Pass relationship read action arguments

[jechol]

Adds read_action_arguments to relationships and passes them through relationship loading.

Explicit loads can already provide arguments to read actions, but relationship definitions could only choose the read_action itself. This adds the missing symmetric piece: a relationship can now declare static arguments for that read action.

This is useful when a relationship should load through a specific read action with relationship-specific argument values, while still allowing explicitly provided load arguments to take precedence.

Includes coverage for a has_many relationship using a read action argument.

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[zachdaniel]

🤔 this is pretty complex. We'd want to survey the following places to make sure that they handle this when building related queries:

• ash_postgres
• ash_sql
• ash_sqlite
• ash_json_api
• ash_graphql
• ash_typescript

If they do any related query building then they'd have to be upgraded to use this option ideally before we release this. (i.e Map.get(relationship, :arguments, %{}))

[jechol]

Thanks! I surveyed all six repositories.

Changes were needed in:

• ash_sql: it builds related queries for joins, so I updated it to pass Map.get(relationship, :read_action_arguments, %{}) to the relationship read action.
  • Use relationship read action arguments in joins ash_sql#237
• ash_graphql: it generates arguments for relationship fields, so I updated both singular and list relationships to expose the relationship-provided values as GraphQL defaults while preserving the action argument's original nullability.
  • Expose relationship read action arguments as GraphQL defaults ash_graphql#455

No changes were needed in ash_postgres, ash_sqlite, ash_json_api, or ash_typescript; they don't independently build related read-action queries from relationship metadata in the relevant paths.

The resulting precedence is:

1. explicitly provided load/query arguments
2. relationship read_action_arguments
3. read action argument defaults

The extension changes use Map.get/3, so they remain compatible before the corresponding Ash version is released.

[jechol]

Quick status update:

• The mix spark.cheat_sheets --check failure was caused by this PR (the new read_action_arguments option wasn't reflected in the generated docs) — fixed in f3430c5.
• The remaining mix test / mix dialyzer failures are unrelated to this PR: they're caused by picosat_nif.so failing to load on the CI runners, and the same error is currently failing CI on main as well (example run).
• The downstream changes you asked me to survey are done and merged: Use relationship read action arguments in joins ash_sql#237 and Expose relationship read action arguments as GraphQL defaults ash_graphql#455. No changes were needed in ash_postgres, ash_sqlite, ash_json_api, or ash_typescript.

So this should be ready for review whenever you have a chance. Thanks!

[zachdaniel]

🚀 Thank you for your contribution! 🚀