[jonthomp]

Problem

parseUnparsed drops a token list whose reduced value is falsy (if (!args) return), so --my-var: 0 compiles to no declaration at all. A var() reading it then falls through to the inherited value, the :root value or its fallback. On main, .zero { --my-var: 0 } .one { --my-var: 1 } .test { opacity: var(--my-var, 0.5) } renders opacity: 0.5 on test zero, where browsers compute opacity: 0.

Solution

The check drops only an undefined result, so a 0 value is kept like any other. The check is in shared parseUnparsed, and no other property's compiled output changes: the rest of the suite passes unchanged.

Tests

• src/__tests__/native/variables.test.tsx covers a custom property declared as 0 and read through var() with a fallback. It fails on main.

Verification

On macOS with Node 24:

• yarn lint clean
• yarn typecheck clean
• yarn test: 87 suites, 1390 tests pass

[Copilot]

🟢 Approval recommended

No active review issues are reported for the change to preserve zero-valued custom properties.

No open issues 🎉

What changed in this PR

Fixes the CSS compiler dropping custom properties declared as 0, so var() uses the declared value instead of an inherited value or fallback.

Changes:

• Updates parseUnparsed to discard only undefined, preserving zero values.
• Adds a regression test verifying that a zero-valued custom property produces opacity: 0 when a fallback is present.

File	Description
src/​compiler/​declarations.ts	Preserves zero values in parsed declarations.
src/​__tests__/​native/​variables.test.tsx	Tests zero-valued custom property resolution through var().

_{Review effort: Balanced}