PR #42 filter parameters (breaking change)

[osteele]

Implement filter parameters.

[Copilot]

Pull request overview

This PR implements named filter arguments (issue #42), enabling Shopify Liquid-compatible filter parameter syntax. The implementation adds support for calling filters with named parameters like {{image | img_url: '580x', scale: 2}} and {{ date | format: 'date' }}.

• Introduced filterParam struct to distinguish between positional and named parameters
• Updated filter application logic to separate and handle both parameter types
• Modified parser grammar to recognize named argument syntax (KEYWORD expr)
• Added comprehensive test coverage for various named argument scenarios

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
expressions/filters.go	Core implementation: added filterParam struct and updated ApplyFilter to handle named arguments via map parameter detection
expressions/expressions.y	Grammar changes: extended filter_params rule to support KEYWORD expr syntax for named parameters
expressions/y.go	Regenerated parser from grammar changes (goyacc output)
expressions/scanner.go	Regenerated scanner with formatting changes (ragel output)
expressions/context.go	Updated ApplyFilter interface signature to accept []filterParam instead of []valueFn
expressions/builders.go	Updated makeFilter function signature to match new parameter type
expressions/filters_test.go	Added comprehensive unit tests for named arguments, including parsing and various argument combinations
liquid_test.go	Added integration tests demonstrating real-world usage from issue #42 examples
README.md	Added detailed documentation with examples of named filter arguments; removed issue #42 from unimplemented features list

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[Copilot]

The named arguments map is only added when len(namedParams) > 0, but filters expecting named arguments should always receive a map parameter even when no named arguments are provided. This breaks filters that rely on checking the map for optional arguments.

For example, when calling {{image | img_url: '300x'}} (no named args), the filter function func(image string, size string, opts map[string]any) will not receive the opts parameter at all, causing a parameter count mismatch error.

Solution: Always pass the namedParams map if the filter accepts named arguments, even when it's empty:

if acceptsNamedArgs {
    args = append(args, namedParams)
}

Suggested change

	if acceptsNamedArgs && len(namedParams) > 0 {
	if acceptsNamedArgs {

[Copilot]

The header comment // Code generated by ragel. DO NOT EDIT. has been removed. According to the //go:generate directive in expressions/parser.go, this comment should be added automatically by sed after ragel generation. This file should not be manually edited.

Additionally, there are numerous whitespace-only changes (removal of blank lines) throughout the file that appear to be formatting changes, which suggests the file may have been manually edited or regenerated with different formatting settings.