Fix to Emacs hang when viewing ClojureDocs for "/"

[metayan]

Emacs hangs terribly with 100% CPU usage and enormous memory consumption if it is forced to highlight "" in a buffer.

Requesting ClojureDocs for / triggers the issue.
This PR prevents it, by correctly removing the namespace - keeping only the symbol name.

---

• The commits are consistent with our contribution guidelines
• You've added tests (if possible) to cover your change(s)
• All tests are passing (eldev test)
• All code in the relevant file passes the linter (eldev lint)

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Steps to reproduce the problem

With cursor after a lone /
Don't do C-c C-d C-c
because it will send Emacs on a memory-eating spree and never return.
Occasionally it's possible to interrupt with C-g, but usually one needs to kill the Emacs process.

CIDER version information

;; CIDER 1.22.0-snapshot, nREPL 1.7.0
;; Clojure 1.12.4, Java 25.0.1

cider master branch
and any version before that, probably since at least 2022

Emacs version

30.2
28.2

Operating system

macOS and Linux

[bbatsov]

You're not really testing cider-clojuredocs-lookup-remove-namespace, but only the built-in replace-regexp-in-string with your test.

[metayan]

Yes, the intention with the test is to show that the regex behaves as intended. Didn't want to break out the replace-regexp-in-string into a new function.

Edit: Saw your comment below now.

[bbatsov]

Nice catch on the bug! The fix works. Two thoughts while we're here:

The regex could be tighter and line up with patterns already in the codebase. cider-namespace-qualified-p (cider-util.el) and cider-resolve--prefix-regexp (cider-resolve.el) both use [^/]+/ for matching namespace prefixes, and the latter is even used the same way (with replace-regexp-in-string ... ""):

(replace-regexp-in-string "\\`[^/]+/" "" sym)

Same behavior on clojure.core// → /, but more explicit about intent ("non-slash chars + slash") and \`` is more precise than ^` (string start vs. line start).

The other thing: the new tests exercise the regex inline, not the production code — if someone tweaks the regex inside cider-clojuredocs-lookup, the tests pass regardless. Worth extracting a tiny helper and pointing the tests at that, mirroring how cider-clojuredocs-replace-special is factored:

(defun cider-clojuredocs--strip-ns (sym)
  "Strip the namespace prefix from SYM, leaving just the symbol name."
  (replace-regexp-in-string "\\`[^/]+/" "" sym))

And then:

(describe "cider-clojuredocs--strip-ns"
  (it "removes the namespace from qualified symbols"
    (expect (cider-clojuredocs--strip-ns "clojure.core/subs") :to-equal "subs")
    (expect (cider-clojuredocs--strip-ns "clojure.string/trim") :to-equal "trim"))
  (it "preserves a slash symbol name (the bug being fixed)"
    (expect (cider-clojuredocs--strip-ns "clojure.core//") :to-equal "/"))
  (it "preserves operator-like names"
    (expect (cider-clojuredocs--strip-ns "clojure.core/+") :to-equal "+"))
  (it "leaves unqualified symbols unchanged"
    (expect (cider-clojuredocs--strip-ns "subs") :to-equal "subs")))

[metayan]

Clever with the "is" comments in the tests. Thanks. Learning...
I'll modify the PR accordingly.

[metayan]

PR modified - with an extra test for unqualified "/" added.
Do you have a way of squashing the three commits into one, or should I do that somehow?

[bbatsov]

Yeah, I can squash when merging. Thanks!