upload: Append file markdown to textarea when placeholder is missing.

Fixes #26037.

web/src/compose_ui.js

@@ -189,7 +189,9 @@ export function replace_syntax(old_syntax, new_syntax, $textarea = $("#compose-t
     // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace#Description
     // for details.
 
+    const old_text = $textarea.val();
     replace($textarea[0], old_syntax, () => new_syntax, "after-replacement");
+    const new_text = $textarea.val();
 
     // When replacing content in a textarea, we need to move the cursor
     // to preserve its logical position if and only if the content we
@@ -207,6 +209,9 @@ export function replace_syntax(old_syntax, new_syntax, $textarea = $("#compose-t
         // Otherwise we simply restore it to it's original position
         $textarea.caret(prev_caret);
     }
+
+    // Return if anything was actually replaced.
+    return old_text !== new_text;
 }
 
 export function compute_placeholder_text(opts) {

web/src/upload.js

@@ -341,12 +341,17 @@ export function setup_upload(config) {
         const split_url = url.split("/");
         const filename = split_url.at(-1);
         const filename_url = "[" + filename + "](" + url + ")";
-        compose_ui.replace_syntax(
+        const $text_area = get_item("textarea", config);
+        const replacement_successful = compose_ui.replace_syntax(
             get_translated_status(file),
             filename_url,
-            get_item("textarea", config),
+            $text_area,
         );
-        compose_ui.autosize_textarea(get_item("textarea", config));
+        if (!replacement_successful) {
+            compose_ui.insert_syntax_and_focus(filename_url, $text_area);
+        }
+
+        compose_ui.autosize_textarea($text_area);
 
         // The uploaded files should be removed since uppy doesn't allow files in the store
         // to be re-uploaded again.

web/tests/upload.test.js

@@ -492,6 +492,7 @@ test("copy_paste", ({override, override_rewire}) => {
 test("uppy_events", ({override_rewire, mock_template}) => {
     $("#compose_banners .upload_banner .moving_bar").css = () => {};
     $("#compose_banners .upload_banner").length = 0;
+    override_rewire(compose_ui, "smart_insert_inline", () => {});
 
     const callbacks = {};
     let state = {};