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node_modules/eslint-plugin-react/lib/rules/jsx-no-useless-fragment.js

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+/**
+ * @fileoverview Disallow useless fragments
+ */
+
+'use strict';
+
+const arrayIncludes = require('array-includes');
+
+const pragmaUtil = require('../util/pragma');
+const jsxUtil = require('../util/jsx');
+const docsUrl = require('../util/docsUrl');
+
+function isJSXText(node) {
+  return !!node && (node.type === 'JSXText' || node.type === 'Literal');
+}
+
+/**
+ * @param {string} text
+ * @returns {boolean}
+ */
+function isOnlyWhitespace(text) {
+  return text.trim().length === 0;
+}
+
+/**
+ * @param {ASTNode} node
+ * @returns {boolean}
+ */
+function isNonspaceJSXTextOrJSXCurly(node) {
+  return (isJSXText(node) && !isOnlyWhitespace(node.raw)) || node.type === 'JSXExpressionContainer';
+}
+
+/**
+ * Somehow fragment like this is useful: <Foo content={<>ee eeee eeee ...</>} />
+ * @param {ASTNode} node
+ * @returns {boolean}
+ */
+function isFragmentWithOnlyTextAndIsNotChild(node) {
+  return node.children.length === 1 &&
+    isJSXText(node.children[0]) &&
+    !(node.parent.type === 'JSXElement' || node.parent.type === 'JSXFragment');
+}
+
+/**
+ * @param {string} text
+ * @returns {string}
+ */
+function trimLikeReact(text) {
+  const leadingSpaces = /^\s*/.exec(text)[0];
+  const trailingSpaces = /\s*$/.exec(text)[0];
+
+  const start = arrayIncludes(leadingSpaces, '\n') ? leadingSpaces.length : 0;
+  const end = arrayIncludes(trailingSpaces, '\n') ? text.length - trailingSpaces.length : text.length;
+
+  return text.slice(start, end);
+}
+
+/**
+ * Test if node is like `<Fragment key={_}>_</Fragment>`
+ * @param {JSXElement} node
+ * @returns {boolean}
+ */
+function isKeyedElement(node) {
+  return node.type === 'JSXElement' &&
+    node.openingElement.attributes &&
+    node.openingElement.attributes.some(jsxUtil.isJSXAttributeKey);
+}
+
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    fixable: 'code',
+    docs: {
+      description: 'Disallow unnecessary fragments',
+      category: 'Possible Errors',
+      recommended: false,
+      url: docsUrl('jsx-no-useless-fragment')
+    },
+    messages: {
+      NeedsMoreChidren: 'Fragments should contain more than one child - otherwise, there‘s no need for a Fragment at all.',
+      ChildOfHtmlElement: 'Passing a fragment to an HTML element is useless.'
+    }
+  },
+
+  create(context) {
+    const reactPragma = pragmaUtil.getFromContext(context);
+    const fragmentPragma = pragmaUtil.getFragmentFromContext(context);
+
+    /**
+     * Test whether a node is an padding spaces trimmed by react runtime.
+     * @param {ASTNode} node
+     * @returns {boolean}
+     */
+    function isPaddingSpaces(node) {
+      return isJSXText(node) &&
+        isOnlyWhitespace(node.raw) &&
+        arrayIncludes(node.raw, '\n');
+    }
+
+    /**
+     * Test whether a JSXElement has less than two children, excluding paddings spaces.
+     * @param {JSXElement|JSXFragment} node
+     * @returns {boolean}
+     */
+    function hasLessThanTwoChildren(node) {
+      if (!node || !node.children || node.children.length < 2) {
+        return true;
+      }
+
+      return (
+        node.children.length -
+        (+isPaddingSpaces(node.children[0])) -
+        (+isPaddingSpaces(node.children[node.children.length - 1]))
+      ) < 2;
+    }
+
+    /**
+     * @param {JSXElement|JSXFragment} node
+     * @returns {boolean}
+     */
+    function isChildOfHtmlElement(node) {
+      return node.parent.type === 'JSXElement' &&
+        node.parent.openingElement.name.type === 'JSXIdentifier' &&
+        /^[a-z]+$/.test(node.parent.openingElement.name.name);
+    }
+
+    /**
+     * @param {JSXElement|JSXFragment} node
+     * @return {boolean}
+     */
+    function isChildOfComponentElement(node) {
+      return node.parent.type === 'JSXElement' &&
+        !isChildOfHtmlElement(node) &&
+        !jsxUtil.isFragment(node.parent, reactPragma, fragmentPragma);
+    }
+
+    /**
+     * @param {ASTNode} node
+     * @returns {boolean}
+     */
+    function canFix(node) {
+      // Not safe to fix fragments without a jsx parent.
+      if (!(node.parent.type === 'JSXElement' || node.parent.type === 'JSXFragment')) {
+        // const a = <></>
+        if (node.children.length === 0) {
+          return false;
+        }
+
+        // const a = <>cat {meow}</>
+        if (node.children.some(isNonspaceJSXTextOrJSXCurly)) {
+          return false;
+        }
+      }
+
+      // Not safe to fix `<Eeee><>foo</></Eeee>` because `Eeee` might require its children be a ReactElement.
+      if (isChildOfComponentElement(node)) {
+        return false;
+      }
+
+      return true;
+    }
+
+    /**
+     * @param {ASTNode} node
+     * @returns {Function | undefined}
+     */
+    function getFix(node) {
+      if (!canFix(node)) {
+        return undefined;
+      }
+
+      return function fix(fixer) {
+        const opener = node.type === 'JSXFragment' ? node.openingFragment : node.openingElement;
+        const closer = node.type === 'JSXFragment' ? node.closingFragment : node.closingElement;
+        const childrenText = context.getSourceCode().getText().slice(opener.range[1], closer.range[0]);
+
+        return fixer.replaceText(node, trimLikeReact(childrenText));
+      };
+    }
+
+    function checkNode(node) {
+      if (isKeyedElement(node)) {
+        return;
+      }
+
+      if (hasLessThanTwoChildren(node) && !isFragmentWithOnlyTextAndIsNotChild(node)) {
+        context.report({
+          node,
+          messageId: 'NeedsMoreChidren',
+          fix: getFix(node)
+        });
+      }
+
+      if (isChildOfHtmlElement(node)) {
+        context.report({
+          node,
+          messageId: 'ChildOfHtmlElement',
+          fix: getFix(node)
+        });
+      }
+    }
+
+    return {
+      JSXElement(node) {
+        if (jsxUtil.isFragment(node, reactPragma, fragmentPragma)) {
+          checkNode(node);
+        }
+      },
+      JSXFragment: checkNode
+    };
+  }
+};