In this post I'll give updates about open source I worked on during July and August 2025.

To see previous OSS updates, go here.

Sponsors

I'd like to thank all the sponsors and contributors that make this work possible. Without you the below projects would not be as mature or wouldn't exist or be maintained at all! So a sincere thank you to everyone who contributes to the sustainability of these projects.

Current top tier sponsors:

• Clojurists Together
• Roam Research
• Nextjournal
• Nubank

Open the details section for more info about sponsoring.

Updates

Although summer hit Europe and I made a train trip to Switzerland for some hiking with my wife, OSS activity continued in the borkiverse. 20 projects saw updates. As usual, babashka, SCI and clj-kondo saw the most activity.

One of the big things I’m looking forward to is speaking at Clojure Conj 2025. At the risk of sounding a bit pretentious, the title of my talk is "Making Tools Developers Actually Use". Babashka started as a quirky interpreter "nobody had asked for" but now many Clojure developers don't want to live without it. Clj-kondo started out as a minimal proof-of-concept linter and now is widely used tool in Clojurian's every day toolset and available even in Cursive today. In the talk I want to reflect on what makes a tool something developers (like myself) actually want to use. I'm excited about this opportunity and about my first time visiting the Conj (don't ask me how I got the Clojure Conj cap on the photo above). Given the rest of the schedule, it's something I wouldn't want to miss.

For babashka, my main focus has been making it feel even more like regular Clojure. One example is the change in how non-daemon threads are handled. Previously, people had to sometimes add @(promise) to keep an httpkit server alive. Now babashka behaves like clojure -X in this regard: if you spawn non-daemon threads, the process waits for them. It’s looks like a small change, but it brings consistency with JVM Clojure, something I'm always aiming for more with babashka. If you want the old behavior, you can still use --force-exit. While implementing this I hit an interesting bug with GraalVM and also found out that clojure -X sometimes stalls when using agents. Maybe more on this next time.

Another change that was introduced is that when code is evaluated through load-string or Compiler/load (which is the same thing in bb), vars like *warn-on-reflection* are bound. This fixes a problem with loading code in non-main threads. E.g. @(future (load-string "(set! *warn-on-reflection* true)")) would fail in previous versions of babashka. You might wonder why you would ever want to do this. Well, a similar thing happens when you execute babashka tasks in parallel and that's where I ran into this problem.

SCI, the interpreter under the hood of babashka and several other projects, got some critical fixes as well. I detected one somewhat embarrasing bug when loading clojure+.hashp in babashka. It had code that looked like:

(def config {})
(let [config {}
      _ (alter-var-root #'config (constantly config))
     ]
  ...)

In the expression (alter-var-root #'config (constantly config)) the var #'config was mistaken for the local config since SCI's analyzer used a resolve-like function that also resolves locals. This fails horribly. In 6 years of SCI it's the first time I encountered this bug though. After fixing this problem, I noticed that babashka's CI acted up. On every commit, babashka CI tests dozens of Clojure libraries by running their test suites. I noticed that specter's tests were failing. It turned out that one test actually worked prior to fixing the above bug exactly because the SCI analyzer's resolve returned a node that evaluated to a local value. But there is no way I could just leave that bug in, so I had to make a pull request to specter as well to set this straight. A new specter version was released that works both with older version of babashka and the new version.

One other headscratcher in SCI was on the ClojureScript side of things and had to do with munging. In interop like (.-foo-bar #js {:foo-bar 1}) ClojureScript munges the field name in the interop form to foo_bar but in the object it stays "foo-bar". The munging of this name wasn't applied in SCI as an oversight. So in SCI (and thus in nbb, joyride, scittle, etc.) the above expression would return 1 whereas in ClojureScript it would return nil. In contrast, (.-foo-bar #js {:foo_bar 1}) would return nil in SCI but 1 in CLJS. Although fixing this could mean a breaking change in SCI-based scripting environments I decided to align it with CLJS anyway, as switching between SCI and CLJS should not introduce these kinds of surprises.

Other improvements in SCI were made in the area of better using type hints on instance method interop.

And then there’s clj-kondo, the linter that is supposed to spark joy ✨, as far as a linter is able to do that in a developer's life. Two new linters were added, including one that catches suspicious uses of locking. This linter was inspired by a similar rule in splint. Lots of smaller improvements were made like sorting findings and imported files such that they are consistent across multiple runs that use the --parallel option and across operating systems. And as usual bugfixes and preventing false positives.

One happy improvement to scittle is that referencing a library that was introduced by a <script> tag now was made a lot easier. You can find the docs about that here. The tl;dr of this is that when a library registers itself as a global, you can just use that global in :require now: (require '["JSConfetti" :as confetti]).

Of course, none of this happens in isolation. I’m deeply grateful to the community and the sponsors who make this work sustainable: Clojurists Together, Roam Research, Nextjournal, Nubank, and many other companies and individuals. Every bit of support means I can keep refining these tools, fixing edge cases, and thinking about the long-term direction.

Here are updates about the projects/libraries I've worked on in the last two months in detail.

• babashka: native, fast starting Clojure interpreter for scripting.

  • Bump clojure to 1.12.2
  • #1843: BREAKING (potententially): non-daemon thread handling change. Similar to JVM clojure, babashka now waits for non-daemon threads to finish. This means you don't have to append @(promise) anymore when you spawn an httpkit server, for example. For futures and agents, bb uses a thread pool that spawns daemon threads, so that pool isn't preventing an exit. This behavior is similar to clojure -X. You can get back the old behavior where bb always forced an exit and ignored running non-daemon threads with --force-exit.
  • #1690: bind clojure.test/*test-out* to same print-writer as *out* in nREPL server
  • Add Compiler/demunge
  • Add clojure.lang.TaggedLiteral/create
  • Add java.util.TimeZone/setDefault
  • Add println-str
  • SCI: Var literal or special form gets confused with local of same name
  • #1852: (.getContextClassLoader (Thread/currentThread)) should be able to return results from babashka classpath
  • Bump deps.clj to 1.12.2.1565
  • Bind more vars like *warn-on-reflection* during load{string,reader} (same as JVM Clojure) so can load code in other than than the main thread
  • #1845: expose cheshire.generate/{add-encoder,encode-str}
  • Bump timbre to 6.8.0
  • Bump clojure.tools.logging to 1.3.0
  • Improve interop using type hints on qualified instance methods
  • Bump Jsoup to 1.21.2
  • Bump fs to 0.5.7
  • Bump cheshire to 6.1.0
  • Pods: no exception on destroy when there's still calls in progress

• SCI: Configurable Clojure/Script interpreter suitable for scripting

  • Add println-str
  • Fix #997: Var is mistaken for local when used under the same name in a let body
  • Fix regression introduced in #987
  • Fix #963: respect :param-tags on qualified instance method
  • Add *suppress-read*
  • Add load-reader
  • Fix #872: *loaded-libs* is now the single source of truth about loaded libs
  • Fix #981: respect type hint on instance method callee
  • Add core dynamic vars like *warn-on-reflection* and bind them during load-string etc. such that set!-ing then in a future works.
  • Fix #984: support alternative set! syntax in CLJS
  • Fix #987: method or property name in interop should be munged
  • Fix #986: preserve error location for js static method
  • Fix #990: fix merge-opts with :bindings + deprecate :bindings (replaced by :namespaces {'user ...})

• clj-kondo: static analyzer and linter for Clojure code that sparks joy.
  

  • Unreleased
  • #2588: false positive type mismatch about symbol accepting var
  • Require clojure 1.10.3 is the minimum clojure version
  • #2564: detect calling set with wrong number of arguments
  • #2257: support ignore hint on invalid symbol
  • Sort findings on filename, row, column and now additionally on message too
  • #2602: Sort auto-imported configs to avoid differences based on OS or file system
  • #2603: warn on :inline-def with nested deftest
  • #2606: make it easy for users to know how inline-config files should be version controlled (@lread)
  • #2610: ignores may show up unordered due to macros
  • #2615: emit inline-configs config.edn in a git-diff-friendly way (@lread)
  • 2025.07.28
  • #2580: false positive type mismatch with quoted value
  • Fix some :locking-suspicious-lock false positives
  • #2582: :condition-always-true false positives
  • 2025.07.26
  • #2560: NEW linter: :locking-suspicious-lock: report when locking is used on a single arg, interned value or local object
  • #2519: NEW linter: :unresolved-protocol-method. See docs (@emerson-matos)
  • #2555: false positive with clojure.string/replace and partial as replacement fn
  • #2566: Expand :condition-always-true check. (@NoahTheDuke)
  • #2350: support schema.core/defprotocol (@emerson-matos)
  • #2571: false positive unresolved symbol when ignoring expression that goes through macroexpansion hook
  • #2575: false positive type mismatch with nested keyword call and str
  • Bump SCI to 0.10.47
  • Drop memoization for hook fns and configuration, solves memory issue with Cursive + big projects like metabase
  • Optimizations to compensate for dropping caching, performance should be similar (or better depending on the size of your project)
  • #2568: support :deprecated-namespace for .cljc namespaces

• clerk: Moldable Live Programming for Clojure

  • Upgrade to Reagent and fix unsafe HTML rendering
  • Add viewers for HTML markdown nodes
  • Support file watching in babashka
  • Support server side rendering of formulas using KaTeX

• squint: CLJS syntax to JS compiler

  • v0.8.153 (2025-08-31)
  • Fix #704: while didn't compile correctly
  • Add clojure.string/includes?
  • Emit less code for varargs functions
  • Fix solidJS example
  • Documentation improvements (@lread)
  • Fix #697: ClassCastException in statement function when passed Code records
  • v0.8.152 (2025-07-18)
  • Fix #680: support import attributes using :with option in require, e.g. :with {:type :json}
  • v0.8.151 (2025-07-15)
  • Implement not= as function
  • Fix #684: JSX output
  • v0.8.150 (2025-07-09)
  • #678: Implement random-uuid (@rafaeldelboni)
  • Fix #681: support unsafe HTML via [:$ ...] tag

• scittle: Execute Clojure(Script) directly from browser script tags via SCI

  • v0.7.27 (2025-08-21)
  • #95: support string requires of globalThis js deps (@chr15m). See docs.
  • Potentially breaking: (.-foo-bar {}) now behaves as {}.foo_bar, i.e. the property or method name is munged.
  • v0.7.26 (2025-08-20)
  • #121: add cjohansen/dataspex plugin (@jeroenvandijk)
  • #118: add goog.string/format (@jeroenvandijk)
  • Support alternative (set! #js {} -a 1) CLJS syntax (by bumping SCI)
  • Add source maps to distribution
  • Add dev versions of all modules in the dev folder of the distribution + a dev/scitte.cljs-devtools.js module

• edamame: configurable EDN and Clojure parser with location metadata and more

  • Fix #132: Add counterpart to Clojure's *suppress-read*: :suppress-read

• sci.configs: A collection of ready to be used SCI configs.

  • Add config for dataspex

• nbb: Scripting in Clojure on Node.js using SCI

  • nREPL improvement for vim-fireplace

• Nextjournal Markdown

  • Drop KaTeX dependency by inlining TeXMath lib

• babashka.nrepl-client

  • Add :responses key with raw responses

• fs - File system utility library for Clojure

  • Documentation improvements
  • Fix wrong typehint

• cherry: Experimental ClojureScript to ES6 module compiler

  • not= is now a function

• CLI: Turn Clojure functions into CLIs!

  • #122: introduce new :repeated-opts option to enforce repeating the option for accepting multiple values (e.g. --foo 1 --foo 2 rather than --foo 1 2)

• deps.clj: A faithful port of the clojure CLI bash script to Clojure

  • Fixed Java download program that respects CLJ_JVM_OPTS for downloading tools jar.
  • Released several versions catching up with the clojure CLI

• pod-babashka-fswatcher: babashka filewatcher pod

  • Pod protocol fix: don't send done with async messages
  • Robustness improvements
  • Bump fsnotify

• sci.nrepl: nREPL server for SCI projects that run in the browser

  • Send current working directory in describe message (for tools like clojure-mcp)
  • Add "session-closed" to close op reply

• pod-babashka-go-sqlite3: A babashka pod for interacting with sqlite3

  • JSON1 support

• http-server: serve static assets

  • 0.1.15
  • #22: fix off-by-one error in range requests (@jyn514)
  • 0.1.14
  • #21: Add :not-found option for handling unfound files. The option is a function of the request and should return a map with :status and :body.
  • #19: Add text/html MIME types for asp and aspx file extensions (@respatialized)
  • 0.1.13
  • #16: support range requests (jmglov)
  • #13: add an ending slash to the dir link, and don't encode the slashes (@KDr2)
  • #12: Add headers to index page (rather than just file responses)

Contributions to third party projects:

• specter: Clojure(Script)'s missing piece

  • Fix babashka support by removing optimizations that only worked due to SCI bug

• clojure-test-suite: Dialect-independent tests for clojure.core, and others, focused on characterizing how Clojure JVM behaves so that other dialects to reach parity.

  • Added babashka to the test suite

Other projects

These are (some of the) other projects I'm involved with but little to no activity happened in the past month.