refactor: expose tech but warn without safety var (#3916)

`Player#tech` can now be called without passing an object into it. It no longer requires passing an object into it, so, current code will not break.
If nothing is passed in, a warning will be logged about knowing what you're doing. If anything is passed in, the warning is silenced.

src/js/player.js

@@ -6,6 +6,7 @@ import Component from './component.js';
 
 import document from 'global/document';
 import window from 'global/window';
+import tsml from 'tsml';
 import * as Events from './utils/events.js';
 import * as Dom from './utils/dom.js';
 import * as Fn from './utils/fn.js';
@@ -920,32 +921,25 @@ class Player extends Component {
   }
 
   /**
-   * Return a reference to the current {@link Tech}, but only if given an object with the
-   * `IWillNotUseThisInPlugins` property having a true value. This is try and prevent misuse
-   * of techs by plugins.
+   * Return a reference to the current {@link Tech}.
+   * It will print a warning by default about the danger of using the tech directly
+   * but any argument that is passed in will silence the warning.
    *
-   * @param {Object} safety
-   *        An object that must contain `{IWillNotUseThisInPlugins: true}`
-   *
-   * @param {boolean} safety.IWillNotUseThisInPlugins
-   *        Must be set to true or else this function will throw an error.
+   * @param {*} [safety]
+   *        Anything passed in to silence the warning
    *
    * @return {Tech}
    *         The Tech
    */
   tech(safety) {
-    if (safety && safety.IWillNotUseThisInPlugins) {
-      return this.tech_;
-    }
-    const errorText = `
-      Please make sure that you are not using this inside of a plugin.
-      To disable this alert and error, please pass in an object with
-      \`IWillNotUseThisInPlugins\` to the \`tech\` method. See
-      https://github.com/videojs/video.js/issues/2617 for more info.
-    `;
-
-    window.alert(errorText);
-    throw new Error(errorText);
+    if (safety === undefined) {
+      log.warn(tsml`
+        Using the tech directly can be dangerous. I hope you know what you're doing.
+        See https://github.com/videojs/video.js/issues/2617 for more info.
+      `);
+    }
+
+    return this.tech_;
   }
 
   /**

test/unit/player.test.js

@@ -1209,29 +1209,38 @@ QUnit.test('you can clear error in the error event', function(assert) {
 });
 
 QUnit.test('Player#tech will return tech given the appropriate input', function(assert) {
+  const oldLogWarn = log.warn;
+  let warning;
+
+  log.warn = function(_warning) {
+    warning = _warning;
+  };
+
   const tech_ = {};
-  const returnedTech = Player.prototype.tech.call({tech_}, {IWillNotUseThisInPlugins: true});
+  const returnedTech = Player.prototype.tech.call({tech_}, true);
 
   assert.equal(returnedTech, tech_, 'We got back the tech we wanted');
+  assert.notOk(warning, 'no warning was logged');
+
+  log.warn = oldLogWarn;
 });
 
-QUnit.test('Player#tech alerts and throws without the appropriate input', function(assert) {
-  let alertCalled;
-  const oldAlert = window.alert;
+QUnit.test('Player#tech logs a warning when called without a safety argument', function(assert) {
+  const oldLogWarn = log.warn;
+  const warningRegex = new RegExp('https://github.com/videojs/video.js/issues/2617');
+  let warning;
 
-  window.alert = () => {
-    alertCalled = true;
+  log.warn = function(_warning) {
+    warning = _warning;
   };
 
   const tech_ = {};
 
-  assert.throws(function() {
-    Player.prototype.tech.call({tech_});
-  }, new RegExp('https://github.com/videojs/video.js/issues/2617'),
-  'we threw an error');
+  Player.prototype.tech.call({tech_});
+
+  assert.ok(warningRegex.test(warning), 'we logged a warning');
 
-  assert.ok(alertCalled, 'we called an alert');
-  window.alert = oldAlert;
+  log.warn = oldLogWarn;
 });
 
 QUnit.test('player#reset loads the Html5 tech and then techCalls reset', function(assert) {