Fix behavior of paragraph hopping key bindings.

[jart]

The default emacs behavior for the forward-paragraph and
backward-paragraph functions is to hop between blank lines in a source
code file. This breaks in js2-mode in the presence of javadoc
@clauses.

This commit fixes this behavior by adding advice to the following
standard emacs functions, which only applies to js2-mode:

• forward-paragraph
• backward-paragraph
• fill-paragraph

The existing functionality for filling paragraphs within javadocs is
preserved.

Video explanation: http://youtu.be/cXerimuxNK8

[dgutov]

Hi Justine,

I realize the implementation took some effort, but I'm against merging this for a few reasons:

• I'm not sure this is the right thing to do. The fact that the three -paragraph- commands share the same notions of where the paragraphs start and end, makes sense. Making one of them work on different paragraphs will be surprising. I don't know how many people use fill-paragraph in comments with js2-mode, but some of them probably expect backward-paragraph not to jump over jsdoc comments.

• This is most likely the wrong way to do it. The presence of six defadvice forms is a big hint. Since you only want fill-paragraph to work differently from the rest, it would be easier to set js2-paragraph-start to \n\n, and then either define js2-mode-specific version of fill-paragraph that would bind the required vars locally and then call fill-paragraph, or write a special fill-forward-paragraph-function (see that var's description) that would take jsdoc clauses into account.

  This question has never come up before, and I wasn't anywhere near when js2-paragraph-start definition was written, so if that approach appeals to you, you should M-x report-emacs-bug and argue the case to the Emacs core developers (they can commit the patch to GNU ELPA, and I'll propagate it here). They might have a more informed opinion on the subject.

  Or you can write a couple of functions, or a new minor mode, that do the same. Maybe publish it for similar-minded users.

• All legally significant contributions must be accompanied with copyright assignment to FSF. I really should have added this to the README long time ago, sorry.