New: Add prefer-exponentiation-operator rule (fixes #10482) (#12360)

* New: Add prefer-exponentiation-operator rule (fixes #10482)

* Check ClassDeclaration

docs/rules/prefer-exponentiation-operator.md

@@ -0,0 +1,46 @@
+# Disallow the use of `Math.pow` in favor of the `**` operator (prefer-exponentiation-operator)
+
+Introduced in ES2016, the infix exponentiation operator `**` is an alternative for the standard `Math.pow` function.
+
+Infix notation is considered to be more readable and thus more preferable than the function notation.
+
+## Rule Details
+
+This rule disallows calls to `Math.pow` and suggests using the `**` operator instead.
+
+Examples of **incorrect** code for this rule:
+
+```js
+/*eslint prefer-exponentiation-operator: "error"*/
+
+const foo = Math.pow(2, 8);
+
+const bar = Math.pow(a, b);
+
+let baz = Math.pow(a + b, c + d);
+
+let quux = Math.pow(-1, n);
+```
+
+Examples of **correct** code for this rule:
+
+```js
+/*eslint prefer-exponentiation-operator: "error"*/
+
+const foo = 2 ** 8;
+
+const bar = a ** b;
+
+let baz = (a + b) ** (c + d);
+
+let quux = (-1) ** n;
+```
+
+## When Not To Use It
+
+This rule should not be used unless ES2016 is supported in your codebase.
+
+## Further Reading
+
+* [MDN Arithmetic Operators - Exponentiation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Exponentiation)
+* [Issue 5848: Exponentiation operator ** has different results for numbers and variables from 50 upwards](https://bugs.chromium.org/p/v8/issues/detail?id=5848)

lib/rules/index.js

@@ -238,6 +238,7 @@ module.exports = new LazyLoadingRuleMap(Object.entries({
     "prefer-arrow-callback": () => require("./prefer-arrow-callback"),
     "prefer-const": () => require("./prefer-const"),
     "prefer-destructuring": () => require("./prefer-destructuring"),
+    "prefer-exponentiation-operator": () => require("./prefer-exponentiation-operator"),
     "prefer-named-capture-group": () => require("./prefer-named-capture-group"),
     "prefer-numeric-literals": () => require("./prefer-numeric-literals"),
     "prefer-object-spread": () => require("./prefer-object-spread"),

lib/rules/prefer-exponentiation-operator.js

@@ -0,0 +1,189 @@
+/**
+ * @fileoverview Rule to disallow Math.pow in favor of the ** operator
+ * @author Milos Djermanovic
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const astUtils = require("./utils/ast-utils");
+const { CALL, ReferenceTracker } = require("eslint-utils");
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+const PRECEDENCE_OF_EXPONENTIATION_EXPR = astUtils.getPrecedence({ type: "BinaryExpression", operator: "**" });
+
+/**
+ * Determines whether the given node needs parens if used as the base in an exponentiation binary expression.
+ * @param {ASTNode} base The node to check.
+ * @returns {boolean} `true` if the node needs to be parenthesised.
+ */
+function doesBaseNeedParens(base) {
+    return (
+
+        // '**' is right-associative, parens are needed when Math.pow(a ** b, c) is converted to (a ** b) ** c
+        astUtils.getPrecedence(base) <= PRECEDENCE_OF_EXPONENTIATION_EXPR ||
+
+        // An unary operator cannot be used immediately before an exponentiation expression
+        base.type === "UnaryExpression"
+    );
+}
+
+/**
+ * Determines whether the given node needs parens if used as the exponent in an exponentiation binary expression.
+ * @param {ASTNode} exponent The node to check.
+ * @returns {boolean} `true` if the node needs to be parenthesised.
+ */
+function doesExponentNeedParens(exponent) {
+
+    // '**' is right-associative, there is no need for parens when Math.pow(a, b ** c) is converted to a ** b ** c
+    return astUtils.getPrecedence(exponent) < PRECEDENCE_OF_EXPONENTIATION_EXPR;
+}
+
+/**
+ * Determines whether an exponentiation binary expression at the place of the given node would need parens.
+ * @param {ASTNode} node A node that would be replaced by an exponentiation binary expression.
+ * @param {SourceCode} sourceCode A SourceCode object.
+ * @returns {boolean} `true` if the expression needs to be parenthesised.
+ */
+function doesExponentiationExpressionNeedParens(node, sourceCode) {
+    const parent = node.parent;
+
+    const needsParens = (
+        parent.type === "ClassDeclaration" ||
+        (
+            parent.type.endsWith("Expression") &&
+            astUtils.getPrecedence(parent) >= PRECEDENCE_OF_EXPONENTIATION_EXPR &&
+            !(parent.type === "BinaryExpression" && parent.operator === "**" && parent.right === node) &&
+            !((parent.type === "CallExpression" || parent.type === "NewExpression") && parent.arguments.includes(node)) &&
+            !(parent.type === "MemberExpression" && parent.computed && parent.property === node) &&
+            !(parent.type === "ArrayExpression")
+        )
+    );
+
+    return needsParens && !astUtils.isParenthesised(sourceCode, node);
+}
+
+/**
+ * Optionally parenthesizes given text.
+ * @param {string} text The text to parenthesize.
+ * @param {boolean} shouldParenthesize If `true`, the text will be parenthesised.
+ * @returns {string} parenthesised or unchanged text.
+ */
+function parenthesizeIfShould(text, shouldParenthesize) {
+    return shouldParenthesize ? `(${text})` : text;
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "disallow the use of `Math.pow` in favor of the `**` operator",
+            category: "Stylistic Issues",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/prefer-exponentiation-operator"
+        },
+
+        schema: [],
+        fixable: "code",
+
+        messages: {
+            useExponentiation: "Use the '**' operator instead of 'Math.pow'."
+        }
+    },
+
+    create(context) {
+        const sourceCode = context.getSourceCode();
+
+        /**
+         * Reports the given node.
+         * @param {ASTNode} node 'Math.pow()' node to report.
+         * @returns {void}
+         */
+        function report(node) {
+            context.report({
+                node,
+                messageId: "useExponentiation",
+                fix(fixer) {
+                    if (
+                        node.arguments.length !== 2 ||
+                        node.arguments.some(arg => arg.type === "SpreadElement") ||
+                        sourceCode.getCommentsInside(node).length > 0
+                    ) {
+                        return null;
+                    }
+
+                    const base = node.arguments[0],
+                        exponent = node.arguments[1],
+                        baseText = sourceCode.getText(base),
+                        exponentText = sourceCode.getText(exponent),
+                        shouldParenthesizeBase = doesBaseNeedParens(base),
+                        shouldParenthesizeExponent = doesExponentNeedParens(exponent),
+                        shouldParenthesizeAll = doesExponentiationExpressionNeedParens(node, sourceCode);
+
+                    let prefix = "",
+                        suffix = "";
+
+                    if (!shouldParenthesizeAll) {
+                        if (!shouldParenthesizeBase) {
+                            const firstReplacementToken = sourceCode.getFirstToken(base),
+                                tokenBefore = sourceCode.getTokenBefore(node);
+
+                            if (
+                                tokenBefore &&
+                                tokenBefore.range[1] === node.range[0] &&
+                                !astUtils.canTokensBeAdjacent(tokenBefore, firstReplacementToken)
+                            ) {
+                                prefix = " "; // a+Math.pow(++b, c) -> a+ ++b**c
+                            }
+                        }
+                        if (!shouldParenthesizeExponent) {
+                            const lastReplacementToken = sourceCode.getLastToken(exponent),
+                                tokenAfter = sourceCode.getTokenAfter(node);
+
+                            if (
+                                tokenAfter &&
+                                node.range[1] === tokenAfter.range[0] &&
+                                !astUtils.canTokensBeAdjacent(lastReplacementToken, tokenAfter)
+                            ) {
+                                suffix = " "; // Math.pow(a, b)in c -> a**b in c
+                            }
+                        }
+                    }
+
+                    const baseReplacement = parenthesizeIfShould(baseText, shouldParenthesizeBase),
+                        exponentReplacement = parenthesizeIfShould(exponentText, shouldParenthesizeExponent),
+                        replacement = parenthesizeIfShould(`${baseReplacement}**${exponentReplacement}`, shouldParenthesizeAll);
+
+                    return fixer.replaceText(node, `${prefix}${replacement}${suffix}`);
+                }
+            });
+        }
+
+        return {
+            Program() {
+                const scope = context.getScope();
+                const tracker = new ReferenceTracker(scope);
+                const trackMap = {
+                    Math: {
+                        pow: { [CALL]: true }
+                    }
+                };
+
+                for (const { node } of tracker.iterateGlobalReferences(trackMap)) {
+                    report(node);
+                }
+            }
+        };
+    }
+};