[charlespwd]

Warning

Research / WIP
Experimental output from liquid-factory, shared for design and code feedback. This is a research draft for the WIP3 stack, not a merge-ready language change.

In this PR

Add array literals to the native shared expression grammar, including nested arrays and trailing commas.

Problem

Templates build fixed lists with 'top,bottom' | split: ',' and empty lists with '' | split: ','.

Solution

Templates can write {% assign rows = ['top', 'bottom'] %} or use literals directly in filters, conditions, loops and render arguments.

ArrayLiteral evaluates its elements in the current context and returns a fresh container. Tags reuse the shared parser, so no tag-specific array implementation is needed. A leading [ constructs an array in every shared-parser call, with no reject_bare_brackets option or legacy unnamed-bracket branch.

Paired specs: Shopify/liquid-spec#169, adding specs/liquid_ruby/array_literals.yml.

Ruby API migration

Remove reject_bare_brackets: from Parser.new calls. The shared parser now has one leading-bracket grammar, including in Context#[]:

• context['[key]'] evaluates an array containing the value of key.
• Use context['self[key]'] for the indirect variable lookup previously expressed by bare brackets.

Existing native-template results stay unchanged. Typed legacy lookup-string APIs remain separate; this change does not add a replacement parser mode.

Feature boundary

Outcome

Construct an Array directly with [] or [expression, ...] wherever the native parser accepts an expression.

Scope

• Empty, nested and expression-valued arrays, whitespace and one optional trailing comma at each level.
• Ordinary Array behavior in output, filters, conditions, case/when, loops, cycle, assignment and lookups on assigned variables.
• Existing expression-taking tag positions, including render/include arguments, use the shared grammar.
• Literal-owned containers are fresh on each evaluation. Element values retain their existing semantics.
• Existing native-template output stays unchanged. The shared Parser and Context#[] now use the same array grammar for leading brackets; self[...] remains explicit lookup.

Acceptance boundary

• The paired specs/liquid_ruby/array_literals.yml contains the approved preservation, constructor and malformed-input cases.
• Existing native-template indexed/dotted/self lookup results, WIP3 expression semantics and shared-for metadata/modifiers remain unchanged.
• The exact render/include examples and inherited assignment-score/resource limits are covered in test/integration/array_literal_test.rb.
• Malformed arrays, key-value elements and direct postfix access such as [1, 2][0] remain syntax errors.

Non-goals

Hash literals, mixed array/hash literal nesting, arithmetic, filtered parentheses, interpolation, new postfix grammar and changes to for-argument separators.

Dependencies

• Parent implementation: Shopify/liquid#2133, liquid-factory-shared-expressions-in-for at 372f77cbebd9c9c5319d967a1a988d7c5878b225.
• Parent specs: Shopify/liquid-spec#168, the same branch name at 736ebca7b4377dbd8bf59232649fa00c69b21ea3.
• These dependencies are present at the pinned bases. This pair is stacked on those branches, not on main or the independent hash-literal feature.

The cases are examples, not proof that every possible template preserves its output.

[isaacbowen]

@charlespwd platform-grade prior art over in Mechanic: https://learn.mechanic.dev/platform/liquid/keyword-literals/array