add max-switch-cases rule (#77)

Author: andrea-guarino-sonarsource

README.md

@@ -23,6 +23,7 @@ Rules in this category aim to find places in code which have a high chance to be
 Code Smells, or maintainability issues, are raised for places of code which might be costly to change in the future. These rules also help to keep the high code quality and readability. And finally some rules report issues on different suspicious code patters.
 
 * Cognitive Complexity of functions should not be too high ([`cognitive-complexity`])
+* "switch" statements should not have too many "case" clauses ([`max-switch-cases`])
 * Two branches in a conditional structure should not have exactly the same implementation ([`no-duplicated-branches`])
 * Functions should not have identical implementations ([`no-identical-functions`])
 * Boolean checks should not be inverted ([`no-inverted-boolean-check`])
@@ -34,6 +35,7 @@ Code Smells, or maintainability issues, are raised for places of code which migh
 * A "while" loop should be used instead of a "for" loop ([`prefer-while`]) (:wrench: *fixable*) 
 
 [`cognitive-complexity`]: ./docs/rules/cognitive-complexity.md
+[`max-switch-cases`]: ./docs/rules/max-switch-cases.md
 [`no-all-duplicated-branches`]: ./docs/rules/no-all-duplicated-branches.md
 [`no-duplicated-branches`]: ./docs/rules/no-duplicated-branches.md
 [`no-element-overwrite`]: ./docs/rules/no-element-overwrite.md

docs/rules/max-switch-cases.md

@@ -0,0 +1,13 @@
+## max-switch-cases
+
+When `switch` statements have large sets of `case` clauses, it is usually an attempt to map two sets of data. A real map structure would be more readable and maintainable, and should be used instead.
+
+#Options
+
+This rule has a numeric option (defaulted to 30) to specify the maximum number of switch cases.
+
+```
+{
+  "max-switch-cases": ["error", 10]
+}
+```

ruling/snapshots/max-switch-cases

@@ -0,0 +1,2 @@
+src/create-react-app/packages/react-scripts/fixtures/kitchensink/src/App.js: 53
+src/three.js/src/loaders/Loader.js: 175

src/index.ts

@@ -21,6 +21,7 @@ import { Linter } from "eslint";
 
 const sonarjsRules: [string, Linter.RuleLevel][] = [
   ["cognitive-complexity", "error"],
+  ["max-switch-cases", "error"],
   ["no-all-duplicated-branches", "error"],
   ["no-duplicated-branches", "error"],
   ["no-element-overwrite", "error"],

src/rules/max-switch-cases.ts

@@ -0,0 +1,65 @@
+/*
+ * eslint-plugin-sonarjs
+ * Copyright (C) 2018 SonarSource SA
+ * mailto:info AT sonarsource DOT com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+// https://jira.sonarsource.com/browse/RSPEC-1479
+
+import { Rule } from "eslint";
+import { Node, SwitchStatement, SwitchCase } from "estree";
+
+const MESSAGE = "Reduce the number of non-empty switch cases from {{numSwitchCases}} to at most {{maxSwitchCases}}.";
+
+const DEFAULT_MAX_SWITCH_CASES = 30;
+let maxSwitchCases = DEFAULT_MAX_SWITCH_CASES;
+
+const rule: Rule.RuleModule = {
+  meta: {
+    schema: [
+      {
+        type: "integer",
+        minimum: 0,
+      },
+    ],
+  },
+  create(context: Rule.RuleContext) {
+    if (context.options.length > 0) {
+      maxSwitchCases = context.options[0];
+    }
+    return { SwitchStatement: (node: Node) => visitSwitchStatement(node as SwitchStatement, context) };
+  },
+};
+
+function visitSwitchStatement(switchStatement: SwitchStatement, context: Rule.RuleContext) {
+  const nonEmptyCases = switchStatement.cases.filter(
+    switchCase => switchCase.consequent.length > 0 && !isDefaultCase(switchCase),
+  );
+  if (nonEmptyCases.length > maxSwitchCases) {
+    const switchKeyword = context.getSourceCode().getFirstToken(switchStatement);
+    context.report({
+      message: MESSAGE,
+      loc: switchKeyword!.loc,
+      data: { numSwitchCases: nonEmptyCases.length + "", maxSwitchCases: maxSwitchCases + "" },
+    });
+  }
+}
+
+function isDefaultCase(switchCase: SwitchCase) {
+  return switchCase.test === null;
+}
+
+export = rule;

tests/rules/max-switch-cases.test.ts

@@ -0,0 +1,87 @@
+/*
+ * eslint-plugin-sonarjs
+ * Copyright (C) 2018 SonarSource SA
+ * mailto:info AT sonarsource DOT com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+import { RuleTester } from "eslint";
+
+const ruleTester = new RuleTester({ parserOptions: { ecmaVersion: 2018 } });
+import rule = require("../../src/rules/max-switch-cases");
+
+ruleTester.run("max-switch-cases", rule, {
+  valid: [
+    {
+      code: `switch(i) {
+      case 1:
+        f();
+      case 2:
+        g();
+    }`,
+    },
+    // default branch is excluded
+    {
+      code: `switch(i) {
+      case 1:
+        f();
+      case 2:
+        g();
+      default:
+        console.log("foo");
+    }`,
+      options: [2],
+    },
+    // empty branches are not counted
+    {
+      code: `switch(i) {
+      case 1:
+      case 2:
+        g();
+      case 3:
+        console.log("foo");
+    }`,
+      options: [2],
+    },
+    // empty switch statement
+    {
+      code: `switch(i) {}`,
+    },
+  ],
+  invalid: [
+    {
+      code: `switch(i) {
+        case 1:
+          f();
+        case 2:
+          g();
+      }`,
+      options: [1],
+      errors: [
+        {
+          message: message(2, 1),
+          line: 1,
+          endLine: 1,
+          column: 1,
+          endColumn: 7,
+        },
+      ],
+    },
+  ],
+});
+
+function message(numSwitchCases: number, maxSwitchCases: number) {
+  return `Reduce the number of non-empty switch cases from ${numSwitchCases} to at most ${maxSwitchCases}.`;
+}