New rule: static-this (#4475)

src/configs/all.ts

@@ -145,6 +145,7 @@ 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/language/rule/rule.ts

@@ -166,7 +166,7 @@ export interface ReplacementJson {
 }
 export class Replacement {
     public static applyFixes(content: string, fixes: Fix[]): string {
-        return this.applyAll(content, flatMap(fixes, arrayify));
+        return Replacement.applyAll(content, flatMap(fixes, arrayify));
     }
 
     public static applyAll(content: string, replacements: Replacement[]) {
@@ -180,7 +180,7 @@ export class Replacement {
         text: string,
         sourceFile?: ts.SourceFile,
     ): Replacement {
-        return this.replaceFromTo(node.getStart(sourceFile), node.getEnd(), text);
+        return Replacement.replaceFromTo(node.getStart(sourceFile), node.getEnd(), text);
     }
 
     public static replaceFromTo(start: number, end: number, text: string) {

src/rules/code-examples/staticThis.examples.ts

@@ -0,0 +1,50 @@
+/**
+ * @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 Lint from "../../index";
+
+// tslint:disable: object-literal-sort-keys
+export const codeExamples = [
+    {
+        description: "Disallows the `this` keyword usage in static context.",
+        config: Lint.Utils.dedent`
+            "rules": { "static-this": true }
+        `,
+        pass: Lint.Utils.dedent`
+            class Pass {
+                static getName() {
+                    return 'name'
+                }
+
+                static getFullname() {
+                    return \`full \${Pass.getName()}\`
+                }
+            }
+        `,
+        fail: Lint.Utils.dedent`
+            class Fail {
+                static getName() {
+                    return 'name'
+                }
+
+                static getFullname() {
+                    return \`full \${this.getName()}\`
+                }
+            }
+       `,
+    },
+];

src/rules/staticThisRule.ts

@@ -0,0 +1,84 @@
+/**
+ * @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";
+import { Replacement } from "../language/rule/rule";
+
+import { codeExamples } from "./code-examples/staticThis.examples";
+
+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.",
+        hasFix: true,
+        options: null,
+        optionsDescription: "",
+        optionExamples: [true],
+        /* tslint:disable:max-line-length */
+        rationale: Lint.Utils.dedent`
+            Static \`this\` usage can be confusing for newcomers.
+            It can also become imprecise when used with extended classes when a static \`this\` of a parent class no longer specifically refers to the parent class.
+        `,
+        /* tslint:enable:max-line-length */
+        type: "functionality",
+        typescriptOnly: false,
+        codeExamples,
+    };
+    /* tslint:enable:object-literal-sort-keys */
+
+    public static FAILURE_STRING =
+        "Use the parent class name instead of `this` when in a `static` context.";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        return this.applyWithFunction(sourceFile, walk);
+    }
+}
+
+function walk(ctx: Lint.WalkContext<void>) {
+    let currentParentClass: ts.ClassLikeDeclaration | undefined;
+
+    const cb = (node: ts.Node): void => {
+        const originalParentClass = currentParentClass;
+
+        if (
+            utils.isClassLikeDeclaration(node.parent) &&
+            utils.hasModifier(node.modifiers, ts.SyntaxKind.StaticKeyword)
+        ) {
+            currentParentClass = node.parent;
+            ts.forEachChild(node, cb);
+            currentParentClass = originalParentClass;
+        }
+
+        if (node.kind === ts.SyntaxKind.ThisKeyword && currentParentClass !== undefined) {
+            let fix: Replacement | undefined;
+            if (currentParentClass.name !== undefined) {
+                fix = Lint.Replacement.replaceNode(node, currentParentClass.name.text);
+            }
+
+            ctx.addFailureAtNode(node, Rule.FAILURE_STRING, fix);
+            return;
+        }
+
+        ts.forEachChild(node, cb);
+    };
+
+    ts.forEachChild(ctx.sourceFile, cb);
+}

src/rules/unifiedSignaturesRule.ts

@@ -38,17 +38,17 @@ export class Rule extends Lint.Rules.AbstractRule {
     /* tslint:enable:object-literal-sort-keys */
 
     public static FAILURE_STRING_OMITTING_SINGLE_PARAMETER(otherLine?: number) {
-        return `${this.FAILURE_STRING_START(otherLine)} with an optional parameter.`;
+        return `${Rule.FAILURE_STRING_START(otherLine)} with an optional parameter.`;
     }
     public static FAILURE_STRING_OMITTING_REST_PARAMETER(otherLine?: number) {
-        return `${this.FAILURE_STRING_START(otherLine)} with a rest parameter.`;
+        return `${Rule.FAILURE_STRING_START(otherLine)} with a rest parameter.`;
     }
     public static FAILURE_STRING_SINGLE_PARAMETER_DIFFERENCE(
         otherLine: number | undefined,
         type1: string,
         type2: string,
     ) {
-        return `${this.FAILURE_STRING_START(otherLine)} taking \`${type1} | ${type2}\`.`;
+        return `${Rule.FAILURE_STRING_START(otherLine)} taking \`${type1} | ${type2}\`.`;
     }
     private static FAILURE_STRING_START(otherLine?: number): string {
         // For only 2 overloads we don't need to specify which is the other one.

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

@@ -0,0 +1,65 @@
+class StaticThis {
+    static value = 0;
+    static staticValue = StaticThis.value;
+
+    static _color = undefined;
+
+    static get color() {
+        return StaticThis._color;
+    }
+
+    static set color(color) {
+        StaticThis._color = color;
+    }
+
+    static getTypeOf() {
+        return StaticThis;
+    }
+
+    private _value = 5;
+
+    getValue() {
+        return this._value;
+    }
+
+    get length() {
+        return this._value;
+    }
+
+    set length(value) {
+        this._value = value;
+    }
+}
+
+class Child extends StaticThis {
+    static word = 'Hello';
+    static staticValue = Child.word;
+
+    static getTypeOf() {
+        return Child;
+    }
+}
+
+const AnonymClass = class {
+    static getTypeOf() {
+        return this;
+    }
+}
+
+class AnonymClassChild extends AnonymClass {
+    static getTypeOf() {
+        return AnonymClassChild;
+    }
+}
+
+const NamedClass = class Name {
+    static getTypeOf() {
+        return Name;
+    }
+}
+
+class NamedClassChild extends NamedClass {
+    static getTypeOf() {
+        return NamedClassChild;
+    }
+}

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

@@ -0,0 +1,75 @@
+class StaticThis {
+    static value = 0;
+    static staticValue = this.value;
+                         ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+
+    static _color = undefined;
+
+    static get color() {
+        return this._color;
+               ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+    }
+
+    static set color(color) {
+        this._color = color;
+        ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+    }
+
+    static getTypeOf() {
+        return this;
+               ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+    }
+
+    private _value = 5;
+
+    getValue() {
+        return this._value;
+    }
+
+    get length() {
+        return this._value;
+    }
+
+    set length(value) {
+        this._value = value;
+    }
+}
+
+class Child extends StaticThis {
+    static word = 'Hello';
+    static staticValue = this.word;
+                         ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+
+    static getTypeOf() {
+        return this;
+               ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+    }
+}
+
+const AnonymClass = class {
+    static getTypeOf() {
+        return this;
+               ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+    }
+}
+
+class AnonymClassChild extends AnonymClass {
+    static getTypeOf() {
+        return this;
+               ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+    }
+}
+
+const NamedClass = class Name {
+    static getTypeOf() {
+        return this;
+               ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+    }
+}
+
+class NamedClassChild extends NamedClass {
+    static getTypeOf() {
+        return this;
+               ~~~~ [Use the parent class name instead of `this` when in a `static` context.]
+    }
+}

test/rules/static-this/tslint.json

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