This release requires Erlang/OTP 24 and later.

Elixir v1.15 is a smaller release with focused improvements
on compilation and boot times. This release also completes
our integration process with Erlang/OTP logger, bringing new
features such as log rotation and compaction out of the box.

You will also find additional convenience functions in Code,
Map, Keyword, all Calendar modules, and others.

Compile and boot-time improvements

The last several releases brought improvements to compilation
time and this version is no different. In particular, Elixir
now caches and prunes load paths before compilation, ensuring your
project (and dependencies!) compile faster and in an environment
closer to production.

In a nutshell the Erlang VM loads modules from code paths. Each
application that ships with Erlang and Elixir plus each dependency
become an entry in your code path. The larger the code path, the
more work Erlang has to do in order to find a module.

In previous versions, Mix would only add entries to the load paths.
Therefore, if you compiled 20 dependencies and you went to compile
the 21st, the code path would have 21 entries (plus all Erlang and
Elixir apps). This allowed modules from unrelated dependencies to
be seen and made compilation slower the more dependencies you had.
With this release, we will now prune the code paths to only the ones
listed as dependencies, bringing the behaviour closer to mix release.

Furthermore, Erlang/OTP 26 allows us to start applications
concurrently and cache the code path lookups, decreasing the cost of
booting applications. The combination of Elixir v1.15 and Erlang/OTP 26
should reduce the boot time of applications, such as when starting
iex -S mix or running a single test with mix test, from 5% to 30%.

The compiler is also smarter in several ways: @behaviour declarations
no longer add compile-time dependencies and aliases in patterns and
guards add no dependency whatsoever, as no dispatching happens. Furthermore,
Mix now tracks the digests of @external_resource files, reducing the
amount of recompilation when swapping branches. Finally, dependencies
are automatically recompiled when their compile-time configuration changes.

Potential incompatibilities

Due to the code path pruning, if you have an application or dependency
that does not specify its dependencies on Erlang and Elixir application,
it may no longer compile successfully in Elixir v1.15. You can temporarily
disable code path pruning by setting prune_code_paths: false in your
mix.exs, although doing so may lead to runtime bugs that are only
manifested inside a mix release.

Compiler warnings and errors

The Elixir compiler can now emit many errors for a single file, making
sure more feedback is reported to developers before compilation is aborted.

In Elixir v1.14, an undefined function would be reported as:

** (CompileError) undefined function foo/0 (there is no such import)
    my_file.exs:1

In Elixir v1.15, the new reports will look like:

error: undefined function foo/0 (there is no such import)
  my_file.exs:1

** (CompileError) nofile: cannot compile file (errors have been logged)

A new function, called Code.with_diagnostics/2, has been added so this
information can be leveraged by editors, allowing them to point to several
errors at once.

Integration with Erlang/OTP logger

This release provides additional features such as global logger
metadata and file logging (with rotation and compaction) out-of-the-box!

This release also soft-deprecates Elixir’s Logger Backends in
favor of Erlang’s Logger handlers. Elixir will automatically
convert your :console backend configuration into the new
configuration. Previously, you would set:

config :logger, :console,
  level: :error,
  format: "$time $message $metadata"

Which is now translated to the equivalent:

config :logger, :default_handler,
  level: :error

config :logger, :default_formatter,
  format: "$time $message $metadata"

If you use Logger.Backends.Console or other backends, they are
still fully supported and functional. If you implement your own
backends, you want to consider migrating to
:logger_backends
in the long term.

See the new Logger documentation for more information on the
new features and on compatibility.

v1.15.0-rc.0 (2022-05-22)

1. Enhancements

EEx

• [EEx] Include source code snippets in syntax errors

Elixir

• [Calendar] Add support for epoch time (%s) to Calendar.strftime/2
• [Code] Code.format_string!/2 now converts 'charlists' into ~c"charlists" by default
• [Code] Add :on_undefined_variable to the compiler options to preserve the warning behaviour which was deprecated back in Elixir v1.4
• [Code] Add Code.loaded?/1 and Code.ensure_all_loaded(!)/1
• [Code] Add Code.prepend_paths/1, Code.append_paths/1, and Code.delete_paths/1
• [Code] Add Code.with_diagnostics/2 to return diagnostics when compiling and evaluating code
• [Code.Fragment] Support nested expressions in Code.Fragment.cursor_context/1
• [Code.Fragment] Keep operators and no paren calls in Code.Fragment.container_cursor_to_quoted/1
• [Date] Add Date.before?/2 and Date.after?/2
• [DateTime] Add DateTime.before?/2 and DateTime.after?/2
• [DateTime] Support precision in DateTime.utc_now/2
• [Inspect] Inspect now renders 'charlists' as ~c"charlists" by default
• [Kernel] Break down case and cond inside dbg/2
• [Kernel] Add t:nonempty_binary/0 and t:nonempty_bitstring/0
• [Kernel] Treat @behaviours as runtime dependencies
• [Kernel] Do not add runtime dependencies for alias references in patterns and guards
• [Kernel] Warn for nested calls without parens inside keywords
• [Kernel] Support for multi-letter uppercase sigils
• [Kernel] Introduce mechanism to collect several errors in a module. Previously, as soon as there was a compilation error, compilation would fail. Now the compiler became a bit smarter and will report multiple errors whenever possible as multiple error: ... messages, similar to warning: ...
• [Kernel.CLI] Support --sname undefined/--name undefined so a name is automatically generated
• [Keyword] Add Keyword.split_with/2
• [Macro] Improve error message when piping into an expression ending in bracket-based access
• [Macro.Env] Add Macro.Env.lookup_alias_as/2
• [Map] Add Map.split_with/2
• [Map] Add Map.intersect/2 and Map.intersect/3
• [MapSet] Add MapSet.split_with/2
• [MapSet] Optimize most functions
• [NaiveDateTime] Add NaiveDateTime.beginning_of_day/1 and NaiveDateTime.end_of_day/1
• [NaiveDateTime] Add NaiveDateTime.before?/2 and NaiveDateTime.after?/2
• [NaiveDateTime] Support precision in NaiveDateTime.utc_now/2
• [OptionParser] Support :return_separator option
• [Process] Add Process.alias/0,1 and Process.unalias/1
• [Range] Add Range.split/2
• [String] Update Unicode to version 15.0.0
• [String] Add :fast_ascii mode to String.valid?/2
• [Supervisor] Add support for automatic shutdown in Supervisor
• [System] Support :lines in System.cmd/3 to capture output line by line
• [Task] Remove head of line blocking on Task.yield_many/2
• [Task] Enable selective receive optimizations in Erlang/OTP 26+
• [Task.Supervisor] Do not copy args on temporary Task.Supervisor.start_child/2
• [Time] Add Time.before?/2 and Time.after?/2
• [URI] Add URI.append_path/2

ExUnit

• [ExUnit] Add more color configuration to ExUnit CLI formatter
• [ExUnit.Callbacks] Accept {module, function} tuples in ExUnit setup callbacks
• [ExUnit.Doctest] Add ExUnit.DocTest.doctest_file/2
• [ExUnit.Formatter] When comparing two anonymous functions, defined at the same place but capturing a different environment, we will now also diff the environments

IEx

• [IEx] Make pry opt-in on dbg with --dbg pry
• [IEX] Support IEX_HOME
• [IEx.Autocomplete] Only provide aliases when autocompleting alias, import, and require
• [IEx.Autocomplete] Provide field completion on map and struct updates
• [IEx.Helpers] Add runtime_info(:allocators)
• [IEx.Info] Implement protocol for Range, DateTime, and Regex

Logger

• [Logger] Add Logger.add_handlers/1 and Logger.default_formatter/1
• [Logger] Introduce default_formatter and default_handler configuration for Logger which configures Erlang/OTP logger
• [Logger] Add :always_evaluate_messages configuration to Logger
• [Logger.Formatter] Implement the Erlang Logger formatter API
• [Logger.Formatter] Add support for ports in Logger metadata

Mix

• [mix app.start] Allow applications to be started concurrently via the :start_concurrently configuration
• [mix compile] Set --all-warnings by default
• [mix compile] Reduce the amount of filesystem lookups for path dependencies by storing timestamps in manifests
• [mix compile] Track digests of @external_resources
• [mix compile.app] Write optional_applications to .app file
• [mix compile.elixir] Add --purge-consolidation-path-if-stale which will purge the given consolidation path if compilation is required
• [mix deps.compile] Automatically recompile dependencies if their compile env changes
• [mix deps.get] Automatically install Hex and Rebar on mix deps.get/mix deps.update
• [mix deps.get] Support --check-locked which raises if changes to the lockfile are required
• [mix eval] Allow passing additional arguments
• [mix format] Support --no-exit option
• [mix format] Allow multiple formatters per file extension and sigil
• [mix format] Show diffs whenever --check-formatted fails
• [mix format] Allow the formatting root to be configured
• [mix loadpaths] Cache deps and archive loadpaths in Erlang/OTP 26
• [mix profile.fprof] Support --trace-to-file to improve performance when working with large outputs
• [mix release] Allow passing additional arguments to the eval command
• [mix xref graph] Support --output flag
• [Mix.Project] Support def cli to unify all CLI defaults in a single place
• [Mix.Project] Add Mix.Project.deps_tree/1

2. Bug fixes

Elixir

• [Code.Formatter] Fix a scenario where a keyword followed by parenthesis could go above the maximum line length
• [Code.Formatter] Remove unnecessary parens in nullary type funs
• [Exception] Fix operator precedence when printing guards in Exception.blame/3
• [File] Do not raise if there are file system race conditions in File.cp/2
• [File] Do not raise when deleting write-only empty directories on File.rm_rf/1
• [Kernel] Expand macros on the left side of → in try/rescue
• [Kernel] Raise on misplaced ... inside typespecs
• [Kernel] Do not import behaviour_info and module_info functions from Erlang modules
• [Kernel.ParallelCompiler] Make sure compiler doesn’t crash when there are stray messages in the inbox
• [Kernel.ParallelCompiler] Track compile and runtime warnings separately
• [System] Fix race condition when a script would terminate before System.stop/1 executes
• [URI] Make sure URI.merge/2 works accordingly with relative paths

ExUnit

• [ExUnit] Fix crash when @tag capture_log: true was set to true and the Logger application was shut down in the middle of the test
• [ExUnit] Do not merge context as tags inside the runner to reduce memory usage when emitting events to formatters
• [ExUnit] Do not expand or collect vars from quote in ExUnit assertions

IEx

• [IEx] Do not spawn a process to read IO. This fixes a bug where multiline paste stopped working
  whenever the input reader was killed
• [IEx] Do not perform completion for prompts triggered during code evaluation

Mix

• [mix compile] Include cwd in compiler cache key
• [mix release] Fix Windows service when invoking erlsrv.exe in path with spaces

3. Soft deprecations (no warnings emitted)

Elixir

• [File] File.cp/3 and File.cp_r/3 with a function as third argument
  is deprecated in favor of a keyword list
• [Kernel.ParallelCompiler] Require the :return_diagnostics option to be
  set to true when compiling or requiring code

Logger

• [Logger] add_backend/2, remove_backend/2, and configure_backend/2 have been deprecated
  in favor of the new :logger_backends dependency
• [Logger] The :console configuration has been deprecated in favor of :default_formatter
• [Logger] The :backends configuration has been deprecated in favor of Logger.add_handlers/1

Mix

• [Mix.Project] :preferred_cli_env is deprecated in favor of :preferred_envs in def cli
• [Mix.Project] :preferred_cli_target is deprecated in favor of :preferred_targets in def cli
• [mix local] The environment variable HEX_MIRROR is deprecated in favor of HEX_BUILDS_URL

4. Hard deprecations

Elixir

• [Calendar] Calendar.ISO.day_of_week/3 is deprecated in favor of Calendar.ISO.day_of_week/4
• [Exception] Exception.exception?/1 is deprecated in favor of Kernel.is_exception/1
• [Kernel] Deprecate ... as a valid function call identifier
• [Regex] Regex.regex?/1 is deprecated in favor of Kernel.is_struct/2

Logger

• [Logger] Logger.warn/2 is deprecated in favor of Logger.warning/2