[matthew-dean]

Exposes Less v5's collapseNesting enum through the public Less render options.

Why

collapseNesting became an enum in Jess 2.0.0-alpha.20:

• false (default) — keep authored nesting (native CSS nested output).
• 'native' — the CSS Nesting desugaring: parent wrapped in :is(), child selector lists distributed, so each branch keeps its own specificity (matching the browser and Less 4.x).
• 'compact' — like 'native' but also folds same-combinator descendant runs into a single :is().
• true — deprecated alias for 'native'.

The wrapper still coerced the option to a boolean (opts.collapseNesting === true), so a 'native' or 'compact' request silently fell through to nested output. This passes the validated enum straight to the compiler; true continues to map to the flattened projection, and an unknown value is rejected with a clear error.

Tests

lessc-alpha now asserts:

• false / 'native' / 'compact' / true each pass through to output: [{ collapseNesting: <value> }].
• an unknown value throws.
• 'native' distributes a child selector list (:is(.a, .b) .c, :is(.a, .b) .d) while 'compact' folds it (:is(.a, .b) :is(.c, .d)).

Full packages/less alpha suite passes (91 fixtures, packed-consumer proof against Jess 2.0.0-alpha.20).

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[greptile-apps]

Confidence Score: 4/5

The PR should not merge until explicitly undefined collapseNesting values retain the normal omitted-option behavior instead of aborting rendering.

Summary

• Preserves true as the deprecated native-mode alias.
• Rejects unknown explicit mode values.
• Adds coverage for selector-list distribution and compact folding.
• Introduces a regression for explicitly undefined optional values.

_{Reviews (1) · Last reviewed commit: "feat(options): pass collapseNesting enum..."}