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app_vue/node_modules/eslint/lib/rules/no-unused-expressions.js

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+/**
+ * @fileoverview Flag expressions in statement position that do not side effect
+ * @author Michael Ficarra
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+/**
+ * Returns `true`.
+ * @returns {boolean} `true`.
+ */
+function alwaysTrue() {
+    return true;
+}
+
+/**
+ * Returns `false`.
+ * @returns {boolean} `false`.
+ */
+function alwaysFalse() {
+    return false;
+}
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "disallow unused expressions",
+            category: "Best Practices",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/no-unused-expressions"
+        },
+
+        schema: [
+            {
+                type: "object",
+                properties: {
+                    allowShortCircuit: {
+                        type: "boolean",
+                        default: false
+                    },
+                    allowTernary: {
+                        type: "boolean",
+                        default: false
+                    },
+                    allowTaggedTemplates: {
+                        type: "boolean",
+                        default: false
+                    },
+                    enforceForJSX: {
+                        type: "boolean",
+                        default: false
+                    }
+                },
+                additionalProperties: false
+            }
+        ],
+
+        messages: {
+            unusedExpression: "Expected an assignment or function call and instead saw an expression."
+        }
+    },
+
+    create(context) {
+        const config = context.options[0] || {},
+            allowShortCircuit = config.allowShortCircuit || false,
+            allowTernary = config.allowTernary || false,
+            allowTaggedTemplates = config.allowTaggedTemplates || false,
+            enforceForJSX = config.enforceForJSX || false;
+
+        // eslint-disable-next-line jsdoc/require-description
+        /**
+         * @param {ASTNode} node any node
+         * @returns {boolean} whether the given node structurally represents a directive
+         */
+        function looksLikeDirective(node) {
+            return node.type === "ExpressionStatement" &&
+                node.expression.type === "Literal" && typeof node.expression.value === "string";
+        }
+
+        // eslint-disable-next-line jsdoc/require-description
+        /**
+         * @param {Function} predicate ([a] -> Boolean) the function used to make the determination
+         * @param {a[]} list the input list
+         * @returns {a[]} the leading sequence of members in the given list that pass the given predicate
+         */
+        function takeWhile(predicate, list) {
+            for (let i = 0; i < list.length; ++i) {
+                if (!predicate(list[i])) {
+                    return list.slice(0, i);
+                }
+            }
+            return list.slice();
+        }
+
+        // eslint-disable-next-line jsdoc/require-description
+        /**
+         * @param {ASTNode} node a Program or BlockStatement node
+         * @returns {ASTNode[]} the leading sequence of directive nodes in the given node's body
+         */
+        function directives(node) {
+            return takeWhile(looksLikeDirective, node.body);
+        }
+
+        // eslint-disable-next-line jsdoc/require-description
+        /**
+         * @param {ASTNode} node any node
+         * @param {ASTNode[]} ancestors the given node's ancestors
+         * @returns {boolean} whether the given node is considered a directive in its current position
+         */
+        function isDirective(node, ancestors) {
+            const parent = ancestors[ancestors.length - 1],
+                grandparent = ancestors[ancestors.length - 2];
+
+            return (parent.type === "Program" || parent.type === "BlockStatement" &&
+                    (/Function/u.test(grandparent.type))) &&
+                    directives(parent).indexOf(node) >= 0;
+        }
+
+        /**
+         * The member functions return `true` if the type has no side-effects.
+         * Unknown nodes are handled as `false`, then this rule ignores those.
+         */
+        const Checker = Object.assign(Object.create(null), {
+            isDisallowed(node) {
+                return (Checker[node.type] || alwaysFalse)(node);
+            },
+
+            ArrayExpression: alwaysTrue,
+            ArrowFunctionExpression: alwaysTrue,
+            BinaryExpression: alwaysTrue,
+            ChainExpression(node) {
+                return Checker.isDisallowed(node.expression);
+            },
+            ClassExpression: alwaysTrue,
+            ConditionalExpression(node) {
+                if (allowTernary) {
+                    return Checker.isDisallowed(node.consequent) || Checker.isDisallowed(node.alternate);
+                }
+                return true;
+            },
+            FunctionExpression: alwaysTrue,
+            Identifier: alwaysTrue,
+            JSXElement() {
+                return enforceForJSX;
+            },
+            JSXFragment() {
+                return enforceForJSX;
+            },
+            Literal: alwaysTrue,
+            LogicalExpression(node) {
+                if (allowShortCircuit) {
+                    return Checker.isDisallowed(node.right);
+                }
+                return true;
+            },
+            MemberExpression: alwaysTrue,
+            MetaProperty: alwaysTrue,
+            ObjectExpression: alwaysTrue,
+            SequenceExpression: alwaysTrue,
+            TaggedTemplateExpression() {
+                return !allowTaggedTemplates;
+            },
+            TemplateLiteral: alwaysTrue,
+            ThisExpression: alwaysTrue,
+            UnaryExpression(node) {
+                return node.operator !== "void" && node.operator !== "delete";
+            }
+        });
+
+        return {
+            ExpressionStatement(node) {
+                if (Checker.isDisallowed(node.expression) && !isDirective(node, context.getAncestors())) {
+                    context.report({ node, messageId: "unusedExpression" });
+                }
+            }
+        };
+    }
+};