How to get :reflow to behave more intelligently (like Emacs' fill-paragraph)?

[pekp]

I'm not really sure whether this should be a feature request or a bug report. Let me ask this here first - maybe I've overlooked something.

I'm a long time (25+ years) Emacs user that moved to Helix about a year ago. I'm really enjoying the experience and I find that Helix is a fantastic text editor, especially due to its out-of-the-box tree-sitter and lsp-integration.

I find that Helix' improved-over-vi modal approach especially shines for sources that are structured like programming languages and where one frequently needs to navigate between units of text that have different structural properties about them (types, variable names, functions, etc.).

When I edit longer text files (books chapters, readmes, etc.) I still find myself reaching for Emacs. In "letter-soup" everything is just a paragraph, a sentence, a word, or a letter, and Emacs's non-modal approach just works beautifully.

Helix is especially lacking when it comes to reflowing text. There are two features that I especially miss.

One is purely about the "user-interface" of Emacs' built-in fill-paragraph function that is bound to M-q (Alt + q).

Let me give you an example. Emacs is always in insert mode. Say I'm editing the following text.

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis
aut[e]
iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Emacs' cursor is over the "e" in "aute" (which I've indicated above with aut[e]). When I press M-q Emacs turns this into

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis aut[e] iure reprehenderit in voluptate velit esse cillum dolore eu fugiat
nulla pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa
qui officia deserunt mollit anim id est laborum.

The cursor stays over the "e" in "aute". This is critical to preserve mental context!

0. Let's compare how this works in Helix. Again we're starting with

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis
aut[e]
iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

1. If I'm in insert mode I need to hit ESC to change into normal mode.
2. Then I need to select the entire paragraph with mip:

[Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis
aute
iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.]

3. Then I need to type :reflow:

[Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud
exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat. Quis
aute iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla
pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui
officia deserunt mollit anim id est laborum.]

The original cursor position aut[e] is lost - and with it my mental context!

I'm aware of Helix' C-s (save_selection) and C-o (jump-backward): one could assume that saving the current cursor position to the jump-list and restoring it works around this problem. But they don't help either! Here I'm not even sure whether we're not running into a bug in Helix!

If after step 1. above we insert a step 1b. where we hit C-s we might think that is is possible to restore the original cursor position after we conclude step 3. However this turns out to be impossible! For some reason C-o "restores" the selection

[Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud
exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat. Quis
aut]e iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla
pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui
officia deserunt mollit anim id est laborum.

(which never explicitly existed) and not

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud
exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat. Quis
aut[e] iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla
pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui
officia deserunt mollit anim id est laborum.

as one could reasonably expect.

I noticed this because I tried to define the key A-q in my config.toml to emulate something like fill-paragraph and failed.

I tried a very large number of variations of

[keys.insert]
A-q = ["normal_mode", "save_selection", ... ??? ... , "jump_backward", "insert_mode"]

[keys.normal]
A-q = ["save_selection", ... ??? ... , "jump_backward"]

And could not find one that gives me a good-enough approximation of M-q/fill-paragraph behavior from Emacs.

Another problem was that I could not find a Helix command that corresponds to the key sequence mip. "@mip" doesn't work. Helix just tells me that "macro keybindings may not be used in command sequences". Is here even a comment that corresponds to mip? The self-documenting aspect of Emacs makes it easy to answer such questions (with C-h k = describe-key). In Helix one is forced to examine the documentation for Match mode, which turns up nothing.

There is another feature of Emacs that I really miss in Helix. Emacs' fill-paragraph preserves paragraphs wheres Helix' :reflow does not!

In Emacs fill-paragraph applied to

[Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis
aute
iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis
aute
iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis
aute
iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.]

results in

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis aut[e] iure reprehenderit in voluptate velit esse cillum dolore eu fugiat
nulla pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa
qui officia deserunt mollit anim id est laborum.

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis aut[e] iure reprehenderit in voluptate velit esse cillum dolore eu fugiat
nulla pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa
qui officia deserunt mollit anim id est laborum.

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis aut[e] iure reprehenderit in voluptate velit esse cillum dolore eu fugiat
nulla pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa
qui officia deserunt mollit anim id est laborum.

Whereas Helix' :reflow results in

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed eiusmod tempor
incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat.
Quis aute iure reprehenderit in voluptate velit esse cillum dolore eu fugiat
nulla pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa
qui officia deserunt mollit anim id est laborum. Lorem ipsum dolor sit amet,
consectetur adipiscing elit, sed eiusmod tempor incidunt ut labore et dolore
magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco
laboris nisi ut aliquid ex ea commodi consequat. Quis aute iure reprehenderit
in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint
obcaecat cupiditat non proident, sunt in culpa qui officia deserunt mollit
anim id est laborum. Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed eiusmod tempor incidunt ut labore et dolore magna aliqua. Ut enim ad minim
veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi
consequat. Quis aute iure reprehenderit in voluptate velit esse cillum dolore eu
fugiat nulla pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in
culpa qui officia deserunt mollit anim id est laborum.

which is just an abomination. Emacs' fill-paragraph is also smart about indentation, numbered lists and bullet points, whereas Helix is pretty dumb in all of those regards.

I realize that Helix does not aspire to become Emacs on purpose and by design. I completely agree with this. But when Emacs does something better, there is no reason to not seek inspiration there.

[waddie]

I think the jump list may be a bug. It looks like the head of the range is preserved but the anchor gets reset to the start of the replacement range. But equally, that might be intentional/unavoidable/a unfortunate consequence of the current implementation. If you search past issues for reflow stuff, there have been a lot of complications with it over the years.

Since the head seems still to be in the right place though, you could just <C-o><A-;>l to get back to your saved jump point:

I don’t think there’s a : command for tree-sitter matches, only the mi/a keybindings. You can’t put an @ sequence in a [":foo"] binding, but you can type anything in a @foo sequence e.g. @mip:reflow<ret>

Putting it all together: @<C-s>mip:reflow<ret><C-o><A-;>l. Save jump point, match in paragraph, reflow, jump back, reverse selection, move right 1 char:

As far as the abominable behaviour goes, it seems consistent to me:

Helix follows the selection → action model. This means that whatever you are going to act on (a word, a paragraph, a line, etc.) is selected first and the action itself (delete, change, yank, etc.) comes second. A cursor is simply a single width selection.

If you tell it to :reflow 3 paragraphs as a single selection, that’s what it will do. If you want them reflowed as 3 paragraphs, make 3 selections:

[pekp]

Thank you for your explanations, Waddie! Especially the last paragraph helped me get a better grasp of the Helix philosophy with regard to multiple selections.

With your help I also managed to get a "good-enough" emulation of fill-paragraph bound to A-q which now works both in normal and in insert mode.

I had to put the following into my config:

[keys.normal]
A-q = "@<C-s>mip:reflow<ret><C-o><A-;>l"

[keys.insert]
A-q = "@<esc><C-s>mip:reflow<ret><C-o>li"

Note that they are not symmetrical! For some strange reason anchor and head need to be swapped in the first case, while they must not be swapped in the second. I suspect that this is a bug.

[pekp]

I filed a bug report.