jsx-max-props-per-line: Fix when prop spans multiple lines

In this patch we now consider props to be on the same "line" if the line
of where one prop ends matches the line of where the next prop begins.

e.g.
```
<App foo={{
}} bar />
```

`foo` and `bar` are now considered to be on the same line. Previously,
we would only look at the line in which the prop begins.

Author: kentor

docs/rules/jsx-max-props-per-line.md

@@ -4,12 +4,16 @@ Limiting the maximum of props on a single line can improve readability.
 
 ## Rule Details
 
-This rule checks all JSX elements and verifies that the number of props per line do not exceed the maximum allowed. A spread attribute counts as one prop. This rule is off by default and when on the default maximum of props on one line is `1`.
+This rule checks all JSX elements and verifies that the number of props per line do not exceed the maximum allowed. Props are considered to be in a new line if there is a line break between the start of the prop and the end of the previous prop. A spread attribute counts as one prop. This rule is off by default and when on the default maximum of props on one line is `1`.
 
 The following patterns are considered warnings:
 
 ```jsx
 <Hello lastName="Smith" firstName="John" />;
+
+<Hello foo={{
+  bar
+}} baz />;
 ```
 
 The following patterns are not considered warnings:

lib/rules/jsx-max-props-per-line.js

@@ -5,8 +5,6 @@
 
 'use strict';
 
-var has = require('has');
-
 // ------------------------------------------------------------------------------
 // Rule Definition
 // ------------------------------------------------------------------------------
@@ -45,30 +43,31 @@ module.exports = {
 
     return {
       JSXOpeningElement: function (node) {
-        var props = {};
+        if (!node.attributes.length) {
+          return;
+        }
+
+        var firstProp = node.attributes[0];
+        var linePartitionedProps = [[firstProp]];
 
-        node.attributes.forEach(function(decl) {
-          var line = decl.loc.start.line;
-          if (props[line]) {
-            props[line].push(decl);
+        node.attributes.reduce(function(last, decl) {
+          if (last.loc.end.line === decl.loc.start.line) {
+            linePartitionedProps[linePartitionedProps.length - 1].push(decl);
           } else {
-            props[line] = [decl];
+            linePartitionedProps.push([decl]);
           }
+          return decl;
         });
 
-        for (var line in props) {
-          if (!has(props, line)) {
-            continue;
-          }
-          if (props[line].length > maximum) {
-            var name = getPropName(props[line][maximum]);
+        linePartitionedProps.forEach(function(propsInLine) {
+          if (propsInLine.length > maximum) {
+            var name = getPropName(propsInLine[maximum]);
             context.report({
-              node: props[line][maximum],
+              node: propsInLine[maximum],
               message: 'Prop `' + name + '` must be placed on a new line'
             });
-            break;
           }
-        }
+        });
       }
     };
   }

tests/lib/rules/jsx-max-props-per-line.js

@@ -89,5 +89,24 @@ ruleTester.run('jsx-max-props-per-line', rule, {
     ].join('\n'),
     errors: [{message: 'Prop `this.props` must be placed on a new line'}],
     parserOptions: parserOptions
+  }, {
+    code: [
+      '<App',
+      '  foo={{',
+      '  }} bar',
+      '/>'
+    ].join('\n'),
+    errors: [{message: 'Prop `bar` must be placed on a new line'}],
+    parserOptions: parserOptions
+  }, {
+    code: [
+      '<App',
+      '  foo={{',
+      '  }} bar baz',
+      '/>'
+    ].join('\n'),
+    options: [{maximum: 2}],
+    errors: [{message: 'Prop `baz` must be placed on a new line'}],
+    parserOptions: parserOptions
   }]
 });