fr(datepicker): Allow changing format of the days shown as column headers

[DmitryEfimenko]

Feature Description

Currently, when using NativeDateAdapter, the days are formatted to use one letter:

When using MomentDateAdapter, the days are formatted to use two letters:

I'm not sure if this discrepancy is intentional or if it is at least known about. In either case, the developer does not have any control to change that without writing a custom DateAdapter.

Use Case

I have a requirement to display three letters for each day.

Proposed Implementation 1

Add a couple properties to the MAT_DATE_FORMATS:

export declare type MatDateFormats = {
    parse: { ... };
    display: {
        ...
        dayShortLabel: string;
        dayShortA11yLabel: string;
    };
};

I personally like this option better then the one below.

Proposed Implementation 2

Allow developer to implement a custom component to replace this portion of the calendar similar to how it's done with @Input() calendarHeaderComponent.

The workaround

As a scrappy workaround, I extended the MomentDateAdapter and overrode it's private property: the _localeData. Of course this makes this solution fragile to future updates.

import { Inject, Optional } from '@angular/core';
import { MAT_DATE_LOCALE } from '@angular/material';
import {
  MAT_MOMENT_DATE_ADAPTER_OPTIONS,
  MatMomentDateAdapterOptions,
  MomentDateAdapter,
} from '@angular/material-moment-adapter';

export class MyMomentDateAdapter extends MomentDateAdapter {
  constructor(
    @Optional() @Inject(MAT_DATE_LOCALE) dateLocale: string,
    @Optional() @Inject(MAT_MOMENT_DATE_ADAPTER_OPTIONS) options?: MatMomentDateAdapterOptions
  ) {
    super(dateLocale, options);

    // IMPORTANT! USE OF PRIVATE API:
    // MomentDateAdapter uses 'narrow' format for days displayed as column headers:
    // https://github.com/angular/components/blob/5e34de2fd2ae04d15f9bdbedc7835408633a2fa4/src/material/datepicker/month-view.ts#L268
    this['_localeData'].narrowDaysOfWeek = this['_localeData'].shortDaysOfWeek;
  }
}

Then use it in the module:

providers: [
  {
    provide: DateAdapter,
    useClass: MyMomentDateAdapter,
    deps: [MAT_DATE_LOCALE, MAT_MOMENT_DATE_ADAPTER_OPTIONS]
  }
]

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