fix: respect errors and warnings from minimizer without code

src/index.js

@@ -622,7 +622,7 @@ class CssMinimizerPlugin {
                 innerSourceMap,
                 true,
               );
-            } else {
+            } else if (item.code) {
               output.source = new RawSource(item.code);
             }
           }
@@ -632,7 +632,7 @@ class CssMinimizerPlugin {
               inputSourceMap && CssMinimizerPlugin.isSourceMap(inputSourceMap);
 
             for (const error of result.errors) {
-              output.warnings.push(
+              output.errors.push(
                 CssMinimizerPlugin.buildError(
                   error,
                   name,
@@ -691,6 +691,10 @@ class CssMinimizerPlugin {
           }
         }
 
+        if (!output.source) {
+          return;
+        }
+
         const newInfo = { minimized: true };
         const { source } = output;
 

src/minify.js

@@ -34,8 +34,10 @@ async function minify(options) {
     );
 
     if (typeof minifyResult.code !== "string") {
-      throw new Error(
-        "minimizer function doesn't return the 'code' property or result is not a string value",
+      result.errors.push(
+        new Error(
+          "minimizer function doesn't return the 'code' property or result is not a string value",
+        ),
       );
     }
 

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

@@ -1,19 +1,58 @@
 // Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
 
+exports[`"minify" option should work and allow to return errors and warnings from custom function without code: assets 1`] = `
+{
+  "foo.css": "body {
+  font-weight: bold;
+}
+
+body {
+  color: red;
+}
+body a {
+  text-align: center;
+}
+",
+}
+`;
+
+exports[`"minify" option should work and allow to return errors and warnings from custom function without code: error 1`] = `
+[
+  "Error: foo.css from Css Minimizer plugin
+Error 1",
+  "Error: foo.css from Css Minimizer plugin
+Error: Error 2",
+  "Error: foo.css from Css Minimizer plugin
+Error: minimizer function doesn't return the 'code' property or result is not a string value",
+]
+`;
+
+exports[`"minify" option should work and allow to return errors and warnings from custom function without code: warning 1`] = `
+[
+  "Warning: foo.css from Css Minimizer plugin
+Warning 1",
+  "Warning: foo.css from Css Minimizer plugin
+Warning 2",
+]
+`;
+
 exports[`"minify" option should work and allow to return errors and warnings from custom function: assets 1`] = `
 {
   "foo.css": ".test { color: red; }",
 }
 `;
 
-exports[`"minify" option should work and allow to return errors and warnings from custom function: error 1`] = `[]`;
-
-exports[`"minify" option should work and allow to return errors and warnings from custom function: warning 1`] = `
+exports[`"minify" option should work and allow to return errors and warnings from custom function: error 1`] = `
 [
   "Error: foo.css from Css Minimizer plugin
 Error 1",
   "Error: foo.css from Css Minimizer plugin
 Error: Error 2",
+]
+`;
+
+exports[`"minify" option should work and allow to return errors and warnings from custom function: warning 1`] = `
+[
   "Warning: foo.css from Css Minimizer plugin
 Warning 1",
   "Warning: foo.css from Css Minimizer plugin
@@ -471,7 +510,15 @@ exports[`"minify" option should work with "csso" minifier: warning 1`] = `[]`;
 
 exports[`"minify" option should work with empty code: assets 1`] = `
 {
-  "foo.css": "",
+  "foo.css": "body {
+  color: red;
+}
+a {
+  color: blue;
+}
+
+/*# sourceMappingURL=foo.css.map*/",
+  "foo.css.map": "{"version":3,"file":"foo.css","mappings":"AAAA;EACE,UAAU;AACZ;AACA;EACE,WAAW;AACb,C","sources":["webpack:///./foo.css"],"sourcesContent":["body {\\n  color: red;\\n}\\na {\\n  color: blue;\\n}"],"names":[],"sourceRoot":""}",
 }
 `;
 

test/minify-option.test.js

@@ -1293,4 +1293,39 @@ describe('"minify" option', () => {
     expect(getErrors(stats)).toMatchSnapshot("error");
     expect(getWarnings(stats)).toMatchSnapshot("warning");
   });
+
+  it("should work and allow to return errors and warnings from custom function without code", async () => {
+    const compiler = getCompiler({
+      entry: {
+        foo: path.join(__dirname, "fixtures", "sourcemap", "foo.scss"),
+      },
+      module: {
+        rules: [
+          {
+            test: /.s?css$/i,
+            use: [
+              MiniCssExtractPlugin.loader,
+              { loader: "css-loader", options: { sourceMap: true } },
+              { loader: "sass-loader", options: { sourceMap: true } },
+            ],
+          },
+        ],
+      },
+    });
+
+    new CssMinimizerPlugin({
+      minify: async () => ({
+        warnings: ["Warning 1", new Error("Warning 2")],
+        errors: ["Error 1", new Error("Error 2")],
+      }),
+    }).apply(compiler);
+
+    const stats = await compile(compiler);
+
+    expect(readAssets(compiler, stats, /\.css(\.map)?$/)).toMatchSnapshot(
+      "assets",
+    );
+    expect(getErrors(stats)).toMatchSnapshot("error");
+    expect(getWarnings(stats)).toMatchSnapshot("warning");
+  });
 });