issue-41925 fix: skip duplicate props when transferring props from an…

…chor to link (#42158)

Fixes issue #41925 by skipping duplicate props. I've tested the changes
locally - the duplicate prop is being skipped successfully. The
new-link.test.js suite is also passing.

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## Bug

- [x] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

Co-authored-by: Ishaq Ibrahim <ishaq.ibrahim@convertdigital.com.au>

packages/next-codemod/transforms/__testfixtures__/new-link/handle-duplicate-props.input.js

@@ -0,0 +1,9 @@
+import Link from 'next/link'
+
+export default function Page() {
+  return (
+    <Link href="/about">
+      <a href="/about" className="some-class">Link</a>
+    </Link>
+  );
+}

packages/next-codemod/transforms/__testfixtures__/new-link/handle-duplicate-props.output.js

@@ -0,0 +1,9 @@
+import Link from 'next/link'
+
+export default function Page() {
+  return (
+    <Link href="/about" className="some-class">
+      Link
+    </Link>
+  );
+}

packages/next-codemod/transforms/__tests__/new-link.test.js

@@ -11,6 +11,7 @@ const fixtures = [
   'spread-props',
   'link-string',
   'styled-jsx',
+  'handle-duplicate-props'
 ]
 
 for (const fixture of fixtures) {

packages/next-codemod/transforms/new-link.ts

@@ -86,13 +86,24 @@ export default function transformer(file: FileInfo, api: API) {
         const hasProps = props.length > 0
 
         if (hasProps) {
-          // Add props to <Link>
-          $link.get('attributes').value.push(...props)
+          // Add only unique props to <Link> (skip duplicate props)
+          const linkPropNames = $link
+            .get('attributes')
+            .value.map((linkProp) => linkProp?.name?.name)
+          const uniqueProps = []
+
+          props.forEach((anchorProp) => {
+            if (!linkPropNames.includes(anchorProp?.name?.name)) {
+              uniqueProps.push(anchorProp)
+            }
+          })
+
+          $link.get('attributes').value.push(...uniqueProps)
+
           // Remove props from <a>
           props.length = 0
         }
 
-        //
         const childrenProps = $childrenWithA.get('children')
         $childrenWithA.replaceWith(childrenProps.value)
       })