fix: Preserve locals when rendering inline partial for object

[moberegger]

Ran into an odd bug.

Given a template like

# locals (json:, foo:, my_local: 'default')

json.extract! foo, :id, :name
json.myLocal my_local

Rendering to a collection inline like

json.foos, @foos, partial: 'foos/foo', as: :foo, my_local: 'custom'

Would correctly render with the value of my_local with the value of 'custom'

{
  "foos": [
    "id": 1,
    "name": "Test",
    "myLocal": "custom"
  ]
}

But rendering a single object wasn't picking up the value for the local

json.foo, @foo, partial: 'foos/foo', as: :foo, my_local: 'custom'

{
  "foo": {
    "id": 1,
    "name": "Test",
    "myLocal": "default"
  }
}

The reason is because this render path in _set_inline_partial would set a key for locals before the render is done in _render_partial_with_options. _render_partial_with_options attempts to pluck key args for locals, but since the key is already there, they are effectively ignored.

The fix was to not have _set_inline_partial set locals, and instead defer that logic to _render_partial_with_options.

I added some extra tests cases to cover this.

• A test for rendering an object to an inline partial (there were no tests for this)
• A test for rendering an object to an inline partial with locals
• A test for rendering a collection to an inline partial with locals

I also updated the docs to include an example for rendering an object to an inline partial. This is supported by the library, but was seemingly undocumented. Also documented rendering to partials inline with other locals, which was also supported by the library but seemingly undocumented.

[moberegger]

Ugh. I had the test use strict locals, which aren't supported by older versions of Rails. I'll figure out another way to do it...

[moberegger]

Filed upstream: rails#613

[Copilot]

Pull request overview

Fixes an inconsistency in Jbuilder’s inline partial rendering so that additional locals passed when rendering a single object under a key are preserved (matching the existing collection behavior), and adds documentation/tests for these supported render forms.

Changes:

• Adjust inline-partial rendering internals to defer locals construction to _render_partial_with_options, preserving passed locals for single-object inline partials.
• Expand test coverage for inline partial rendering under a key (single object + locals, collection + locals).
• Update README examples for inline partial rendering and correct minor documentation typos.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
lib/jbuilder/jbuilder_template.rb	Changes inline partial object path to avoid pre-setting options[:locals], preserving locals passed via keyword args.
test/jbuilder_template_test.rb	Adds regression tests for inline partial rendering under a key (single + locals, collection + locals).
test/test_helper.rb	Updates the Post test struct to include :title used by new partial logic/tests.
README.md	Documents inline partial rendering for objects/collections under a key and passing additional locals; fixes small doc wording.

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[Copilot]

Inline object partial rendering now sets the object on the top-level options hash (options[options[:as]] = object) so _render_partial_with_options can derive options[:locals]. However, if the caller explicitly provides locals: (e.g., json.post @post, partial: 'posts/post', as: :post, locals: { include_title: true }), _render_partial_with_options will keep the provided options[:locals] and will not include the :post local, so the partial will not receive the object local and can fail with an undefined post.

Consider handling this case by merging the object into options[:locals] when options[:locals] is already present (instead of only setting the top-level key), and add a regression test for inline object partial + locals:.

Suggested change

	options[options[:as]] = object
	options[options[:as]] = object
	options[:locals] = (options[:locals] || {}).merge(options[:as] => object)

[moberegger]

Explicitly providing locals to inline renders is not documented, so I don' think this needs to be supported.

Prior to this PR, it wasn't possible to "mix" these key args, either. So something like

# Note - the use of `locals:` here for an inline render is not documented. It is only documented for `json.partial!`
json.foos, @foos, partial: 'foos/foo', as: :foo, my_local: :foo, locals: { my_other_local: :bar }

wouldn't work. It has to be one or the other.