Decouple drag target index from click target index

Reducing the complexity of the logic and fixing tab add/close actions

Author: krassowski

packages/widgets/src/tabbar.ts

@@ -1046,16 +1046,25 @@ export class TabBar<T> extends Widget {
     this.document.addEventListener('mouseup', this, true); // <DEPRECATED>
     this.document.addEventListener('pointerup', this, true);
 
+    if (scrollBeforeButtonClicked || scrollAfterButtonClicked) {
+      this.beginScrolling(scrollBeforeButtonClicked ? '-' : '+');
+      return;
+    }
+
+    this._clickedTabIndex = index;
+
     // Do nothing else if the middle button or add button is clicked.
     if (event.button === 1 || addButtonClicked) {
       return;
     }
-    if (scrollBeforeButtonClicked || scrollAfterButtonClicked) {
-      this.beginScrolling(scrollBeforeButtonClicked ? '-' : '+');
+
+    // Do nothing else if the close icon is clicked.
+    let icon = tabs[index].querySelector(this.renderer.closeIconSelector);
+    if (icon && icon.contains(event.target as HTMLElement)) {
       return;
     }
 
-    // Initialize the non-measured parts of the drag data.
+    // Initialize the non-measured parts of the drag data,
     this._dragData = {
       tab: tabs[index] as HTMLElement,
       index: index,
@@ -1077,12 +1086,6 @@ export class TabBar<T> extends Widget {
       detachRequested: false
     };
 
-    // Do nothing else if the close icon is clicked.
-    let icon = tabs[index].querySelector(this.renderer.closeIconSelector);
-    if (icon && icon.contains(event.target as HTMLElement)) {
-      return;
-    }
-
     // Add the extra listeners if the tabs are movable.
     if (this.tabsMovable) {
       this.document.addEventListener('mousemove', this, true); // <DEPRECATED>
@@ -1218,35 +1221,32 @@ export class TabBar<T> extends Widget {
       return;
     }
 
-    // Do nothing if no drag is in progress.
     const data = this._dragData;
-    if (!data) {
-      if (this._scrollData) {
-        this.stopScrolling();
-      }
-      return;
-    }
 
     // Stop the event propagation.
     event.preventDefault();
     event.stopPropagation();
 
     // Remove the extra mouse event listeners.
-    this.document.removeEventListener('mousemove', this, true); // <DEPRECATED>
     this.document.removeEventListener('mouseup', this, true); // <DEPRECATED>
-    this.document.removeEventListener('pointermove', this, true);
     this.document.removeEventListener('pointerup', this, true);
-    this.document.removeEventListener('keydown', this, true);
-    this.document.removeEventListener('contextmenu', this, true);
 
-    // Handle a release when the drag is not active.
-    if (!data.dragActive) {
+    // Remove extra mouse event listeners which are only added when drag is in progress.
+    if (data) {
+      this.document.removeEventListener('mousemove', this, true); // <DEPRECATED>
+      this.document.removeEventListener('pointermove', this, true);
+      this.document.removeEventListener('keydown', this, true);
+      this.document.removeEventListener('contextmenu', this, true);
+    }
+
+    // Handle a release when the drag is not active or not in progress.
+    if (!data || !data.dragActive) {
       // Clear the drag data.
       this._dragData = null;
 
+      // Handle mouse release if scrolling was in progress.
       if (this._scrollData) {
         this.stopScrolling();
-        return;
       }
       // Handle clicking the add button.
       let addButtonClicked =
@@ -1266,12 +1266,12 @@ export class TabBar<T> extends Widget {
       });
 
       // Do nothing if the release is not on the original pressed tab.
-      if (index !== data.index) {
+      if (index !== this._clickedTabIndex) {
         return;
       }
 
       // Do nothing if neither press nor release was on a tab.
-      if (index === -1 && data.index === -1) {
+      if (index === -1 && this._clickedTabIndex === -1) {
         return;
       }
 
@@ -1549,6 +1549,7 @@ export class TabBar<T> extends Widget {
   }
 
   private _name: string;
+  private _clickedTabIndex: number = -1;
   private _currentIndex = -1;
   private _titles: Title<T>[] = [];
   private _orientation: TabBar.Orientation;