noRestrictedGlobalsRule.ts

/**
 * @license
 * Copyright 2014 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 {
    isBindingElement,
    isComputedPropertyName,
    isIdentifier,
    isPropertyAccessExpression,
} from "tsutils";
import * as ts from "typescript";

import * as Lint from "../index";

export class Rule extends Lint.Rules.TypedRule {
    /* tslint:disable:object-literal-sort-keys */
    public static metadata: Lint.IRuleMetadata = {
        ruleName: "no-restricted-globals",
        description: "Disallow specific global variables.",
        rationale: Lint.Utils.dedent`
            \`\`\`ts
            function broken(evt: Event) {
                // Meant to do something with \`evt\` but typed it incorrectly.
                Event.target;  // compiler error
                event.target;  // should be a lint failure
            }

            Early Internet Explorer versions exposed the current DOM event as a global variable 'event',
            but using this variable has been considered a bad practice for a long time.
            Restricting this will make sure this variable isn’t used in browser code.
            \`\`\`
        `,
        descriptionDetails: Lint.Utils.dedent`
            Disallowing usage of specific global variables can be useful if you want to allow
            a set of global variables by enabling an environment, but still want to disallow
            some of those.
        `,
        optionsDescription: Lint.Utils.dedent`
            This rule takes a list of strings, where each string is a global to be restricted.
            \`event\`, \`name\` and \`length\` are restricted by default.
        `,
        options: {
            type: "list",
            items: { type: "string" },
        },
        optionExamples: [[true, "name", "length", "event"]],
        type: "functionality",
        typescriptOnly: false,
        requiresTypeInfo: true,
    };
    /* tslint:enable:object-literal-sort-keys */

    public static FAILURE_STRING(name: string) {
        return `Unexpected global variable '${name}'. Use a local parameter or variable instead.`;
    }

    public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
        const bannedList =
            this.ruleArguments.length > 0 ? this.ruleArguments : ["event", "name", "length"];
        const bannedGlobals = new Set(bannedList);
        if (sourceFile.isDeclarationFile) {
            return [];
        } else {
            return this.applyWithFunction(
                sourceFile,
                walk,
                bannedGlobals,
                program.getTypeChecker(),
            );
        }
    }
}

function walk(ctx: Lint.WalkContext<Set<string>>, checker: ts.TypeChecker): void {
    return ts.forEachChild(ctx.sourceFile, function recur(node: ts.Node | undefined): void {
        if (node == undefined) {
            return;
        }

        // Handles `const { bar, length: { x: y = () => event } } = foo`
        if (isBindingElement(node)) {
            recur(node.initializer);
            recur(node.name);
            if (node.propertyName != undefined && isComputedPropertyName(node.propertyName)) {
                recur(node.propertyName);
            }
        } else if (isPropertyAccessExpression(node)) {
            // Ignore `y` in `x.y`, but recurse to `x`.
            recur(node.expression);
        } else if (isIdentifier(node)) {
            checkIdentifier(node);
        } else {
            ts.forEachChild(node, recur);
        }
    });

    function checkIdentifier(node: ts.Identifier): void {
        if (!ctx.options.has(node.text)) {
            return;
        }

        const symbol = checker.getSymbolAtLocation(node);
        const declarations = symbol === undefined ? undefined : symbol.declarations;
        if (declarations === undefined || declarations.length === 0) {
            return;
        }

        const isAmbientGlobal = declarations.some(decl => decl.getSourceFile().isDeclarationFile);

        if (isAmbientGlobal) {
            ctx.addFailureAtNode(node, Rule.FAILURE_STRING(node.text));
        }
    }
}