Add --warnings-as-errors flag for non-zero exit code

lib/ex_doc/application.ex

@@ -17,6 +17,11 @@ defmodule ExDoc.Application do
         match?("makeup_" <> _, Atom.to_string(app)),
         do: Application.ensure_all_started(app)
 
-    Supervisor.start_link([ExDoc.Refs], strategy: :one_for_one)
+    children = [
+      ExDoc.Refs,
+      ExDoc.WarningCounter
+    ]
+
+    Supervisor.start_link(children, strategy: :one_for_one)
   end
 end

lib/ex_doc/cli.ex

@@ -29,14 +29,25 @@ defmodule ExDoc.CLI do
           source_ref: :string,
           version: :boolean,
           formatter: :keep,
-          quiet: :boolean
+          quiet: :boolean,
+          warnings_as_errors: :boolean
         ]
       )
 
-    if List.keymember?(opts, :version, 0) do
-      print_version()
-    else
-      generate(args, opts, generator)
+    cond do
+      List.keymember?(opts, :version, 0) ->
+        print_version()
+
+      opts[:warnings_as_errors] == true and ExDoc.WarningCounter.count() > 0 ->
+        IO.puts(
+          :stderr,
+          "Doc generation failed due to warnings while using the --warnings-as-errors option"
+        )
+
+        exit({:shutdown, ExDoc.WarningCounter.count()})
+
+      true ->
+        generate(args, opts, generator)
     end
   end
 
@@ -159,29 +170,30 @@ defmodule ExDoc.CLI do
       ex_doc "Project" "1.0.0" "_build/dev/lib/project/ebin" -c "docs.exs"
 
     Options:
-      PROJECT             Project name
-      VERSION             Version number
-      BEAMS               Path to compiled beam files
-      -n, --canonical     Indicate the preferred URL with rel="canonical" link element
-      -c, --config        Give configuration through a file instead of a command line.
-                          See "Custom config" section below for more information.
-      -f, --formatter     Docs formatter to use (html or epub), default: html and epub
-      -p, --homepage-url  URL to link to for the site name
-          --paths         Prepends the given path to Erlang code path. The path might contain a glob
-                          pattern but in that case, remember to quote it: --paths "_build/dev/lib/*/ebin".
-                          This option can be given multiple times
-          --language      Identify the primary language of the documents, its value must be
-                          a valid [BCP 47](https://tools.ietf.org/html/bcp47) language tag, default: "en"
-      -l, --logo          Path to the image logo of the project (only PNG or JPEG accepted)
-                          The image size will be 64x64 and copied to the assets directory
-      -m, --main          The entry-point page in docs, default: "api-reference"
-          --package       Hex package name
-          --proglang      The project's programming language, default: "elixir"
-          --source-ref    Branch/commit/tag used for source link inference, default: "master"
-      -u, --source-url    URL to the source code
-      -o, --output        Path to output docs, default: "doc"
-      -v, --version       Print ExDoc version
-      -q, --quiet         Only output warnings and errors
+      PROJECT              Project name
+      VERSION              Version number
+      BEAMS                Path to compiled beam files
+      -n, --canonical      Indicate the preferred URL with rel="canonical" link element
+      -c, --config         Give configuration through a file instead of a command line.
+                           See "Custom config" section below for more information.
+      -f, --formatter      Docs formatter to use (html or epub), default: html and epub
+      -p, --homepage-url   URL to link to for the site name
+          --paths          Prepends the given path to Erlang code path. The path might contain a glob
+                           pattern but in that case, remember to quote it: --paths "_build/dev/lib/*/ebin".
+                           This option can be given multiple times
+          --language       Identify the primary language of the documents, its value must be
+                           a valid [BCP 47](https://tools.ietf.org/html/bcp47) language tag, default: "en"
+      -l, --logo           Path to the image logo of the project (only PNG or JPEG accepted)
+                           The image size will be 64x64 and copied to the assets directory
+      -m, --main           The entry-point page in docs, default: "api-reference"
+          --package        Hex package name
+          --proglang       The project's programming language, default: "elixir"
+          --source-ref     Branch/commit/tag used for source link inference, default: "master"
+      -u, --source-url     URL to the source code
+      -o, --output         Path to output docs, default: "doc"
+      -v, --version        Print ExDoc version
+      -q, --quiet          Only output warnings and errors
+      --warnings-as-errors Exit with non-zero status if doc generation has one or more warnings
 
     ## Custom config
 

lib/ex_doc/config.ex

@@ -40,7 +40,8 @@ defmodule ExDoc.Config do
             version: nil,
             authors: nil,
             skip_undefined_reference_warnings_on: [],
-            package: nil
+            package: nil,
+            warnings_as_errors: false
 
   @type t :: %__MODULE__{
           apps: [atom()],
@@ -75,7 +76,8 @@ defmodule ExDoc.Config do
           version: nil | String.t(),
           authors: nil | [String.t()],
           skip_undefined_reference_warnings_on: [String.t()],
-          package: :atom | nil
+          package: :atom | nil,
+          warnings_as_errors: boolean()
         }
 
   @spec build(String.t(), String.t(), Keyword.t()) :: ExDoc.Config.t()

lib/ex_doc/language.ex

@@ -140,6 +140,8 @@ defmodule ExDoc.Language do
   def get(:erlang, _module), do: {:ok, ExDoc.Language.Erlang}
 
   def get(language, module) when is_atom(language) and is_atom(module) do
+    ExDoc.WarningCounter.increment()
+
     IO.warn(
       "skipping module #{module}, reason: unsupported language (#{language})",
       []

lib/ex_doc/markdown/earmark.ex

@@ -48,6 +48,7 @@ defmodule ExDoc.Markdown.Earmark do
   defp print_messages(messages, options) do
     for {severity, line, message} <- messages do
       file = options[:file]
+      ExDoc.WarningCounter.increment()
       IO.warn("#{inspect(__MODULE__)} (#{severity}) #{file}:#{line} #{message}", [])
     end
   end

lib/ex_doc/retriever.ex

@@ -83,6 +83,7 @@ defmodule ExDoc.Retriever do
             docs
 
           {:error, reason} ->
+            ExDoc.WarningCounter.increment()
             IO.warn("skipping module #{inspect(module)}, reason: #{reason}", [])
             false
         end

lib/ex_doc/warning_counter.ex

@@ -0,0 +1,21 @@
+defmodule ExDoc.WarningCounter do
+  @moduledoc false
+
+  use Agent
+
+  def start_link(_opts) do
+    Agent.start_link(fn -> 0 end, name: __MODULE__)
+  end
+
+  def count do
+    Agent.get(__MODULE__, & &1)
+  end
+
+  def increment do
+    Agent.update(__MODULE__, &(&1 + 1))
+  end
+
+  def reset do
+    Agent.update(__MODULE__, fn _ -> 0 end)
+  end
+end

lib/mix/tasks/docs.ex

@@ -24,6 +24,8 @@ defmodule Mix.Tasks.Docs do
 
     * `--open` - open browser window pointed to the documentation
 
+    * `--warnings-as-errors` - Exits with non-zero exit code if any warnings are found
+
   The command line options have higher precedence than the options
   specified in your `mix.exs` file below.
 
@@ -309,7 +311,8 @@ defmodule Mix.Tasks.Docs do
     formatter: :keep,
     language: :string,
     output: :string,
-    open: :boolean
+    open: :boolean,
+    warnings_as_errors: :boolean
   ]
 
   @aliases [n: :canonical, f: :formatter, o: :output]
@@ -363,7 +366,16 @@ defmodule Mix.Tasks.Docs do
         browser_open(index)
       end
 
-      index
+      if options[:warnings_as_errors] == true and ExDoc.WarningCounter.count() > 0 do
+        Mix.shell().info([
+          :red,
+          "Doc generation failed due to warnings while using the --warnings-as-errors option"
+        ])
+
+        exit({:shutdown, ExDoc.WarningCounter.count()})
+      else
+        index
+      end
     end
   end
 

test/ex_doc/cli_test.exs

@@ -35,6 +35,38 @@ defmodule ExDoc.CLITest do
     assert io == "ExDoc v#{ExDoc.version()}\n"
   end
 
+  describe "--warnings-as-errors" do
+    test "exits with code 0 when no warnings" do
+      {[html, epub], _io} = run(["ExDoc", "1.2.3", @ebin, "--warnings-as-errors"])
+
+      assert html ==
+               {"ExDoc", "1.2.3",
+                [formatter: "html", apps: [:ex_doc], source_beam: @ebin, warnings_as_errors: true]}
+
+      assert epub ==
+               {"ExDoc", "1.2.3",
+                [formatter: "epub", apps: [:ex_doc], source_beam: @ebin, warnings_as_errors: true]}
+    end
+
+    test "exits with 1 with warnings" do
+      ExDoc.WarningCounter.increment()
+
+      fun = fn ->
+        run(["ExDoc", "1.2.3", @ebin, "--warnings-as-errors"])
+      end
+
+      io =
+        capture_io(:stderr, fn ->
+          assert catch_exit(fun.()) == {:shutdown, 1}
+        end)
+
+      assert io =~
+               "Doc generation failed due to warnings while using the --warnings-as-errors option\n"
+    after
+      ExDoc.WarningCounter.reset()
+    end
+  end
+
   test "too many arguments" do
     assert catch_exit(run(["ExDoc", "1.2.3", "/", "kaboom"])) == {:shutdown, 1}
   end

test/mix/tasks/docs_test.exs

@@ -181,4 +181,10 @@ defmodule Mix.Tasks.DocsTest do
       ] = run([], app: :umbrella, apps_path: "apps/", docs: [ignore_apps: [:foo]])
     end)
   end
+
+  test "accepts warnings_as_errors in :warnings_as_errors" do
+    assert catch_exit(run([], app: :ex_doc, docs: [warnings_as_errors: true])) == {:shutdown, 1}
+  after
+    ExDoc.WarningCounter.reset()
+  end
 end