feat: add fallback if custom getLocalIdent returns null

README.md

@@ -848,6 +848,8 @@ Default: `undefined`
 
 Allows to specify a function to generate the classname.
 By default we use built-in function to generate a classname.
+If the custom function returns `null` or `undefined`, we fall back to the
+built-in function to generate the classname.
 
 **webpack.config.js**
 
@@ -1245,7 +1247,7 @@ module.exports = {
 
 ### 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 `compileType` 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.  
+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 `compileType` 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.
 Meanwhile all files matching `*.module.scss` are treated as `CSS Modules` in this example.
 
 An example case is assumed where a project requires canvas drawing variables to be synchronized with CSS - canvas drawing uses the same color (set by color name in JavaScript) as HTML background (set by class name in CSS).

src/utils.js

@@ -283,11 +283,32 @@ function getModulesPlugins(options, loaderContext) {
       extractImports(),
       modulesScope({
         generateScopedName(exportName) {
-          return getLocalIdent(loaderContext, localIdentName, exportName, {
-            context: localIdentContext,
-            hashPrefix: localIdentHashPrefix,
-            regExp: localIdentRegExp,
-          });
+          let localIdent = getLocalIdent(
+            loaderContext,
+            localIdentName,
+            exportName,
+            {
+              context: localIdentContext,
+              hashPrefix: localIdentHashPrefix,
+              regExp: localIdentRegExp,
+            }
+          );
+
+          // A null/undefined value signals that we should invoke the default
+          // getLocalIdent method.
+          if (localIdent == null && getLocalIdent !== defaultGetLocalIdent) {
+            localIdent = defaultGetLocalIdent(
+              loaderContext,
+              localIdentName,
+              exportName,
+              {
+                context: localIdentContext,
+                hashPrefix: localIdentHashPrefix,
+                regExp: localIdentRegExp,
+              }
+            );
+          }
+          return localIdent;
         },
         exportGlobals: options.modules.exportGlobals,
       }),

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

@@ -487,6 +487,49 @@ exports[`"modules" option issue #1063: result 1`] = `
 
 exports[`"modules" option issue #1063: warnings 1`] = `Array []`;
 
+exports[`"modules" option issue #1191 - fallback to default getLocalIdent: errors 1`] = `Array []`;
+
+exports[`"modules" option issue #1191 - fallback to default getLocalIdent: module 1`] = `
+"// Imports
+import ___CSS_LOADER_API_IMPORT___ from \\"../../../../src/runtime/api.js\\";
+var ___CSS_LOADER_EXPORT___ = ___CSS_LOADER_API_IMPORT___(false);
+// Module
+___CSS_LOADER_EXPORT___.push([module.id, \\".some-class {\\\\n  color: red;\\\\n}\\\\n\\", \\"\\"]);
+// Exports
+___CSS_LOADER_EXPORT___.locals = {
+	\\"some-class\\": \\"some-class\\"
+};
+export default ___CSS_LOADER_EXPORT___;
+"
+`;
+
+exports[`"modules" option issue #1191 - fallback to default getLocalIdent: result 1`] = `
+Object {
+  "css1": Array [
+    Array [
+      "./modules/issue-1191/issue-1191.css",
+      ".some-class {
+  color: red;
+}
+",
+      "",
+    ],
+  ],
+  "css2": Array [
+    Array [
+      "./modules/issue-1191/issue-1191-custom.css",
+      ".custom-some-class {
+  color: red;
+}
+",
+      "",
+    ],
+  ],
+}
+`;
+
+exports[`"modules" option issue #1191 - fallback to default getLocalIdent: warnings 1`] = `Array []`;
+
 exports[`"modules" option should avoid unnecessary "require": errors 1`] = `Array []`;
 
 exports[`"modules" option should avoid unnecessary "require": module 1`] = `

test/fixtures/modules/issue-1191/issue-1191-custom.css

@@ -0,0 +1,3 @@
+.some-class {
+  color: red;
+}

test/fixtures/modules/issue-1191/issue-1191.css

@@ -0,0 +1,3 @@
+.some-class {
+  color: red;
+}

test/fixtures/modules/issue-1191/issue-1191.js

@@ -0,0 +1,8 @@
+import css1 from './issue-1191.css';
+import css2 from './issue-1191-custom.css';
+
+const wrapper = { css1, css2 }
+
+__export__ = wrapper;
+
+export default wrapper;

test/modules-option.test.js

@@ -657,6 +657,28 @@ describe('"modules" option', () => {
     expect(getErrors(stats)).toMatchSnapshot('errors');
   });
 
+  it('issue #1191 - fallback to default getLocalIdent', async () => {
+    const compiler = getCompiler('./modules/issue-1191/issue-1191.js', {
+      modules: {
+        getLocalIdent: (ctx, localIdentName, localName) =>
+          ctx.resourcePath.includes('custom') ? `custom-${localName}` : null,
+        localIdentName: '[local]',
+      },
+    });
+    const stats = await compile(compiler);
+
+    expect(
+      getModuleSource('./modules/issue-1191/issue-1191.css', stats)
+    ).toMatchSnapshot('module');
+
+    expect(getExecutedCode('main.bundle.js', compiler, stats)).toMatchSnapshot(
+      'result'
+    );
+
+    expect(getWarnings(stats)).toMatchSnapshot('warnings');
+    expect(getErrors(stats)).toMatchSnapshot('errors');
+  });
+
   it('should work with the `exportGlobals` option (the `mode` option is `global`)', async () => {
     const compiler = getCompiler(
       './modules/exportGlobals-global/exportGlobals.js',