[SuperEditor] Add tap handler to add an empty paragraph when tapping below the end of document (Resolves #2395)

[angelosilvestre]

[SuperEditor] Add tap handler to add an empty paragraph when tapping below the end of document. Resolves #2395

Currently, tapping below the end of the document places the caret at the end of the last selectable component.

This PR modifies the ContentTapDelegate to expose the DocumentLayout, so apps can query the information necessary to make decisions.

This PR also introduces a SuperEditorAddEmptyParagraphTapHandler, so apps can choose to add an empty paragraph to the end of the document instead.

This is a breaking change, but resolving it is pretty simple:

-TapHandlingInstruction onTap(DocumentPosition tapPosition) {
+TapHandlingInstruction onTap(DocumentTapDetails details) {
+  final tapPosition = details.documentLayout.getDocumentPositionNearestToOffset(details.layoutOffset);
+  if (tapPosition == null) {
+    return TapHandlingInstruction.continueHandling;
+  }

Also, now multiple factories are allowed, which is also a breaking change, solvable with:

SuperEditor(
- contentTapDelegateFactory: superEditorAddEmptyParagraphTapHandlerFactory,
+ contentTapDelegateFactories: [superEditorAddEmptyParagraphTapHandlerFactory],
)

[matthew-carroll]

This is a breaking change, but resolving it is pretty simple.

When creating a breaking change with a known solution, please demonstrate that change in the PR so that readers can come here and copy the fix.

[matthew-carroll]

This is definitely far too specific to this one particular goal. There could be 100 different queries that apps might want. We'd end up with 100 properties.

Can you please propose an alternate approach? Can we pass a reference to the document layout and let the implementer check whatever they want?

[angelosilvestre]

I pushed a alternative approach, placing the checks directly on the handler.

[matthew-carroll]

I'm still curious about the concept of passing the document layout. Can you think of any reason why we wouldn't want to pass the layout with the event?

We're currently reporting the "tap position" in terms of the tapped document node. But this is already a bit of overreach on our end. What if the handler wants to find the "nearest position"? Or, if we're currently looking up the nearest position, what if the handler only wants to consider positions that are actually touched?

So I'm wondering, what if we pass the document layout and the global offset? Can you think of any downsides from that? Any hurdles that might get in our way?

[angelosilvestre]

Can you think of any downsides from that? Any hurdles that might get in our way?

I don't have anything against passing the document layout.

Are you saying we should remove tapPosition and let implementers obtain this information directly from the DocumentLayout?

[matthew-carroll]

Are you saying we should remove tapPosition and let implementers obtain this information directly from the DocumentLayout?

Yeah, I think we can leave it up to the client to decide what info they wanna pull out of the layout.

[angelosilvestre]

@matthew-carroll Updated.

[matthew-carroll]

Putting this comment here, but it's related to the delegate, itself.

Should we switch to a chain of responsibility so that multiple delegates can be provided? If we don't, and a developer wants multiple situations to be considered, then that developer will have to implement his own chain of responsibility.

Is there any reason that it's important for us to have only a single delegate?

[angelosilvestre]

Updated to multiple delegates. We would already need multiple delegates for the spellcheck PR.

[matthew-carroll]

This probably doesn't belong in super_editor.dart - we should create a more appropriate source file for such things, or add it to a related existing file.

[angelosilvestre]

Updated.