Feature: SWC Compatibility

[jankapunkt]

The new SWC compiler in Meteor 3.3 is throwing errors with Blaze, because of the usage of arguments.
This PR attempts to replace all arguments with spread operator ...args

[Copilot]

Pull request overview

This draft PR migrates Blaze from using the arguments object to the ES6 spread operator (...args) to ensure compatibility with Meteor 3.3's new SWC compiler. The changes are systematic and comprehensive, affecting the core Spacebars runtime, Blaze templating engine, HTML visitors, and related test files.

Key Changes

• Replaced all arguments object usage with spread operator parameters (...args) across Spacebars, Blaze, HTMLjs, and observe-sequence packages
• Eliminated Array.prototype.slice.call(arguments) patterns in favor of using spread parameters directly as arrays
• Updated function signatures to use rest parameters and destructuring where appropriate

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/spacebars/spacebars-runtime.js	Converted mustache implementation functions and helper functions to use spread operators
packages/spacebars-tests/templating_tests.js	Updated test helper to use spread operator
packages/spacebars-tests/template_tests.js	Updated test functions and fixed variable naming collision (tmpl4→tmpl5)
packages/spacebars-tests/old_templates_tests.js	Updated test functions to use spread operator
packages/spacebars-compiler/templatetag.js	Converted TemplateTag constructor to use spread operator
packages/spacebars-compiler/optimizer.js	Updated TreeTransformer visitAttributes to use spread operator
packages/observe-sequence/observe_sequence_tests.js	Converted ArraySubclass constructor to use spread operator
packages/observe-sequence/observe_sequence.js	Updated warn function to use spread operator
packages/htmljs/visitors.js	Converted visitor methods to use spread operators with proper destructuring
packages/blaze/view.js	Updated event handler to use spread operator
packages/blaze/template.js	Converted event map handler to use spread operator
packages/blaze/preamble.js	Updated Blaze._bind to use spread operator
packages/blaze/exceptions.js	Updated exception wrapper to use spread operator
packages/blaze/events.js	Converted event handler to use spread operator
packages/blaze/attrs.js	Updated UrlHandler update method to use spread operator
packages/blaze-hot/update-templates.js	Updated constructView override to use spread operator

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[jankapunkt]

We can continue with this, once #486 is merged

[nachocodoner]

Looks good to me.

Just double-check that after these changes, and with modern.verbose=true enabled in package.json, there are no errors from the SWC transpiler falling back to Babel. If there are other fallbacks, they should be covered too.

[jankapunkt]

@nachocodoner does it make sense to publish an RC so early adopters can verify?

[nachocodoner]

@jankapunkt: It does make sense. We can also verify it with a Meteor checkout or by copying the packages locally.

Since Blaze is attached to core, and we have already wrapped up 3.4 content and its limits, I’ll plan to do this check myself in the early 3.4.1 beta and include the Blaze package RCs accordingly.

Thanks for these changes!