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node_modules/eslint/lib/linter/code-path-analysis/fork-context.js

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+/**
+ * @fileoverview A class to operate forking.
+ *
+ * This is state of forking.
+ * This has a fork list and manages it.
+ *
+ * @author Toru Nagashima
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const assert = require("assert"),
+    CodePathSegment = require("./code-path-segment");
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Gets whether or not a given segment is reachable.
+ * @param {CodePathSegment} segment A segment to get.
+ * @returns {boolean} `true` if the segment is reachable.
+ */
+function isReachable(segment) {
+    return segment.reachable;
+}
+
+/**
+ * Creates new segments from the specific range of `context.segmentsList`.
+ *
+ * When `context.segmentsList` is `[[a, b], [c, d], [e, f]]`, `begin` is `0`, and
+ * `end` is `-1`, this creates `[g, h]`. This `g` is from `a`, `c`, and `e`.
+ * This `h` is from `b`, `d`, and `f`.
+ * @param {ForkContext} context An instance.
+ * @param {number} begin The first index of the previous segments.
+ * @param {number} end The last index of the previous segments.
+ * @param {Function} create A factory function of new segments.
+ * @returns {CodePathSegment[]} New segments.
+ */
+function makeSegments(context, begin, end, create) {
+    const list = context.segmentsList;
+
+    const normalizedBegin = begin >= 0 ? begin : list.length + begin;
+    const normalizedEnd = end >= 0 ? end : list.length + end;
+
+    const segments = [];
+
+    for (let i = 0; i < context.count; ++i) {
+        const allPrevSegments = [];
+
+        for (let j = normalizedBegin; j <= normalizedEnd; ++j) {
+            allPrevSegments.push(list[j][i]);
+        }
+
+        segments.push(create(context.idGenerator.next(), allPrevSegments));
+    }
+
+    return segments;
+}
+
+/**
+ * `segments` becomes doubly in a `finally` block. Then if a code path exits by a
+ * control statement (such as `break`, `continue`) from the `finally` block, the
+ * destination's segments may be half of the source segments. In that case, this
+ * merges segments.
+ * @param {ForkContext} context An instance.
+ * @param {CodePathSegment[]} segments Segments to merge.
+ * @returns {CodePathSegment[]} The merged segments.
+ */
+function mergeExtraSegments(context, segments) {
+    let currentSegments = segments;
+
+    while (currentSegments.length > context.count) {
+        const merged = [];
+
+        for (let i = 0, length = currentSegments.length / 2 | 0; i < length; ++i) {
+            merged.push(CodePathSegment.newNext(
+                context.idGenerator.next(),
+                [currentSegments[i], currentSegments[i + length]]
+            ));
+        }
+        currentSegments = merged;
+    }
+    return currentSegments;
+}
+
+//------------------------------------------------------------------------------
+// Public Interface
+//------------------------------------------------------------------------------
+
+/**
+ * A class to manage forking.
+ */
+class ForkContext {
+
+    // eslint-disable-next-line jsdoc/require-description
+    /**
+     * @param {IdGenerator} idGenerator An identifier generator for segments.
+     * @param {ForkContext|null} upper An upper fork context.
+     * @param {number} count A number of parallel segments.
+     */
+    constructor(idGenerator, upper, count) {
+        this.idGenerator = idGenerator;
+        this.upper = upper;
+        this.count = count;
+        this.segmentsList = [];
+    }
+
+    /**
+     * The head segments.
+     * @type {CodePathSegment[]}
+     */
+    get head() {
+        const list = this.segmentsList;
+
+        return list.length === 0 ? [] : list[list.length - 1];
+    }
+
+    /**
+     * A flag which shows empty.
+     * @type {boolean}
+     */
+    get empty() {
+        return this.segmentsList.length === 0;
+    }
+
+    /**
+     * A flag which shows reachable.
+     * @type {boolean}
+     */
+    get reachable() {
+        const segments = this.head;
+
+        return segments.length > 0 && segments.some(isReachable);
+    }
+
+    /**
+     * Creates new segments from this context.
+     * @param {number} begin The first index of previous segments.
+     * @param {number} end The last index of previous segments.
+     * @returns {CodePathSegment[]} New segments.
+     */
+    makeNext(begin, end) {
+        return makeSegments(this, begin, end, CodePathSegment.newNext);
+    }
+
+    /**
+     * Creates new segments from this context.
+     * The new segments is always unreachable.
+     * @param {number} begin The first index of previous segments.
+     * @param {number} end The last index of previous segments.
+     * @returns {CodePathSegment[]} New segments.
+     */
+    makeUnreachable(begin, end) {
+        return makeSegments(this, begin, end, CodePathSegment.newUnreachable);
+    }
+
+    /**
+     * Creates new segments from this context.
+     * The new segments don't have connections for previous segments.
+     * But these inherit the reachable flag from this context.
+     * @param {number} begin The first index of previous segments.
+     * @param {number} end The last index of previous segments.
+     * @returns {CodePathSegment[]} New segments.
+     */
+    makeDisconnected(begin, end) {
+        return makeSegments(this, begin, end, CodePathSegment.newDisconnected);
+    }
+
+    /**
+     * Adds segments into this context.
+     * The added segments become the head.
+     * @param {CodePathSegment[]} segments Segments to add.
+     * @returns {void}
+     */
+    add(segments) {
+        assert(segments.length >= this.count, `${segments.length} >= ${this.count}`);
+
+        this.segmentsList.push(mergeExtraSegments(this, segments));
+    }
+
+    /**
+     * Replaces the head segments with given segments.
+     * The current head segments are removed.
+     * @param {CodePathSegment[]} segments Segments to add.
+     * @returns {void}
+     */
+    replaceHead(segments) {
+        assert(segments.length >= this.count, `${segments.length} >= ${this.count}`);
+
+        this.segmentsList.splice(-1, 1, mergeExtraSegments(this, segments));
+    }
+
+    /**
+     * Adds all segments of a given fork context into this context.
+     * @param {ForkContext} context A fork context to add.
+     * @returns {void}
+     */
+    addAll(context) {
+        assert(context.count === this.count);
+
+        const source = context.segmentsList;
+
+        for (let i = 0; i < source.length; ++i) {
+            this.segmentsList.push(source[i]);
+        }
+    }
+
+    /**
+     * Clears all secments in this context.
+     * @returns {void}
+     */
+    clear() {
+        this.segmentsList = [];
+    }
+
+    /**
+     * Creates the root fork context.
+     * @param {IdGenerator} idGenerator An identifier generator for segments.
+     * @returns {ForkContext} New fork context.
+     */
+    static newRoot(idGenerator) {
+        const context = new ForkContext(idGenerator, null, 1);
+
+        context.add([CodePathSegment.newRoot(idGenerator.next())]);
+
+        return context;
+    }
+
+    /**
+     * Creates an empty fork context preceded by a given context.
+     * @param {ForkContext} parentContext The parent fork context.
+     * @param {boolean} forkLeavingPath A flag which shows inside of `finally` block.
+     * @returns {ForkContext} New fork context.
+     */
+    static newEmpty(parentContext, forkLeavingPath) {
+        return new ForkContext(
+            parentContext.idGenerator,
+            parentContext,
+            (forkLeavingPath ? 2 : 1) * parentContext.count
+        );
+    }
+}
+
+module.exports = ForkContext;