Require matching prefix when detecting negatives (#8121)

* Require matching prefix when detecting negatives

* Update changelog

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Types: allow for arbitrary theme values (for 3rd party plugins) ([#7926](https://github.com/tailwindlabs/tailwindcss/pull/7926))
 - Don’t split vars with numbers in them inside arbitrary values ([#8091](https://github.com/tailwindlabs/tailwindcss/pull/8091))
+- Require matching prefix when detecting negatives ([#8121](https://github.com/tailwindlabs/tailwindcss/pull/8121))
 
 ### Added
 

src/lib/generateRules.js

@@ -382,7 +382,11 @@ function* resolveMatchedPlugins(classCandidate, context) {
   const twConfigPrefix = context.tailwindConfig.prefix
 
   const twConfigPrefixLen = twConfigPrefix.length
-  if (candidatePrefix[twConfigPrefixLen] === '-') {
+
+  const hasMatchingPrefix =
+    candidatePrefix.startsWith(twConfigPrefix) || candidatePrefix.startsWith(`-${twConfigPrefix}`)
+
+  if (candidatePrefix[twConfigPrefixLen] === '-' && hasMatchingPrefix) {
     negative = true
     candidatePrefix = twConfigPrefix + candidatePrefix.slice(twConfigPrefixLen + 1)
   }

tests/prefix.test.js

@@ -358,3 +358,19 @@ it('prefix with negative values and variants in the safelist', async () => {
     }
   `)
 })
+
+it('prefix does not detect and generate unnecessary classes', async () => {
+  let config = {
+    prefix: 'tw-_',
+    content: [{ raw: html`-aaa-filter aaaa-table aaaa-hidden` }],
+    corePlugins: { preflight: false },
+  }
+
+  let input = css`
+    @tailwind utilities;
+  `
+
+  const result = await run(input, config)
+
+  expect(result.css).toMatchFormattedCss(css``)
+})