Fix: Corrected notice for invalid (:) plugin names

lib/cli-engine/config-array-factory.js

@@ -802,7 +802,7 @@ class ConfigArrayFactory {
      */
     _loadExtendedPluginConfig(extendName, ctx) {
         const slashIndex = extendName.lastIndexOf("/");
-        const pluginName = extendName.slice("plugin:".length, slashIndex);
+        const pluginName = slashIndex === -1 ? extendName : extendName.slice("plugin:".length, slashIndex);
         const configName = extendName.slice(slashIndex + 1);
 
         if (isFilePath(pluginName)) {
@@ -994,7 +994,7 @@ class ConfigArrayFactory {
             error = resolveError;
             /* istanbul ignore else */
             if (error && error.code === "MODULE_NOT_FOUND") {
-                error.messageTemplate = "plugin-missing";
+                error.messageTemplate = request.indexOf(":") === -1 ? "plugin-missing" : "plugin-invalid";
                 error.messageData = {
                     pluginName: request,
                     resolvePluginsRelativeTo: ctx.pluginBasePath,

lib/shared/naming.js

@@ -43,7 +43,7 @@ function normalizePackageName(name, prefix) {
              */
             normalizedName = normalizedName.replace(/^@([^/]+)\/(.*)$/u, `@$1/${prefix}-$2`);
         }
-    } else if (!normalizedName.startsWith(`${prefix}-`)) {
+    } else if (!normalizedName.startsWith(`${prefix}-`) && normalizedName.indexOf(":") === -1) {
         normalizedName = `${prefix}-${normalizedName}`;
     }
 

messages/plugin-invalid.txt

@@ -0,0 +1,9 @@
+ESLint couldn't find the plugin "<%- pluginName %>".
+
+(The package "<%- pluginName %>" was not found when loaded as a Node module from the directory "<%- resolvePluginsRelativeTo %>".)
+
+It looks like this might not be a valid plugin name. Did you use the name of a preset configuration instead of a plugin?
+
+The plugin "<%- pluginName %>" was referenced from the config file in "<%- importerName %>".
+
+If you still can't figure out the problem, please stop by https://eslint.org/chat to chat with the team.

tests/lib/cli-engine/config-array-factory.js

@@ -1503,6 +1503,24 @@ describe("ConfigArrayFactory", () => {
             }, /Failed to load config "plugin:invalid-config\/bar" to extend from./u);
         });
 
+        it("should throw an error with a message template when a plugin referenced for a plugin config is invalid", () => {
+            try {
+                applyExtends({
+                    extends: "plugin:nonexistent-plugin",
+                    rules: { eqeqeq: 2 }
+                });
+            } catch (err) {
+                assert.strictEqual(err.messageTemplate, "plugin-invalid");
+                assert.deepStrictEqual(err.messageData, {
+                    pluginName: "plugin:nonexistent-plugin",
+                    resolvePluginsRelativeTo: process.cwd(),
+                    importerName: "whatever"
+                });
+                return;
+            }
+            assert.fail("Expected to throw an error");
+        });
+
         it("should throw an error with a message template when a plugin referenced for a plugin config is not found", () => {
             try {
                 applyExtends({

tests/lib/shared/naming.js

@@ -25,7 +25,8 @@ describe("naming", () => {
             ["@z\\foo", "@z/eslint-config-foo"],
             ["@z\\foo\\bar.js", "@z/eslint-config-foo/bar.js"],
             ["@z/eslint-config", "@z/eslint-config"],
-            ["@z/eslint-config-foo", "@z/eslint-config-foo"]
+            ["@z/eslint-config-foo", "@z/eslint-config-foo"],
+            ["plugin:invalid", "plugin:invalid"]
         ], (input, expected) => {
             it(`should return ${expected} when passed ${input}`, () => {
                 const result = naming.normalizePackageName(input, "eslint-config");