UX: when pasting a link use linkify rules

app/assets/javascripts/discourse/app/lib/text.js

@@ -50,6 +50,13 @@ export function generateCookFunction(options) {
   });
 }
 
+export function generateLinkifyFunction(options) {
+  return loadMarkdownIt().then(() => {
+    const prettyText = createPrettyText(options);
+    return prettyText.opts.engine.linkify;
+  });
+}
+
 export function sanitize(text, options) {
   return textSanitize(text, new AllowLister(options));
 }

app/assets/javascripts/discourse/app/mixins/textarea-text-manipulation.js

@@ -1,5 +1,6 @@
 import { bind } from "discourse-common/utils/decorators";
 import Mixin from "@ember/object/mixin";
+import { generateLinkifyFunction } from "discourse/lib/text";
 import toMarkdown from "discourse/lib/to-markdown";
 import { action } from "@ember/object";
 import { isEmpty } from "@ember/utils";
@@ -17,6 +18,14 @@ const isInside = (text, regex) => {
 };
 
 export default Mixin.create({
+  init() {
+    this._super(...arguments);
+    generateLinkifyFunction(this.markdownOptions || {}).then((linkify) => {
+      // When pasting links, we should use the same rules to match links as we do when creating links for a cooked post.
+      this._cachedLinkify = linkify;
+    });
+  },
+
   // ensures textarea scroll position is correct
   _focusTextArea() {
     schedule("afterRender", () => {
@@ -273,18 +282,24 @@ export default Mixin.create({
       }
     }
 
-    if (plainText && !handled && selected.end > selected.start) {
+    if (
-      let isURL;
+      this._cachedLinkify &&
-      try {
+      plainText &&
-        isURL = !!new URL(plainText);
+      !handled &&
-      } catch {
+      selected.end > selected.start
-        isURL = false;
+    ) {
-      }
+      if (this._cachedLinkify.test(plainText)) {
-      if (isURL) {
+        const match = this._cachedLinkify.match(plainText)[0];
-        this._addText(selected, `[${selectedValue}](${plainText})`);
+        if (
+          match &&
+          match.index === 0 &&
+          match.lastIndex === match.raw.length
+        ) {
+          this._addText(selected, `[${selectedValue}](${match.url})`);
           handled = true;
         }
       }
+    }
 
     if (canPasteHtml && !handled) {
       let markdown = toMarkdown(html);