Decode single-digit hexadecimal CSS escapes

packages/tailwindcss/src/index.test.ts

@@ -1645,6 +1645,17 @@ describe('Parsing theme values from CSS', () => {
     `)
   })
 
+  test('normalizes single-digit hexadecimal escapes in theme variable names', async () => {
+    let compiler = await compile(css`
+      @theme {
+        --color-\0: red;
+      }
+      @tailwind utilities;
+    `)
+
+    expect(compiler.build([String.raw`bg-(--color-\0)`])).toContain('--color-\uFFFD: red;')
+  })
+
   // https://github.com/tailwindlabs/tailwindcss/issues/19786
   test('out-of-range escaped CSS variable candidates do not crash the build', async () => {
     // Shouldn't crash

packages/tailwindcss/src/utils/escape.test.ts

@@ -8,6 +8,32 @@ describe('escape', () => {
 })
 
 describe('unescape', () => {
+  test.each([
+    [String.raw`\0`, '\uFFFD'],
+    [String.raw`\1`, '\u0001'],
+    [String.raw`\9`, '\t'],
+    [String.raw`\a`, '\n'],
+    [String.raw`\A`, '\n'],
+    [String.raw`\c`, '\f'],
+    [String.raw`\C`, '\f'],
+    [String.raw`\f`, '\u000f'],
+    [String.raw`\F`, '\u000f'],
+  ])('decodes a single hexadecimal digit in %s', (input, expected) => {
+    expect(unescape(input)).toBe(expected)
+  })
+
+  test.each([
+    [String.raw`\a b`, '\nb'],
+    [String.raw`\00000a`, '\n'],
+    [String.raw`\41`, 'A'],
+    [String.raw`\0 `, '\uFFFD'],
+    [String.raw`\!`, '!'],
+    [String.raw`\g`, 'g'],
+    [String.raw`\\`, '\\'],
+  ])('preserves escape handling in %s', (input, expected) => {
+    expect(unescape(input)).toBe(expected)
+  })
+
   test('removes backslashes', () => {
     expect(unescape(String.raw`red-1\/2`)).toMatchInlineSnapshot(`"red-1/2"`)
   })

packages/tailwindcss/src/utils/escape.ts

@@ -73,12 +73,12 @@ export function escape(value: string) {
 }
 
 export function unescape(escaped: string) {
-  return escaped.replace(/\\([\dA-Fa-f]{1,6}[\t\n\f\r ]?|[\S\s])/g, (match) => {
-    if (match.length <= 2) {
-      return match[1]
+  return escaped.replace(/\\(?:([\dA-Fa-f]{1,6})[\t\n\f\r ]?|([\S\s]))/g, (_, hex, char) => {
+    if (!hex) {
+      return char
     }
 
-    let codePoint = Number.parseInt(match.slice(1).trim(), 16)
+    let codePoint = Number.parseInt(hex, 16)
 
     if (
       // Invalid codepoint: https://infra.spec.whatwg.org/#code-point