Don't repeatedly add backslashes to escape sequences when formatting (#381)

* fix: repeated backslash escaping

* Cleanup

* Bail early if the content didn’t change

* Cleanup

* Move test

* Fix failing tests

* Cleanup code and comments

* Update changelog

---------

Co-authored-by: Jordan Pittman <jordan@cryptica.me>

Author: Sec-ant

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Add support for OXC + Hermes Prettier plugins ([#376](https://github.com/tailwindlabs/prettier-plugin-tailwindcss/pull/376), [#380](https://github.com/tailwindlabs/prettier-plugin-tailwindcss/pull/380))
 - Sort template literals in Angular expressions ([#377](https://github.com/tailwindlabs/prettier-plugin-tailwindcss/pull/377))
+- Don't repeatedly add backslashes to escape sequences when formatting ([#381](https://github.com/tailwindlabs/prettier-plugin-tailwindcss/pull/381))
 
 ## [0.6.13] - 2025-06-19
 

src/index.ts

@@ -28,6 +28,8 @@ import { spliceChangesIntoString, visit } from './utils.js'
 
 let base = await loadPlugins()
 
+const ESCAPE_SEQUENCE_PATTERN = /\\(['"\\nrtbfv0-7xuU])/g
+
 function createParser(
   parserFormat: string,
   transform: (ast: any, context: TransformerContext) => void,
@@ -505,41 +507,41 @@ function sortStringLiteral(
     removeDuplicates,
     collapseWhitespace,
   })
+
   let didChange = result !== node.value
-  node.value = result
 
-  // A string literal was escaped if:
-  // - There are backslashes in the raw value; AND
-  // - The raw value is not the same as the value (excluding the surrounding quotes)
-  let wasEscaped = false
+  if (!didChange) return false
 
-  if (node.extra) {
-    // JavaScript (StringLiteral)
-    wasEscaped =
-      node.extra?.rawValue.includes('\\') &&
-      node.extra?.raw.slice(1, -1) !== node.value
-  } else {
-    // TypeScript (Literal)
-    wasEscaped =
-      node.value.includes('\\') && node.raw.slice(1, -1) !== node.value
-  }
+  node.value = result
 
-  let escaped = wasEscaped ? result.replace(/\\/g, '\\\\') : result
+  // Preserve the original escaping level for the new content
+  let raw = node.extra?.raw ?? node.raw
+  let quote = raw[0]
+  let originalRawContent = raw.slice(1, -1)
+  let originalValue = node.extra?.rawValue ?? node.value
 
   if (node.extra) {
+    // The original list has ecapes so we ensure that the sorted list also
+    // maintains those by replacing backslashes from escape sequences.
+    //
+    // It seems that TypeScript-based ASTs don't need this special handling
+    // which is why this is guarded inside the `node.extra` check
+    if (originalRawContent !== originalValue && originalValue.includes('\\')) {
+      result = result.replace(ESCAPE_SEQUENCE_PATTERN, '\\\\$1')
+    }
+
     // JavaScript (StringLiteral)
-    let raw = node.extra.raw
     node.extra = {
       ...node.extra,
       rawValue: result,
-      raw: raw[0] + escaped + raw.slice(-1),
+      raw: quote + result + quote,
     }
   } else {
     // TypeScript (Literal)
-    let raw = node.raw
-    node.raw = raw[0] + escaped + raw.slice(-1)
+    node.raw = quote + result + quote
   }
-  return didChange
+
+  return true
 }
 
 function isStringLiteral(node: any) {

tests/tests.ts

@@ -111,6 +111,10 @@ export let javascript: TestEntry[] = [
     `;<div class={'object-cover' + (standalone ? ' aspect-square w-full' : ' min-h-0 grow basis-0')}></div>`,
     `;<div class={'object-cover' + (standalone ? ' aspect-square w-full' : ' min-h-0 grow basis-0')}></div>`,
   ],
+  [
+    `;<div class="[&>.a\\_p]:after:content-['\\2'] [&>.a\\_p]:z-0"></div>`,
+    `;<div class="[&>.a\\_p]:z-0 [&>.a\\_p]:after:content-['\\2']"></div>`,
+  ],
 ]
 javascript = javascript.concat(
   javascript.map((test) => [