From b62794a3c5411a290a0510ef1420165864bd07ab Mon Sep 17 00:00:00 2001
From: Durvesh Pilankar <durveshpilankar@meta.com>
Date: Mon, 29 Jun 2026 17:52:47 -0700
Subject: [PATCH] Fix zero-unit stripping inside functions after the first
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normalizeZeroDimensions must not strip the unit from a zero inside a
function (e.g. calc(0px + 1%) — a unitless 0 can't be added to a %). It
tracks the active function via endFunction, but the guard
`node.type === 'function' && !endFunction` only ever recorded the FIRST
function. For a later function, endFunction had already been reset to 0,
so its children were treated as outside a function and their units were
stripped — emitting invalid CSS like `max(1px,2px) calc(0 + 1%)`.

Track every function with Math.max(endFunction, sourceEndIndex); the
existing reset still clears it once walking moves past the last function,
so bare zeros outside functions are still normalized.

Adds a regression test (fails before / passes after).
---
 .../__tests__/transform-value-normalization-test.js    | 10 ++++++++++
 .../src/shared/utils/normalizers/zero-dimensions.js    |  4 ++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/packages/@stylexjs/babel-plugin/__tests__/transform-value-normalization-test.js b/packages/@stylexjs/babel-plugin/__tests__/transform-value-normalization-test.js
index 60a577e15..104f706e4 100644
--- a/packages/@stylexjs/babel-plugin/__tests__/transform-value-normalization-test.js
+++ b/packages/@stylexjs/babel-plugin/__tests__/transform-value-normalization-test.js
@@ -95,6 +95,16 @@ describe('@stylexjs/babel-plugin', () => {
       `);
     });
 
+    test('preserves zero units inside a non-first function', () => {
+      const code = transform(`
+        import stylex from 'stylex';
+        const styles = stylex.create({ x: { width: 'max(1px, 2px) calc(0px + 1%)' } });
+      `);
+      // calc(0 + 1%) is invalid CSS — a unitless 0 cannot be added to a %.
+      expect(code).toContain('calc(0px + 1%)');
+      expect(code).not.toContain('calc(0 + 1%)');
+    });
+
     test('0 timings are all "0s"', () => {
       expect(
         transform(`
diff --git a/packages/@stylexjs/babel-plugin/src/shared/utils/normalizers/zero-dimensions.js b/packages/@stylexjs/babel-plugin/src/shared/utils/normalizers/zero-dimensions.js
index 4d355f2d8..2d6d84c1b 100644
--- a/packages/@stylexjs/babel-plugin/src/shared/utils/normalizers/zero-dimensions.js
+++ b/packages/@stylexjs/babel-plugin/src/shared/utils/normalizers/zero-dimensions.js
@@ -32,8 +32,8 @@ export default function normalizeZeroDimensions(
   let endFunction = 0;
 
   ast.walk((node) => {
-    if (node.type === 'function' && !endFunction) {
-      endFunction = node.sourceEndIndex ?? 0;
+    if (node.type === 'function') {
+      endFunction = Math.max(endFunction, node.sourceEndIndex ?? 0);
     }
     if (endFunction > 0 && node.sourceIndex > endFunction) {
       endFunction = 0;