fix: domain CHECK constraint ordering with function dependencies

[mistermoe]

closes #254

split out from #255

Problem

@alecthomas explained the problem quite well in #254 so I won't repeat that here.

Fix

Extended the existing function dependency handling pattern to cover domains. The codebase already splits tables into those with/without function dependencies and creates them at appropriate points relative to function creation. This change applies the same approach to domains:

1. Domain ordering: Domains with CHECK constraints referencing functions are deferred until after functions are created
2. Table ordering: Tables using deferred domains are also deferred until after those domains exist

Domain constraint expression normalization

While testing the ordering fix, discovered that PostgreSQL always returns fully-qualified function names in constraint definitions (e.g., public.validate_id(VALUE)), but source SQL typically uses unqualified names. This caused constraint definitions to not match on re-comparison, producing spurious diffs.

Fix: Strip same-schema prefixes from function calls in domain CHECK constraints, matching the existing pattern in normalizePolicyExpression (added for Issue #220). This ensures consistent comparison regardless of whether the source SQL includes schema qualification.

Alternative considered: Normalize expressions to always use fully-qualified names — would require adding schema prefixes to source expressions.

[Copilot]

Pull request overview

This PR fixes migration ordering and comparison for PostgreSQL domains whose CHECK constraints depend on functions, ensuring both domains and tables using them are created in a dependency-safe order and compared without spurious diffs.

Changes:

• Extend generateCreateSQL to treat domains with function dependencies similarly to function-dependent tables: create functions first, then dependent domains, then tables that use those domains.
• Add domain-aware dependency helpers (domainReferencesNewFunction, tableUsesDeferredDomain) and wire them into the create ordering.
• Normalize domain CHECK constraint expressions to strip same-schema function qualifiers, and add regression test fixtures for function-dependent domains and domain-using tables.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
testdata/diff/create_domain/domain_function_table_dependency/plan.txt	Asserts plan summary and execution order for function → domain → table chain, verifying correct creation sequencing.
testdata/diff/create_domain/domain_function_table_dependency/plan.sql	Captures expected SQL ordering: create function, then domain with CHECK, then table using that domain.
testdata/diff/create_domain/domain_function_table_dependency/plan.json	Encodes the same scenario in JSON plan form, exercising step typing and ordering for function, domain, and table.
testdata/diff/create_domain/domain_function_table_dependency/old.sql	Defines the empty starting schema for the function → domain → table dependency test.
testdata/diff/create_domain/domain_function_table_dependency/new.sql	Defines desired schema with a validating function, a domain using it in CHECK, and a table using the domain.
testdata/diff/create_domain/domain_function_table_dependency/diff.sql	Expected migration SQL used by diff tests to validate the correct statement ordering.
testdata/diff/create_domain/domain_function_check_dependency/plan.txt	Asserts plan summary and ordering for a function-dependent domain without tables, ensuring domains wait for functions.
testdata/diff/create_domain/domain_function_check_dependency/plan.sql	Expected SQL for creating the validating function and dependent domain in correct order.
testdata/diff/create_domain/domain_function_check_dependency/plan.json	JSON representation of the function + domain plan, verifying step metadata for domains with function CHECKs.
testdata/diff/create_domain/domain_function_check_dependency/old.sql	Empty starting schema for the function-dependent domain-only test case.
testdata/diff/create_domain/domain_function_check_dependency/new.sql	Desired schema with a validating function and a domain whose CHECK constraint calls it.
testdata/diff/create_domain/domain_function_check_dependency/diff.sql	Expected migration SQL for the function + domain test used by file-based diff tests.
ir/normalize.go	Enhances domain normalization to accept the domain schema and strip same-schema function qualifiers in CHECK expressions, mirroring policy expression normalization and preventing spurious diffs.
internal/diff/diff.go	Adjusts create-time ordering to (a) partition types into domains with/without new-function dependencies, (b) track deferred domains, (c) classify tables by function/deferred-domain usage, and (d) introduce tableUsesDeferredDomain and domainReferencesNewFunction helpers used by generateCreateSQL.

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[Copilot]

Pull request overview

Copilot reviewed 14 out of 14 changed files in this pull request and generated no new comments.

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[tianzhou]

LGTM