Add rule max-attributes-per-line (resolves #47)

docs/rules/max-attributes-per-line.md

@@ -0,0 +1,122 @@
+# Define the number of attributes allows per line (max-attributes-per-line)
+
+Limits the maximum number of attributes/properties per line to improve readability.
+
+
+## :book: Rule Details
+
+This rule aims to enforce a number of attributes per line in templates.
+It checks all the elements in a template and verifies that the number of attributes per line does not exceed the defined maximum.
+An attribute is considered to be in a new line when there is a line break between two attributes.
+
+There is a configurable number of attributes that are acceptable in one-line case (default 3), as well as how many attributes are acceptable per line in multi-line case (default 1).
+
+:-1: Examples of **incorrect** code for this rule:
+
+```html
+<component lorem="1" ipsum="2" dolor="3" sit="4">
+</component>
+
+<component
+  lorem="1" ipsum="2"
+  dolor="3"
+  sit="4"
+>
+</component>
+```
+
+:+1: Examples of **correct** code for this rule:
+
+```html
+<component lorem="1" ipsum="2" dolor="3">
+</component>
+
+<component
+  lorem="1"
+  ipsum="2"
+  dolor="3"
+  sit="4"
+>
+</component>
+
+```
+
+### :wrench:  Options
+
+```
+{
+  "vue/max-attributes-per-line": [{
+    "singleline": 3,
+    "multiline": {
+      max: 1,
+      allowFirstLine: false
+    }
+  }]
+}
+```
+
+#### `allowFirstLine`
+For multi-line declarations, defines if allows attributes to be put in the first line. (Default false)
+
+:-1: Example of **incorrect** code for this setting:
+```html
+// [{ "multiline": { "allowFirstLine": false }}]
+<component foo="John" bar="Smith"
+  foobar={5555555}>
+</component>;
+```
+
+:+1: Example of **correct** code for this setting:
+```html
+// [{ "multiline": { "allowFirstLine": false }}]
+<component
+  foo="John"
+  bar="Smith"
+  foobar={5555555}
+  >
+</component>;
+```
+
+
+#### `singleline`
+Number of maximum attributes per line when the opening tag is in a single line. (Default is 3)
+
+:-1: Example of **incorrect** code for this setting:
+```html
+// [{"singleline": 2,}]
+<component foo="John" bar="Smith" foobar={5555555}></component>;
+```
+
+:+1: Example of **correct** code for this setting:
+```html
+// [{"singleline": 3,}]
+<component foo="John" bar="Smith" foobar={5555555}></component>;
+```
+
+
+#### `multiline`
+Number of maximum attributes per line when a tag is in multiple lines. (Default is 1)
+
+:-1: Example of **incorrect** code for this setting:
+```html
+// [{"multiline": 1}]
+<component foo="John" bar="Smith"
+  foobar={5555555}>
+</component>;
+```
+
+:+1: Example of **correct** code for this setting:
+```html
+// [{"multiline": 1}]
+<component
+  foo="John"
+  bar="Smith"
+  foobar={5555555}
+  >
+</component>;
+```
+
+## When Not To Use It
+
+If you do not want to check the number of attributes declared per line you can disable this rule.
+

lib/rules/max-attributes-per-line.js

@@ -0,0 +1,161 @@
+/**
+ * @fileoverview Define the number of attributes allows per line
+ * @author Filipa Lacerda
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+const utils = require('../utils')
+
+module.exports = {
+  meta: {
+    docs: {
+      description: 'Define the number of attributes allows per line',
+      category: 'Stylistic Issues',
+      recommended: false
+    },
+    fixable: null,
+    schema: [
+      {
+        type: 'object',
+        properties: {
+          singleline: {
+            anyOf: [
+              {
+                type: 'number',
+                minimum: 1
+              },
+              {
+                type: 'object',
+                properties: {
+                  max: {
+                    type: 'number',
+                    minimum: 1
+                  }
+                },
+                additionalProperties: false
+              }
+            ]
+          },
+          multiline: {
+            anyOf: [
+              {
+                type: 'number',
+                minimum: 1
+              },
+              {
+                type: 'object',
+                properties: {
+                  max: {
+                    type: 'number',
+                    minimum: 1
+                  },
+                  allowFirstLine: {
+                    type: 'boolean'
+                  }
+                },
+                additionalProperties: false
+              }
+            ]
+          }
+        }
+      }
+    ]
+  },
+
+  create: function (context) {
+    const configuration = parseOptions(context.options[0])
+    const multilineMaximum = configuration.multiline
+    const singlelinemMaximum = configuration.singleline
+    const canHaveFirstLine = configuration.allowFirstLine
+
+    utils.registerTemplateBodyVisitor(context, {
+      'VStartTag' (node) {
+        const numberOfAttributes = node.attributes.length
+
+        if (!numberOfAttributes) return
+
+        if (utils.isSingleLine(node) && numberOfAttributes > singlelinemMaximum) {
+          showErrors(node.attributes.slice(singlelinemMaximum), node)
+        }
+
+        if (!utils.isSingleLine(node)) {
+          if (!canHaveFirstLine && node.attributes[0].loc.start.line === node.loc.start.line) {
+            showErrors([node.attributes[0]], node)
+          }
+
+          groupAttrsByLine(node.attributes)
+            .filter(attrs => attrs.length > multilineMaximum)
+            .forEach(attrs => showErrors(attrs.splice(multilineMaximum), node))
+        }
+      }
+    })
+
+    // ----------------------------------------------------------------------
+    // Helpers
+    // ----------------------------------------------------------------------
+    function parseOptions (options) {
+      const defaults = {
+        singleline: 3,
+        multiline: 1,
+        allowFirstLine: false
+      }
+
+      if (options) {
+        if (typeof options.singleline === 'number') {
+          defaults.singleline = options.singleline
+        } else if (options.singleline && options.singleline.max) {
+          defaults.singleline = options.singleline.max
+        }
+
+        if (options.multiline) {
+          if (typeof options.multiline === 'number') {
+            defaults.multiline = options.multiline
+          } else if (typeof options.multiline === 'object') {
+            if (options.multiline.max) {
+              defaults.multiline = options.multiline.max
+            }
+
+            if (options.multiline.allowFirstLine) {
+              defaults.allowFirstLine = options.multiline.allowFirstLine
+            }
+          }
+        }
+      }
+
+      return defaults
+    }
+
+    function showErrors (attributes, node) {
+      attributes.forEach((prop) => {
+        context.report({
+          node: prop,
+          loc: prop.loc,
+          message: 'Attribute "{{propName}}" should be on a new line.',
+          data: {
+            propName: prop.key.name
+          }
+        })
+      })
+    }
+
+    function groupAttrsByLine (attributes) {
+      const propsPerLine = [[attributes[0]]]
+
+      attributes.reduce((previous, current) => {
+        if (previous.loc.end.line === current.loc.start.line) {
+          propsPerLine[propsPerLine.length - 1].push(current)
+        } else {
+          propsPerLine.push([current])
+        }
+        return current
+      })
+
+      return propsPerLine
+    }
+
+    return {}
+  }
+}

lib/utils/index.js

@@ -587,5 +587,14 @@ module.exports = {
         }
       }
     }
+  },
+
+  /**
+   * Check whether the component is declared in a single line or not.
+   * @param {ASTNode} node
+   * @returns {boolean}
+   */
+  isSingleLine (node) {
+    return node.loc.start.line === node.loc.end.line
   }
 }