Implement static-this rule (#4428)

src/configs/all.ts

@@ -141,6 +141,7 @@ export const rules = {
     "prefer-conditional-expression": true,
     radix: true,
     "restrict-plus-operands": true,
+    "static-this": true,
     "strict-boolean-expressions": true,
     "strict-type-predicates": true,
     "switch-default": true,

src/rules/staticThisRule.ts

@@ -0,0 +1,91 @@
+/**
+ * @license
+ * Copyright 2019 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 utils from "tsutils";
+import * as ts from "typescript";
+
+import * as Lint from "../index";
+
+export class Rule extends Lint.Rules.AbstractRule {
+    /* tslint:disable:object-literal-sort-keys */
+    public static metadata: Lint.IRuleMetadata = {
+        ruleName: "static-this",
+        description: "Ban the use of `this` in static methods.",
+        options: null,
+        optionsDescription: "",
+        optionExamples: [true],
+        type: "functionality",
+        typescriptOnly: false,
+    };
+    /* tslint:enable:object-literal-sort-keys */
+
+    public static FAILURE_STRING = "Unallowed `this` usage in static context";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        return this.applyWithWalker(new StaticThisWalker(sourceFile, this.getOptions()));
+    }
+}
+
+const enum ParentType {
+    None,
+    Class,
+    ClassEntity,
+}
+
+class StaticThisWalker extends Lint.RuleWalker {
+    public walk(sourceFile: ts.SourceFile) {
+        let currentParent: ParentType = ParentType.None;
+
+        const cb = (node: ts.Node): void => {
+            const originalParent = currentParent;
+
+            switch (node.kind) {
+                case ts.SyntaxKind.ClassDeclaration:
+                case ts.SyntaxKind.ClassExpression:
+                    currentParent = ParentType.Class;
+                    ts.forEachChild(node, cb);
+                    currentParent = originalParent;
+                    return;
+
+                case ts.SyntaxKind.MethodDeclaration:
+                case ts.SyntaxKind.GetAccessor:
+                case ts.SyntaxKind.SetAccessor:
+                case ts.SyntaxKind.PropertyDeclaration:
+                case ts.SyntaxKind.FunctionDeclaration:
+                case ts.SyntaxKind.FunctionExpression:
+                    if (
+                        ParentType.Class === currentParent &&
+                        utils.hasModifier(node.modifiers, ts.SyntaxKind.StaticKeyword)
+                    ) {
+                        currentParent = ParentType.ClassEntity;
+                        ts.forEachChild(node, cb);
+                        currentParent = originalParent;
+                    }
+                    return;
+
+                case ts.SyntaxKind.ThisKeyword:
+                    if (ParentType.ClassEntity === currentParent) {
+                        return this.addFailureAtNode(node, Rule.FAILURE_STRING);
+                    }
+            }
+
+            ts.forEachChild(node, cb);
+        };
+
+        return ts.forEachChild(sourceFile, cb);
+    }
+}

test/rules/static-this/test.ts.lint

@@ -0,0 +1,14 @@
+class StaticThis {
+    static const staticValue = this.value;
+                               ~~~~ [Unallowed `this` usage in static context]
+    static getInstance() {
+        return this;
+               ~~~~ [Unallowed `this` usage in static context]
+    }
+
+    const value = 5;
+
+    getValue() {
+        return this.value;
+    }
+}

test/rules/static-this/tslint.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "static-this": 1
+  }
+}