remove whitespace after dispatch char?

[oakmac]

From this comment on PR-195, should Standard Clojure Style remove whitespace after the dispatch character # for certain forms?

Some examples:

## NaN
##NaN

#:user {:a 1}
#:user{:a 1}

#::u {:a 1}
#::u{:a 1}

#:: {:a 1}
#::{:a 1}

#inst "2014-05-19T19:12:37.925-00:00"
#inst"2014-05-19T19:12:37.925-00:00"

#js {:onClick (fn [e] (js/console.log e))}
#js{:onClick (fn [e] (js/console.log e))}

#? (:clj true :cljs false}
#?(:clj true :cljs false}

#?@ (:clj [:a :b :c])
#?@(:clj [:a :b :c])

#= (* 2 3)
#=(* 2 3)

cc @yuhan0 - thank you for this suggestion and the examples!

[oakmac]

Off the top of my head I think the following would look the most idiomatic for the above examples:

##NaN

#:user{:a 1}

#::u{:a 1}

#::{:a 1}

#inst "2014-05-19T19:12:37.925-00:00"

#js {:onClick (fn [e] (js/console.log e))}

#?(:clj true :cljs false}

#?@(:clj [:a :b :c])

#=(* 2 3)

So basically "remove the space except for tagged literals". All of the tagged literals examples on the weird characters page have one space after the tag.

[yuhan0]

We should also consider the various expression prefixes, I think the case for them is even less controversial.
It's syntactically valid to leave any amount of whitespace and line breaks between them and the form they apply to:

' aaa
`    bbb
~   
ccc  ~@
  ddd@
eee                                   #'
;; even comments!
fff

But this is very likely to be a formatting mistake or downright misleading

`accidental-markdown-syntax`

;; much later
(def why-is-this-not-working??
  (look closely))

There's one notable edge case: ~ @foo where removing the space changes the expression, see weavejester/cljfmt#345

---

Metadata dispatch character ^ (and the deprecated #^) should also 'stick' to the meta form:

;; good
^:private foo
^long bar
^{:arglists ([a b c])} 
baz

;;; bad
^  :private foo
^
long bar^

{:one :map}
{:or :two?}

---

But with discard macros in my opinion all of the following are fine

#_zero-spaces
#_  one-or-more-spaces
#_#_ stacked up
#_ #_  with or
#_#_without spaces
#_
(intervening line breaks are ok)

;; In particular you don't want to turn this
#_
(defn outdated-impl
  [blah]
  (kept around
        for reference))


;; into this, creating lots of unwanted diffs
#_ (defn outdated-impl
     [blah]
     (kept around
           for reference))

---

Similarly for tagged literals, there are use-cases of it in tooling like #dbg (cider-nrepl) and #p (hashp) where the tag should be allowed to stay on a separate line. And instances where the tag "belongs" stylistically with the opening delimiter, like with the default print-method of records (ie. no spaces). I think this is another case where one should just preserve any existing spacing:

#dbg
(defn something []
  to-be-instrumented)

(defrecord Foo [x])
(->Foo 1) ;; => #user.Foo{:x 1}

#db/id[:db.part/user]

The last example taken from clojure-mode, which by default configures Paredit to not automatically leave spaces between tags and collections. https://github.com/clojure-emacs/clojure-mode/blob/b766094aea28bdc7b44ce1960d96434fe7d1d9cf/clojure-mode.el#L219

---

Otherwise I agree with your assessment, aside from the case of namespaced maps where I can see justification for leaving a linebreak (to prevent excessive indentation)

#:arbitrarily-long.company.domain.database.customer
{:name "Fred"
 :address "123 Example St"}

[yuhan0]

This also brings up the question of inserting whitespaces before dispatch chars:

before	after
foo`bar foo~bar foo~@bar foo@bar foo^bar baz	foo `bar foo ~bar foo ~@bar foo @bar foo ^bar baz

;; but NOT these! # and ' are valid symbol constituents
foo'bar
foo#bar
foo#'bar
foo#_bar