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Changelog for Elixir v1.17

Warnings from gradual set-theoretic types

This release introduces gradual set-theoretic types to infer types from patterns and guards and use them to type check programs, enabling the Elixir compiler to find faults and bugs in codebases without requiring changes to existing software. The underlying principles, theory, and roadmap of our work have been outlined in "The Design Principles of the Elixir Type System" by Giuseppe Castagna, Guillaume Duboc, José Valim.

At the moment, Elixir developers will interact with set-theoretic types only through warnings found by the type system. The current implementation models all data types in the language:

  • binary(), integer(), float(), pid(), port(), reference() - these types are indivisible. This means both 1 and 13 get the same integer() type.

  • atom() - it represents all atoms and it is divisible. For instance, the atom :foo and :hello_world are also valid (distinct) types.

  • map() and structs - maps can be "closed" or "open". Closed maps only allow the specified allows keys, such as %{key: atom(), value: integer()}. Open maps support any other keys in addition to the ones listed and their definition starts with ..., such as %{..., key: atom(), value: integer()}. Structs are closed maps with the __struct__ key.

  • tuple(), list(), and function() - currently they are modelled as indivisible types. The next Elixir versions will also introduce fine-grained types here.

We focused on atoms and maps on this initial release as they are respectively the simplest and the most complex types representations, so we can stress the performance of the type system and quality of error messages. Modelling these types will also provide the most immediate benefits to Elixir developers. Assuming there is a variable named user, holding a %User{} struct with an address field, Elixir v1.17 will emit the following warnings at compile-time:

  • Pattern matching against a map or a struct that does not have the given key, such as %{adress: ...} = user (notice address vs adress)

  • Accessing a key on a map or a struct that does not have the given key, such as user.adress

  • Updating a struct or a map that does not define the given key, such as %{user | adress: ...}

  • Invoking a function on non-modules, such as user.address()

  • Capturing a function on non-modules, such as &user.address/0

  • Performing structural comparisons with structs, such as my_date < ~D[2010-04-17]

  • Performing structural comparisons between non-overlapping types, such as integer >= string

  • Building and pattern matching on binaries without the relevant specifiers, such as <<string>> (this warns because by default it expects an integer)

  • Attempting to rescue an undefined exception or an exception that is not a struct

  • Accessing a field that is not defined in a rescued exception

These new warnings help Elixir developers find bugs earlier and give more confidence when refactoring code, especially around maps and structs. While some of these warnings were emitted in the past, they were discovered using syntax analysis. The new warnings are more reliable, precise, and with better error messages.

Future Elixir versions will continue inferring more types and type checking more constructs, bringing Elixir developers more warnings and quality of life improvements without changes to code. For more details, see our new reference document on gradual set-theoretic types.

The type system was made possible thanks to a partnership between CNRS and Remote. The development work is currently sponsored by Fresha, Starfish*, and Dashbit.

Adding Duration and shift/2 functions

TODO.

v1.17.0-dev

1. Enhancements

Elixir

  • [Access] Add Access.find/1 that mirrors Enum.find/2
  • [Date] Add Date.shift/2 to shift dates with duration and calendar-specific semantics
  • [DateTime] Add DateTime.shift/2 to shift datetimes with duration and calendar-specific semantics
  • [Duration] Add a new Duration data type
  • [GenServer] Add c:GenServer.format_status/1 callback
  • [Kernel] Add Kernel.get_in/1 with safe nil-handling for access and structs
  • [Kernel] Add Kernel.is_non_struct_map/1 guard
  • [Kernel] Add Kernel.to_timeout/1
  • [Kernel] Emit warnings for undefined functions from modules defined within the same context as the caller code
  • [Macro] Add Macro.Env.define_alias/4, Macro.Env.define_import/4, Macro.Env.define_require/4, Macro.Env.expand_alias/4, Macro.Env.expand_import/5, and Macro.Env.expand_require/6 to aid the implementation of language servers and embedded languages
  • [NaiveDateTime] Add NaiveDateTime.shift/2 to shift naive datetimes with duration and calendar-specific semantics
  • [Process] Add Process.set_label/1
  • [String] Add String.byte_slice/3 to slice a string to a maximum number of bytes while keeping it UTF-8 encoded
  • [Time] Add Time.shift/2 to shift times with duration and calendar-specific semantics

ExUnit

  • [ExUnit] Propagate the test process itself as a caller in start_supervised
  • [ExUnit] Include max cases in ExUnit reports

IEx

  • [IEx.Helpers] Warns if recompile was called and the current working directory changed
  • [IEx.Helpers] Add c/0 as an alias to continue/0
  • [IEx.Pry] Add IEx.Pry.annotate_quoted/3 to annotate a quoted expression with pry breakpoints

Logger

  • [Logger] Format :gen_statem reports using Elixir data structures
  • [Logger] Include process label in logger events

Mix

  • [mix deps] Add :depth option to Mix.SCM.Git, thus supporting shallow clones of Git dependencies
  • [mix deps] Warn if :optional is used in combination with :in_umbrella
  • [mix deps.get] Do not add optional dependency requirements if its parent dep was skipped
  • [mix deps.tree] Add --umbrella-only to mix deps.tree
  • [mix test] Add mix test --breakpoints that sets up a breakpoint before each test that will run
  • [mix test] Add mix test --repeat-until-failure to rerun tests until a failure occurs
  • [mix test] Add mix test --slowest-modules to print slowest modules based on all of the tests they hold

2. Bug fixes

Elixir

  • [Code] Address a bug where AST nodes for (a -> b) were not wrapped as part of the literal encoder
  • [Kernel] Resolve inconsistencies of how .. and ... are handled at the AST level
  • [Kernel] Fix parsing precedence of ambiguous operators followed by containers

IEx

  • [IEx.Helpers] Update the history size whenever history is pruned

Mix

  • [mix deps] Fix error message for diverged SCM definition in sibling

3. Soft deprecations (no warnings emitted)

Elixir

  • [GenServer] Deprecate c:GenServer.format_status/2 callback to align with Erlang/OTP 25+

4. Hard deprecations

Elixir

  • [IO] Passing :all to IO.read/2 and IO.binread/2 is deprecated, pass :eof instead
  • [Kernel] Single-quote charlists are deprecated, use ~c instead
  • [Kernel] Deprecate escaping closing delimiter in uppercase sigils
  • [Range] left..right without explicit steps inside patterns and guards is deprecated, write left..right//step instead
  • [Range] Decreasing ranges, such as 10..1 without an explicit step is deprecated, write 10..1//-1 instead

ExUnit

  • [ExUnit.Case] register_test/4 is deprecated in favor of register_test/6 for performance reasons

v1.16

The CHANGELOG for v1.16 releases can be found in the v1.16 branch.