Add linting, commit hooks

Author: lpsinger

.eslintignore

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+.gitignore

.husky/pre-commit

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+#!/usr/bin/env sh
+. "$(dirname -- "$0")/_/husky.sh"
+
+npx lint-staged

lint-staged.config.mjs

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+import { ESLint } from 'eslint'
+import prettier from 'prettier'
+
+// Adapted from https://github.com/okonet/lint-staged#how-can-i-ignore-files-from-eslintignore
+async function eslintRemoveIgnoredFiles(files) {
+  const eslint = new ESLint()
+  const isIgnored = await Promise.all(
+    files.map((file) => {
+      return eslint.isPathIgnored(file)
+    })
+  )
+  const filteredFiles = files.filter((_, i) => !isIgnored[i])
+  return filteredFiles.join(' ')
+}
+
+// Adapted from https://github.com/okonet/lint-staged#how-can-i-ignore-files-from-eslintignore
+function prettierRemoveIgnoredFiles(files) {
+  const filteredFiles = files.filter(
+    (file) => !prettier.getFileInfo(file).isIgnored
+  )
+  return filteredFiles.join(' ')
+}
+
+export default {
+  // Note, this rule should include *.mdx, but mdx linting is broken.
+  // See https://github.com/mdx-js/eslint-mdx/issues/367.
+  '*.{cjs,mjs,js,jsx,ts,tsx}': async (files) => {
+    const filteredFiles = await eslintRemoveIgnoredFiles(files)
+    if (!files) return []
+    return `eslint --cache --fix --max-warnings 0 ${filteredFiles}`
+  },
+  '*.{ts,tsx}': () => 'tsc -p .',
+  '*.{css,scss,cjs,mjs,js,json,jsx,md,mdx,ts,tsx}': async (files) => {
+    const filteredFiles = prettierRemoveIgnoredFiles(files)
+    if (!files) return []
+    return `prettier --write ${filteredFiles}`
+  },
+}