Copy All Content button: Hide if is no content

[Soean]

Description

The "Copy All Content" button should not be visible if there is no content.

Fixes #15500

[jorgefilipecosta]

Works well on my tests 👍

[jorgefilipecosta]

I had some worries that editedPostContent may be null or undefined, but I checked the docs of the selector that ultimately is used, and it refers a string is always returned * @return {string} Post content.

[aduth]

While it's arguably not useful if the post has no content, to avoid introducing inconsistency to the set of menu items available, I wonder if we would just leave it as it was, set the behavior to copy an empty string, and still show notices as if it were successful. Would that not still satisfy #15500, where the concern this change addresses is that there is no response to the button click?

[aduth]

getEditedPostAttribute is a non-trivial selector, but it was previously more necessary because we did not conditionally render the element based on whether there is content or not.

With the addition of this condition, I wonder if we might consider to optimize the rendering to check whether there is content using the more-optimized isEditedPostEmpty (see inline comments for optimization specifics).

It could be applied using a series of higher-order components:

export default compose(
	withSelect( ( select ) => ( {
		hasEditedPostContent: ! select( 'core/editor' ).isEditedPostEmpty(),
	} ) ),
	ifCondition( ( { hasEditedPostContent } ) => hasEditedPostContent ),
	withSelect( ( select ) => ( {
		editedPostContent: select( 'core/editor' ).getEditedPostAttribute( 'content' ),
	} ) ),
	withDispatch( ( dispatch ) => {
		const {
			createNotice,
		} = dispatch( 'core/notices' );

		return {
			createNotice,
		};
	} ),
	withState( { hasCopied: false } )
)( CopyContentMenuItem );