From c93a334f48d8d03165d6c0f39ca46f6259b8cb96 Mon Sep 17 00:00:00 2001
From: Edwin Zhang <edwin.zhang@samsara.com>
Date: Sat, 15 Dec 2018 12:17:39 -0800
Subject: [PATCH 1/4] src/options.json: add emitWarningsAsErrors option for
 validation

---
 src/options.json | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/options.json b/src/options.json
index 1141d84a..668a5a95 100644
--- a/src/options.json
+++ b/src/options.json
@@ -40,6 +40,9 @@
     },
     "sourceMap": {
       "type": [ "string", "boolean" ]
+    },
+    "emitWarningsAsErrors": {
+      "type": ["boolean"]
     }
   },
   "errorMessage": {
@@ -50,7 +53,8 @@
       "syntax": "should be {String|Object} (https://github.com/postcss/postcss-loader#syntax)",
       "stringifier": "should be {String|Object} (https://github.com/postcss/postcss-loader#stringifier)",
       "plugins": "should be {Array|Object|Function} (https://github.com/postcss/postcss-loader#plugins)",
-      "sourceMap": "should be {String|Boolean} (https://github.com/postcss/postcss-loader#sourcemap)"
+      "sourceMap": "should be {String|Boolean} (https://github.com/postcss/postcss-loader#sourcemap)",
+      "emitWarningsAsErrors": "should be {Boolean} (https://github.com/postcss/postcss-loader#emitWarningsAsError)"
     }
   },
   "additionalProperties": true

From 823e596fb3718105f301e9d008fa79fdde787c06 Mon Sep 17 00:00:00 2001
From: Edwin Zhang <edwin.zhang@samsara.com>
Date: Sat, 15 Dec 2018 12:18:41 -0800
Subject: [PATCH 2/4] src/index.js: emitError when emitWarningsAsErrors is set

---
 src/index.js | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/index.js b/src/index.js
index bb576c32..30e09f12 100644
--- a/src/index.js
+++ b/src/index.js
@@ -31,6 +31,7 @@ function loader (css, map, meta) {
   const file = this.resourcePath
 
   const sourceMap = options.sourceMap
+  const emitWarningsAsErrors = options.emitWarningsAsErrors
 
   Promise.resolve().then(() => {
     const length = Object.keys(options)
@@ -40,6 +41,7 @@ function loader (css, map, meta) {
           case 'ident':
           case 'config':
           case 'sourceMap':
+          case 'emitWarningsAsErrors':
             return
           default:
             return option
@@ -142,8 +144,9 @@ function loader (css, map, meta) {
       .then((result) => {
         let { css, map, root, processor, messages } = result
 
-        result.warnings().forEach((warning) => {
-          this.emitWarning(new Warning(warning))
+        result.warnings().forEach(warning => {
+          const emit = emitWarningsAsErrors ? this.emitError : this.emitWarning
+          emit(new Warning(warning))
         })
 
         messages.forEach((msg) => {

From 5c960dd08718b7029518aa7aa19e9734cac4975f Mon Sep 17 00:00:00 2001
From: Edwin Zhang <edwin.zhang@samsara.com>
Date: Sat, 15 Dec 2018 12:19:20 -0800
Subject: [PATCH 3/4] test/Warnings.test.js: add test for emitting warnings as
 errors

---
 test/Warnings.test.js                    | 25 ++++++++++++++++++++++++
 test/__snapshots__/Warnings.test.js.snap |  6 ++++++
 2 files changed, 31 insertions(+)

diff --git a/test/Warnings.test.js b/test/Warnings.test.js
index 7c5875b7..e7f3cbb4 100644
--- a/test/Warnings.test.js
+++ b/test/Warnings.test.js
@@ -30,4 +30,29 @@ describe('Warnings', () => {
       expect(message).toMatchSnapshot()
     })
   })
+
+  test('Emit as Error', () => {
+    const config = {
+      loader: {
+        test: /\.css$/,
+        options: {
+          emitWarningsAsErrors: true,
+          plugins: [
+            plugin()
+          ]
+        }
+      }
+    }
+
+    return webpack('css/index.js', config).then((stats) => {
+      const error = stats.compilation.errors[0]
+
+      const message = error.message
+        .split('\n')
+        .slice(1)
+        .join('\n')
+
+      expect(message).toMatchSnapshot()
+    })
+  })
 })
diff --git a/test/__snapshots__/Warnings.test.js.snap b/test/__snapshots__/Warnings.test.js.snap
index 9524418a..407d63c9 100644
--- a/test/__snapshots__/Warnings.test.js.snap
+++ b/test/__snapshots__/Warnings.test.js.snap
@@ -1,5 +1,11 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`Warnings Emit as Error 1`] = `
+"Warning
+
+(1:5) <Message>"
+`;
+
 exports[`Warnings Plugins 1`] = `
 "Warning
 

From 634681ed6e44459ef5df95f09c0d0b905b82ef87 Mon Sep 17 00:00:00 2001
From: Edwin Zhang <edwin.zhang@samsara.com>
Date: Sat, 15 Dec 2018 12:28:17 -0800
Subject: [PATCH 4/4] README: add emitWarningsAsErrors to the readme

---
 README.md | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/README.md b/README.md
index 6b03ad79..f4ada96d 100644
--- a/README.md
+++ b/README.md
@@ -117,6 +117,7 @@ module.exports = {
 |[`config`](#config)|`{Object}`|`undefined`|Set `postcss.config.js` config path && `ctx`|
 |[`plugins`](#plugins)|`{Array\|Function}`|`[]`|Set PostCSS Plugins|
 |[`sourceMap`](#sourcemap)|`{String\|Boolean}`|`false`|Enable Source Maps|
+|[`emitWarningsAsErrors`](#emitwarningsaserrors)|`{Boolean}`|`false`|Emit warnings as errors|
 
 ### `Exec`
 
@@ -305,6 +306,22 @@ within the CSS directly as an annotation comment.
 /*# sourceMappingURL=data:application/json;base64, ... */
 ```
 
+### `EmitWarningsAsErrors`
+
+Enabling `emitWarningsAsErrors` will emit any warnings from postcss plugins at the error level.
+
+**`webpack.config.js`**
+```js
+{
+  test: /\.css$/,
+  use: [
+    ...,
+    { loader: 'postcss-loader', options: { emitWarningsAsErrors: true } }
+  ]
+}
+```
+
+
 <h2 align="center">Examples</h2>
 
 ### `Stylelint`