Fixes microsoft#25221: Render line highlights for all cursors

Author: alexdima

src/vs/editor/browser/viewParts/currentLineHighlight/currentLineHighlight.ts

@@ -14,8 +14,6 @@ import { registerThemingParticipant } from 'vs/platform/theme/common/themeServic
 import { Selection } from 'vs/editor/common/core/selection';
 import { EditorOption } from 'vs/editor/common/config/editorOptions';
 
-let isRenderedUsingBorder = true;
-
 export abstract class AbstractLineHighlightOverlay extends DynamicViewOverlay {
 	private readonly _context: ViewContext;
 	protected _lineHeight: number;
@@ -57,17 +55,14 @@ export abstract class AbstractLineHighlightOverlay extends DynamicViewOverlay {
 	private _readFromSelections(): boolean {
 		let hasChanged = false;
 
-		// Only render the first selection when using border
-		const renderSelections = isRenderedUsingBorder ? this._selections.slice(0, 1) : this._selections;
-
-		const cursorsLineNumbers = renderSelections.map(s => s.positionLineNumber);
+		const cursorsLineNumbers = this._selections.map(s => s.positionLineNumber);
 		cursorsLineNumbers.sort((a, b) => a - b);
 		if (!arrays.equals(this._cursorLineNumbers, cursorsLineNumbers)) {
 			this._cursorLineNumbers = cursorsLineNumbers;
 			hasChanged = true;
 		}
 
-		const selectionIsEmpty = renderSelections.every(s => s.isEmpty());
+		const selectionIsEmpty = this._selections.every(s => s.isEmpty());
 		if (this._selectionIsEmpty !== selectionIsEmpty) {
 			this._selectionIsEmpty = selectionIsEmpty;
 			hasChanged = true;
@@ -203,7 +198,6 @@ export class CurrentLineMarginHighlightOverlay extends AbstractLineHighlightOver
 }
 
 registerThemingParticipant((theme, collector) => {
-	isRenderedUsingBorder = false;
 	const lineHighlight = theme.getColor(editorLineHighlight);
 	if (lineHighlight) {
 		collector.addRule(`.monaco-editor .view-overlays .current-line { background-color: ${lineHighlight}; }`);
@@ -212,7 +206,6 @@ registerThemingParticipant((theme, collector) => {
 	if (!lineHighlight || lineHighlight.isTransparent() || theme.defines(editorLineHighlightBorder)) {
 		const lineHighlightBorder = theme.getColor(editorLineHighlightBorder);
 		if (lineHighlightBorder) {
-			isRenderedUsingBorder = true;
 			collector.addRule(`.monaco-editor .view-overlays .current-line { border: 2px solid ${lineHighlightBorder}; }`);
 			collector.addRule(`.monaco-editor .margin-view-overlays .current-line-margin { border: 2px solid ${lineHighlightBorder}; }`);
 			if (theme.type === 'hc') {