fix: emit warnings on broken @import

lib/Warning.js

@@ -0,0 +1,20 @@
+module.exports = class Warning extends Error {
+  constructor(warning) {
+    super(warning);
+    const { text, line, column } = warning;
+    this.name = 'Warning';
+
+    // Based on https://github.com/postcss/postcss/blob/master/lib/warning.es6#L74
+    // We don't need `plugin` properties.
+    this.message = `${this.name}\n\n`;
+
+    if (typeof line !== 'undefined') {
+      this.message += `(${line}:${column}) `;
+    }
+
+    this.message += `${text}`;
+
+    // We don't need stack https://github.com/postcss/postcss/blob/master/docs/guidelines/runner.md#31-dont-show-js-stack-for-csssyntaxerror
+    this.stack = false;
+  }
+};

lib/postcss-css-loader-parser.js

@@ -63,6 +63,10 @@ module.exports = postcss.plugin(
         }
 
         if (!url.replace(/\s/g, '').length) {
+          result.warn(`Unable to find uri in '${atrule.toString()}'`, {
+            node: atrule,
+          });
+
           return;
         }
 

lib/processCss.js

@@ -12,6 +12,7 @@ const modulesValues = require('postcss-modules-values');
 
 const cssLoaderParser = require('./postcss-css-loader-parser');
 
+const Warning = require('./Warning');
 const CssSyntaxError = require('./CssSyntaxError');
 const { getLocalIdent } = require('./utils');
 
@@ -83,6 +84,12 @@ module.exports = function processCss(inputSource, inputMap, options, callback) {
         : null,
     })
     .then((result) => {
+      result
+        .warnings()
+        .forEach((warning) =>
+          options.loaderContext.emitWarning(new Warning(warning))
+        );
+
       callback(null, {
         source: result.css,
         map: result.map && result.map.toJSON(),

test/__snapshots__/import-option.test.js.snap

@@ -240,4 +240,64 @@ exports.push([module.id, \\"@import URL(test.css);\\\\n@import url();\\\\n@impor
 "
 `;
 
-exports[`import option true: warnings 1`] = `Array []`;
+exports[`import option true: warnings 1`] = `
+Array [
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(12:1) Unable to find uri in '@import url()'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(13:1) Unable to find uri in '@import url('')'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(14:1) Unable to find uri in '@import url(\\"\\")'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(17:1) Unable to find uri in '@import '''",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(18:1) Unable to find uri in '@import \\"\\"'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(19:1) Unable to find uri in '@import \\"   \\"'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(20:1) Unable to find uri in '@import \\"
+\\"'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(22:1) Unable to find uri in '@import url()'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(23:1) Unable to find uri in '@import url('')'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(24:1) Unable to find uri in '@import url(\\"\\")'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(37:1) Unable to find uri in '@import '",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(38:1) Unable to find uri in '@import foo-bar'",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(40:1) It looks like you didn't end your @import statement correctly. Child nodes are attached to it.",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(5:1) Unable to find uri in '@import URL(test.css)'",
+]
+`;

test/__snapshots__/loader.test.js.snap

@@ -392,7 +392,7 @@ exports[`loader should compile with empty css entry point: warnings 1`] = `Array
 
 exports[`loader should throw error on invalid css syntax: errors 1`] = `
 Array [
-  [ModuleBuildError: Module build failed (from \`replaced original path\`):
+  "ModuleBuildError: Module build failed (from \`replaced original path\`):
 CssSyntaxError
 
 (2:3) Unknown word
@@ -402,7 +402,7 @@ CssSyntaxError
     |   ^
   3 | }
   4 | 
-],
+",
 ]
 `;
 

test/helpers.js

@@ -308,12 +308,11 @@ exports.evaluated = evaluated;
 
 function normalizeErrors(errors) {
   return errors.map((error) => {
-    // eslint-disable-next-line no-param-reassign
-    error.message = stripAnsi(error.message)
+    const message = error.toString();
+
+    return stripAnsi(message)
       .replace(/\(from .*?\)/, '(from `replaced original path`)')
       .replace(/at(.*?)\(.*?\)/g, 'at$1(`replaced original path`)');
-
-    return error;
   });
 }
 

test/import-option.test.js

@@ -1,4 +1,4 @@
-const { webpack, evaluated } = require('./helpers');
+const { webpack, evaluated, normalizeErrors } = require('./helpers');
 
 describe('import option', () => {
   it('true', async () => {
@@ -11,8 +11,10 @@ describe('import option', () => {
     expect(evaluated(module.source, modules)).toMatchSnapshot(
       'module (evaluated)'
     );
-    expect(stats.compilation.warnings).toMatchSnapshot('warnings');
-    expect(stats.compilation.errors).toMatchSnapshot('errors');
+    expect(normalizeErrors(stats.compilation.warnings)).toMatchSnapshot(
+      'warnings'
+    );
+    expect(normalizeErrors(stats.compilation.errors)).toMatchSnapshot('errors');
   });
 
   it('false', async () => {