In this post I'll give updates about open source I worked on during May and June 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

Here are updates about the projects/libraries I've worked on in the last two months, 19 in total!

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

  • Bump edamame (support old-style #^ metadata)
  • Bump SCI: fix satisfies? for protocol extended to nil
  • Bump rewrite-clj to 1.2.50
  • 1.12.204 (2025-06-24)
  • Compatibility with clerk's main branch
  • #1834: make taoensso/trove work in bb by exposing another timbre var
  • Bump timbre to 6.7.1
  • Protocol method should have :protocol meta
  • Add print-simple
  • Make bash install script work on Windows for GHA
  • Upgrade Jsoup to 1.21.1
  • 1.12.203 (2025-06-18)
  • Support with-redefs + intern (see SCI issue #973
  • #1832: support clojure.lang.Var/intern
  • Re-allow init as task name
  • 1.12.202 (2025-06-15)
  • Support clojure.lang.Var/{get,clone,reset}ThreadBindingFrame for JVM Clojure compatibility
  • #1741: fix taoensso.timbre/spy and include test
  • Add taoensso.timbre/set-ns-min-level! and taoensso.timbre/set-ns-min-level
  • 1.12.201 (2025-06-12)
  • #1825: Add Nextjournal Markdown as built-in Markdown library
  • Promesa compatibility (pending PR here)
  • Upgrade clojure to 1.12.1
  • #1818: wrong argument order in clojure.java.io/resource implementation
  • Add java.text.BreakIterator
  • Add classes for compatibility with promesa:
    • java.lang.Thread$Builder$OfPlatform
    • java.util.concurrent.ForkJoinPool
    • java.util.concurrent.ForkJoinPool$ForkJoinWorkerThreadFactory
    • java.util.concurrent.ForkJoinWorkerThread
    • java.util.concurrent.SynchronousQueue
  • Add taoensso.timbre/set-min-level!
  • Add taoensso.timbre/set-config!
  • Bump fs to 0.5.26
  • Bump jsoup to 1.20.1
  • Bump edamame to 1.4.30
  • Bump taoensso.timbre to 6.7.0
  • Bump pods: more graceful error handling when pod quits unexpectedly
  • #1815: Make install-script wget-compatible (@eval)
  • #1822: type should prioritize :type metadata
  • ns-name should work on symbols
  • :clojure.core/eval-file should affect *file* during eval
  • #1179: run :init in tasks only once
  • #1823: run :init in tasks before task specific requires
  • Fix resolve when *ns* is bound to symbol
  • Bump deps.clj to 1.12.1.1550
  • Bump http-client to 0.4.23

• SCI: Configurable Clojure/Script interpreter suitable for scripting

  • 0.10.47 (2025-06-27)
  • Security issue: function recursion can be forced by returning internal keyword as return value
  • Fix #975: Protocol method should have :protocol var on metadata
  • Fix #971: fix satisfies? for protocol that is extended to nil
  • Fix #977: Can't analyze sci.impl.analyzer with splint
  • 0.10.46 (2025-06-18)
  • Fix #957: sci.async/eval-string+ should return promise with :val nil for ns form rather than :val <Promise>
  • Fix #959: Java interop improvement: instance method invocation now leverages type hints
  • Bump edamame to 1.4.30
  • Give metadata :type key priority in type implementation
  • Fix #967: ns-name should work on symbols
  • Fix #969: ^:clojure.core/eval-file metadata should affect binding of *file* during evaluation
  • Sync sci.impl.Reflector with changes in clojure.lang.Reflector in clojure 1.12.1
  • Fix :static-methods option for class with different name in host
  • Fix #973: support with-redefs on core vars, e.g. intern. The fix for this issue entailed quite a big refactor of internals which removes "magic" injection of ctx in core vars that need it.
  • Add unchecked-set and unchecked-get for CLJS compatibility

• clerk: Moldable Live Programming for Clojure

  • Make clerk compatible with babashka

• quickblog: light-weight static blog engine for Clojure and babashka

  • 0.4.7 (2025-06-12)
  • Switch to Nextjournal Markdown for markdown rendering The minimum babashka version to be used with quickblog is now v1.12.201 since it comes with Nextjournal Markdown built-in.
  • Link to previous and next posts; see "Linking to previous and next posts" in the README (@jmglov)
  • Fix flaky caching tests (@jmglov)
  • Fix argument passing in test runner (@jmglov)
  • Add --date to api/new. (@jmglov)
  • Support Selmer template for new posts in api/new; see Templates > New posts in README. (@jmglov)
  • Add 'language-xxx' to pre/code blocks
  • Fix README.md with working version in quickstart example
  • Fix #104: fix caching with respect to previews
  • Fix #104: document :preview option

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

  • 1.4.31 (2025-06-25)
  • Fix #124: add :imports to parse-ns-form
  • Fix #125: Support #^:foo deprecated metadata reader macro (@NoahTheDuke)
  • Fix #127: expose continue value that indicates continue-ing parsing (@NoahTheDuke)
  • Fix #122: let :auto-resolve-ns affect syntax-quote
  • 1.4.30
  • #120: fix :auto-resolve-ns failing case

• squint: CLJS syntax to JS compiler

  • #678: Implement random-uuid (@rafaeldelboni)
  • v0.8.149 (2025-06-19)
  • #671: Implement trampoline (@rafaeldelboni)
  • Fix #673: remove experimental atom as promise option since it causes unexpected behavior
  • Fix #672: alias may contain dots
  • v0.8.148 (2025-05-25)
  • Fix #669: munge refer-ed + renamed var
  • v0.8.147 (2025-05-09)
  • Fix #661: support throw in expression position
  • Fix #662: Fix extending protocol from other namespace to nil
  • Better solution for multiple expressions in return context in combination with pragmas
  • Add an ajv example

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

  • #2560: NEW linter: :locking-suspicious-lock: report when locking is used on a single arg, interned value or local object
  • #2555: false positive with clojure.string/replace and partial as replacement fn
  • 2025.06.05
  • #2541: NEW linter: :discouraged-java-method. See docs
  • #2522: support :config-in-ns on :missing-protocol-method
  • #2524: support :redundant-ignore on :missing-protocol-method
  • #2536: false positive with format and whitespace flag after percent
  • #2535: false positive :missing-protocol-method when using alias in method
  • #2534: make :redundant-ignore aware of .cljc
  • #2527: add test for using ns-group + config-in-ns for :missing-protocol-method linter
  • #2218: use ReentrantLock to coordinate writes to cache directory within same process
  • #2533: report inline def under fn and defmethod
  • #2521: support :langs option in :discouraged-var to narrow to specific language
  • #2529: add :ns to &env in :macroexpand-hook macros when executing in CLJS
  • #2547: make redundant-fn-wrapper report only for all cljc branches
  • #2531: add :name data to :unresolved-namespace finding for clojure-lsp

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

  • A configuration for replicant was added

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

  • v0.7.23 (2025-06-18)
  • #107: add replicant plugin (@jeroenvandijk)
  • #102: add applied-science/js-interop plugin (@chr15m)
  • #105: add goog.string/htmlEscape (@ikappaki )
  • #113: add unchecked-set and unchecked-get

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

  • 1.3.204 (2025-05-15)
  • #389: fix regression caused by #387
  • 1.3.203 (2025-05-13)
  • #387: bump import-meta-resolve to fix deprecation warnings on Node 22+
  • 1.3.202 (2025-05-12)
  • Fix nbb nrepl server for Deno
  • 1.3.201 (2025-05-08)
  • Deno improvements for loading jsr: and npm: deps, including react in combination with reagent
  • #382: prefix all node imports with node:

• quickdoc: Quick and minimal API doc generation for Clojure

  • v0.2.5 (2025-05-01)
  • Fix #32: fix anchor links to take into account var names that differ only by case
  • v0.2.4 (2025-05-01)
  • Revert source link in var title and move back to <sub>
  • Specify clojure 1.11 as the minimal Clojure version in deps.edn
  • Fix macro information
  • Fix #39: fix link when var is named multiple times in docstring
  • Upgrade clj-kondo to 2025.04.07
  • Add explicit org.babashka/cli dependency

• Nextjournal Markdown

  • 0.7.186
  • Make library more GraalVM native-image friendly
  • 0.7.184
  • Consolidate utils in nextjournal.markdown.utils
  • 0.7.181
  • Hiccup JVM compatibility for fragments (see #34)
  • Support HTML blocks (:html-block) and inline HTML (:html-inline) (see #7)
  • Bump commonmark to 0.24.0
  • Bump markdown-it to 14.1.0
  • Render :code according to spec into <pre> and <code> block with language class (see #39)
  • No longer depend on applied-science/js-interop
  • Accept parsed result in ->hiccup function
  • Expose nextjournal.markdown.transform through main nextjournal.markdown namespace
  • Stabilize API and no longer mark library alpha

• babashka.nrepl-client

  • Add :responses key with raw responses

• speculative

  • Add spec for even?

• http-client: babashka's http-client

  • 0.4.23 (2025-06-06)
  • #75: override existing content type header in multipart request
  • Accept :request-method in addition to :request to align more with other clients
  • Accept :url in addition to :uri to align more with other clients

• unused-deps: Find unused deps in a clojure project

  • This is a brand new project!

• fs - File system utility library for Clojure

  • #147: fs/unzip should allow selective extraction of files (@sogaiu)
  • #145: fs/modified-since works only with ms precision but should support the precision of the filesystem

• cherry: Experimental ClojureScript to ES6 module compiler

  • Fix cherry.embed which is used by malli

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

  • Released several versions catching up with the clojure CLI

Other projects

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

In this post I'll give updates about open source I worked on during March and April 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.

Blog posts

I blogged about an important improvement in babashka regarding type hints here.

Interviews

Also I did an interview with Jiri from Clojure Corner by Flexiana, viewable here.

Updates

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

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

  • Improve Java reflection based on provided type hints (read blog post here)
  • Add compatibility with the fusebox library
  • Fix virtual ThreadBuilder interop
  • Add java.util.concurrent.ThreadLocalRandom
  • Add java.util.concurrent.locks.ReentrantLock
  • Add classes:
    • java.time.chrono.ChronoLocalDate
    • java.time.temporal.TemporalUnit
    • java.time.chrono.ChronoLocalDateTime
    • java.time.chrono.ChronoZonedDateTime
    • java.time.chrono.Chronology
  • #1806: Add cheshire.factory namespace (@lread)
  • Bump GraalVM to 24
  • Bump SCI to 0.9.45
  • Bump edamame to 1.4.28
  • #1801: Add java.util.regex.PatternSyntaxException
  • Bump core.async to 1.8.735
  • Bump cheshire to 6.0.0
  • Bump babashka.cli to 0.8.65

• clerk: Moldable Live Programming for Clojure

  • Replace tools.analyzer with a more light-weight analyzer which also adds support for Clojure 1.12

• squint: CLJS syntax to JS compiler

  • #653: respect :context expr in compile-string
  • #657: respect :context expr in set! expression
  • #659: fix invalid code produced for REPL mode with respect to return
  • #651 Support :require + :rename + allow renamed value to be used in other :require clause
  • Fix #649: reset ns when compiling file and fix initial global object
  • Fix #647: emit explicit null when written in else branch of if
  • Fix #640: don't emit anonymous function if it is a statement (@jonasseglare)
  • Fix #643: Support lexicographic compare of arrays (@jonasseglare)
  • Fix #602: support hiccup-style shorthand for id and class attributes in #jsx and #html
  • Fix #635: range fixes
  • Fix #636: add run!
  • defclass: elide constructor when not provided
  • Fix #603: don't emit multiple returns
  • Drop constructor requirement for defclass

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

  • #2522: support :config-in-ns on :missing-protocol-method
  • #2524: support :redundant-ignore on :missing-protocol-method
  • #1292: NEW linter: :missing-protocol-method. See docs
  • #2512: support vars ending with ., e.g. py. according to clojure analyzer
  • #2516: add new --repro flag to ignore home configuration
  • #2493: reduce image size of native image
  • #2496: Malformed deftype form results in NPE
  • #2499: Fix (alias) bug (@Noahtheduke)
  • #2492: Report unsupported escape characters in strings
  • #2502: add end locations to invalid symbol
  • #2511: fix multiple parse errors caused by incomplete forms
  • document var-usages location info edge cases (@sheluchin)
  • Upgrade to GraalVM 24
  • Bump datalog parser
  • Bump built-in cache

• SCI: Configurable Clojure/Script interpreter suitable for scripting

  • Fix #957: sci.async/eval-string+ should return promise with :val nil for ns form rather than :val <Promise>
  • Fix #959: Java interop improvement: instance method invocation now leverages type hints
  • Fix #942: improve error location of invalid destructuring
  • Add volatile? to core vars
  • Fix #950: interop on local in CLJS
  • Bump edamame to 1.4.28

• quickdoc: Quick and minimal API doc generation for Clojure

  • Fix #32: fix anchor links to take into account var names that differ only by case
  • Revert source link in var title and move back to <sub>
  • Specify clojure 1.11 as the minimal Clojure version in deps.edn
  • Fix macro information
  • Fix #39: fix link when var is named multiple times in docstring
  • Upgrade clj-kondo to 2025.04.07
  • Add explicit org.babashka/cli dependency

• CLI: Turn Clojure functions into CLIs!

  • #119: format-table now formats multiline cells appropriately (@lread)
  • Remove pom.xml and project.clj for cljdoc
  • #116: Un-deprecate :collect option to support custom transformation of arguments to collections (@lread)
  • Support :collect in :spec

• process: Clojure library for shelling out / spawning sub-processes

  • #163, #164: Program resolution strategy for exec and Windows now matches macOS/Linux/PowerShell (@lread)
  • Fix memory leak by executing shutdown hook when process finishes earlier than VM exit (@maxweber)

• html: Html generation library inspired by squint's html tag

  • Fix #3: allow dynamic attribute value: (html [:a {:a (+ 1 2 3)}])
  • Fix #9: shortcuts for id and classes

• cherry: Experimental ClojureScript to ES6 module compiler

  • Add cljs.pprint/pprint
  • Add add-tap
  • Bump squint compiler common which brings in new #html id and class shortcuts + additional features and optimizations, such as an optimization for aset

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

  • Add better Deno + jsr: dependency support, stay tuned.

• instaparse-bb: Use instaparse from babashka

  • Several improvements which makes babashka compatible with test.chuck. See this screenshot!

• edamame: Configurable EDN/Clojure parser with location metadata

  • #117: throw on triple colon keyword

• fs - File system utility library for Clojure

  • #141: fs/match doesn't match when root dir contains glob or regex characters in path
  • #138: Fix fs/update-file to support paths (@rfhayashi)

• sql pods: babashka pods for SQL databases

  • Upgrade to GraalVM 23, fixes encoding issue with Korean characters

Other projects

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

Consider the following Clojure code:

(def thread-pool (java.util.concurrent.Executors/newCachedThreadPool))
(def fut (.submit thread-pool (fn [] 3)))
@fut ;;=> ?

I didn't use any type hints, but the names of the vars should give you an idea what's happening:

• a thread pool is created
• a piece of work in the form of a function is submitted
• the thread pool returns a future which we can dereference to do a blocking wait and get the result.

What result would you expect this program to give? My initial guess would be 3.

However, in babashka the result would sometimes be nil (version 1.12.199 on macOS Apple silicon does for example). I've seen this happen in JVM Clojure too in CI (given no type hints, and thus relying on Clojure reflection). I discovered this problem when trying to make bb run the fusebox library and executing its test suite in CI using babashka.

What's the mechanism behind this flakiness? The .submit method in the snippet above is overloaded. When Clojure is doing reflection, it finds the most suitable method for .submit given the instance object and the arguments. In this case the type of the instance object (the thread-pool value) is of type java.util.concurrent.ThreadPoolExecutor, which has three overloads (inherited from java.util.concurrent.AbstractExecutorService):

• public Future<?> submit(Runnable task)
• public <T> Future<T> submit(Runnable task, T result)
• public <T> Future<T> submit(Callable<T> task)

Only two of those match the number of arguments we used in the snippet, so we are left with:

• public Future<?> submit(Runnable task)
• public <T> Future<T> submit(Callable<T> task)

Clojure's reflector will try to see if the argument type to .submit matches any of these methods. Since we called it with a function, in this case it matches both. If multiple methods match, it will try to pick the most specific method using clojure.lang.Compiler/subsumes. Since Runnable and Callable are two distinct types (one doesn't inherit from the other), Clojure's reflector just returns the first method it deemed most suitable. So it could be either method. The java documentation mentions the submit method with the Runnable argument first, but this isn't necessarily the order in which Java reflection will list those methods. I have found out that the order may even be indeterministic over multiple CI runs and JVM implementations or versions. What the exact cause of this indeterminism is, I don't know, but I found out the hard way that it exists 😅.

So when does the above snippet return nil? When the Runnable overload is chosen, since Runnable is an interface with run method that returns void (which is nil in Clojure). Let me show this using a snippet that uses JVM Clojure type hinting, where we don't rely on reflection:

(set! *warn-on-reflection* true)

(def ^java.util.concurrent.ThreadPoolExecutor thread-pool
  (java.util.concurrent.Executors/newCachedThreadPool))
(def fut (.submit thread-pool ^Runnable (fn [] 3)))
@fut  ;; => nil

Now let's do the same with Callable:

(set! *warn-on-reflection* true)

(def ^java.util.concurrent.ThreadPoolExecutor thread-pool
  (java.util.concurrent.Executors/newCachedThreadPool))
(def fut (.submit thread-pool ^Callable (fn [] 3)))
@fut ;; => 3

So we see the issue: depending on the overload of .submit we get a different value when we dereference the future, either nil or the value returned from the function.

So far, babashka has relied exclusively on runtime reflection to implement Java interop. So we do get into a problem with the above snippet, unless we add type hints. But so far babashka, or more specifically, SCI hasn't made use of type hints to determine the most suitable method. The Clojure compiler does this, but as you know, SCI interprets code and doesn't make use of the clojure Compiler. It does use a forked version of clojure.lang.Reflector, clojure's runtime reflection code, aptly renamed to sci.impl.Reflector. So far, pretty much the only change to that code was making some methods public that were used internally by SCI. To fix the above problem, SCI now actually makes use of type hints and passes these to sci.impl.Reflector. So in the newly published version of babashka, this code:

(def thread-pool (java.util.concurrent.Executors/newCachedThreadPool))
(def fut (.submit thread-pool ^Callable (fn [] 3)))
@fut ;;=> 3

will consistently return 3 and when changing Callable to Runnable, you'll get nil. Note that the above snippet will still have the ambiguous behavior in JVM Clojure, since it doesn't have enough type hints to figure out the right method at compile time and clojure.lang.Reflector does nothing with type hints. Once the Clojure compiler finds out that you're calling .submit on a java.util.concurrent.ExecutorService though, the code will run with the expected method.

Can you think of more methods in the Java standard library which have this ambiguity when relying solely on Clojure reflection? I'd love to hear about those to see if they work reliably in babashka given some extra help through type hints.

Thanks to Tim Pote for thinking along when fixing the issues in babashka and reading a preview of this blog post.