Prevent Svelte files from breaking when there are duplicate classes (#359)

* fix: prevent Svelte from breaking when there are duplicate classes

* fix: pass removeDuplicates every time sortTemplateLiteral calls sortClasses

* chore: remove redundant test

* Update comments

* Update changelog

---------

Co-authored-by: Jordan Pittman <[email protected]>

Author: dsantolo

CHANGELOG.md

@@ -7,7 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
+- Prevent Svelte files from breaking when there are duplicate classes ([#359](https://github.com/tailwindlabs/prettier-plugin-tailwindcss/pull/359))
 
 ## [0.6.12] - 2025-05-30
 

src/index.ts

@@ -454,6 +454,7 @@ function sortStringLiteral(
   node: any,
   {
     env,
+    removeDuplicates,
     collapseWhitespace = { start: true, end: true },
   }: {
     env: TransformerEnv
@@ -463,6 +464,7 @@ function sortStringLiteral(
 ) {
   let result = sortClasses(node.value, {
     env,
+    removeDuplicates,
     collapseWhitespace,
   })
   let didChange = result !== node.value
@@ -513,6 +515,7 @@ function sortTemplateLiteral(
   node: any,
   {
     env,
+    removeDuplicates,
     collapseWhitespace = { start: true, end: true },
   }: {
     env: TransformerEnv
@@ -530,6 +533,7 @@ function sortTemplateLiteral(
 
     quasi.value.raw = sortClasses(quasi.value.raw, {
       env,
+      removeDuplicates,
       // Is not the first "item" and does not start with a space
       ignoreFirst: i > 0 && !/^\s/.test(quasi.value.raw),
 
@@ -553,6 +557,7 @@ function sortTemplateLiteral(
           ignoreFirst: i > 0 && !/^\s/.test(quasi.value.cooked),
           ignoreLast:
             i < node.expressions.length && !/\s$/.test(quasi.value.cooked),
+          removeDuplicates,
           collapseWhitespace: collapseWhitespace && {
             start: collapseWhitespace && collapseWhitespace.start && i === 0,
             end:
@@ -946,7 +951,7 @@ function transformSvelte(ast: any, { env, changes }: TransformerContext) {
           env,
           ignoreFirst: i > 0 && !/^\s/.test(value.raw),
           ignoreLast: i < attr.value.length - 1 && !/\s$/.test(value.raw),
-          removeDuplicates: false,
+          removeDuplicates: true,
           collapseWhitespace: false,
         })
         value.data = same
@@ -955,7 +960,7 @@ function transformSvelte(ast: any, { env, changes }: TransformerContext) {
               env,
               ignoreFirst: i > 0 && !/^\s/.test(value.data),
               ignoreLast: i < attr.value.length - 1 && !/\s$/.test(value.data),
-              removeDuplicates: false,
+              removeDuplicates: true,
               collapseWhitespace: false,
             })
       } else if (value.type === 'MustacheTag') {

tests/plugins.test.ts

@@ -444,6 +444,26 @@ import Custom from '../components/Custom.astro'
           `<div\n class={\`underline \n flex\`}></div>`,
           `<div\n  class={\`flex \n underline\`}\n></div>`,
         ],
+
+        // Duplicates can be removed in simple attributes
+        [
+          `<div class="flex flex underline flex flex"></div>`,
+          `<div class="flex underline"></div>`,
+        ],
+
+        // Duplicates cannot be removed in string literals otherwise invalid
+        // code will be produced during printing.
+        [
+          `<div class={'flex underline flex'}></div>`,
+          `<div class={'flex flex underline'}></div>`,
+        ],
+
+        // Duplicates cannot be removed in template literals otherwise invalid
+        // code will be produced during printing.
+        [
+          `<div class={\`flex underline flex\`}></div>`,
+          `<div class={\`flex flex underline\`}></div>`,
+        ],
       ],
     },
   },