The focus behind Elixir v1.13 has been on tooling, mainly tooling related to code formatting, code fragments, code reflection, and code recompilation. A lot of this functionality will directly impact developers working on large codebases and provide meaningful quality of life improvements for those working on Elixir tooling and environments, such as IDEs, notebooks, etc.

Elixir v1.13 comes with many improvements to the compiler, so it recompiles your files less frequently. In particular:

• The digest of the files are considered in addition to their size. This avoids recompiling many files when switching or rebasing branches.

• Changing your mix.exs will no longer trigger a full recompilation, unless you specifically change the configurations used by the Elixir compiler (:elixirc_paths and :elixirc_options).

• Changing compile-time configuration files (config/config.exs and any other file imported from it) now only recompiles the project files that depend on the reconfigured applications, instead of a full recompilation. However, if you change the configuration of your application itself, the whole project is still recompiled.

• Adding, updating or removing a dependency now only recompiles the project files that depend on the modified a dependency.

• If your project has both Erlang and Elixir files, changing an Erlang file will now recompile only the Elixir files that depend on it.

In a nutshell, Elixir went from triggering full recompilations whenever any of mix.exs, config/config.exs, src/*, and mix.lock changed on disk to semantic recompilations. Now it only fully recompiles when:

• you change the compilation options in mix.exs
• you change the configuration for the current project in config/config.exs

mix xref is a tool that analyzes relationships between files. By analyzing the compile-time and runtime dependencies between files, it allows developers to understand what files have to be recompiled whenever a file changes.

Elixir v1.13 comes with many improvements to mix xref, such as:

• mix xref graph now supports --label to be set to "compile-direct" and "compile-connected", which returns the direct compile-time dependencies ("compile-direct") or just those that generate additional transitive dependencies ("compile-connected")

• A new mix xref trace FILE subcommand receives a file and returns all dependencies in said file, including the line and what caused said dependency (a function/macro call, an alias, a struct, etc).

• All mix xref subcommands support the --fail-above flag, which allows you to enforce your project has at most a certain number of compile-time cycles, transitive compile-time dependencies, etc.

• mix xref graph now supports multiple --sink and --source to be given.

With these improvements, it has become simpler to understand the impact code recompilation has in our codebases and how to limit it.

The Code module also got a companion module called Code.Fragment, which hosts functions that work on incomplete code, as is often the scenario in editors, command line, etc. The module contains different heuristics to analyze the source code and return context informational.

Thanks to these improvements, IEx' autocomplete got several quality of life improvements, such as the autocompletion of sigils, structs, and paths. For example, typing ~<TAB> now shows:

iex(1)> ~
~C (sigil_C)    ~D (sigil_D)    ~N (sigil_N)    ~R (sigil_R)
~S (sigil_S)    ~T (sigil_T)    ~U (sigil_U)    ~W (sigil_W)
~c (sigil_c)    ~r (sigil_r)    ~s (sigil_s)    ~w (sigil_w)

Adding the sigil letter and pressing tab then shows the available delimiters:

iex(1)> ~r
"      """    '      '''    (      /      <      [      {      |

Similarly, %<TAB> now shows only the available structs (exceptions excluded), instead of all modules:

iex(1)> %File.St
File.Stat      File.Stream

Finally, new compilation tracers have been added, alongside a handful of functions in Module to retrieve module metadata, which can be used to enrich suggestions in programming environments.

The mix format task has been augmented with the notion of plugins. Plugins can teach the formatter how to format new files and how to format sigils, via the Mix.Tasks.Format behaviour.

For example, imagine that your project uses Markdown in two distinct ways: via a custom ~M sigil and via files with the .md and .markdown extensions. A custom plugin would look like this:

defmodule MixMarkdownFormatter do
  @behaviour Mix.Tasks.Format

  def features(_opts) do
    [sigils: [:M], extensions: [".md", ".markdown"]]
  end

  def format(contents, opts) do
    # logic that formats markdown
  end
end

Now any application can use your formatter as follows:

# .formatters.exs
[
  # Define the desired plugins
  plugins: [MixMarkdownFormatter],
  # Remember to update the inputs list to include the new extensions
  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}", "posts/*.{md,markdown}"]
]

Finally, the Code has also been augmented with two functions: Code.string_to_quoted_with_comments/2 and Code.quoted_to_algebra/2. Those functions allow someone to retrieve the Elixir AST with their original source code comments, and then convert this AST to formatted code. In other words, those functions provide a wrapper around the Elixir Code Formatter, supporting developers who wish to create tools that directly manipulate and custom format Elixir source code.

• [EEx] Add :parser_options to EEx functions

• [CLI] Support --short-version on the CLI that does not boot the VM
• [Code] Add Code.string_to_quoted_with_comments/2 and Code.quoted_to_algebra/2
• [Code] Add more :token_metadata to aliases and remote calls when parsing strings
• [Code] Add Code.Fragment module to provide best-effort information from code fragments. The module currently provides an updated Code.Fragment.cursor_context/2 with operator support and Code.Fragment.surround_context/2 which looks at a given position in a fragment and find its surrounding delimiters
• [Code] Allow custom sigil formatting on Code.format_string!/2
• [Code] Add {:on_module, bytecode, :none} trace to compilation tracers
• [Enum] Optimize Enum.concat/1 for lists of lists
• [Exception] Better format Elixir exceptions in Erlang
• [Inspect] Allow default inspect fun to be set globally with Inspect.Opts.default_inspect_fun/1
• [IO] Allow :eof to be given as limit to IO.getn/2
• [Kernel] Make get_in consistently abort when nil values are found
• [Kernel] Improve compilation times by reducing the amount of copies of the AST across compiler processes
• [Kernel] Raise if trying to define a module with a slash in its name
• [Kernel] Warn when ?\ is used and there is no need for a escape character
• [Kernel] Track structs in typespecs as export deps instead of compile-time deps
• [Kernel] Add power operator (**/2)
• [Keyword] Add Keyword.validate/2
• [Keyword] Implement Keyword.filter/2 and Keyword.map/2
• [List] Add List.keyfind!/3
• [Macro.Env] Add the following reflection functions: required?/2, lookup_import/2, fetch_alias/2, and fetch_macro_alias/2
• [Map] Implement Map.filter/2 and Map.map/2
• [Module] Support :nillify_clauses in Module.get_definition/3
• [Module] Add Module.attributes_in/1 and Module.overridables_in/1
• [OptionParser] Add "did you mean?" suggestions to OptionParser.ParseError messages
• [Record] Add record reflection via @__records__
• [Task] Add Task.completed/1

• [ExUnit.CaptureIO] Add with_io/3 to return result with captured io
• [ExUnit.CaptureLog] Add with_log/2 to return result with captured logs

• [IEx.Autocomplete] Add path autocompletion whenever when the cursor follows "./ or "/ or "DRIVER: where DRIVER is a single letter
• [IEx.Autocomplete] Add autocompletion for sigils and structs
• [IEx.Helpers] Allow multiple modules to be given to r/1

• [Logger] Add Logger.put_application_level/2

• [mix archive.install] Run loadconfig before building archive
• [mix compile] Move Elixir version check to before deps are compiled, in order to give feedback earlier
• [mix compile.elixir] Do not recompile files if their modification time change but their contents are still the same and the .beam files are still on disk
• [mix compile.elixir] Do not recompile all Elixir sources when Erlang modules change, only dependent ones
• [mix compile.elixir] Do not recompile Elixir files if mix.exs changes, instead recompile only files using Mix.Project or trigger a recompilation if a compiler option changes
• [mix compile.elixir] Only recompile needed files when a dependency is added, updated or removed
• [mix compile.elixir] Only recompile needed files when a dependency is configured
• [mix deps] Add :subdir option to git deps
• [mix escript.install] Run loadconfig before building escript
• [mix format] Support :plugins in mix format that can hook into custom extensions and sigils
• [mix format] Add Mix.Tasks.Format.formatter_for_file/2
• [mix local.rebar] No longer support sub_dirs in Rebar 2 to help migration towards Rebar 3
• [mix local.rebar] Support --if-missing option when installing Rebar
• [mix local.rebar] Set REBAR_PROFILE=prod when compiling Rebar dependencies
• [mix test] Support --profile-require=time to profile the time loading test files themselves
• [mix test] Allow filtering modules from coverage using regex
• [mix test] Allow the exit status of ExUnit to be configured and set the default to 2
• [mix test] Exit with a status of 3 when coverage falls below threshold
• [mix test] Write failed manifest when suite fails due to --warnings-as-errors
• [mix xref] Support multiple sinks and sources in mix xref graph
• [mix xref] Add trace subcommand to print compilation dependencies between files
• [mix xref] Add --fail-above option to mix xref
• [mix xref] Add --label compile-connected to mix xref
• [mix xref] Add --label compile-direct to mix xref (instead of --only-direct)

• [EEx] Accept EEx expressions where -> is followed by newline

• [Application] Warn if Application.compile_env or Application.compile_env! are called without a require
• [Code] Ensure bindings with no context are returned as atoms instead of {binding, nil} in eval operations
• [Kernel] Raise if __CALLER__ or __ENV__ or __STACKTRACE__ are used in match
• [Kernel] Improve error message on invalid argument for byte_size from binary concat
• [Kernel] Raise when aliasing non-Elixir modules without :as
• [Kernel] Allow unquote_splicing inside %{...} without parens
• [Kernel] Ensure that waiting on a struct expansion inside a typespec is correctly tracked as waiting time in the compiler
• [Kernel] Correctly parse the atom . as a keyword list key
• [Kernel] Do not leak variables from the first generator in with and for special forms
• [Kernel] Fix column number on strings with NFD characters
• [OptionParser] Validate switch types/modifiers early on to give more precise feedback
• [Protocol] Add defdelegate to the list of unallowed macros inside protocols as protocols do not allow function definitions
• [Protocol] Warn if @callback, @macrocallback and @optional_callbacks are defined inside protocol
• [Protocol] Ensure protocol metadata is deterministic on consolidation
• [URI] Only percent decode if followed by hex digits (according to https://url.spec.whatwg.org/#percent-decode)
• [Version] Ensure proper precedence of and/or in version requirements

• [ExUnit] Invalidate a module's tests in ExUnit.run/0 results if that module's setup_all fails
• [ExUnit] Fix count in formatter if a module's setup_all fails

• [IEx] Fix the loss of .iex.exs context after a pry session

• [Logger] Raise clear error message for invalid :compile_time_purge_matching configuration

• [mix compile.elixir] Recompile file if @external_resource is deleted
• [mix compile.elixir] Print number of compiling files on all compiler cycles. This will make the Compiling N files (.ex) show up multiple times if necessary
• [mix deps] Raise if local dep is unavailable while compiling
• [mix deps.unlock] Fix blank output when dependency is not locked
• [mix local.install] Do not respect MIX_DEPS_PATH for install commands
• [mix release] Improve release scripts to make sure shell errors cascade by avoiding exporting and defining variables at once
• [mix release] Do not boot release if RELEASE_COOKIE is empty
• [mix release] Allow release running as a daemon to be restarted
• [mix test] Allow coverage engine to also tag case, cond, and receive branches where the right side is a literal
• [Mix.Shell] Add default option to Mix.Shell.yes?

• [IO] :all on IO.getn is deprecated in favor of :eof
• [Code] Environment options in Code.eval_quoted/3 and Code.eval_string/3, such as :aliases and :tracers, have been deprecated in favor of passing an environment

• [mix format] Mix.Tasks.Format.formatter_opts_for_file/2 is deprecated in favor of Mix.Tasks.Format.formatter_for_file/2

• [Code] Code.cursor_context/2 is deprecated, use Code.Fragment.cursor_context/2 instead
• [Macro] Macro.to_string/2 is deprecated, use Macro.to_string/1 instead
• [System] System.get_pid/0 is deprecated, use System.pid/0 instead
• [Version] Using ! or != in version requirements is deprecated, use ~> or >= instead

• [mix escript.build] :strip_beam option is deprecated in favor of :strip_beams
• [Mix] :exit_code in Mix.raise/2 has been deprecated in favor of :exit_status
• [Mix.Config] Mix.Config is deprecated in favor of Config module

The CHANGELOG for v1.12 releases can be found in the v1.12 branch.