feat: adds no-default-alt-text from The Hub; scaffolds tests

Author: andrialexandrou

.gitignore

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+node_modules

accessibility-rules.js

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+const noDefaultAltText = require('./no-default-alt-text')
+
+module.exports.noDefaultAltText = noDefaultAltText
+
+module.exports.all = [
+    noDefaultAltText
+]

no-default-alt-text.js

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+// Regex to match alt text that is the same as the default image filename 
+// e.g. "Screen Shot 2020-10-20 at 2 52 27 PM"
+// e.g. "Screenshot 2020-10-20 at 2 52 27 PM"
+const altTextRegex = /^Screen\s?shot \d{4}-\d{2}-\d{2} at \d \d{2} \d{2} [A|P]M$/gi
+const altTextTagRegex = /alt=\"Screen\s?shot \d{4}-\d{2}-\d{2} at \d \d{2} \d{2} [A|P]M\"/gi
+
+module.exports = {
+    "names": ["GH001", "no-default-alt-text"],
+    "description": "Images should not use the MacOS default screenshot filename as alternate text (alt text). For more information see: https://primer.style/design/accessibility/alternative-text-for-images",
+    "information": new URL("https://primer.style/design/accessibility/alternative-text-for-images"),
+    "tags": ["accessibility", "images"],
+    "function": function GH001(params, onError) {
+        params.tokens.filter(t => t.type === "inline").forEach(token => {
+            token.children.filter(t => t.type === "image").forEach(image => {
+                if (image.content.match(altTextRegex)) {
+                    onError({
+                        lineNumber: image.lineNumber,
+                        details: `For image: ${image.content}`
+                    })
+                }
+            })
+        })
+
+        let lineNumber = 1
+        params.lines.forEach(line => {
+            if (line.match(altTextTagRegex)) {
+                onError({
+                    lineNumber: lineNumber,
+                    details: `For line: ${line}`
+                })
+            }
+            lineNumber++
+        })
+    }
+}