Fix double encoding in new url transform

Closes GH-797.

lib/index.js

@@ -84,7 +84,6 @@
 import {unreachable} from 'devlop'
 import {toJsxRuntime} from 'hast-util-to-jsx-runtime'
 import {urlAttributes} from 'html-url-attributes'
-import {sanitizeUri} from 'micromark-util-sanitize-uri'
 // @ts-expect-error: untyped.
 import {Fragment, jsx, jsxs} from 'react/jsx-runtime'
 import remarkParse from 'remark-parse'
@@ -297,5 +296,26 @@ export function Markdown(options) {
  *   Safe URL.
  */
 export function defaultUrlTransform(value) {
-  return sanitizeUri(value, safeProtocol)
+  // Same as:
+  // <https://github.com/micromark/micromark/blob/929275e/packages/micromark-util-sanitize-uri/dev/index.js#L34>
+  // But without the `encode` part.
+  const colon = value.indexOf(':')
+  const questionMark = value.indexOf('?')
+  const numberSign = value.indexOf('#')
+  const slash = value.indexOf('/')
+
+  if (
+    // If there is no protocol, it’s relative.
+    colon < 0 ||
+    // If the first colon is after a `?`, `#`, or `/`, it’s not a protocol.
+    (slash > -1 && colon > slash) ||
+    (questionMark > -1 && colon > questionMark) ||
+    (numberSign > -1 && colon > numberSign) ||
+    // It is a protocol, it should be allowed.
+    safeProtocol.test(value.slice(0, colon))
+  ) {
+    return value
+  }
+
+  return ''
 }

package.json

@@ -81,7 +81,6 @@
     "hast-util-to-jsx-runtime": "^2.0.0",
     "html-url-attributes": "^3.0.0",
     "mdast-util-to-hast": "^13.0.0",
-    "micromark-util-sanitize-uri": "^2.0.0",
     "remark-parse": "^11.0.0",
     "remark-rehype": "^11.0.0",
     "unified": "^11.0.0",

test.jsx

@@ -326,6 +326,13 @@ test('react-markdown', async function (t) {
     )
   })
 
+  await t.test('should support hash (`&`) in a URL', function () {
+    assert.equal(
+      asHtml(<Markdown children="[](a?b&c=d)" />),
+      '<p><a href="a?b&amp;c=d"></a></p>'
+    )
+  })
+
   await t.test('should support hash (`#`) in a URL', function () {
     assert.equal(
       asHtml(<Markdown children="[](a#javascript:alert(1))" />),