View Source mix compile.elixir (Mix v1.18.0-dev)

Compiles Elixir source files.

Elixir is smart enough to recompile only files that have changed and their dependencies. This means if lib/a.ex is invoking a function defined over lib/b.ex at compile time, whenever lib/b.ex changes, lib/a.ex is also recompiled.

Note Elixir considers a file as changed if its source file has changed on disk since the last compilation AND its contents are no longer the same.


If a module depends on external files, those can be annotated with the @external_resource module attribute. If these files change, the Elixir module is automatically recompiled.


A module may export a __mix_recompile__?/0 function that can cause the module to be recompiled using custom rules. For example, to recompile whenever a file is changed in a given directory, you can use a combination of @external_resource for existing files and a __mix_recompile__?/0 check to verify when new entries are added to the directory itself:

defmodule MyModule do
  paths = Path.wildcard("*.txt")
  @paths_hash :erlang.md5(paths)

  for path <- paths do
    @external_resource path

  def __mix_recompile__?() do
    Path.wildcard("*.txt") |> :erlang.md5() != @paths_hash

Compiler calls __mix_recompile__?/0 for every module being compiled (or previously compiled) and thus it is very important to do there as little work as possible to not slow down the compilation.

If module has @compile {:autoload, false}, __mix_recompile__?/0 will not be used.

Command line options

  • --all-warnings (--no-all-warnings) - prints all warnings, including previous compilations (default is true except on errors)
  • --docs (--no-docs) - attaches (or not) documentation to compiled modules
  • --debug-info (--no-debug-info) - attaches (or not) debug info to compiled modules
  • --force - forces compilation regardless of modification times
  • --ignore-module-conflict - does not emit warnings if a module was previously defined
  • --long-compilation-threshold N - sets the "long compilation" threshold (in seconds) to N (see the docs for Kernel.ParallelCompiler.compile/2)
  • --purge-consolidation-path-if-stale PATH - deletes and purges modules in the given protocol consolidation path if compilation is required
  • --profile - if set to time, outputs timing information of compilation steps
  • --tracer - adds a compiler tracer in addition to any specified in the mix.exs file
  • --verbose - prints each file being compiled
  • --warnings-as-errors - exit with non-zero status if compilation has one or more warnings


  • :elixirc_paths - directories to find source files. Defaults to ["lib"].

  • :elixirc_options - compilation options that apply to Elixir's compiler. See Code.put_compiler_option/2 for a complete list of options. These options are often overridable from the command line using the switches above.

  • [xref: [exclude: ...]] - a list of module or {module, function, arity} that should not be warned on in case on undefined modules or undefined application warnings.