Elixir v1.19 announcement

_includes/search.html

@@ -1,7 +1,5 @@
 <div class="widget news">
-  <h3>
-    News: <a href="/blog/2025/08/05/global-elixir-meetups/">Global Elixir Meetups announced</a>
-  </h3>
+  <h3>News: <a href="/blog/2025/10/15/elixir-v1-19-0-released/">Elixir v1.19.0 released</a></h3>
 </div>
 
 <div class="widget search">

_posts/2024-08-15-welcome-elixir-language-server-team.markdown

@@ -7,6 +7,8 @@ category: Announcements
 excerpt: "Announcing the official Elixir Language Server team to work on the code intelligence infrastructure to be used across tools and editors"
 ---
 
+> Update: [the new language server is called Expert and is now available as open source](https://github.com/elixir-lang/expert).
+
 I am glad to welcome Elixir's official Language Server team, formed by (in alphabetical order):
 
 * [Jonatan Kłosko](https://github.com/jonatanklosko)

_posts/2025-10-15-elixir-v1-19-0-released.markdown

@@ -0,0 +1,219 @@
+---
+layout: post
+title: "Elixir v1.19 released: enhanced type checking and up to 4x faster compilation for large projects"
+authors:
+- José Valim
+category: Releases
+excerpt: "Elixir v1.19 released: type checking of protocols, type inference of anonymous functions, improved compile times, and more"
+---
+
+Elixir v1.19 brings further improvements to the type system and compilation times, allowing us to find more bugs, faster.
+
+## Type system improvements
+
+This release improves the type system around two key areas, anonymous functions and protocols. To make these enhancements possible, while they seem simple on the surface, we had to go beyond the existing literature, extending the existing theory and developing new techniques, which we will outline in future articles. For now, let's look at what's new.
+
+### Type checking of protocol dispatch and implementations
+
+This release adds type checking when dispatching and implementing protocols.
+
+For example, string interpolation in Elixir uses the `String.Chars` protocol. If you pass a value that does not implement said protocol, Elixir will now emit a warning accordingly.
+
+Here is an example passing a range, which cannot be converted into a string, to an interpolation:
+
+```elixir
+defmodule Example do
+  def my_code(first..last//step = range) do
+    "hello #{range}"
+  end
+end
+```
+
+the above emits the following warnings:
+
+```
+warning: incompatible value given to string interpolation:
+
+    data
+
+it has type:
+
+    %Range{first: term(), last: term(), step: term()}
+
+but expected a type that implements the String.Chars protocol, it must be one of:
+
+    dynamic(
+      %Date{} or %DateTime{} or %NaiveDateTime{} or %Time{} or %URI{} or %Version{} or
+        %Version.Requirement{}
+    ) or atom() or binary() or float() or integer() or list(term())
+```
+
+Warnings are also emitted if you pass a data type that does not implement the `Enumerable` protocol as a generator to for-comprehensions:
+
+```elixir
+defmodule Example do
+  def my_code(%Date{} = date) do
+    for(x <- date, do: x)
+  end
+end
+```
+
+will emit:
+
+```
+warning: incompatible value given to for-comprehension:
+
+    x <- date
+
+it has type:
+
+    %Date{year: term(), month: term(), day: term(), calendar: term()}
+
+but expected a type that implements the Enumerable protocol, it must be one of:
+
+    dynamic(
+      %Date.Range{} or %File.Stream{} or %GenEvent.Stream{} or %HashDict{} or %HashSet{} or
+        %IO.Stream{} or %MapSet{} or %Range{} or %Stream{}
+    ) or fun() or list(term()) or non_struct_map()
+```
+
+### Type checking and inference of anonymous functions
+
+Elixir v1.19 can now type infer and type check anonymous functions. Here is a trivial example:
+
+```elixir
+defmodule Example do
+  def run do
+    fun = fn %{} -> :map end
+    fun.("hello")
+  end
+end
+```
+
+The example above has an obvious typing violation, as the anonymous function expects a map but a string is given. With Elixir v1.19, the following warning is now printed:
+
+```
+    warning: incompatible types given on function application:
+
+        fun.("hello")
+
+    given types:
+
+        binary()
+
+    but function has type:
+
+        (dynamic(map()) -> :map)
+
+    typing violation found at:
+    │
+  6 │     fun.("hello")
+    │        ~
+    │
+    └─ mod.exs:6:8: Example.run/0
+```
+
+Function captures, such as `&String.to_integer/1`, will also propagate the type as of Elixir v1.19, arising more opportunity for Elixir's type system to catch bugs in our programs.
+
+### Acknowledgements
+
+The type system was made possible thanks to a partnership between [CNRS](https://www.cnrs.fr/) and [Remote](https://remote.com/). The development work is currently sponsored by [Fresha](https://www.fresha.com/), [Starfish*](https://starfish.team/), and [Dashbit](https://dashbit.co/).
+
+## Faster compile times in large projects
+
+This release includes two compiler improvements that can lead up to 4x faster builds in large codebases.
+
+While Elixir has always compiled the given files in project or a dependency in parallel, the compiler would sometimes be unable to use all of the machine resources efficiently. This release addresses two common limitations, delivering performance improvements that scale with codebase size and available CPU cores.
+
+### Code loading bottlenecks
+
+Prior to this release, Elixir would load modules as soon as they were defined. However, because the Erlang part of code loading happens within a single process (the code server), this would make it a bottleneck, reducing parallelization, especially on large projects.
+
+This release makes it so modules are loaded lazily. This reduces the pressure on the code server and the amount of work during compilation, with reports of more than two times faster compilation for large projects. The benefits depend on the codebase size and the number of CPU cores available.
+
+Implementation wise, [the parallel compiler already acts as a mechanism to resolve modules during compilation](https://elixir-lang.org/blog/2012/04/24/a-peek-inside-elixir-s-parallel-compiler/), so we built on that. By making sure the compiler controls both module compilation and module loading, it can also better guarantee deterministic builds.
+
+There are two potential regressions with this approach. The first one happens if you spawn processes during compilation which invoke other modules defined within the same project. For example:
+
+```elixir
+defmodule MyLib.SomeModule do
+  list = [...]
+
+  Task.async_stream(list, fn item ->
+    MyLib.SomeOtherModule.do_something(item)
+  end)
+end
+```
+
+Because the spawned module is not visible by the compiler, it won't be able to load `MyLib.SomeOtherModule`. You have two options, either use [`Kernel.ParallelCompiler.pmap/2`](https://hexdocs.pm/elixir/Kernel.ParallelCompiler.html#pmap/2) or explicitly call [`Code.ensure_compiled!(MyLib.SomeOtherModule)`](https://hexdocs.pm/elixir/Code.html#ensure_compiled!/1) before spawning the process that uses said module.
+
+The second one is related to `@on_load` callbacks (typically used for [NIFs](https://www.erlang.org/doc/system/nif.html)) that invoke other modules defined within the same project. For example:
+
+```elixir
+defmodule MyLib.SomeModule do
+  @on_load :init
+
+  def init do
+    MyLib.AnotherModule.do_something()
+  end
+
+  def something_else do
+    ...
+  end
+end
+
+MyLib.SomeModule.something_else()
+```
+
+The reason this fails is because `@on_load` callbacks are invoked within the code server and therefore they have limited ability to load additional modules. It is generally advisable to limit invocation of external modules during `@on_load` callbacks but, in case it is strictly necessary, you can set `@compile {:autoload, true}` in the invoked module to address this issue in a forward and backwards compatible manner.
+
+Both snippets above could actually lead to non-deterministic compilation failures in the past, and as a result of these changes, compiling these cases are now deterministic.
+
+### Parallel compilation of dependencies
+
+This release introduces a variable called `MIX_OS_DEPS_COMPILE_PARTITION_COUNT`, which instructs `mix deps.compile` to compile dependencies in parallel.
+
+While fetching dependencies and compiling individual Elixir dependencies already happened in parallel, as outlined in the previous section, there were pathological cases where performance gains would be left on the table, such as when compiling dependencies with native code or dependencies where one or two large files would take most of the compilation time.
+
+By setting `MIX_OS_DEPS_COMPILE_PARTITION_COUNT` to a number greater than 1, Mix will now compile multiple dependencies at the same time, using separate OS processes. Empirical testing shows that setting it to half of the number of cores on your machine is enough to maximize resource usage. The exact speed up will depend on the number of dependencies and the number of machine cores and some users reported up to 4x faster compilation times when using our release candidates. If you plan to enable it on CI or build servers, keep in mind it will most likely have a direct impact on memory usage too.
+
+## Erlang/OTP 28 support
+
+Elixir v1.19 officially supports Erlang/OTP 28.1+ and later. In order to support the new Erlang/OTP 28 representation for regular expressions, structs can now control how they are escaped into abstract syntax trees by defining a `__escape__/1` callback.
+
+On the other hand, the new representation for regular expressions in Erlang/OTP 28+ implies they can no longer be used as default values for struct fields. Therefore, this is not allowed:
+
+```elixir
+defmodule Foo do
+  defstruct regex: ~r/foo/
+end
+```
+
+You can, however, still use regexes when initializing the structs themselves:
+
+```elixir
+defmodule Foo do
+  defstruct [:regex]
+
+  def new do
+    %Foo{regex: ~r/foo/}
+  end
+end
+```
+
+## OpenChain certification
+
+Elixir v1.19 is also our first release following OpenChain compliance, [as previously announced](https://elixir-lang.org/blog/2025/02/26/elixir-openchain-certification/). In a nutshell:
+
+  * Elixir releases now include a Source SBoM in CycloneDX 1.6 or later and SPDX 2.3 or later formats.
+  * Each release is attested along with the Source SBoM.
+
+These additions offer greater transparency into the components and licenses of each release, supporting more rigorous supply chain requirements.
+
+This work was performed by [Jonatan Männchen](https://maennchen.dev) and sponsored by the [Erlang Ecosystem Foundation](https://erlef.org).
+
+## Summary
+
+There are many other goodies in this release, such as improved option parsing, better debuggability and performance in ExUnit, the addition of `mix help Mod`, `mix help Mod.fun`, `mix help Mod.fun/arity`, and `mix help app:package` to make documentation accessible via shell for humans and agents, and much more. [See the CHANGELOG](https://hexdocs.pm/elixir/1.19/changelog.html) for the complete release notes.
+
+Happy coding!