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app_vue/node_modules/eslint/lib/rules/no-unreachable-loop.js

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+/**
+ * @fileoverview Rule to disallow loops with a body that allows only one iteration
+ * @author Milos Djermanovic
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+const allLoopTypes = ["WhileStatement", "DoWhileStatement", "ForStatement", "ForInStatement", "ForOfStatement"];
+
+/**
+ * Determines whether the given node is the first node in the code path to which a loop statement
+ * 'loops' for the next iteration.
+ * @param {ASTNode} node The node to check.
+ * @returns {boolean} `true` if the node is a looping target.
+ */
+function isLoopingTarget(node) {
+    const parent = node.parent;
+
+    if (parent) {
+        switch (parent.type) {
+            case "WhileStatement":
+                return node === parent.test;
+            case "DoWhileStatement":
+                return node === parent.body;
+            case "ForStatement":
+                return node === (parent.update || parent.test || parent.body);
+            case "ForInStatement":
+            case "ForOfStatement":
+                return node === parent.left;
+
+            // no default
+        }
+    }
+
+    return false;
+}
+
+/**
+ * Creates an array with elements from the first given array that are not included in the second given array.
+ * @param {Array} arrA The array to compare from.
+ * @param {Array} arrB The array to compare against.
+ * @returns {Array} a new array that represents `arrA \ arrB`.
+ */
+function getDifference(arrA, arrB) {
+    return arrA.filter(a => !arrB.includes(a));
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "problem",
+
+        docs: {
+            description: "disallow loops with a body that allows only one iteration",
+            category: "Possible Errors",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/no-unreachable-loop"
+        },
+
+        schema: [{
+            type: "object",
+            properties: {
+                ignore: {
+                    type: "array",
+                    items: {
+                        enum: allLoopTypes
+                    },
+                    uniqueItems: true
+                }
+            },
+            additionalProperties: false
+        }],
+
+        messages: {
+            invalid: "Invalid loop. Its body allows only one iteration."
+        }
+    },
+
+    create(context) {
+        const ignoredLoopTypes = context.options[0] && context.options[0].ignore || [],
+            loopTypesToCheck = getDifference(allLoopTypes, ignoredLoopTypes),
+            loopSelector = loopTypesToCheck.join(","),
+            loopsByTargetSegments = new Map(),
+            loopsToReport = new Set();
+
+        let currentCodePath = null;
+
+        return {
+            onCodePathStart(codePath) {
+                currentCodePath = codePath;
+            },
+
+            onCodePathEnd() {
+                currentCodePath = currentCodePath.upper;
+            },
+
+            [loopSelector](node) {
+
+                /**
+                 * Ignore unreachable loop statements to avoid unnecessary complexity in the implementation, or false positives otherwise.
+                 * For unreachable segments, the code path analysis does not raise events required for this implementation.
+                 */
+                if (currentCodePath.currentSegments.some(segment => segment.reachable)) {
+                    loopsToReport.add(node);
+                }
+            },
+
+            onCodePathSegmentStart(segment, node) {
+                if (isLoopingTarget(node)) {
+                    const loop = node.parent;
+
+                    loopsByTargetSegments.set(segment, loop);
+                }
+            },
+
+            onCodePathSegmentLoop(_, toSegment, node) {
+                const loop = loopsByTargetSegments.get(toSegment);
+
+                /**
+                 * The second iteration is reachable, meaning that the loop is valid by the logic of this rule,
+                 * only if there is at least one loop event with the appropriate target (which has been already
+                 * determined in the `loopsByTargetSegments` map), raised from either:
+                 *
+                 * - the end of the loop's body (in which case `node === loop`)
+                 * - a `continue` statement
+                 *
+                 * This condition skips loop events raised from `ForInStatement > .right` and `ForOfStatement > .right` nodes.
+                 */
+                if (node === loop || node.type === "ContinueStatement") {
+
+                    // Removes loop if it exists in the set. Otherwise, `Set#delete` has no effect and doesn't throw.
+                    loopsToReport.delete(loop);
+                }
+            },
+
+            "Program:exit"() {
+                loopsToReport.forEach(
+                    node => context.report({ node, messageId: "invalid" })
+                );
+            }
+        };
+    }
+};