Fix links sometimes not activating

This was a very long standing bug that was hard to nail down a repro case. Turns
out this was because at some point the current link can get cleared and re-evaluated,
I think because of a different fix we made. That caused the object check to fail.
So the fix there is to check link equality, not js object equality.

Additionally I found we don't dispose of old linkifiers when open is called
multiple times.

See microsoft/vscode#230010

src/browser/CoreBrowserTerminal.ts

@@ -69,7 +69,8 @@ export class CoreBrowserTerminal extends CoreTerminal implements ITerminal {
   private _helperContainer: HTMLElement | undefined;
   private _compositionView: HTMLElement | undefined;
 
-  public linkifier: ILinkifier2 | undefined;
+  private readonly _linkifier: MutableDisposable<ILinkifier2> = this._register(new MutableDisposable());
+  public get linkifier(): ILinkifier2 | undefined { return this._linkifier.value; }
   private _overviewRulerRenderer: OverviewRulerRenderer | undefined;
   private _viewport: Viewport | undefined;
 
@@ -485,7 +486,7 @@ export class CoreBrowserTerminal extends CoreTerminal implements ITerminal {
     this._mouseService = this._instantiationService.createInstance(MouseService);
     this._instantiationService.setService(IMouseService, this._mouseService);
 
-    this.linkifier = this._register(this._instantiationService.createInstance(Linkifier, this.screenElement));
+    const linkifier = this._linkifier.value = this._register(this._instantiationService.createInstance(Linkifier, this.screenElement));
 
     // Performance: Add viewport and helper elements from the fragment
     this.element.appendChild(fragment);
@@ -515,7 +516,7 @@ export class CoreBrowserTerminal extends CoreTerminal implements ITerminal {
     this._selectionService = this._register(this._instantiationService.createInstance(SelectionService,
       this.element,
       this.screenElement,
-      this.linkifier
+      linkifier
     ));
     this._instantiationService.setService(ISelectionService, this._selectionService);
     this._register(this._selectionService.onRequestScrollLines(e => this.scrollLines(e.amount, e.suppressScrollEvent)));

src/browser/Linkifier.ts

@@ -227,7 +227,7 @@ export class Linkifier extends Disposable implements ILinkifier2 {
       return;
     }
 
-    if (this._mouseDownLink === this._currentLink && this._linkAtPosition(this._currentLink.link, position)) {
+    if (this._mouseDownLink && linkEquals(this._mouseDownLink.link, this._currentLink.link) && this._linkAtPosition(this._currentLink.link, position)) {
       this._currentLink.link.activate(event, this._currentLink.link.text);
     }
   }
@@ -391,3 +391,13 @@ export class Linkifier extends Disposable implements ILinkifier2 {
     return { x1, y1, x2, y2, cols: this._bufferService.cols, fg };
   }
 }
+
+function linkEquals(a: ILink, b: ILink): boolean {
+  return (
+    a.text === b.text &&
+    a.range.start.x === b.range.start.x &&
+    a.range.start.y === b.range.start.y &&
+    a.range.end.x === b.range.end.x &&
+    a.range.end.y === b.range.end.y
+  );
+}