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

Author: kdawgwilk

lib/ex_doc/config.ex

@@ -43,7 +43,8 @@ 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()],
@@ -78,6 +79,7 @@ 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()
         }
 end

lib/mix/tasks/docs.ex

@@ -21,6 +21,8 @@ defmodule Mix.Tasks.Docs do
     * `--language` - Specifies the language to annotate the
       EPUB output in valid [BCP 47](https://tools.ietf.org/html/bcp47)
 
+    * `--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.
 
@@ -299,7 +301,8 @@ defmodule Mix.Tasks.Docs do
     canonical: :string,
     formatter: :keep,
     language: :string,
-    output: :string
+    output: :string,
+    warnings_as_errors: :boolean
   ]
 
   @aliases [n: :canonical, f: :formatter, o: :output]