src/vs/editor/contrib/suggest/suggestController.ts/SuggestController/getOverwriteInfo
class SuggestController:	getOverwriteInfo(item: CompletionItem, toggleMode: boolean): { overwriteBefore: number, overwriteAfter: number } {
		assertType(this.editor.hasModel());

		let replace = this.editor.getOption(EditorOption.suggest).insertMode === 'replace';
		if (toggleMode) {
			replace = !replace;
		}
		const overwriteBefore = item.position.column - item.editStart.column;
		const overwriteAfter = (replace ? item.editReplaceEnd.column : item.editInsertEnd.column) - item.position.column;
		const columnDelta = this.editor.getPosition().column - item.position.column;
		const suffixDelta = this._lineSuffix.value ? this._lineSuffix.value.delta(this.editor.getPosition()) : 0;

		return {
			overwriteBefore: overwriteBefore + columnDelta,
			overwriteAfter: overwriteAfter + suffixDelta
		};
	}