Allow "mix format" to read exported configuration from dependencies

lib/mix/lib/mix/tasks/format.ex

@@ -36,18 +36,24 @@ defmodule Mix.Tasks.Format do
   If any of the `--check-*` flags are given and a check fails, the formatted
   contents won't be written to disk nor printed to stdout.
 
-  ## .formatter.exs
+  ## `.formatter.exs`
 
   The formatter will read a `.formatter.exs` in the current directory for
   formatter configuration. It should return a keyword list with any of the
   options supported by `Code.format_string!/2`.
 
-  The `.formatter.exs` also supports an `:inputs` field which specifies the
-  default inputs to be used by this task:
+  The `.formatter.exs` also supports other options:
 
-      [
-        inputs: ["mix.exs", "{config,lib,test}/**/*.{ex,exs}"]
-      ]
+    * `:inputs` (a list of paths and patterns) - specifies the default inputs
+      to be used by this task. For example, `["mix.exs", "{config,lib,test}/**/*.{ex,exs}"]`.
+
+    * `:import_deps` (a list of dependencies as atoms) - specifies a list
+       of dependencies whose formatter configuration will be imported.
+       See the "Importing dependencies configuration" section below for more
+       information.
+
+    * `:export` (a keyword list) - specifies formatter configuration to be exported. See the
+      "Importing dependencies configuration" section below.
 
   ## When to format code
 
@@ -65,6 +71,43 @@ defmodule Mix.Tasks.Format do
   of patterns and files to `mix format`, as showed at the top of this task
   documentation. This list can also be set in the `.formatter.exs` under the
   `:inputs` key.
+
+  ## Importing dependencies configuration
+
+  This task supports importing formatter configuration from dependencies.
+
+  A dependency that wants to export formatter configuration needs to have a `.formatter.exs` file
+  at the root of the project. In this file, the dependency can export a `:export` option with
+  configuration to export. For now, only one option is supported under `:export`:
+  `:export_locals_without_parens` (whose value has the same shape as the value of the
+  `:locals_without_parens` in `Code.format_string!/2`).
+
+  The functions listed under `:locals_without_parens` in the `:export` option of a dependency
+  can be imported in a project by listing that dependency in the `:import_deps`
+  option of the formatter configuration file of the project.
+
+  For example, consider I have a project `my_app` that depends on `my_dep`.
+  `my_dep` wants to export some configuration, so `my_dep/.formatter.exs`
+  would look like this:
+
+      # my_dep/.formatter.exs
+      [
+        # Regular formatter configuration for my_dep
+        # ...
+
+        export: [
+          locals_without_parens: [some_dsl_call: 2, some_dsl_call: 3]
+        ]
+      ]
+
+  In order to import configuration, `my_app`'s `.formatter.exs` would look like
+  this:
+
+      # my_app/.formatter.exs
+      [
+        import_deps: [:my_dep]
+      ]
+
   """
 
   @switches [
@@ -74,9 +117,12 @@ defmodule Mix.Tasks.Format do
     dry_run: :boolean
   ]
 
+  @deps_manifest "cached_formatter_deps"
+
   def run(args) do
     {opts, args} = OptionParser.parse!(args, strict: @switches)
     formatter_opts = eval_dot_formatter(opts)
+    formatter_opts = fetch_deps_opts(formatter_opts)
 
     args
     |> expand_args(formatter_opts)
@@ -87,20 +133,8 @@ defmodule Mix.Tasks.Format do
 
   defp eval_dot_formatter(opts) do
     case dot_formatter(opts) do
-      {:ok, dot_formatter} ->
-        {formatter_opts, _} = Code.eval_file(dot_formatter)
-
-        unless Keyword.keyword?(formatter_opts) do
-          Mix.raise(
-            "Expected #{inspect(dot_formatter)} to return a keyword list, " <>
-              "got: #{inspect(formatter_opts)}"
-          )
-        end
-
-        formatter_opts
-
-      :error ->
-        []
+      {:ok, dot_formatter} -> eval_file_with_keyword_list(dot_formatter)
+      :error -> []
     end
   end
 
@@ -112,6 +146,93 @@ defmodule Mix.Tasks.Format do
     end
   end
 
+  # This function reads exported configuration from the imported dependencies and deals with
+  # caching the result of reading such configuration in a manifest file.
+  defp fetch_deps_opts(formatter_opts) do
+    deps = Keyword.get(formatter_opts, :import_deps, [])
+
+    cond do
+      deps == [] ->
+        formatter_opts
+
+      is_list(deps) ->
+        # Since we have dependencies listed, we write the manifest even if those dependencies
+        # don't export anything so that we avoid lookups everytime.
+        deps_manifest = Path.join(Mix.Project.manifest_path(), @deps_manifest)
+
+        dep_parenless_calls =
+          if deps_dot_formatters_stale?(deps_manifest) do
+            dep_parenless_calls = eval_deps_opts(deps)
+            write_deps_manifest(deps_manifest, dep_parenless_calls)
+            dep_parenless_calls
+          else
+            read_deps_manifest(deps_manifest)
+          end
+
+        Keyword.update(
+          formatter_opts,
+          :locals_without_parens,
+          dep_parenless_calls,
+          &(&1 ++ dep_parenless_calls)
+        )
+
+      true ->
+        Mix.raise("Expected :import_deps to return a list of dependencies, got: #{inspect(deps)}")
+    end
+  end
+
+  defp deps_dot_formatters_stale?(deps_manifest) do
+    Mix.Utils.stale?([".formatter.exs" | Mix.Project.config_files()], [deps_manifest])
+  end
+
+  defp read_deps_manifest(deps_manifest) do
+    deps_manifest |> File.read!() |> :erlang.binary_to_term()
+  end
+
+  defp write_deps_manifest(deps_manifest, parenless_calls) do
+    File.mkdir_p!(Path.dirname(deps_manifest))
+    File.write!(deps_manifest, :erlang.term_to_binary(parenless_calls))
+  end
+
+  defp eval_deps_opts(deps) do
+    deps_paths = Mix.Project.deps_paths()
+
+    for dep <- deps,
+        dep_path = assert_valid_dep_and_fetch_path(dep, deps_paths),
+        dep_dot_formatter = Path.join(dep_path, ".formatter.exs"),
+        File.regular?(dep_dot_formatter),
+        dep_opts = eval_file_with_keyword_list(dep_dot_formatter),
+        parenless_call <- dep_opts[:export][:locals_without_parens] || [],
+        uniq: true,
+        do: parenless_call
+  end
+
+  defp assert_valid_dep_and_fetch_path(dep, deps_paths) when is_atom(dep) do
+    case Map.fetch(deps_paths, dep) do
+      {:ok, path} ->
+        path
+
+      :error ->
+        Mix.raise(
+          "Found a dependency in :import_deps that the project doesn't depend on: #{inspect(dep)}"
+        )
+    end
+  end
+
+  defp assert_valid_dep_and_fetch_path(dep, _deps_paths) do
+    Mix.raise("Dependencies in :import_deps should be atoms, got: #{inspect(dep)}")
+  end
+
+  defp eval_file_with_keyword_list(path) do
+    {opts, _} = Code.eval_file(path)
+
+    unless Keyword.keyword?(opts) do
+      Mix.raise("Expected #{inspect(path)} to return a keyword list, got: #{inspect(opts)}")
+    end
+
+    opts
+  end
+
   defp expand_args([], formatter_opts) do
     if inputs = formatter_opts[:inputs] do
       expand_files_and_patterns(List.wrap(inputs), ".formatter.exs")

lib/mix/test/mix/tasks/format_test.exs

@@ -5,6 +5,16 @@ defmodule Mix.Tasks.FormatTest do
 
   import ExUnit.CaptureIO
 
+  defmodule FormatWithDepsApp do
+    def project do
+      [
+        app: :format_with_deps,
+        version: "0.1.0",
+        deps: [{:my_dep, "0.1.0", path: "deps/my_dep"}]
+      ]
+    end
+  end
+
   test "formats the given files", context do
     in_tmp context.test, fn ->
       File.write!("a.ex", """
@@ -174,6 +184,59 @@ defmodule Mix.Tasks.FormatTest do
     end
   end
 
+  test "can read exported configuration from dependencies", context do
+    Mix.Project.push(__MODULE__.FormatWithDepsApp)
+
+    in_tmp context.test, fn ->
+      File.write!(".formatter.exs", """
+      [import_deps: [:my_dep]]
+      """)
+
+      File.write!("a.ex", """
+      my_fun :foo, :bar
+      """)
+
+      File.mkdir_p!("deps/my_dep/")
+
+      File.write!("deps/my_dep/.formatter.exs", """
+      [export: [locals_without_parens: [my_fun: 2]]]
+      """)
+
+      Mix.Tasks.Format.run(["a.ex"])
+
+      assert File.read!("a.ex") == """
+             my_fun :foo, :bar
+             """
+
+      manifest_path = Path.join(Mix.Project.manifest_path(), "cached_formatter_deps")
+
+      assert File.regular?(manifest_path)
+
+      # Let's check that the manifest gets updated if it's stale.
+      File.touch!(manifest_path, {{1970, 1, 1}, {0, 0, 0}})
+
+      Mix.Tasks.Format.run(["a.ex"])
+
+      assert File.stat!(manifest_path).mtime > {{1970, 1, 1}, {0, 0, 0}}
+    end
+  end
+
+  test "validates dependencies in :import_deps", context do
+    Mix.Project.push(__MODULE__.FormatWithDepsApp)
+
+    in_tmp context.test, fn ->
+      File.write!(".formatter.exs", """
+      [import_deps: [:nonexistent_dep]]
+      """)
+
+      message =
+        "Found a dependency in :import_deps that the project doesn't " <>
+          "depend on: :nonexistent_dep"
+
+      assert_raise Mix.Error, message, fn -> Mix.Tasks.Format.run([]) end
+    end
+  end
+
   test "raises on invalid arguments", context do
     in_tmp context.test, fn ->
       assert_raise Mix.Error, ~r"Expected one or more files\/patterns to be given", fn ->