✨ add es/no-optional-chaining rule (#34)

docs/rules/README.md

@@ -24,6 +24,7 @@ There are multiple configs which enable all rules in this category: `plugin:es/n
 | [es/no-global-this](./no-global-this.md) | disallow the `globalThis` variable. |  |
 | [es/no-import-meta](./no-import-meta.md) | disallow `import.meta` meta property. |  |
 | [es/no-nullish-coalescing-operators](./no-nullish-coalescing-operators.md) | disallow nullish coalescing operators. |  |
+| [es/no-optional-chaining](./no-optional-chaining.md) | disallow optional chaining. |  |
 | [es/no-promise-all-settled](./no-promise-all-settled.md) | disallow `Promise.allSettled` function. |  |
 
 ## ES2019

docs/rules/no-optional-chaining.md

@@ -0,0 +1,28 @@
+# disallow optional chaining (es/no-optional-chaining)
+
+This rule reports ES2020 [Optional Chaining](https://github.com/tc39/proposal-optional-chaining) as errors.
+
+## Examples
+
+⛔ Examples of **incorrect** code for this rule:
+
+<eslint-playground type="bad" code="/*eslint es/no-optional-chaining: error */
+var x = a?.b
+var x = a?.[b]
+foo?.()
+" />
+
+👌 Examples of **correct** code for this rule:
+
+<eslint-playground type="good" code="/*eslint es/no-optional-chaining: error */
+var x = a != null ? a.b : undefined
+var x = a && a.b
+var x = a != null ? a[b] : undefined
+var x = a && a[b]
+foo && foo()
+" />
+
+## 📚 References
+
+- [Rule source](https://github.com/mysticatea/eslint-plugin-es/blob/v3.0.1/lib/rules/no-optional-chaining.js)
+- [Test source](https://github.com/mysticatea/eslint-plugin-es/blob/v3.0.1/tests/lib/rules/no-optional-chaining.js)

lib/index.js

@@ -129,6 +129,7 @@ module.exports = {
         "no-object-values": require("./rules/no-object-values"),
         "no-octal-numeric-literals": require("./rules/no-octal-numeric-literals"),
         "no-optional-catch-binding": require("./rules/no-optional-catch-binding"),
+        "no-optional-chaining": require("./rules/no-optional-chaining"),
         "no-promise": require("./rules/no-promise"),
         "no-promise-all-settled": require("./rules/no-promise-all-settled"),
         "no-property-shorthands": require("./rules/no-property-shorthands"),

lib/rules/no-optional-chaining.js

@@ -0,0 +1,61 @@
+/**
+ * @author Yosuke Ota <https://github.com/ota-meshi>
+ * See LICENSE file in root directory for full license.
+ */
+"use strict"
+
+module.exports = {
+    meta: {
+        docs: {
+            description: "disallow optional chaining.",
+            category: "ES2020",
+            recommended: false,
+            url:
+                "http://mysticatea.github.io/eslint-plugin-es/rules/no-optional-chaining.html",
+        },
+        fixable: null,
+        messages: {
+            forbidden: "ES2020 optional chaining is forbidden.",
+        },
+        schema: [],
+        type: "problem",
+    },
+    create(context) {
+        const sourceCode = context.getSourceCode()
+
+        /**
+         * Checks if the given token is a `?.` token or not.
+         * @param {Token} token The token to check.
+         * @returns {boolean} `true` if the token is a `?.` token.
+         */
+        function isQuestionDotToken(token) {
+            return (
+                token.value === "?." &&
+                (token.type === "Punctuator" || // espree has been parsed well.
+                    // espree@7.1.0 doesn't parse "?." tokens well. Therefore, get the string from the source code and check it.
+                    sourceCode.getText(token) === "?.")
+            )
+        }
+
+        return {
+            "CallExpression[optional=true]"(node) {
+                context.report({
+                    node: sourceCode.getTokenAfter(
+                        node.callee,
+                        isQuestionDotToken
+                    ),
+                    messageId: "forbidden",
+                })
+            },
+            "MemberExpression[optional=true]"(node) {
+                context.report({
+                    node: sourceCode.getTokenAfter(
+                        node.object,
+                        isQuestionDotToken
+                    ),
+                    messageId: "forbidden",
+                })
+            },
+        }
+    },
+}

tests/lib/rules/no-optional-chaining.js

@@ -0,0 +1,90 @@
+/**
+ * @author Yosuke Ota <https://github.com/ota-meshi>
+ * See LICENSE file in root directory for full license.
+ */
+"use strict"
+
+const RuleTester = require("../../tester")
+const rule = require("../../../lib/rules/no-optional-chaining.js")
+
+if (!RuleTester.isSupported(2020)) {
+    //eslint-disable-next-line no-console
+    console.log("Skip the tests of no-optional-chaining.")
+    return
+}
+
+new RuleTester().run("no-optional-chaining", rule, {
+    valid: ["var x = a.b", "var x = a[b]", "foo()"],
+    invalid: [
+        {
+            code: "var x = a?.b",
+            errors: [
+                {
+                    message: "ES2020 optional chaining is forbidden.",
+                    column: 10,
+                    endColumn: 12,
+                },
+            ],
+        },
+        {
+            code: "var x = a?.[b]",
+            errors: [
+                {
+                    message: "ES2020 optional chaining is forbidden.",
+                    column: 10,
+                    endColumn: 12,
+                },
+            ],
+        },
+        {
+            code: "foo?.()",
+            errors: [
+                {
+                    message: "ES2020 optional chaining is forbidden.",
+                    column: 4,
+                    endColumn: 6,
+                },
+            ],
+        },
+        {
+            code: "var x = ((a?.b)?.c)?.()",
+            errors: [
+                {
+                    message: "ES2020 optional chaining is forbidden.",
+                    column: 12,
+                    endColumn: 14,
+                },
+                {
+                    message: "ES2020 optional chaining is forbidden.",
+                    column: 16,
+                    endColumn: 18,
+                },
+                {
+                    message: "ES2020 optional chaining is forbidden.",
+                    column: 20,
+                    endColumn: 22,
+                },
+            ],
+        },
+        {
+            code: "var x = a/*?.*/?.b",
+            errors: [
+                {
+                    message: "ES2020 optional chaining is forbidden.",
+                    column: 16,
+                    endColumn: 18,
+                },
+            ],
+        },
+        {
+            code: "var x = '?.'?.['?.']",
+            errors: [
+                {
+                    message: "ES2020 optional chaining is forbidden.",
+                    column: 13,
+                    endColumn: 15,
+                },
+            ],
+        },
+    ],
+})