Add linting of source in markdown files

package.json

@@ -189,6 +189,7 @@
 		"lint-css": "wp-scripts lint-style '**/*.scss'",
 		"lint-css:fix": "npm run lint-css -- --fix",
 		"lint-types": "tsc",
+		"lint-md": "wp-scripts lint-md",
 		"package-plugin": "./bin/build-plugin-zip.sh",
 		"pot-to-php": "./bin/pot-to-php.js",
 		"publish:check": "lerna updated",

packages/scripts/config/.eslintrc-md.js

@@ -0,0 +1,19 @@
+// eslint config for markdown documentation
+
+// This configuration is used when parsing JS code blocks
+// in documentation. It attempts to allow for snippets of
+// codes which may define variables unused, or use variables
+// that are assumed to be defined.
+module.exports = {
+	root: true,
+	plugins: [
+		'markdown',
+	],
+	extends: [
+		'plugin:@wordpress/eslint-plugin/recommended',
+	],
+	"rules": {
+		"no-undef": "off",
+		"no-unused-vars": "off"
+	},
+};

packages/scripts/package.json

@@ -46,6 +46,7 @@
 		"cross-spawn": "^5.1.0",
 		"decompress-zip": "^0.2.2",
 		"eslint": "^6.1.0",
+		"eslint-plugin-markdown": "1.0.1",
 		"jest": "^24.7.1",
 		"jest-puppeteer": "^4.3.0",
 		"js-yaml": "^3.13.1",

packages/scripts/scripts/lint-md.js

@@ -0,0 +1,46 @@
+/**
+ * External dependencies
+ */
+const { sync: spawn } = require( 'cross-spawn' );
+const { sync: resolveBin } = require( 'resolve-bin' );
+
+/**
+ * Internal dependencies
+ */
+const {
+	fromConfigRoot,
+	getArgsFromCLI,
+	hasArgInCLI,
+	hasFileArgInCLI,
+	hasProjectFile,
+} = require( '../utils' );
+
+const args = getArgsFromCLI();
+
+const defaultFilesArgs = hasFileArgInCLI() ? [] : [ '**/*.md' ];
+
+// See: https://eslint.org/docs/user-guide/configuring#using-configuration-files-1.
+const hasLintConfig = hasArgInCLI( '-c' ) || hasArgInCLI( '--config' );
+
+// When a configuration is not provided by the project, use from the default
+// provided with the scripts module. Instruct ESLint to avoid discovering via
+// the `--no-eslintrc` flag, as otherwise it will still merge with inherited.
+const defaultConfigArgs = ! hasLintConfig ?
+	[ '--no-eslintrc', '--config', fromConfigRoot( '.eslintrc-md.js' ) ] :
+	[];
+
+// See: https://eslint.org/docs/user-guide/configuring#ignoring-files-and-directories.
+const hasIgnoredFiles = hasArgInCLI( '--ignore-path' ) ||
+	hasProjectFile( '.eslintignore' );
+
+const defaultIgnoreArgs = ! hasIgnoredFiles ?
+	[ '--ignore-path', fromConfigRoot( '.eslintignore' ) ] :
+	[];
+
+const result = spawn(
+	resolveBin( 'eslint' ),
+	[ ...defaultConfigArgs, ...defaultIgnoreArgs, ...args, ...defaultFilesArgs ],
+	{ stdio: 'inherit' }
+);
+
+process.exit( result.status );