Good way to dynamically open / close a popover (or tooltip) using angular, based on expression?

You can also build your own extended triggers. This will apply to both Tooltip and Popover.

First extend the Tooltip triggers as follows:

// define additional triggers on Tooltip and Popover
app.config(['$tooltipProvider', function($tooltipProvider){
    $tooltipProvider.setTriggers({
        'show': 'hide'
    });
}]);

Then define the trigger on the HTML tag like this:

<div id="RegisterHelp" popover-trigger="show" popover-placement="left" popover="{{ 'Login or register here'}}">

And now you can call hide and show from JavaScript, this is a show in 3 seconds.

$("#RegisterHelp").trigger('show');
//Close the info again
$timeout(function () {
    $("#RegisterHelp").trigger('hide');
}, 3000);

As it turns out, it's not very difficult to decorate either the ui-bootstrap tooltip or the popover with a custom directive. This is written in typescript, but the javascript parts of it should be obvious. This single piece of code works to decorate either a tooltip or a popover:

'use strict';

module App.Directives.TooltipToggle {

    export interface DirectiveSettings {
        directiveName: string;
        directive: any[];
        directiveConfig?: any[];
    }

    export function directiveSettings(tooltipOrPopover = 'tooltip'): DirectiveSettings {

        var directiveName = tooltipOrPopover;

        // events to handle show & hide of the tooltip or popover
        var showEvent = 'show-' + directiveName;
        var hideEvent = 'hide-' + directiveName;

        // set up custom triggers
        var directiveConfig = ['$tooltipProvider', ($tooltipProvider: ng.ui.bootstrap.ITooltipProvider): void => {
            var trigger = {};
            trigger[showEvent] = hideEvent;
            $tooltipProvider.setTriggers(trigger);
        }];

        var directiveFactory = (): any[] => {
            return ['$timeout', ($timeout: ng.ITimeoutService): ng.IDirective => {
                var d: ng.IDirective = {
                    name: directiveName,
                    restrict: 'A',
                    link: (scope: ng.IScope, element: JQuery, attr: ng.IAttributes) => {

                        if (angular.isUndefined(attr[directiveName + 'Toggle'])) return;

                        // set the trigger to the custom show trigger
                        attr[directiveName + 'Trigger'] = showEvent;

                        // redraw the popover when responsive UI moves its source
                        var redrawPromise: ng.IPromise<void>;
                        $(window).on('resize', (): void => {
                            if (redrawPromise) $timeout.cancel(redrawPromise);
                            redrawPromise = $timeout((): void => {
                                if (!scope['tt_isOpen']) return;
                                element.triggerHandler(hideEvent);
                                element.triggerHandler(showEvent);

                            }, 100);
                        });

                        scope.$watch(attr[directiveName + 'Toggle'], (value: boolean): void => {
                            if (value && !scope['tt_isOpen']) {
                                // tooltip provider will call scope.$apply, so need to get out of this digest cycle first
                                $timeout((): void => {
                                    element.triggerHandler(showEvent);
                                });
                            }
                            else if (!value && scope['tt_isOpen']) {
                                $timeout((): void => {
                                    element.triggerHandler(hideEvent);
                                });
                            }
                        });
                    }
                };
                return d;
            }];
        };

        var directive = directiveFactory();

        var directiveSettings: DirectiveSettings = {
            directiveName: directiveName,
            directive: directive,
            directiveConfig: directiveConfig,
        };

        return directiveSettings;
    }
}

With this single piece of code, you can set up programmatic hide and show of either a tooltip or popover like so:

var tooltipToggle = App.Directives.TooltipToggle.directiveSettings();
var popoverToggle = App.Directives.TooltipToggle.directiveSettings('popover');
var myModule = angular.module('my-mod', ['ui.bootstrap.popover', 'ui.bootstrap.tpls'])
    .directive(tooltipToggle.directiveName, tooltipToggle.directive)
        .config(tooltipToggle.directiveConfig)
    .directive(popoverToggle.directiveName, popoverToggle.directive)
        .config(popoverToggle.directiveConfig);

Usage:

<span tooltip="This field is required."
    tooltip-toggle="formName.fieldName.$error.required"
    tooltip-animation="false" tooltip-placement="right"></span>

or

<span popover="This field is required."
    popover-toggle="formName.fieldName.$error.required"
    popover-animation="false" popover-placement="right"></span>

So we are reusing everything else that comes with the ui-bootstrap tooltip or popover, and only implementing the -toggle attribute. The decorative directive watches that attribute, and fires custom events to show or hide, which are then handled by the ui-bootstrap tooltip provider.

Update:

Since this answer seems to be helping others, here is the code written as javascript (the above typescript more or less compiles to this javascript):

'use strict';

function directiveSettings(tooltipOrPopover) {

    if (typeof tooltipOrPopover === "undefined") {
        tooltipOrPopover = 'tooltip';
    }

    var directiveName = tooltipOrPopover;

    // events to handle show & hide of the tooltip or popover
    var showEvent = 'show-' + directiveName;
    var hideEvent = 'hide-' + directiveName;

    // set up custom triggers
    var directiveConfig = ['$tooltipProvider', function ($tooltipProvider) {
        var trigger = {};
        trigger[showEvent] = hideEvent;
        $tooltipProvider.setTriggers(trigger);
    }];

    var directiveFactory = function() {
        return ['$timeout', function($timeout) {
            var d = {
                name: directiveName,
                restrict: 'A',
                link: function(scope, element, attr) {
                    if (angular.isUndefined(attr[directiveName + 'Toggle']))
                        return;

                    // set the trigger to the custom show trigger
                    attr[directiveName + 'Trigger'] = showEvent;

                    // redraw the popover when responsive UI moves its source
                    var redrawPromise;
                    $(window).on('resize', function() {
                        if (redrawPromise) $timeout.cancel(redrawPromise);
                        redrawPromise = $timeout(function() {
                            if (!scope['tt_isOpen']) return;
                            element.triggerHandler(hideEvent);
                            element.triggerHandler(showEvent);

                        }, 100);
                    });

                    scope.$watch(attr[directiveName + 'Toggle'], function(value) {
                        if (value && !scope['tt_isOpen']) {
                            // tooltip provider will call scope.$apply, so need to get out of this digest cycle first
                            $timeout(function() {
                                element.triggerHandler(showEvent);
                            });
                        }
                        else if (!value && scope['tt_isOpen']) {
                            $timeout(function() {
                                element.triggerHandler(hideEvent);
                            });
                        }
                    });
                }
            };
            return d;
        }];
    };

    var directive = directiveFactory();

    var directiveSettings = {
        directiveName: directiveName,
        directive: directive,
        directiveConfig: directiveConfig,
    };

    return directiveSettings;
}