Add policy-to-function dependency tracking

[vshulev]

Summary

This adds support for tracking dependencies between RLS policies and user-defined functions that they reference in USING/CHECK expressions.

Previously, pg-schema-diff could create policies before the functions they depend on, causing migration failures like:

ERROR: function is_admin(uuid) does not exist

This happened because the dependency graph didn't track policy→function relationships, so when both a function and a policy referencing it were added, the policy could be created first.

Changes

• Query pg_depend to extract function dependencies from policies (similar to existing cross-table policy dependency tracking)
• Add FunctionDependencies field to the Policy struct
• Update dependency graph to order function creation before policies that use them
• Update dependency graph to order policy deletion before function deletion
• Add acceptance tests for policy-to-function dependencies (add and drop scenarios)
• Add schema test for function dependency extraction

Test plan

• All existing tests pass
• New acceptance tests for adding policy with new function
• New acceptance tests for dropping policy and function it references
• New acceptance tests for non-public schema scenarios
• Schema test verifying FunctionDependencies extraction

🤖 Generated with Claude Code

[gemini-code-assist]

Summary of Changes

Hello @vshulev, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances pg-schema-diff by introducing robust dependency tracking for Row Level Security (RLS) policies that utilize user-defined functions. Previously, migrations could fail due to incorrect ordering, where policies were created before their required functions. The changes ensure that the schema migration process correctly identifies and orders these dependencies, guaranteeing that functions are always in place before policies that reference them are applied, and are removed only after dependent policies are gone.

Highlights

• Policy-to-Function Dependency Tracking: Implemented a mechanism to track dependencies between RLS policies and user-defined functions referenced in their USING/CHECK expressions.
• Migration Order Correction: Resolved issues where pg-schema-diff could create policies before their dependent functions, preventing migration failures.
• Dependency Graph Enhancement: Updated the dependency graph to ensure functions are created before policies that use them, and policies are dropped before their dependent functions.
• Schema and Query Updates: Modified the pg_policy query to extract function dependencies and updated the Policy struct to store this information.
• Comprehensive Testing: Added new acceptance tests covering add and drop scenarios for policy-to-function dependencies, including non-public schema cases, and a schema test for dependency extraction.

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[gemini-code-assist]

Code Review

This pull request successfully implements policy-to-function dependency tracking, addressing a critical issue where RLS policies could be created before their dependent functions, leading to migration failures. The changes are comprehensive, covering SQL query modifications to extract function dependencies, updates to the Go schema representation, and crucial adjustments to the SQL generation logic to ensure correct ordering of policy and function DDL statements. The addition of new acceptance and schema tests thoroughly validates the new functionality for both add and drop scenarios, including non-public schemas. The code is well-structured, clearly commented, and directly resolves the identified problem, significantly improving the robustness of schema migrations involving RLS policies and user-defined functions.