Added a no-duplicate-switch-case rule

src/rules/noDuplicateSwitchCaseRule.ts

@@ -0,0 +1,66 @@
+/**
+ * @license
+ * Copyright 2017 Palantir Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as ts from "typescript";
+
+import * as Lint from "../index";
+
+export class Rule extends Lint.Rules.AbstractRule {
+    public static metadata: Lint.IRuleMetadata = {
+        description: "Prevents duplicate cases in switch statements.",
+        optionExamples: [true],
+        options: null,
+        optionsDescription: "",
+        ruleName: "no-duplicate-switch-case",
+        type: "functionality",
+        typescriptOnly: false,
+    };
+
+    public static readonly FAILURE_STRING_FACTORY = (text: string) => `Duplicate switch case: '${text}'.`;
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        return this.applyWithFunction(sourceFile, walk);
+    }
+}
+
+function walk(ctx: Lint.WalkContext<void>): void {
+    ts.forEachChild(ctx.sourceFile, function cb(node: ts.Node): void {
+        if (node.kind === ts.SyntaxKind.CaseBlock) {
+            visitCaseBlock(node as ts.CaseBlock);
+        }
+
+        ts.forEachChild(node, cb);
+    });
+
+    function visitCaseBlock(node: ts.CaseBlock): void {
+        const previousCases = new Set<string>();
+
+        for (const clause of node.clauses) {
+            if (clause.kind === ts.SyntaxKind.DefaultClause) {
+                continue;
+            }
+
+            const text = clause.expression.getText(ctx.sourceFile);
+            if (!previousCases.has(text)) {
+                previousCases.add(text);
+                continue;
+            }
+
+            ctx.addFailureAtNode(clause.expression, Rule.FAILURE_STRING_FACTORY(text));
+        }
+    }
+}

test/rules/no-duplicate-switch-case/test.ts.lint

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+const withNumber = (value: number) => {
+    switch (value):
+        case 0:
+            break;
+
+        case 1:
+            break;
+
+        case 0:
+             ~       [error % ("0")]
+        case 1: {
+             ~       [error % ("1")]
+            break;
+        }
+};
+
+class WithString {
+    constructor(param: string) {
+        switch (param) {
+            case "aaa":
+                break;
+
+            case "bbb":
+            case "ccc":
+                break;
+
+            case "bbb":
+                 ~~~~~       [error % ('"bbb"')]
+            case "ddd":
+                switch (param.length) {
+                    case 0:
+                        break;
+
+                    case 0:
+                         ~       [error % ("0")]
+                    case 1:
+                        break;
+
+                    default:
+                        break;
+                }
+
+            case "eee":
+            case "eee":
+                 ~~~~~       [error % ('"eee"')]
+                break;
+
+            case "default":
+                break;
+
+            case 0:
+                break;
+
+            case "1":
+                break;
+
+            default:
+                break;
+        }
+    }
+
+    test(obj: object) {
+        switch (obj) {
+            case undefined:
+                break;
+
+            case null:
+            case Infinity:
+                break;
+
+            case this:
+            case null:
+                 ~~~~       [error % ("null")]
+                break;
+
+            default:
+                break;
+        }
+    }
+}
+
+[error]: Duplicate switch case: '%s'.

test/rules/no-duplicate-switch-case/tslint.json

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+{
+  "rules": {
+    "no-duplicate-switch-case": [true]
+  }
+}