refactor(material/sort): explicit sort direction

Author: lekhmanrus

src/material/sort/sort-direction.ts

@@ -7,3 +7,5 @@
  */
 
 export type SortDirection = 'asc' | 'desc' | '';
+
+export type SortDirectionExplicit = Exclude<SortDirection, ''>;

src/material/sort/sort-header.ts

@@ -26,7 +26,7 @@ import {ENTER, SPACE} from '@angular/cdk/keycodes';
 import {merge, Subscription} from 'rxjs';
 import {MatSort, MatSortable} from './sort';
 import {matSortAnimations} from './sort-animations';
-import {SortDirection} from './sort-direction';
+import {SortDirection, SortDirectionExplicit} from './sort-direction';
 import {getSortHeaderNotContainedWithinSortError} from './sort-errors';
 import {MatSortHeaderIntl} from './sort-header-intl';
 
@@ -130,7 +130,7 @@ export class MatSortHeader extends _MatSortHeaderBase
   @Input() arrowPosition: 'before' | 'after' = 'after';
 
   /** Overrides the sort start value of the containing MatSort for this MatSortable. */
-  @Input() start: 'asc' | 'desc';
+  @Input() start: SortDirectionExplicit;
 
   /** Overrides the disable clear value of the containing MatSort for this MatSortable. */
   @Input()

src/material/sort/sort.ts

@@ -26,7 +26,7 @@ import {
   mixinInitialized,
 } from '@angular/material/core';
 import {Subject} from 'rxjs';
-import {SortDirection} from './sort-direction';
+import {SortDirection, SortDirectionExplicit} from './sort-direction';
 import {
   getSortDuplicateSortableIdError,
   getSortHeaderMissingIdError,
@@ -39,7 +39,7 @@ export interface MatSortable {
   id: string;
 
   /** Starting sort direction. */
-  start: 'asc' | 'desc';
+  start: SortDirectionExplicit;
 
   /** Whether to disable clearing the sorting state. */
   disableClear: boolean;
@@ -91,7 +91,7 @@ export class MatSort extends _MatSortBase
    * The direction to set when an MatSortable is initially sorted.
    * May be overriden by the MatSortable's sort start.
    */
-  @Input('matSortStart') start: 'asc' | 'desc' = 'asc';
+  @Input('matSortStart') start: SortDirectionExplicit = 'asc';
 
   /** The sort direction of the currently active MatSortable. */
   @Input('matSortDirection')
@@ -192,7 +192,7 @@ export class MatSort extends _MatSortBase
 }
 
 /** Returns the sort direction cycle to use given the provided parameters of order and clear. */
-function getSortDirectionCycle(start: 'asc' | 'desc',
+function getSortDirectionCycle(start: SortDirectionExplicit,
                                disableClear: boolean): SortDirection[] {
   let sortOrder: SortDirection[] = ['asc', 'desc'];
   if (start == 'desc') { sortOrder.reverse(); }

tools/public_api_guard/material/sort.md

@@ -73,7 +73,7 @@ export class MatSort extends _MatSortBase implements CanDisable, HasInitialized,
     sort(sortable: MatSortable): void;
     sortables: Map<string, MatSortable>;
     readonly sortChange: EventEmitter<Sort>;
-    start: 'asc' | 'desc';
+    start: SortDirectionExplicit;
     readonly _stateChanges: Subject<void>;
     // (undocumented)
     static ɵdir: i0.ɵɵDirectiveDeclaration<MatSort, "[matSort]", ["matSort"], { "disabled": "matSortDisabled"; "active": "matSortActive"; "start": "matSortStart"; "direction": "matSortDirection"; "disableClear": "matSortDisableClear"; }, { "sortChange": "matSortChange"; }, never>;
@@ -85,7 +85,7 @@ export class MatSort extends _MatSortBase implements CanDisable, HasInitialized,
 export interface MatSortable {
     disableClear: boolean;
     id: string;
-    start: 'asc' | 'desc';
+    start: SortDirectionExplicit;
 }
 
 // @public
@@ -143,7 +143,7 @@ export class MatSortHeader extends _MatSortHeaderBase implements CanDisable, Mat
     _showIndicatorHint: boolean;
     // (undocumented)
     _sort: MatSort;
-    start: 'asc' | 'desc';
+    start: SortDirectionExplicit;
     _toggleOnInteraction(): void;
     _updateArrowDirection(): void;
     _viewState: ArrowViewStateTransition;
@@ -181,6 +181,9 @@ export interface Sort {
 // @public
 export type SortDirection = 'asc' | 'desc' | '';
 
+// @public (undocumented)
+export type SortDirectionExplicit = Exclude<SortDirection, ''>;
+
 // (No @packageDocumentation comment for this package)
 
 ```