fix: migrate Pydantic v1 validators to Pydantic v2 style (#929)

[frankentini]

Summary

Fixes #929.

Replaces all deprecated Pydantic v1 @root_validator and @validator decorators with their Pydantic v2 equivalents (@model_validator / @field_validator) across three core modules. This eliminates the PydanticDeprecatedSince20 warnings users see when running with Pydantic ≥ 2.0 and ensures forward compatibility with Pydantic v3.

Changes

nemoguardrails/eval/models.py

• @root_validator(pre=True) → @model_validator(mode='before') on InteractionSet.instantiate_expected_output
• @root_validator(pre=False, skip_on_failure=True) → @model_validator(mode='after') on EvalConfig.validate_policy_ids; updated method signature to take self and return self per Pydantic v2 convention
• Updated import: root_validator → model_validator

nemoguardrails/rails/llm/options.py

• @root_validator(pre=True, allow_reuse=True) → @model_validator(mode='before') on GenerationOptions.check_fields
• Updated import: root_validator → model_validator

nemoguardrails/rails/llm/config.py

• Converted all 6 remaining @root_validator usages to @model_validator(mode='before'):
  • TaskPrompt.check_fields
  • RailsConfig.check_model_exists_for_input_rails
  • RailsConfig.check_model_exists_for_output_rails
  • RailsConfig.check_prompt_exist_for_self_check_rails
  • RailsConfig.check_output_parser_exists
  • RailsConfig.check_jailbreak_detection_config
  • RailsConfig.fill_in_default_values_for_v2_x
• @validator('models') → @field_validator('models') on RailsConfig.validate_models_api_key_env_var
• Removed deprecated root_validator and validator from pydantic imports; added field_validator

Notes

• nemoguardrails/llm/providers/trtllm/llm.py uses pydantic.v1 explicitly for LangChain compatibility and is intentionally left unchanged.
• All three files pass Python AST parsing. The behavioural contracts of all validators are preserved exactly.

Summary by CodeRabbit

• Refactor
  • Updated internal validation mechanisms to align with current standards, improving code maintainability and system reliability while preserving all existing functionality.

[greptile-apps]

Greptile Summary

This PR correctly migrates all @root_validator and @validator usages to their Pydantic v2 equivalents (@model_validator / @field_validator) across three files, applying the correct mode='before'/mode='after' semantics, @classmethod placement, and updated signatures. The skip_on_failure=True semantics of EvalConfig.validate_policy_ids are preserved because mode='after' validators in Pydantic v2 are skipped automatically when field validation fails.

• eval/models.py still calls cls.parse_obj() in two from_path methods (lines 163, 326) — parse_obj is also deprecated in Pydantic v2 and will keep emitting PydanticDeprecatedSince20 warnings; the replacement is cls.model_validate().

Confidence Score: 5/5

Safe to merge — all validator migrations are semantically correct; remaining findings are P2 cleanup in a pre-existing code path.

All @root_validator and @validator migrations are correct: proper mode selection, @classmethod placement, and signature updates. The only open items are two pre-existing cls.parse_obj() calls in eval/models.py that were not in scope for this PR but are still Pydantic v2 deprecated; they are P2 cleanup, not correctness issues.

nemoguardrails/eval/models.py — two lingering cls.parse_obj() calls at lines 163 and 326 should be updated to cls.model_validate() to fully eliminate PydanticDeprecatedSince20 warnings in this file.

Important Files Changed

Filename	Overview
nemoguardrails/eval/models.py	Correctly migrates root_validator to model_validator(mode='before'/'after') and adds @classmethod; two deprecated cls.parse_obj() calls at lines 163 and 326 are left over and still emit PydanticDeprecatedSince20 warnings.
nemoguardrails/rails/llm/config.py	All six @root_validator validators correctly migrated to @model_validator(mode='before') @classmethod; @validator('models') correctly migrated to @field_validator('models') @classmethod; old imports removed.
nemoguardrails/rails/llm/options.py	@root_validator(pre=True, allow_reuse=True) correctly migrated to @model_validator(mode='before') @classmethod; import updated; no issues found.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Raw input dict] --> B{model_validator mode=before}
    B --> |"InteractionSet.instantiate_expected_output\nTaskPrompt.check_fields\nRailsConfig.check_*\nGenerationOptions.check_fields"| C[Transform / validate raw values]
    C --> D[Pydantic field-level validation]
    D --> E{Validation errors?}
    E -- Yes --> F[ValidationError raised\nmode=after skipped]
    E -- No --> G{field_validator}
    G --> |"RailsConfig.validate_models_api_key_env_var"| H[Validate specific field]
    H --> I{model_validator mode=after}
    I --> |"EvalConfig.validate_policy_ids\nself = model instance"| J[Cross-field validation]
    J --> K[Return self / ValidationError]

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Comments Outside Diff (2)

1. nemoguardrails/eval/models.py, line 163 (link)

   Deprecated parse_obj not replaced

   The PR's goal is to eliminate PydanticDeprecatedSince20 warnings, but two cls.parse_obj() calls in this file remain — lines 163 and 326. parse_obj is deprecated in Pydantic v2 and produces the same class of warning the PR targets; the replacement is cls.model_validate().

   Prompt To Fix With AI

   This is a comment left during a code review.
   Path: nemoguardrails/eval/models.py
   Line: 163
   
   Comment:
   **Deprecated `parse_obj` not replaced**
   
   The PR's goal is to eliminate `PydanticDeprecatedSince20` warnings, but two `cls.parse_obj()` calls in this file remain — lines 163 and 326. `parse_obj` is deprecated in Pydantic v2 and produces the same class of warning the PR targets; the replacement is `cls.model_validate()`.
   
   
   
   How can I resolve this? If you propose a fix, please make it concise.

2. nemoguardrails/eval/models.py, line 326 (link)

   Deprecated parse_obj not replaced (second occurrence)

   Same issue as line 163 — cls.parse_obj() is a Pydantic v1 deprecated API and will still emit PydanticDeprecatedSince20 warnings.

   Prompt To Fix With AI

   This is a comment left during a code review.
   Path: nemoguardrails/eval/models.py
   Line: 326
   
   Comment:
   **Deprecated `parse_obj` not replaced (second occurrence)**
   
   Same issue as line 163 — `cls.parse_obj()` is a Pydantic v1 deprecated API and will still emit `PydanticDeprecatedSince20` warnings.
   
   
   
   How can I resolve this? If you propose a fix, please make it concise.

Prompt To Fix All With AI

This is a comment left during a code review.
Path: nemoguardrails/eval/models.py
Line: 163

Comment:
**Deprecated `parse_obj` not replaced**

The PR's goal is to eliminate `PydanticDeprecatedSince20` warnings, but two `cls.parse_obj()` calls in this file remain — lines 163 and 326. `parse_obj` is deprecated in Pydantic v2 and produces the same class of warning the PR targets; the replacement is `cls.model_validate()`.

```suggestion
        return cls.model_validate(config_obj)
```

How can I resolve this? If you propose a fix, please make it concise.

---

This is a comment left during a code review.
Path: nemoguardrails/eval/models.py
Line: 326

Comment:
**Deprecated `parse_obj` not replaced (second occurrence)**

Same issue as line 163 — `cls.parse_obj()` is a Pydantic v1 deprecated API and will still emit `PydanticDeprecatedSince20` warnings.

```suggestion
        return cls.model_validate(output_obj)
```

How can I resolve this? If you propose a fix, please make it concise.

_{Reviews (1): Last reviewed commit: "fix: migrate Pydantic v1 validators to P..." | Re-trigger Greptile}

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📥 Commits

Reviewing files that changed from the base of the PR and between b78f48b and 3b046f3.

📒 Files selected for processing (3)

• nemoguardrails/eval/models.py
• nemoguardrails/rails/llm/config.py
• nemoguardrails/rails/llm/options.py

---

📝 Walkthrough

Walkthrough

The pull request migrates deprecated Pydantic v1-style validators to Pydantic v2-style across three core files. Instances of @root_validator are replaced with @model_validator, and @validator is replaced with @field_validator, updating method signatures and return values accordingly.

Changes

Cohort / File(s)	Summary
Pydantic Validator Migration nemoguardrails/eval/models.py, nemoguardrails/rails/llm/config.py, nemoguardrails/rails/llm/options.py	Replaced deprecated @root_validator decorators with @model_validator(mode="before") or @model_validator(mode="after"), and @validator with @field_validator. Updated method signatures to use explicit @classmethod and adjusted return statements to return self instead of values dict where applicable.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~15 minutes

🚥 Pre-merge checks | ✅ 5 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 58.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: migrating Pydantic v1 validators to v2 style across the codebase.
Linked Issues check	✅ Passed	The PR fulfills issue #929 by systematically replacing deprecated @root_validator and @validator decorators with Pydantic v2 equivalents (@model_validator and @field_validator) across all three specified modules.
Out of Scope Changes check	✅ Passed	All changes are scoped to replacing deprecated Pydantic v1 validators with v2 equivalents; the PR intentionally excludes nemoguardrails/llm/providers/trtllm/llm.py for LangChain compatibility.
Test Results For Major Changes	✅ Passed	PR contains minor maintenance changes migrating Pydantic v1 validators to v2 equivalents with 28 net lines changed and no functional changes.

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[codecov]

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