[FIX] mail: incorrect message order on previous messages load

Discuss models use relationnal fields. Since [1], the implementation
of the `unshift` method changed for `many` fields. The new
implementation is incorrect: unshifting several records results in an
insertion on the inverse order which differs from the native
implementation.

This issue broke the loading of older messages in discuss: older
messages are inserted with the `unshift` method thus in the inverse
order.

[1]: https://github.com/odoo/odoo/pull/136539

closes odoo/odoo#140747

Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/static/src/core/common/record.js

@@ -215,8 +215,8 @@ export class RecordList extends Array {
     }
     /** @param {R[]} records */
     unshift(...records) {
-        for (const val of records) {
-            const r = this._insert(val, (r3) => {
+        for (let i = records.length - 1; i >= 0; i--) {
+            const r = this._insert(records[i], (r3) => {
                 this.data.unshift(r3.localId);
                 r3.__uses__.add(this);
             });

addons/mail/static/tests/core/record_tests.js

@@ -149,3 +149,32 @@ QUnit.test("Trusted insert on html field with { html: true }", async (assert) =>
     assert.strictEqual(hello.body.toString(), "<p>hello</p>");
     assert.strictEqual(world.body, "<p>world</p>");
 });
+
+QUnit.test("Unshift preserves order", async (assert) => {
+    (class Message extends Record {
+        static id = "id";
+        id;
+    }).register();
+    (class Thread extends Record {
+        static id = "name";
+        name;
+        messages = Record.many("Message");
+    }).register();
+    const store = await start();
+    const thread = store.Thread.insert({ name: "General" });
+    thread.messages.unshift({ id: 3 }, { id: 2 }, { id: 1 });
+    assert.deepEqual(
+        thread.messages.map((msg) => msg.id),
+        [3, 2, 1]
+    );
+    thread.messages.unshift({ id: 6 }, { id: 5 }, { id: 4 });
+    assert.deepEqual(
+        thread.messages.map((msg) => msg.id),
+        [6, 5, 4, 3, 2, 1]
+    );
+    thread.messages.unshift({ id: 7 });
+    assert.deepEqual(
+        thread.messages.map((msg) => msg.id),
+        [7, 6, 5, 4, 3, 2, 1]
+    );
+});

addons/mail/static/tests/thread/thread_tests.js

@@ -49,7 +49,7 @@ QUnit.test("load more messages from channel (auto-load on scroll)", async () =>
     });
     for (let i = 0; i <= 60; i++) {
         pyEnv["mail.message"].create({
-            body: "not empty",
+            body: i.toString(),
             model: "discuss.channel",
             res_id: channelId,
         });
@@ -60,6 +60,7 @@ QUnit.test("load more messages from channel (auto-load on scroll)", async () =>
     await contains(".o-mail-Thread", { scroll: "bottom" });
     await scroll(".o-mail-Thread", 0);
     await contains(".o-mail-Message", { count: 60 });
+    await contains(".o-mail-Message", { text: "30", after: [".o-mail-Message", { text: "29" }] });
 });
 
 QUnit.test("show message subject when subject is not the same as the thread name", async () => {