# Changelog for Elixir v1.15

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) my_file.exs: 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.

### Potential incompatibilities

As part of this effort, the behaviour where undefined variables were
transformed into nullary function calls, often leading to confusing error
reports, has been disabled during project compilation. You can invoke
`Code.compiler_options(on_undefined_variable: :warn)` at the top of
your `mix.exs` to bring the old behaviour back.

## 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:

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

Which is now translated to the equivalent:

```elixir
config :logger, :default_handler,
  level: :error

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

If you use `Logger.Backends.Console` with a custom device or other
backends, they are still fully supported and functional. If you
implement your own backends, you want to consider migrating to
[`:logger_backends`](https://github.com/elixir-lang/logger_backends)
in the long term.

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

## v1.15.2 (2023-07-01)

### 1. Bug fixes

#### IEx

  * [IEx] Fix CLI being unable to boot on Windows

## v1.15.1 (2023-06-30)

### 1. Enhancements

  * [Code] `Code.string_to_quoted/2` honors `:static_atoms_encoder` for multi-letter sigils

### 2. Bug fixes

#### ExUnit

  * [ExUnit.CaptureLog] Fix race condition on concurrent `capture_log`
  * [ExUnit.CaptureLog] Respect options passed to nested `capture_log` calls
  * [ExUnit.Doctest] Properly compile doctests without results terminated by fences
  * [ExUnit.Doctest] Allow variables defined in doctests to be used in expectation

#### IEx

  * [IEx] Ensure `pry` works on Erlang/OTP 25 and earlier while IEx is booting
  * [IEx] `Code.Fragment.surround_context` considers surround context around spaces and parens

#### Logger

  * [Logger] Do not assume Logger has been loaded at compile-time
  * [Logger.Formatter] Properly handle `:function` as metadata

#### Mix

  * [mix compile] Ensure the current project is available on the code path after its Elixir sources are compiled
  * [mix compile] Guarantee yecc/leex are available when emitting warnings from previous runs
  * [mix compile] Fix bug where an external resource was deleted after its
  mtime was successfully retrieved
  * [mix compile] Track removed modules and exports across local deps
  * [mix deps] Fix an issue where dependencies could not be started in an umbrella projects
  * [mix release] Properly handle optional dependencies when there is a conflict in the application start mode
  * [mix release] Remove `--werl` from release scripts on Erlang/OTP 26

## v1.15.0 (2023-06-19)

### 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`
  * [File] Support distributed `File.Stream`
  * [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 `@behaviour`s 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] Raise instead of warning on undefined variables. Previously, an undefined variable would attempt to invoke a function of the same name, which led to confusing error messages, especially to newcomers. To enable the previous behaviour, invoke `Code.compiler_options(on_undefined_variable: :warn)` at the top of your `mix.exs`
  * [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`
  * [Module] Mark functions as generated in "Docs" chunk
  * [Module] Add `Module.get_last_attribute/3`
  * [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] Reduce tasks footprint by avoiding unecessary work during spawning
  * [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.Case] Add `ExUnit.Case.get_last_registered_test/1`
  * [ExUnit.Doctest] Add `ExUnit.DocTest.doctest_file/2`
  * [ExUnit.Doctest] Include `doctest_data` in doctest tags
  * [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] Raise when macros are given to dialyzer
  * [Kernel.ParallelCompiler] Make sure compiler doesn't crash when there are stray messages in the inbox
  * [Kernel.ParallelCompiler] Track compile and runtime warnings separately
  * [Module] Ensure that `Module.get_attribute/3` returns `nil` and not the given default value when an attribute has been explicitly set as `nil`
  * [System] Fix race condition when a script would terminate before `System.stop/1` executes
  * [Task] Do not double log Task failure reports
  * [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] Mark test cases as invalid when an exit occurs during `setup_all`
  * [ExUnit] Do not expand or collect vars from quote in ExUnit assertions
  * [ExUnit.DocTest] Ensure proper line is returned when failing to parse doctest results
  * [ExUnit.Doctest] Fix line information when a doctest with multiple assertions fails

#### 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
  * [mix xref] Raise early if `mix xref` is used at the umbrella root

### 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] Require pin variable when accessing variable inside binary size in match
  * [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`

## v1.14

The CHANGELOG for v1.14 releases can be found [in the v1.14 branch](https://github.com/elixir-lang/elixir/blob/v1.14/CHANGELOG.md).
