fix(linear-progress): Restore buffer after determinate is toggl… (#5156)

Author: ericfromgoogle

packages/mdc-linear-progress/foundation.ts

@@ -49,6 +49,7 @@ export class MDCLinearProgressFoundation extends MDCFoundation<MDCLinearProgress
   private isDeterminate_!: boolean;
   private isReversed_!: boolean;
   private progress_!: number;
+  private buffer_!: number;
 
   constructor(adapter?: Partial<MDCLinearProgressAdapter>) {
     super({...MDCLinearProgressFoundation.defaultAdapter, ...adapter});
@@ -58,13 +59,15 @@ export class MDCLinearProgressFoundation extends MDCFoundation<MDCLinearProgress
     this.isDeterminate_ = !this.adapter_.hasClass(cssClasses.INDETERMINATE_CLASS);
     this.isReversed_ = this.adapter_.hasClass(cssClasses.REVERSED_CLASS);
     this.progress_ = 0;
+    this.buffer_ = 1;
   }
 
   setDeterminate(isDeterminate: boolean) {
     this.isDeterminate_ = isDeterminate;
     if (this.isDeterminate_) {
       this.adapter_.removeClass(cssClasses.INDETERMINATE_CLASS);
       this.setScale_(this.adapter_.getPrimaryBar(), this.progress_);
+      this.setScale_(this.adapter_.getBuffer(), this.buffer_);
     } else {
       this.adapter_.addClass(cssClasses.INDETERMINATE_CLASS);
       this.setScale_(this.adapter_.getPrimaryBar(), 1);
@@ -80,6 +83,7 @@ export class MDCLinearProgressFoundation extends MDCFoundation<MDCLinearProgress
   }
 
   setBuffer(value: number) {
+    this.buffer_ = value;
     if (this.isDeterminate_) {
       this.setScale_(this.adapter_.getBuffer(), value);
     }

test/unit/mdc-linear-progress/foundation.test.js

@@ -81,6 +81,17 @@ test('#setDeterminate restores previous progress value after toggled from false
   td.verify(mockAdapter.setStyle(primaryBar, 'transform', 'scaleX(0.123)'), {times: 2});
 });
 
+test('#setDeterminate restores previous buffer value after toggled from false to true', () => {
+  const {foundation, mockAdapter} = setupTest();
+  const buffer = {};
+  td.when(mockAdapter.getBuffer()).thenReturn(buffer);
+  foundation.init();
+  foundation.setBuffer(0.123);
+  foundation.setDeterminate(false);
+  foundation.setDeterminate(true);
+  td.verify(mockAdapter.setStyle(buffer, 'transform', 'scaleX(0.123)'), {times: 2});
+});
+
 test('#setDeterminate updates progress value set while determinate is false after determinate is true', () => {
   const {foundation, mockAdapter} = setupTest();
   const primaryBar = {};