fix(select): panel in multiple mode not overlapping trigger

src/lib/select/select-animations.ts

@@ -23,38 +23,43 @@ export const transformPlaceholder: AnimationTriggerMetadata = trigger('transform
   state('floating-ltr', style({
     top: '-22px',
     left: '-2px',
-    transform: `scale(0.75)`
+    transform: 'scale(0.75)'
   })),
   state('floating-rtl', style({
     top: '-22px',
     left: '2px',
-    transform: `scale(0.75)`
+    transform: 'scale(0.75)'
   })),
-  transition('* => *', animate(`400ms cubic-bezier(0.25, 0.8, 0.25, 1)`))
+  transition('* => *', animate('400ms cubic-bezier(0.25, 0.8, 0.25, 1)'))
 ]);
 
 /**
  * This animation transforms the select's overlay panel on and off the page.
  *
- * When the panel is attached to the DOM, it expands its width 32px, scales it up to
- * 100% on the Y axis, fades in its border, and translates slightly up and to the
+ * When the panel is attached to the DOM, it expands its width by the amount of padding, scales it
+ * up to 100% on the Y axis, fades in its border, and translates slightly up and to the
  * side to ensure the option text correctly overlaps the trigger text.
  *
  * When the panel is removed from the DOM, it simply fades out linearly.
  */
 export const transformPanel: AnimationTriggerMetadata = trigger('transformPanel', [
   state('showing', style({
     opacity: 1,
-    minWidth: 'calc(100% + 32px)',
-    transform: `scaleY(1)`
+    minWidth: 'calc(100% + 32px)', // 32px = 2 * 16px padding
+    transform: 'scaleY(1)'
+  })),
+  state('showing-multiple', style({
+    opacity: 1,
+    minWidth: 'calc(100% + 64px)', // 64px = 48px padding on the left + 16px padding on the right
+    transform: 'scaleY(1)'
   })),
   transition('void => *', [
     style({
       opacity: 0,
       minWidth: '100%',
-      transform: `scaleY(0)`
+      transform: 'scaleY(0)'
     }),
-    animate(`150ms cubic-bezier(0.25, 0.8, 0.25, 1)`)
+    animate('150ms cubic-bezier(0.25, 0.8, 0.25, 1)')
   ]),
   transition('* => void', [
     animate('250ms 100ms linear', style({opacity: 0}))
@@ -66,10 +71,10 @@ export const transformPanel: AnimationTriggerMetadata = trigger('transformPanel'
  * select's options. It is time delayed to occur 100ms after the overlay
  * panel has transformed in.
  */
-export const fadeInContent: AnimationTriggerMetadata  =  trigger('fadeInContent', [
+export const fadeInContent: AnimationTriggerMetadata = trigger('fadeInContent', [
   state('showing', style({opacity: 1})),
   transition('void => showing', [
     style({opacity: 0}),
-    animate(`150ms 100ms cubic-bezier(0.55, 0, 0.55, 0.2)`)
+    animate('150ms 100ms cubic-bezier(0.55, 0, 0.55, 0.2)')
   ])
 ]);

src/lib/select/select.html

@@ -13,12 +13,28 @@
   <span class="mat-select-underline"></span>
 </div>
 
-<ng-template cdk-connected-overlay [origin]="origin" [open]="panelOpen" hasBackdrop (backdropClick)="close()"
-  backdropClass="cdk-overlay-transparent-backdrop" [positions]="_positions" [minWidth]="_triggerWidth"
-  [offsetY]="_offsetY" (attach)="_onAttached()" (detach)="close()">
-  <div class="mat-select-panel {{ 'mat-' + color }}" [ngClass]="panelClass" [@transformPanel]="'showing'"
-    (@transformPanel.done)="_onPanelDone()" (keydown)="_handlePanelKeydown($event)"
-      [style.transformOrigin]="_transformOrigin" [class.mat-select-panel-done-animating]="_panelDoneAnimating">
+<ng-template
+  cdk-connected-overlay
+  hasBackdrop
+  backdropClass="cdk-overlay-transparent-backdrop"
+  [origin]="origin"
+  [open]="panelOpen"
+  [positions]="_positions"
+  [minWidth]="_triggerWidth"
+  [offsetY]="_offsetY"
+  (backdropClick)="close()"
+  (attach)="_onAttached()"
+  (detach)="close()">
+
+  <div
+    class="mat-select-panel {{ 'mat-' + color }}"
+    [ngClass]="panelClass"
+    [@transformPanel]="multiple ? 'showing-multiple' : 'showing'"
+    (@transformPanel.done)="_onPanelDone()"
+    (keydown)="_handlePanelKeydown($event)"
+    [style.transformOrigin]="_transformOrigin"
+    [class.mat-select-panel-done-animating]="_panelDoneAnimating">
+
     <div class="mat-select-content" [@fadeInContent]="'showing'" (@fadeInContent.done)="_onFadeInDone()">
       <ng-content></ng-content>
     </div>

src/lib/select/select.ts

@@ -838,16 +838,18 @@ export class MdSelect implements AfterContentInit, OnDestroy, OnInit, ControlVal
     const overlayRect = this.overlayDir.overlayRef.overlayElement.getBoundingClientRect();
     const viewportRect = this._viewportRuler.getViewportRect();
     const isRtl = this._isRtl();
+    const paddingWidth = this.multiple ? SELECT_MULTIPLE_PANEL_PADDING_X + SELECT_PANEL_PADDING_X :
+                                         SELECT_PANEL_PADDING_X * 2;
+
     let offsetX = this.multiple ? SELECT_MULTIPLE_PANEL_PADDING_X : SELECT_PANEL_PADDING_X;
 
     if (!isRtl) {
       offsetX *= -1;
     }
 
-    const leftOverflow = 0 - (overlayRect.left + offsetX
-        - (isRtl ? SELECT_PANEL_PADDING_X * 2 : 0));
+    const leftOverflow = 0 - (overlayRect.left + offsetX - (isRtl ? paddingWidth : 0));
     const rightOverflow = overlayRect.right + offsetX - viewportRect.width
-        + (isRtl ? 0 : SELECT_PANEL_PADDING_X * 2);
+                          + (isRtl ? 0 : paddingWidth);
 
     if (leftOverflow > 0) {
       offsetX += leftOverflow + SELECT_PANEL_VIEWPORT_PADDING;