transclude: true is probably a bad default for component helper

[sarod]

PR #12933 introduces the new component helper which is great.
However I found that using transclude:true as a default is probably a mistake as:

• Most component don't need it. And it's find to enable it when you need it.
• It doesn't play well with some native directive also requiring transclusion (namely ngSwitchWhen)

For instance when creating a simple component with

module.component('myComp', 
  {
    template:'<div></div>'
  }
);

And use it in a template like this:

<div ng-switch="x">
  <my-comp ng-switch-when="1"></my-comp>
  <div ng-switch-when="2"></div>
</div>

I get the following error:

[$compile:multidir] Multiple directives [ngSwitchWhen, myComp (module: myApp)] asking for transclusion on: <my-comp ng-switch-when="1">

[petebacondarwin]

@sarod - thanks for this feedback.
A simple workaround for your case is to set transclude to be false:

module.component('myComp', 
  {
    transclude: false,
    template:'<div></div>'
  }
);

I am willing to consider that many components do not require transclusion. Moreover that if you want multislot transclusion then you would still need to provide the transclude property.

So perhaps it would be better to default transclude to false.

What do others think? @shahata ?

[gkalpak]

Indeed false might be a more reasonable default for transclude.

Not directly related to this, but (off the top of my head) shouldn't transclude: 'element' and transclude: true be able to co-exist on an element ?

[shahata]

We decided to set transclude to true under the assumption that it has no unwanted side effects. If that is not the case we should either reconsider or find a way to work around those side effects.

[Narretz]

transclude: false is a good idea. Maybe we should also suggest that component directives should not have other directives on them? Moving to components, I'd personnally keep them separate from each other / other directives.

[lgalfaso]

I think that transclude: false is a safer default

[petebacondarwin]

OK, good call @sarod - let's change the default to false. This will be a breaking change in RC1.

@Narretz - although we should discourage multiple components on a single element, it seems like a common case to use a component on an element that has a structural directive, such as ng-if, ng-repeat, ng-swtich-when and so on. It just happens that these guys all use transclusion too.

As @gkalpak points out - perhaps we ought to support element transclusion and content transclusion on the same element...