Adds explicit-heading rule

src/rules/__tests__/implicit-heading.test.js

@@ -0,0 +1,52 @@
+const rule = require('../explicit-heading')
+const {RuleTester} = require('eslint')
+
+const ruleTester = new RuleTester({
+  parserOptions: {
+    ecmaVersion: 'latest',
+    sourceType: 'module',
+    ecmaFeatures: {
+      jsx: true
+    }
+  }
+})
+
+ruleTester.run('explicit-heading', rule, {
+  valid: [
+  `import {Heading} from '@primer/react';
+  <Heading as="h1">Heading level 1</Heading>
+  `,
+  `import {Heading} from '@primer/react';
+  <Heading as="h2">Heading level 2</Heading>
+  `,
+  `import {Heading} from '@primer/react';
+  <Heading as="H3">Heading level 2</Heading>
+  `,
+],
+invalid: [    
+  {
+    code: `
+    import {Heading} from '@primer/react';
+
+    <Heading>Heading without "as"</Heading>
+    `,
+    errors: [
+      {
+        messageId: 'nonExplicitHeadingLevel'
+      }
+    ]
+  },
+  {
+    code: `
+    import {Heading} from '@primer/react';
+
+    <Heading as="span">Heading component used as "span"</Heading>
+    `,
+    errors: [
+      {
+        messageId: 'invalidAsValue'
+      }
+    ]
+  },
+]
+})

src/rules/explicit-heading.js

@@ -0,0 +1,60 @@
+const {isPrimerComponent} = require('../utils/is-primer-component')
+const {getJSXOpeningElementName} = require('../utils/get-jsx-opening-element-name')
+const {getJSXOpeningElementAttribute} = require('../utils/get-jsx-opening-element-attribute')
+
+const validHeadings = ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'];
+
+const isHeading = elem => getJSXOpeningElementName(elem) === 'Heading'
+const isUsingAs = elem => {
+    const asUsage = getJSXOpeningElementAttribute(elem, 'as');
+
+    if (!asUsage) return;
+
+    return asUsage.value;
+}
+
+const isValidAs = value => validHeadings.includes(value.toLowerCase());
+const isInvalid = elem => {
+    const elemAs = isUsingAs(elem);
+
+    if (!elemAs) return 'nonExplicitHeadingLevel'; 
+    if(!isValidAs(elemAs.value)) return 'invalidAsValue';
+
+    return false;
+}
+
+module.exports = {
+    meta: {
+        type: "problem",
+        schema: [
+            {
+              properties: {
+                skipImportCheck: {
+                  type: 'boolean'
+                }
+              }
+            }
+          ],
+          messages: {
+            nonExplicitHeadingLevel: "Heading must have an explicit heading level applied through `as` prop.",
+            invalidAsValue: "Usage of `as` must only be used for headings (h1-h6)."
+          }
+    },
+    create: function(context) {
+        return {
+            // callback functions
+            JSXOpeningElement(jsxNode) {
+                if (isPrimerComponent(jsxNode.name, context.getScope(jsxNode)) && isHeading(jsxNode)) {
+                    const error = isInvalid(jsxNode);
+
+                    if (error) {
+                      context.report({
+                        node: jsxNode,
+                        messageId: error
+                      })
+                    }
+                }
+            }
+        };
+    }
+};