[FIX] web: read records up to list limit

Fine-tuning of commit e7fab23420
In a one2many with more than one page with a limit of k records, add a line l.
It increments the list limit to k+1. Remove a line above (of index <= k).
It will try to load a line l' to replace it, that it will find on page 2.
However when deciding if it should read missing fields on that record, it will
scan at most u records, skipping virtual ids.
Here u is the min between the current number of lines and the list limit
without the temporary increase due to the added record.
Since there are at least two pages, u = k.
However since l is in the list at index k, then l' won't be read, and since it
was on page 2 its data hasn't been loaded.
Therefore the js would traceback when trying to evaluate it.

opw 1913361

closes odoo/odoo#29338

addons/web/static/src/js/views/basic/basic_model.js

@@ -3958,11 +3958,24 @@ var BasicModel = AbstractModel.extend({
         }
         return def.then(function () {
             var resIDs = [];
-            // generate the current count and res_ids list by applying the changes
-            var currentCount = list.count;
             var currentResIDs = list.res_ids;
-            var effectiveLimit = (list.limit || 0) - (list.tempLimitIncrement || 0);
-            var upperBound = effectiveLimit ? Math.min(list.offset + effectiveLimit, currentCount) : currentCount;
+            // if new records have been added to the list, their virtual ids have
+            // been pushed at the end of res_ids (or at the beginning, depending
+            // on the editable property), ignoring completely the current page
+            // where the records have actually been created ; for that reason,
+            // we use orderedResIDs which is a freezed order with the virtual ids
+            // at the correct position where they were actually inserted ; however,
+            // when we use orderedResIDs, we must filter out ids that are not in
+            // res_ids, which correspond to records that have been removed from
+            // the relation (this information being taken into account in res_ids
+            // but not in orderedResIDs)
+            if (list.orderedResIDs) {
+                currentResIDs = list.orderedResIDs.filter(function (resID) {
+                    return list.res_ids.indexOf(resID) >= 0;
+                });
+            }
+            var currentCount = currentResIDs.length;
+            var upperBound = list.limit ? Math.min(list.offset + list.limit, currentCount) : currentCount;
             var fieldNames = list.getFieldNames();
             for (var i = list.offset; i < upperBound; i++) {
                 var resId = currentResIDs[i];

addons/web/static/tests/fields/relational_fields_tests.js

@@ -3999,6 +3999,50 @@ QUnit.module('relational_fields', {
         form.destroy();
     });
 
+    QUnit.test('delete a record while adding another one in a multipage', function (assert) {
+        // in a many2one with at least 2 pages, add a new line. Delete the line above it.
+        // (the onchange makes it so that the virtualID is inserted in the middle of the currentResIDs.)
+        // it should load the next line to display it on the page.
+        assert.expect(2);
+
+        this.data.partner.records[0].turtles = [2, 3];
+        this.data.partner.onchanges.turtles = function (obj) {
+           obj.turtles = [[5]].concat(obj.turtles);
+        };
+
+        var form = createView({
+            View: FormView,
+            model: 'partner',
+            data: this.data,
+            arch:'<form string="Partners">' +
+                    '<sheet>' +
+                        '<group>' +
+                            '<field name="turtles">' +
+                                '<tree editable="bottom" limit="1" decoration-muted="turtle_bar == False">' +
+                                    '<field name="turtle_foo"/>' +
+                                    '<field name="turtle_bar"/>' +
+                                '</tree>' +
+                            '</field>' +
+                        '</group>' +
+                    '</sheet>' +
+                 '</form>',
+            res_id: 1,
+        });
+
+        form.$buttons.find('.o_form_button_edit').click();
+        // add a line (virtual record)
+        form.$('.o_field_x2many_list_row_add a').click();
+        form.$('.o_input').val('pi').trigger('input');
+        // delete the line above it
+        form.$('.o_list_record_delete').first().click();
+        // the next line should be displayed below the newly added one
+        assert.strictEqual(form.$('.o_data_row').length, 2, "should have 2 records");
+        assert.strictEqual(form.$('.o_data_row').text(), 'pikawa',
+            "should display the correct records on page 1");
+
+        form.destroy();
+    });
+
     QUnit.test('onchange returning a command 6 for an x2many', function (assert) {
         assert.expect(2);
 
@@ -6231,7 +6275,7 @@ QUnit.module('relational_fields', {
                 '</form>',
             res_id: 1,
             mockRPC: function (route, args) {
-                assert.step(args.method + ' ' + args.model)
+                assert.step(args.method + ' ' + args.model);
                 return this._super(route, args);
             },
             viewOptions: {