From 4bdeb5c97ec3334a479520189015ed97c1932e0f Mon Sep 17 00:00:00 2001
From: golopot <golopot@gmail.com>
Date: Thu, 16 May 2019 20:48:45 +0800
Subject: [PATCH] Start reporting fragments in html element

---
 README.md                                  |  2 +-
 docs/rules/jsx-no-useless-fragment.md      | 18 +++++++++--
 lib/rules/jsx-no-useless-fragment.js       | 26 +++++++++++++---
 lib/types.d.ts                             |  2 ++
 tests/lib/rules/jsx-no-useless-fragment.js | 35 +++++++++++++++++++++-
 5 files changed, 75 insertions(+), 8 deletions(-)

diff --git a/README.md b/README.md
index 463cff4ceb..77decc5a46 100644
--- a/README.md
+++ b/README.md
@@ -169,7 +169,7 @@ Enable the rules that you would like to use.
 * [react/jsx-no-literals](docs/rules/jsx-no-literals.md): Prevent usage of unwrapped JSX strings
 * [react/jsx-no-target-blank](docs/rules/jsx-no-target-blank.md): Prevent usage of unsafe `target='_blank'`
 * [react/jsx-no-undef](docs/rules/jsx-no-undef.md): Disallow undeclared variables in JSX
-* [react/jsx-no-useless-fragment](docs/rules/jsx-no-useless-fragment.md): Disallow fragments with less than 2 children
+* [react/jsx-no-useless-fragment](docs/rules/jsx-no-useless-fragment.md): Disallow unnescessary fragments
 * [react/jsx-one-expression-per-line](docs/rules/jsx-one-expression-per-line.md): Limit to one expression per line in JSX
 * [react/jsx-curly-brace-presence](docs/rules/jsx-curly-brace-presence.md): Enforce curly braces or disallow unnecessary curly braces in JSX
 * [react/jsx-fragments](docs/rules/jsx-fragments.md): Enforce shorthand or standard form for React fragments
diff --git a/docs/rules/jsx-no-useless-fragment.md b/docs/rules/jsx-no-useless-fragment.md
index 8e2f9e3fed..a096d133d4 100644
--- a/docs/rules/jsx-no-useless-fragment.md
+++ b/docs/rules/jsx-no-useless-fragment.md
@@ -1,6 +1,6 @@
-# Disallow fragments with less than 2 children (react/jsx-no-useless-fragment)
+# Disallow unnecessary fragments (react/jsx-no-useless-fragment)
 
-A fragment is redundant if it only wraps a single child.
+A fragment is redundant if it contains only one child, or if it is the child of a html element.
 
 ## Rule Details
 
@@ -18,6 +18,13 @@ The following patterns are considered warnings:
 <Fragment>foo</Fragment>
 
 <React.Fragment>foo</React.Fragment>
+
+<section>
+  <>
+    <div />
+    <div />
+  </>
+</section>
 ```
 
 The following patterns are **not** considered warnings:
@@ -31,4 +38,11 @@ The following patterns are **not** considered warnings:
 <>foo {bar}</>
 
 <> {foo}</>
+
+<SomeComponent>
+  <>
+    <div />
+    <div />
+  </>
+</SomeComponent>
 ```
diff --git a/lib/rules/jsx-no-useless-fragment.js b/lib/rules/jsx-no-useless-fragment.js
index 5a0380cd5c..9c9d5f9b33 100644
--- a/lib/rules/jsx-no-useless-fragment.js
+++ b/lib/rules/jsx-no-useless-fragment.js
@@ -62,7 +62,8 @@ module.exports = {
       url: docsUrl('jsx-no-useless-fragment')
     },
     messages: {
-      NeedsMoreChidren: 'Fragments should contain more than one child.'
+      NeedsMoreChidren: 'Fragments should contain more than one child.',
+      ChildOfHtmlElement: 'Fragment in a html element is useless.'
     }
   },
 
@@ -79,22 +80,39 @@ module.exports = {
       ) < 2;
     }
 
-    function checkChildrenLength(node) {
+    /**
+     * @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);
+    }
+
+    function checkNode(node) {
       if (hasLessThanTwoChildren(node)) {
         context.report({
           node,
           messageId: 'NeedsMoreChidren'
         });
       }
+
+      if (isChildOfHtmlElement(node)) {
+        context.report({
+          node,
+          messageId: 'ChildOfHtmlElement'
+        });
+      }
     }
 
     return {
       JSXElement(node) {
         if (isFragment(node, context)) {
-          checkChildrenLength(node);
+          checkNode(node);
         }
       },
-      JSXFragment: checkChildrenLength
+      JSXFragment: checkNode
     };
   }
 };
diff --git a/lib/types.d.ts b/lib/types.d.ts
index d1ae21f948..91e5b4bd48 100644
--- a/lib/types.d.ts
+++ b/lib/types.d.ts
@@ -9,6 +9,8 @@ declare global {
   type Token = eslint.AST.Token;
   type Fixer = eslint.Rule.RuleFixer;
   type JSXAttribute = ASTNode;
+  type JSXElement = ASTNode;
+  type JSXFragment = ASTNode;
   type JSXSpreadAttribute = ASTNode;
 
   interface Context extends eslint.SourceCode {
diff --git a/tests/lib/rules/jsx-no-useless-fragment.js b/tests/lib/rules/jsx-no-useless-fragment.js
index eb53b73a15..4c7d887009 100644
--- a/tests/lib/rules/jsx-no-useless-fragment.js
+++ b/tests/lib/rules/jsx-no-useless-fragment.js
@@ -47,7 +47,15 @@ ruleTester.run('jsx-no-uselses-fragment', rule, {
     },
     '<NotFragment />',
     '<React.NotFragment />',
-    '<NotReact.Fragment />'
+    '<NotReact.Fragment />',
+    {
+      code: '<Foo><><div /><div /></></Foo>',
+      parser: parsers.BABEL_ESLINT
+    },
+    {
+      code: '<div p={<>{"a"}{"b"}</>} />',
+      parser: parsers.BABEL_ESLINT
+    }
   ],
   invalid: [
     {
@@ -95,6 +103,31 @@ ruleTester.run('jsx-no-uselses-fragment', rule, {
       code: '<></>',
       errors: [{messageId: 'NeedsMoreChidren'}],
       parser: parsers.BABEL_ESLINT
+    },
+    {
+      code: '<div><>foo</></div>',
+      errors: [{messageId: 'NeedsMoreChidren'}, {messageId: 'ChildOfHtmlElement'}],
+      parser: parsers.BABEL_ESLINT
+    },
+    {
+      code: '<div><>{"a"}{"b"}</></div>',
+      errors: [{messageId: 'ChildOfHtmlElement'}],
+      parser: parsers.BABEL_ESLINT
+    },
+    {
+      code: `
+        <section>
+          <Eeee />
+          <Eeee />  
+          <>{"a"}{"b"}</>
+        </section>`,
+      errors: [{messageId: 'ChildOfHtmlElement'}],
+      parser: parsers.BABEL_ESLINT
+    },
+
+    {
+      code: '<div><Fragment>{"a"}{"b"}</Fragment></div>',
+      errors: [{messageId: 'ChildOfHtmlElement'}]
     }
   ]
 });