Selection rendering breaks composition

[pjasiun]

This check should prevent changing selection on composition: https://github.com/ckeditor/ckeditor5-engine/blob/cc5c39ec02a8096a92b246a331d9240eef1e272d/src/view/renderer.js#L428

It works for the regular navigation, but because of some reason during the composition, when I press left arrow to change the character value, the offsets do not match, selection is rerendered and composition is broken.

[Reinmar]

That's why I said that during composition ALL rendering must be stopped.

[Reinmar]

This is iteration 3 as it doesn't involve a cleanup but rather a bug fix.

[pjasiun]

The long discussion unfortunately landed in the PR: ckeditor/ckeditor5-engine#861.

[Reinmar]

Proof that we can't render anything during composition: ckeditor/ckeditor5-typing#110 (comment).

[f1ames]

Blocking selection during composition may be problematic due to the way how renderer works now. The fact that some nodes may be replaced during composition (see ckeditor/ckeditor5-engine#1334 for more details) results in selection changing its position:

In the above example I simply blocked the renderer._updateSelection during composition. After inserting the first character renderer updates the nodes like:

1. Initial: <strong>^Bold</strong>
2. Character X inserted which causing rerender in renderer._updateChildren (with insert/delete):
   <strong>XBold^Bold</strong>
3. Selection is moved by DOM element manipulation.

So in this case to make selection stay where it is we could:

• Correct its position (which happens now and this issue was created to prevent such situations).
• Fix the way rendering works (very tricky as mentioned in https://github.com/ckeditor/ckeditor5-engine/issues/1334#issuecomment-370483247).
• Maybe some other fix outside rendering mechanism (typing?), but I'm not sure.

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