Changelog for Elixir v1.12

Elixir v1.12 is out with improvements to scripting, tighter Erlang/OTP 24 integration, stepped ranges, and dozen of new functions across the standard library. Overall this is a small release, which continues our tradition of bringing Elixir developers quality of live improvements every 6 months.

Scripting improvements: Mix.install/2 and System.trap_signal/3

Elixir v1.12 brings new conveniences for those using Elixir for scripting (via .exs files). Elixir has been capable of managing dependencies for a quite long time, but it could only be done within Mix projects. In particular, the Elixir team is wary of global dependencies as any scripts that rely on system packages are brittle and hard to reproduce whenever your system changes.

Mix.install/2 is meant to be a sweetspot between single-file scripts and full-blown Mix projects. With Mix.install/2, you can list your dependencies on top of your scripts. When you execute the script for the first time, Elixir will download, compile, and cache your dependencies before running your script. Future invocations of the script will simply read the compiled artefacts from the cache:

IO.puts Jason.encode!(%{hello: :world})

Mix.install/2 also performs protocol consolidation, which gives script developers an option to execute their code in the most performant format possible.

Note: Mix.install/2 is currently experimental and it may change in future releases.

Another improvement to scripting is the ability to trap exit signals via System.trap_signal/3. All you need is the signal name and a callback that will be invoked when the signal triggers. For example, ExUnit leverages this functionality to print all currently running tests when you abort the test suite via SIGQUIT (Ctrl+\\):

$ mix test

Aborting test suite, the following have not completed:

* test query building [test/ecto/query_test.exs:48]
* test placeholders in Repo.insert_all [test/ecto/repo_test.exs:502]

Showing results so far...

78 doctests, 1042 tests, 0 failures

This is particularly useful when your tests get stuck and you want to know which one is the culprit.

Important: Trapping signals may have strong implications on how a system shuts down and behave in production and therefore it is extremely discouraged for libraries to set their own traps. Instead, they should redirect users to configure them themselves. The only cases where it is acceptable for libraries to set their own traps is when using Elixir in script mode, such as in .exs files and via Mix tasks.

Tighter Erlang/OTP 24 integration

Erlang/OTP 24 ships with JIT compilation support and Elixir developers don't have to do anything to reap its benefits. There are many other features in Erlang/OTP 24 to look forwards to and Elixir v1.12 provides integration with many of them: such as support for 16bit floats in bitstrings as well as performance improvements in the compiler and during code evaluation.

Another excellent feature in Erlang/OTP 24 is the implementation of EEP 54, which provides extended error information for many functions in Erlang's stdlib. Elixir v1.12 fully leverages this feature to improve reporting for errors coming from Erlang. For example, in earlier OTP versions, inserting an invalid argument into a ETS table that no longer exists would simply error with ArgumentError:

Interactive Elixir (1.11.0)
iex(1)> ets =, [])
iex(2)> :ets.delete(ets)
iex(3)> :ets.insert(ets, :should_be_a_tuple)
** (ArgumentError) argument error
    (stdlib 3.15) :ets.insert(#Reference<0.3845811859.2669281281.223553>, :should_be_a_tuple)

However, in Elixir v1.12 with Erlang/OTP 24:

Interactive Elixir (1.12.0)
iex(1)> ets =, [])
iex(2)> :ets.delete(ets)
iex(3)> :ets.insert(ets, :should_be_a_tuple)
** (ArgumentError) errors were found at the given arguments:

  * 1st argument: the table identifier does not refer to an existing ETS table
  * 2nd argument: not a tuple

    (stdlib 3.15) :ets.insert(#Reference<0.105641012.1058144260.76455>, :should_be_a_tuple)

Stepped ranges

Elixir has support for ranges from before its v1.0 release. Ranges support only integers and are inclusive, using the mathematic notation a..b. Ranges in Elixir are either increasing 1..10 or decreasing 10..1 and the direction of the range was always inferred from the starting and stop positions. Ranges are always lazy as its values are emitted as they are enumerated rather than being computed upfront.

Unfortunately, due to this inference, it is not possible to have empty ranges. For example, if you want to create a list of n elements, you can express it with a range from 1..n, as 1..0 is a decreasing range with two elements.

Elixir v1.12 supports stepped ranges via the first..last//step notation. For example: 1..10//2 will emit the numbers 1, 3, 5, 7, and 9. You can consider the // operator to perform "range division", as it effectively divides and rounds up the number of elements in the range by step. Steps can be either positive (increasing ranges) or negative (decreasing ranges). Stepped ranges bring more expressive power to Elixir ranges and they elegantly solve the empty range problem, as they allow the direction of the steps to be explicitly declared instead of inferred.

As of Elixir v1.12, implicitly decreasing ranges are soft-deprecated and warnings will be emitted in future Elixir versions based on our deprecation policy.

Additional functions

Elixir v1.12 has the additional of many functions across the standard library. The Enum module received additions such as Enum.count_until/2, Enum.product/1, Enum.zip_with/2, and more. The Integer module now includes Integer.pow/2 and Integer.extended_gcd/2. Finally, the Kernel module got two new functions, Kernel.then/2 and Kernel.tap/2, which are specially useful in |> pipelines.

v1.12.0 (2021-04-03)

1. Enhancements


  • [EEx.Engine] Add EEx.Engine.handle_text/3 callback that receives text metadata
  • [EEx.Engine] Emit warnings for unused "do" expression in EEx



  • [ExUnit] Intercept SIGQUIT (via Ctrl+\) and show a list of all aborted tests as well as intermediate test results
  • [ExUnit] Interpolate module attributes in match assertions diffs
  • [ExUnit] Print how much time is spent on async vs sync tests
  • [ExUnit] Improve error messages for doctests
  • [ExUnit] Compile doctests faster (often by two times)


  • [IEx] Make IEx' parser configurable to allow special commands
  • [IEx] Show function signature when pressing tab after the opening parens of a function
  • [IEx] If an IEx expression starts with a binary operator, such as |>, automatically pipe in the result of the last expression


  • [Mix] Add Mix.install/2 for dynamically installing a list of dependencies
  • [Mix] Support :exit_code option in Mix.raise/2
  • [Mix] Discard MIX_ENV and MIX_TARGET values if they are empty strings
  • [Mix] Print the time taken to execute a task with on MIX_DEBUG=1
  • [mix compile.erlang] Compile multiple files in parallel
  • [mix] Deep merge configuration and ensure argv is set when executing config/runtime.exs
  • [mix release] Add RELEASE_PROG to releases with the name of the executable starting the release
  • [mix release] Support remote.vm.args to customize how the connecting VM boots
  • [mix test] Run all available tests if there are no pending --failed tests. This provides a better workflow as you no longer need to toggle the --failed flag between runs

2. Bug fixes


  • [CLI] Ensure -e "" (with an empty string) parses correctly on Windows
  • [Inspect] Do not override user supplied :limit option for derived implementations
  • [Kernel] Allow heredoc inside a heredoc interpolation
  • [Kernel] Preserve CRLF on heredocs
  • [Kernel] Public functions without documentation now appear as an empty map on Code.fetch_docs/1, unless they start with underscore, where they remain as :none. This aligns Elixir's implementation with EEP48
  • [Kernel] Do not crash when complex literals (binaries and maps) are used in guards
  • [Kernel] Properly parse keywords (such as end) followed by the :: operator
  • [Macro] Macro.decompose_call/1 now also consider tuples with more than 2 elements to not be valid calls
  • [Macro] Fix Macro.to_string/1 double-escaping of escape characters in sigils
  • [Macro] Fix Macro.underscore/1 on digits preceded by capitals: "FOO10" now becomes "foo10" instead of "fo_o10"
  • [Macro] Preserve underscores between digits on Macro.underscore/1
  • [OptionParser] Properly parse when numbers follow-up aliases, for example, -ab3 is now parsed as -a -b 3
  • [Path] Fix Path.relative_to/2 when referencing self
  • [Task] Ensure Task.async_stream/2 with ordered: false discard results as they are emitted, instead of needlessly accumulating inside the stream manager
  • [URI] Do not discard empty paths on URI.merge/2


  • [ExUnit.Case] Make @tag tmp_dir an absolute directory, avoiding inconsistencies if the test changes the current working directory
  • [ExUnit.Diff] Fix cases where the diffing algorithm would fail to print a pattern correct


  • [IEx] Fix auto-completion inside remote shells


  • [mix app.config] Do not emit false positive warnings when configured dependencies that have runtime: false set
  • [mix compile.elixir] Ensure that a manifest is generated even with no source code
  • [mix compile.elixir] Make sure export dependencies trigger recompilation when the dependency is removed as well as when the whole file is removed
  • [mix compile.elixir] Do not emit false positive warnings when a path dependency adds a module that is then used by the current application in the same mix compile cycle
  • [mix test] Ensure protocols within the current project are consolidated when --cover is given
  • [mix release] Improve compliance of release scripts with stripped down Linux installations
  • [mix release] Preserve file mode when copying non-beam ebin files
  • [mix xref] Ensure args are passed to the underlying mix compile call

3. Soft-deprecations (no warnings emitted)


  • [Kernel] Using start..stop to match on ranges is soft-deprecated and will warn on future Elixir versions. Use start..stop//step instead
  • [Kernel] Using start..stop to create decreasing ranges is soft-deprecated and will warn on future versions. Use start..stop//-1 instead

4. Hard-deprecations


  • [EEx.Engine] use EEx.Engine is deprecated in favor of explicit delegation


  • [Kernel] The binary operator ^^^ is deprecated. If you are using Bitwise.^^^/2, use Bitwise.bxor/2 instead
  • [Kernel] Deprecate @foo() in favor of @foo
  • [System] Deprecate System.stacktrace/0 (it was already deprecated outside of catch/rescue and now it is deprecated everywhere)


  • [mix compile] The :xref compiler is deprecated and it has no effect. Please remove it from your mix.exs file.


The CHANGELOG for v1.11 releases can be found in the v1.11 branch.