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node_modules/eslint/lib/rules/no-extra-boolean-cast.js

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+/**
+ * @fileoverview Rule to flag unnecessary double negation in Boolean contexts
+ * @author Brandon Mills
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const astUtils = require("./utils/ast-utils");
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "disallow unnecessary boolean casts",
+            category: "Possible Errors",
+            recommended: true,
+            url: "https://eslint.org/docs/rules/no-extra-boolean-cast"
+        },
+
+        schema: [],
+        fixable: "code",
+
+        messages: {
+            unexpectedCall: "Redundant Boolean call.",
+            unexpectedNegation: "Redundant double negation."
+        }
+    },
+
+    create(context) {
+        const sourceCode = context.getSourceCode();
+
+        // Node types which have a test which will coerce values to booleans.
+        const BOOLEAN_NODE_TYPES = [
+            "IfStatement",
+            "DoWhileStatement",
+            "WhileStatement",
+            "ConditionalExpression",
+            "ForStatement"
+        ];
+
+        /**
+         * Check if a node is in a context where its value would be coerced to a boolean at runtime.
+         * @param {ASTNode} node The node
+         * @param {ASTNode} parent Its parent
+         * @returns {boolean} If it is in a boolean context
+         */
+        function isInBooleanContext(node, parent) {
+            return (
+                (BOOLEAN_NODE_TYPES.indexOf(parent.type) !== -1 &&
+                    node === parent.test) ||
+
+                // !<bool>
+                (parent.type === "UnaryExpression" &&
+                    parent.operator === "!")
+            );
+        }
+
+        /**
+         * Check if a node has comments inside.
+         * @param {ASTNode} node The node to check.
+         * @returns {boolean} `true` if it has comments inside.
+         */
+        function hasCommentsInside(node) {
+            return Boolean(sourceCode.getCommentsInside(node).length);
+        }
+
+        return {
+            UnaryExpression(node) {
+                const ancestors = context.getAncestors(),
+                    parent = ancestors.pop(),
+                    grandparent = ancestors.pop();
+
+                // Exit early if it's guaranteed not to match
+                if (node.operator !== "!" ||
+                        parent.type !== "UnaryExpression" ||
+                        parent.operator !== "!") {
+                    return;
+                }
+
+                if (isInBooleanContext(parent, grandparent) ||
+
+                    // Boolean(<bool>) and new Boolean(<bool>)
+                    ((grandparent.type === "CallExpression" || grandparent.type === "NewExpression") &&
+                        grandparent.callee.type === "Identifier" &&
+                        grandparent.callee.name === "Boolean")
+                ) {
+                    context.report({
+                        node: parent,
+                        messageId: "unexpectedNegation",
+                        fix: fixer => {
+                            if (hasCommentsInside(parent)) {
+                                return null;
+                            }
+
+                            let prefix = "";
+                            const tokenBefore = sourceCode.getTokenBefore(parent);
+                            const firstReplacementToken = sourceCode.getFirstToken(node.argument);
+
+                            if (tokenBefore && tokenBefore.range[1] === parent.range[0] &&
+                                    !astUtils.canTokensBeAdjacent(tokenBefore, firstReplacementToken)) {
+                                prefix = " ";
+                            }
+
+                            return fixer.replaceText(parent, prefix + sourceCode.getText(node.argument));
+                        }
+                    });
+                }
+            },
+            CallExpression(node) {
+                const parent = node.parent;
+
+                if (node.callee.type !== "Identifier" || node.callee.name !== "Boolean") {
+                    return;
+                }
+
+                if (isInBooleanContext(node, parent)) {
+                    context.report({
+                        node,
+                        messageId: "unexpectedCall",
+                        fix: fixer => {
+                            if (!node.arguments.length) {
+                                if (parent.type === "UnaryExpression" && parent.operator === "!") {
+
+                                    // !Boolean() -> true
+
+                                    if (hasCommentsInside(parent)) {
+                                        return null;
+                                    }
+
+                                    const replacement = "true";
+                                    let prefix = "";
+                                    const tokenBefore = sourceCode.getTokenBefore(parent);
+
+                                    if (tokenBefore && tokenBefore.range[1] === parent.range[0] &&
+                                            !astUtils.canTokensBeAdjacent(tokenBefore, replacement)) {
+                                        prefix = " ";
+                                    }
+
+                                    return fixer.replaceText(parent, prefix + replacement);
+                                }
+
+                                // Boolean() -> false
+                                if (hasCommentsInside(node)) {
+                                    return null;
+                                }
+                                return fixer.replaceText(node, "false");
+                            }
+
+                            if (node.arguments.length > 1 || node.arguments[0].type === "SpreadElement" ||
+                                    hasCommentsInside(node)) {
+                                return null;
+                            }
+
+                            const argument = node.arguments[0];
+
+                            if (astUtils.getPrecedence(argument) < astUtils.getPrecedence(node.parent)) {
+                                return fixer.replaceText(node, `(${sourceCode.getText(argument)})`);
+                            }
+                            return fixer.replaceText(node, sourceCode.getText(argument));
+                        }
+                    });
+                }
+            }
+        };
+
+    }
+};