Toggle ignore reader forms

[yuhan0]

Closes #567, #411

Adds 3 new interactive commands:
clojure-toggle-ignore, clojure-toggle-ignore-surrounding-form, and clojure-toggle-defun

I added a bunch of tests which should demonstrate how the commands work.
No default keybindings added yet, I'm not sure if this should count as a "refactoring" and go under the C-c C-r prefix?

Note about naming: the clojure.org guide calls it "discard" (https://clojure.org/guides/weird_characters), but I've seen it mostly referred to as the "ignore" form elsewhere.

---

Before submitting a PR mark the checkboxes for the items you've done (if you
think a checkbox does not apply, then leave it unchecked):

• The commits are consistent with our contribution guidelines.
• You've added tests (if possible) to cover your change(s). Bugfix, indentation, and font-lock tests are extremely important!
• You've run M-x checkdoc and fixed any warnings in the code you've written.
• You've updated the changelog (if adding/changing user-visible functionality).
• You've updated the readme (if adding/changing user-visible functionality).

Thanks!

[bbatsov]

No default keybindings added yet, I'm not sure if this should count as a "refactoring" and go under the C-c C-r prefix?

I don't think that's a refactoring, so no need to use the C-c C-r keymap.

[yuhan0]

Do you have suggestions for good default keybindings? I personally use evil-mode with the mappings
<leader>it -> clojure-toggle-ignore
<leader>is -> clojure-toggle-ignore-surrounding-form (C-u for ignore-defun)

Just realised that the existing family of "refactorings" clojure-cycle-*, clojure-convert-collection-* have a similar scope to this, perhaps I should rename them cycle-ignore instead of toggle-ignore and have it go under the refactor map?

C-c C-r d / C-c C-r D is available (D for discard)
or maybe something involving C-_ or C--

[bbatsov]

If something has only two states - I think that "toggle" is a better name than "cycle". As for the keybinding - perhaps something with # or _ in it? Haven't looked in the keymap soon, but I assume we don't have a lot of good options left.

[yuhan0]

If something has only two states - I think that "toggle" is a better name than "cycle".

Agreed, it was more about consistency with the existing command names (clojure-cycle-if toggles between two states if and if-not, clojure-cycle-privacy between defn and defn-, etc.)

As for the keybinding - perhaps something with # or _ in it? Haven't looked in the keymap soon, but I assume we don't have a lot of good options left.

I find having to switching from the Ctrl to Shift key for a # or _ quite awkward, but I don't use native emacs bindings regularly, so maybe I'll leave this to your judgement :)

[bbatsov]

I've noticed we actually have almost no top-level keybindings so you certainly have some options. Or you can just add them to the menu and people can decide if they want to bind those. I don't have brilliant suggestions, plus I doubt people are going to use such command that much, so perhaps we're overthinking this.

[yuhan0]

Ok, I added them to the menu and the refactor map under C-c C-r - and C-c C-r _ respectively.
I personally use these commands more often than any other refactoring, so it's probably just a matter of workflow style (seeing as it's been requested and reinvented several times now)

[bbatsov]

Fair enough. Thanks for tackling this! We can always adjust the keybindings down the road.