Code snippets in diagnostics

Elixir v1.15 introduced a new compiler diagnostic format and the ability to print multiple error diagnostics per compilation (in addition to multiple warnings).

With Elixir v1.16, we also include code snippets in exceptions and diagnostics raised by the compiler. For example, a syntax error now includes a pointer to where the error happened:

** (SyntaxError) invalid syntax found on lib/my_app.ex:1:17:
    error: syntax error before: '*'
    │
  1 │ [1, 2, 3, 4, 5, *]
    │                 ^
    │
    └─ lib/my_app.ex:1:17

For mismatched delimiters, it now shows both delimiters:

** (MismatchedDelimiterError) mismatched delimiter found on lib/my_app.ex:1:18:
    error: unexpected token: )
    │
  1 │ [1, 2, 3, 4, 5, 6)
    │ │                └ mismatched closing delimiter (expected "]")
    │ └ unclosed delimiter
    │
    └─ lib/my_app.ex:1:18

Errors and warnings diagnostics also include code snippets. When possible, we will show precise spans, such as on undefined variables:

  error: undefined variable "unknown_var"
  │
5 │     a - unknown_var
  │         ^^^^^^^^^^^
  │
  └─ lib/sample.ex:5:9: Sample.foo/1

Otherwise the whole line is underlined:

error: function names should start with lowercase characters or underscore, invalid name CamelCase
  │
3 │   def CamelCase do
  │   ^^^^^^^^^^^^^^^^
  │
  └─ lib/sample.ex:3

A huge thank you to Vinícius Muller for working on the new diagnostics.

Revamped documentation

Elixir’s Getting Started guided has been made part of the Elixir repository and incorporated into ExDoc. This was an opportunity to revisit and unify all official guides and references.

We have also incorporated and extended the work on Understanding Code Smells in Elixir Functional Language, by Lucas Vegi and Marco Tulio Valente, from ASERG/DCC/UFMG, into the official document in the form of anti-patterns. The anti-patterns are divided into four categories: code-related, design-related, process-related, and meta-programming. Our goal is to give all developers examples of potential anti-patterns, with context and examples on how to improve their codebases.

Another ExDoc feature we have incorporated in this release is the addition of cheatsheets, starting with a cheatsheet for the Enum module. If you would like to contribute future cheatsheets to Elixir itself, feel free to start a discussion with an issue.

Finally, we have started enriching our documentation with Mermaid.js diagrams. You can find examples in the GenServer and Supervisor docs.

v1.16.0-rc.0 (2023-10-31)

1. Enhancements

EEx

• [EEx] Include relative file information in diagnostics

Elixir

• [Code] Automatically include columns in parsing options
• [Code] Introduce MismatchedDelimiterError for handling mismatched delimiter exceptions
• [Code.Fragment] Handle anonymous calls in fragments
• [Code.Formatter] Trim trailing whitespace on heredocs with \r\n
• [Kernel] Suggest module names based on suffix and casing errors when the module does not exist in UndefinedFunctionError
• [Kernel.ParallelCompiler] Introduce Kernel.ParallelCompiler.pmap/2 to compile multiple additional entries in parallel
• [Kernel.SpecialForms] Warn if True/False/Nil are used as aliases and there is no such alias
• [Macro] Add Macro.compile_apply/4
• [Module] Add support for @nifs annotation from Erlang/OTP 25
• [Module] Add support for missing @dialyzer configuration
• [String] Update to Unicode 15.1.0
• [Task] Add :limit option to Task.yield_many/2

Mix

• [mix] Add MIX_PROFILE to profile a list of comma separated tasks
• [mix compile.elixir] Optimize scenario where there are thousands of files in lib/ and one of them is changed
• [mix test] Allow testing multiple file:line at once, such as mix test test/foo_test.exs:13 test/bar_test.exs:27

2. Bug fixes

Elixir

• [Code.Fragment] Fix crash in Code.Fragment.surround_context/2 when matching on ->
• [IO] Raise when using IO.binwrite/2 on terminated device (mirroring IO.write/2)
• [Kernel] Do not expand aliases recursively (the alias stored in Macro.Env is already expanded)
• [Kernel] Ensure dbg module is a compile-time dependency
• [Kernel] Warn when a private function or macro uses unquote/1 and the function/macro itself is unused
• [Kernel] Do not define an alias for nested modules starting with Elixir. in their definition
• [Kernel.ParallelCompiler] Consider a module has been defined in @after_compile callbacks to avoid deadlocks
• [Path] Ensure Path.relative_to/2 returns a relative path when the given argument does not share a common prefix with cwd

ExUnit

• [ExUnit] Raise on incorrectly dedented doctests

Mix

• [Mix] Ensure files with duplicate modules are recompiled whenever any of the files change

3. Soft deprecations (no warnings emitted)

Elixir

• [File] Deprecate File.stream!(file, options, line_or_bytes) in favor of keeping the options as last argument, as in File.stream!(file, line_or_bytes, options)
• [Kernel.ParallelCompiler] Deprecate Kernel.ParallelCompiler.async/1 in favor of Kernel.ParallelCompiler.pmap/2
• [Path] Deprecate Path.safe_relative_to/2 in favor of Path.safe_relative/2

4. Hard deprecations

Elixir

• [Date] Deprecate inferring a range with negative step, call Date.range/3 with a negative step instead
• [Enum] Deprecate passing a range with negative step on Enum.slice/2, give first..last//1 instead
• [Kernel] ~R/.../ is deprecated in favor of ~r/.../. This is because ~R/.../ still allowed escape codes, which did not fit the definition of uppercase sigils
• [String] Deprecate passing a range with negative step on String.slice/2, give first..last//1 instead

ExUnit

• [ExUnit.Formatter] Deprecate format_time/2, use format_times/1 instead

Mix

• [mix compile.leex] Require :leex to be added as a compiler to run the leex compiler
• [mix compile.yecc] Require :yecc to be added as a compiler to run the yecc compiler