[FIX] web: readonly monetary field onchange currency

Before this fix:
    A readonly monetary field was not updating
    its currency symbol when selecting another currency.

Scenario:
    1. Activate multi-currency with $ (default) and €
    2. In hr_expense, go to My Expenses to Submit
    3. Create a new expense
    4. Select 'EUR' as currency
        => Unit Price is correctly updated with €, but not Total.

With this fix:
    Total displays the correct currency in edit mode.

Explanation:
    Monetary fields in readonly are relying on _formatValue() to
    display their value.
    _formatValue() uses this.formatOptions.currency, which stores
    the currency at loading of the field. We must update its value
    whenever there is a change of currency.

opw-783378

addons/web/static/src/js/fields/basic_fields.js

@@ -638,6 +638,7 @@ var FieldMonetary = InputField.extend({
         var currencyField = this.nodeOptions.currency_field || this.field.currency_field || 'currency_id';
         var currencyID = this.record.data[currencyField] && this.record.data[currencyField].res_id;
         this.currency = session.get_currency(currencyID);
+        this.formatOptions.currency = this.currency; // _formatValue() uses formatOptions
     },
 });
 

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

@@ -2347,9 +2347,14 @@ QUnit.module('basic_fields', {
     });
 
     QUnit.test('monetary field with real monetary field in model', function (assert) {
-        assert.expect(4);
+        assert.expect(7);
 
         this.data.partner.fields.qux.type = "monetary";
+        this.data.partner.fields.quux = {
+            string: "Quux", type: "monetary", digits: [16,1], searchable: true, readonly: true,
+        };
+
+        (_.find(this.data.partner.records, function (record) { return record.id === 5 })).quux = 4.2;
 
         this.data.partner.onchanges = {
             bar: function (obj) {
@@ -2364,6 +2369,7 @@ QUnit.module('basic_fields', {
             arch:'<form string="Partners">' +
                     '<sheet>' +
                         '<field name="qux"/>' +
+                        '<field name="quux"/>' +
                         '<field name="currency_id"/>' +
                         '<field name="bar"/>' +
                     '</sheet>' +
@@ -2374,7 +2380,9 @@ QUnit.module('basic_fields', {
             },
         });
 
-        assert.strictEqual(form.$('.o_field_monetary').html(), "$&nbsp;9.10",
+        assert.strictEqual(form.$('.o_field_monetary').first().html(), "$&nbsp;9.10",
+            "readonly value should contain the currency");
+        assert.strictEqual(form.$('.o_field_monetary').first().next().html(), "$&nbsp;4.20",
             "readonly value should contain the currency");
 
         form.$buttons.find('.o_form_button_edit').click();
@@ -2385,12 +2393,16 @@ QUnit.module('basic_fields', {
         form.$('input[type="checkbox"]').click(); // Change the field on which the monetary depends
         assert.strictEqual(form.$('.o_field_monetary > input').length, 1,
             "After the onchange, the monetary <input/> should not have been duplicated");
+        assert.strictEqual(form.$('.o_field_monetary[name=quux]').length, 1,
+            "After the onchange, the monetary readonly field should not have been duplicated");
 
         var $dropdown = form.$('.o_field_many2one input').autocomplete('widget');
         form.$('.o_field_many2one input').click();
         $dropdown.find('li:not(.o_m2o_dropdown_option):last').mouseenter().click();
         assert.strictEqual(form.$('.o_field_monetary > span').html(), "€",
             "After currency change, the monetary field currency should have been updated");
+        assert.strictEqual(form.$('.o_field_monetary').first().next().html(), "4.20&nbsp;€",
+            "readonly value should contain the updated currency");
 
         form.destroy();
     });