fix https://github.com/microsoft/vscode/issues/101384

src/vs/editor/common/model/mirrorTextModel.ts

@@ -31,6 +31,7 @@ export class MirrorTextModel {
 	protected _eol: string;
 	protected _versionId: number;
 	protected _lineStarts: PrefixSumComputer | null;
+	private _cachedTextValue: string | null;
 
 	constructor(uri: URI, lines: string[], eol: string, versionId: number) {
 		this._uri = uri;
@@ -38,6 +39,7 @@ export class MirrorTextModel {
 		this._eol = eol;
 		this._versionId = versionId;
 		this._lineStarts = null;
+		this._cachedTextValue = null;
 	}
 
 	dispose(): void {
@@ -49,7 +51,10 @@ export class MirrorTextModel {
 	}
 
 	getText(): string {
-		return this._lines.join(this._eol);
+		if (this._cachedTextValue === null) {
+			this._cachedTextValue = this._lines.join(this._eol);
+		}
+		return this._cachedTextValue;
 	}
 
 	onEvents(e: IModelChangedEvent): void {
@@ -66,6 +71,7 @@ export class MirrorTextModel {
 		}
 
 		this._versionId = e.versionId;
+		this._cachedTextValue = null;
 	}
 
 	protected _ensureLineStarts(): void {