feat: allow the exportLocalsConvention option can be a function useful for named export (#1351)

Author: cap-Bernardito

README.md

@@ -1031,6 +1031,9 @@ module.exports = {
 };
 ```
 
+To set a custom name for namedExport, can use [`exportLocalsConvention`](#exportLocalsConvention) option as a function.
+Example below in the [`examples`](#examples) section.
+
 ##### `exportGlobals`
 
 Type: `Boolean`
@@ -1060,11 +1063,13 @@ module.exports = {
 
 ##### `exportLocalsConvention`
 
-Type: `String`
+Type: `String|Function`
 Default: based on the `modules.namedExport` option value, if `true` - `camelCaseOnly`, otherwise `asIs`
 
 Style of exported class names.
 
+###### `String`
+
 By default, the exported JSON keys mirror the class names (i.e `asIs` value).
 
 > ⚠ Only `camelCaseOnly` value allowed if you set the `namedExport` value to `true`.
@@ -1110,6 +1115,58 @@ module.exports = {
 };
 ```
 
+###### `Function`
+
+**webpack.config.js**
+
+```js
+module.exports = {
+  module: {
+    rules: [
+      {
+        test: /\.css$/i,
+        loader: "css-loader",
+        options: {
+          modules: {
+            exportLocalsConvention: function (name) {
+              return name.replace(/-/g, "_");
+            },
+          },
+        },
+      },
+    ],
+  },
+};
+```
+
+**webpack.config.js**
+
+```js
+module.exports = {
+  module: {
+    rules: [
+      {
+        test: /\.css$/i,
+        loader: "css-loader",
+        options: {
+          modules: {
+            exportLocalsConvention: function (name) {
+              return [
+                name.replace(/-/g, "_"),
+                // dashesCamelCase
+                name.replace(/-+(\w)/g, (match, firstLetter) =>
+                  firstLetter.toUpperCase()
+                ),
+              ];
+            },
+          },
+        },
+      },
+    ],
+  },
+};
+```
+
 ##### `exportOnlyLocals`
 
 Type: `Boolean`
@@ -1434,6 +1491,31 @@ module.exports = {
 };
 ```
 
+### Named export with custom export names
+
+**webpack.config.js**
+
+```js
+module.exports = {
+  module: {
+    rules: [
+      {
+        test: /\.css$/i,
+        loader: "css-loader",
+        options: {
+          modules: {
+            namedExport: true,
+            exportLocalsConvention: function (name) {
+              return name.replace(/-/g, "_");
+            },
+          },
+        },
+      },
+    ],
+  },
+};
+```
+
 ### Separating `Interoperable CSS`-only and `CSS Module` features
 
 The following setup is an example of allowing `Interoperable CSS` features only (such as `:import` and `:export`) without using further `CSS Module` functionality by setting `mode` option for all files that do not match `*.module.scss` naming convention. This is for reference as having `ICSS` features applied to all files was default `css-loader` behavior before v4.

src/index.js

@@ -216,7 +216,17 @@ export default async function loader(content, map, meta) {
   }
 
   const importCode = getImportCode(imports, options);
-  const moduleCode = getModuleCode(result, api, replacements, options, this);
+
+  let moduleCode;
+
+  try {
+    moduleCode = getModuleCode(result, api, replacements, options, this);
+  } catch (error) {
+    callback(error);
+
+    return;
+  }
+
   const exportCode = getExportCode(
     exports,
     replacements,

src/options.json

@@ -145,12 +145,19 @@
             "exportLocalsConvention": {
               "description": "Style of exported classnames.",
               "link": "https://github.com/webpack-contrib/css-loader#localsconvention",
-              "enum": [
-                "asIs",
-                "camelCase",
-                "camelCaseOnly",
-                "dashes",
-                "dashesOnly"
+              "anyOf": [
+                {
+                  "enum": [
+                    "asIs",
+                    "camelCase",
+                    "camelCaseOnly",
+                    "dashes",
+                    "dashesOnly"
+                  ]
+                },
+                {
+                  "instanceof": "Function"
+                }
               ]
             },
             "exportOnlyLocals": {

src/utils.js

@@ -485,6 +485,12 @@ function getFilter(filter, resourcePath) {
 }
 
 function getValidLocalName(localName, exportLocalsConvention) {
+  if (typeof exportLocalsConvention === "function") {
+    const result = exportLocalsConvention(localName);
+
+    return Array.isArray(result) ? result[0] : result;
+  }
+
   if (exportLocalsConvention === "dashesOnly") {
     return dashesCamelCase(localName);
   }
@@ -588,6 +594,7 @@ function getModulesOptions(rawOptions, loaderContext) {
     }
 
     if (
+      typeof modulesOptions.exportLocalsConvention === "string" &&
       modulesOptions.exportLocalsConvention !== "camelCaseOnly" &&
       modulesOptions.exportLocalsConvention !== "dashesOnly"
     ) {
@@ -957,42 +964,50 @@ function getExportCode(exports, replacements, needToUseIcssPlugin, options) {
 
   let localsCode = "";
 
-  const addExportToLocalsCode = (name, value) => {
-    if (options.modules.namedExport) {
-      localsCode += `export var ${name} = ${JSON.stringify(value)};\n`;
-    } else {
-      if (localsCode) {
-        localsCode += `,\n`;
-      }
+  const addExportToLocalsCode = (names, value) => {
+    const normalizedNames = Array.isArray(names)
+      ? new Set(names)
+      : new Set([names]);
 
-      localsCode += `\t${JSON.stringify(name)}: ${JSON.stringify(value)}`;
+    for (const name of normalizedNames) {
+      if (options.modules.namedExport) {
+        localsCode += `export var ${name} = ${JSON.stringify(value)};\n`;
+      } else {
+        if (localsCode) {
+          localsCode += `,\n`;
+        }
+
+        localsCode += `\t${JSON.stringify(name)}: ${JSON.stringify(value)}`;
+      }
     }
   };
 
   for (const { name, value } of exports) {
+    if (typeof options.modules.exportLocalsConvention === "function") {
+      addExportToLocalsCode(
+        options.modules.exportLocalsConvention(name),
+        value
+      );
+
+      // eslint-disable-next-line no-continue
+      continue;
+    }
+
     switch (options.modules.exportLocalsConvention) {
       case "camelCase": {
-        addExportToLocalsCode(name, value);
-
         const modifiedName = camelCase(name);
 
-        if (modifiedName !== name) {
-          addExportToLocalsCode(modifiedName, value);
-        }
+        addExportToLocalsCode([name, modifiedName], value);
         break;
       }
       case "camelCaseOnly": {
         addExportToLocalsCode(camelCase(name), value);
         break;
       }
       case "dashes": {
-        addExportToLocalsCode(name, value);
-
         const modifiedName = dashesCamelCase(name);
 
-        if (modifiedName !== name) {
-          addExportToLocalsCode(modifiedName, value);
-        }
+        addExportToLocalsCode([name, modifiedName], value);
         break;
       }
       case "dashesOnly": {