASH_CONFIG used)
    • scanner (default configuration in the plugin, if explicitly set)
• Statistics calculation:
  • All statistics are calculated from the final aggregated SARIF report
  • Suppressed findings are counted separately and do not contribute to actionable findings
  • Scanner status is determined by comparing actionable findings to the threshold

Scanner	Suppressed	Critical	High	Medium	Low	Info	Actionable	Result	Threshold
bandit	0	0	0	0	4191	0	0	PASSED	MEDIUM (global)
cdk-nag	0	0	0	0	0	0	0	PASSED	MEDIUM (global)
cfn-nag	0	0	0	0	0	0	0	MISSING	MEDIUM (global)
checkov	0	0	0	0	0	0	0	PASSED	MEDIUM (global)
detect-secrets	0	0	0	0	0	0	0	PASSED	MEDIUM (global)
grype	0	0	0	0	0	0	0	MISSING	MEDIUM (global)
npm-audit	0	0	0	0	0	0	0	PASSED	MEDIUM (global)
opengrep	0	0	0	0	0	0	0	MISSING	MEDIUM (global)
semgrep	0	19	0	0	0	0	19	FAILED	MEDIUM (global)
syft	0	0	0	0	0	0	0	MISSING	MEDIUM (global)

Top 7 Hotspots

Files with the highest number of security findings:

Finding Count	File Location
7	.github/workflows/workflow.yml
3	.github/workflows/security.yaml
2	.github/workflows/docs.yml
2	.github/workflows/lint.yaml
2	.github/workflows/run_pytest.yaml
2	.github/workflows/security-pr-comment.yaml
1	pyproject.toml

Detailed Findings

Show 19 actionable findings

Finding 1: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/docs.yml:19

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

- uses: actions/checkout@v4

---

Finding 2: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/docs.yml:22

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: astral-sh/setup-uv@v5

---

Finding 3: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/lint.yaml:16

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

- uses: actions/checkout@v4

---

Finding 4: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/lint.yaml:18

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: astral-sh/setup-uv@v5

---

Finding 5: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/run_pytest.yaml:16

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

- uses: actions/checkout@v4

---

Finding 6: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/run_pytest.yaml:18

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: astral-sh/setup-uv@v5

---

Finding 7: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/security-pr-comment.yaml:20

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: actions/download-artifact@v4

---

Finding 8: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/security-pr-comment.yaml:27

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: actions/github-script@v7

---

Finding 9: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/security.yaml:18

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

- uses: actions/checkout@v4

---

Finding 10: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/security.yaml:20

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: astral-sh/setup-uv@v5

---

Finding 11: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/security.yaml:42

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: actions/upload-artifact@v4

---

Finding 12: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/workflow.yml:18

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

- uses: actions/checkout@v4

---

Finding 13: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/workflow.yml:22

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: astral-sh/setup-uv@v5

---

Finding 14: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/workflow.yml:28

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: actions/upload-artifact@v4

---

Finding 15: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/workflow.yml:45

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: actions/download-artifact@v4

---

Finding 16: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/workflow.yml:50

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: pypa/gh-action-pypi-publish@release/v1

---

Finding 17: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/workflow.yml:64

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: actions/download-artifact@v4

---

Finding 18: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag

• Severity: HIGH
• Scanner: semgrep
• Rule ID: yaml.github-actions.security.github-actions-mutable-action-tag.github-actions-mutable-action-tag
• Location: .github/workflows/workflow.yml:69

Description:
GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.

Code Snippet:

uses: pypa/gh-action-pypi-publish@release/v1

---

Finding 19: package_managers.uv.uv-missing-dependency-cooldown.uv-missing-dependency-cooldown

• Severity: HIGH
• Scanner: semgrep
• Rule ID: package_managers.uv.uv-missing-dependency-cooldown.uv-missing-dependency-cooldown
• Location: pyproject.toml:116-117

Description:
This pyproject.toml configures uv but does not set a dependency cooldown. Newly published packages can be malicious or unstable. Add exclude-newer = "7 days" under [tool.uv] to wait 7 days before resolving newly published package versions. Added in: 0.9.17 Reference: https://docs.astral.sh/uv/concepts/resolution/#dependency-cooldowns

Code Snippet:

[tool.uv]
default-groups = ["dev"]

---

Report generated by Automated Security Helper (ASH) at 2026-07-16T22:11:53+00:00

[adiadd]

appreciate this vincil! just a couple things:

blocking:

• the PEP 604 branch in is_structured_field_type does more than parity: its direct-model arm silently changes the default comparator and threshold for Model | None fields, and the behavior reverts on python 3.14. details and two fix options on configuration_helper.py:180-181.

non-blocking:

• the five duplicated union blocks could collapse to a two-token change (get_origin(annotation) in (Union, types.UnionType)) in 4 of the 5 methods, which would also make the blocking issue impossible by construction. see configuration_helper.py:168.

• __init_subclass__ validation now raises at import time for PEP 604 spellings it used to silently accept, correct but worth a PR-description note and a test (structured_model.py:281).

• test gaps: None vs [] / None vs None for the PEP 604 spelling, and a from_json round-trip so the two branches only unit tests reach get integration coverage (comments inline).

• or arg is list in _is_list_field is another non-parity spot and untested (structured_model.py:734), and _is_optional_structured_model / _extract_structured_class_from_optional in the same file are still PEP-604-blind, fine out of scope but worth a follow-up issue (configuration_helper.py:417,447).

nits, none blocking: style drift between the five new blocks (some hoist none_type = type(None), some inline it), the pep604 arm of TestIssue139Validation mostly duplicates the earlier tests, a direct per-field match=True assertion on items would pin the issue's exact symptom, and a one-line docs note on supported annotation syntax would help. also worth filing follow-ups beyond this PR: _unwrap_optional (structured_model.py:1384) is PEP-604-blind so schema export silently emits {"type": "string"} for these fields, data_extractors.py:205 misses both spellings in HTML reports, and field_helper.py:48 has a dead duplicate is_structured_field_type with no union handling at all.

appreciate it!

[vawsgit]

Thanks for the thorough review @adiadd — you were right on every point, and taking the refactor you suggested made most of them fall out for free. Pushed b9f9473.

Blocking — resolved via the refactor

Collapsed all five typing.Union / types.UnionType branches to a single get_origin(annotation) in (Union, types.UnionType) check (verified: get_origin/get_args normalize both spellings identically on 3.12, and the union types unify on 3.14). This removes ~88 duplicated lines and makes the divergent direct-Model | None arm structurally impossible — is_structured_field_type now only recognizes list-wrapped models, so Model | None has parity with Optional[Model] (both → LevenshteinComparator, no silent match-decision flips, no 3.14 revert). Added a test asserting the two spellings resolve identically.

Non-blocking — addressed

• or arg is list asymmetry (_is_list_field): dropped, so list | None now matches bare list / Optional[list] behavior.
• __init_subclass__ import-time ValueError: added tests asserting it fires for both the PEP 604 and Optional[List[...]] spellings, plus a note in the PR description.
• Test gaps: added None vs [], None vs None, a per-field true-negative assertion pinning the exact [BUG]: Empty list fields inside a structured-list item scored as mismatch instead of true negative #139 symptom, and a from_json round-trip that exercises _is_list_structured_model / _extract_structured_class_from_list (previously unit-only).

Full suite: 1109 passed, 2 skipped, 0 failures.

Follow-ups — filed as separate issues

All four out-of-scope spots you flagged are now tracked:

• from_json drops nested extra_fields for PEP 604 Model | None fields #160 — from_json drops nested extra_fields for PEP 604 Model | None (_is_optional_structured_model / _extract_structured_class_from_optional)
• _unwrap_optional is PEP-604-blind: schema export emits {"type": "string"} for X | None #161 — _unwrap_optional is PEP-604-blind; schema export emits {"type": "string"}
• HTML report thresholds miss optional/union-wrapped nested models (both spellings) #162 — HTML report thresholds miss optional/union-wrapped nested models (data_extractors.py:205, both spellings)
• Remove dead duplicate FieldHelper.is_structured_field_type (no union handling, no callers) #163 — remove dead duplicate FieldHelper.is_structured_field_type (field_helper.py:48, no union handling, no callers)