Set up Prettier and eslint.

I (@benjamn) removed husky and made eslint run before tests, because I
don't want any pre-commit hooks in this repository. I tend to use Git in
ways that conflict with the assumptions these tools make.

.editorconfig

@@ -1,2 +1,13 @@
-[*.js]
+[*]
+insert_final_newline = true
+
+[{package.json}]
 indent_style = space
+indent_size = 2
+
+[{*.js, *.ts}]
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = true
+end_of_line = lf
+charset = utf-8

.eslintrc.js

@@ -0,0 +1,16 @@
+module.exports = {
+  parser: "@typescript-eslint/parser",
+  parserOptions: {
+    ecmaVersion: 6,
+    sourceType: "module",
+    ecmaFeatures: {
+      jsx: true,
+    },
+  },
+  rules: {
+    "no-var": "error",
+    "no-case-declarations": "error",
+    "no-fallthrough": "error",
+  },
+  ignorePatterns: ["test/data"],
+};

.gitignore

@@ -5,6 +5,7 @@
 
 # Ignore TypeScript-emitted files
 *.js
+!.*rc.js
 *.d.ts
 # Except...
 !/types/**/*.d.ts

.prettierignore

@@ -0,0 +1 @@
+**/*.d.ts

.prettierrc.js

@@ -0,0 +1,14 @@
+module.exports = {
+  printWidth: 100,
+  trailingComma: "all",
+  singleQuote: false,
+
+  overrides: [
+    {
+      files: "*.md",
+      options: {
+        printWidth: 60,
+      },
+    },
+  ],
+};

package.json

@@ -24,12 +24,20 @@
   "scripts": {
     "mocha": "test/run.sh",
     "debug": "test/run.sh --inspect-brk",
-    "test": "npm run build && npm run mocha",
+    "test": "npm run lint && npm run build && npm run mocha",
     "build": "npm run clean && tsc",
+    "lint": "eslint --ext .ts .",
+    "format": "prettier --write '{lib,test}/**.ts' '*rc.js'",
     "clean": "ts-emit-clean",
     "prepack": "npm run build",
     "postpack": "npm run clean"
   },
+  "lint-staged": {
+    "*.ts": [
+      "eslint",
+      "prettier -c"
+    ]
+  },
   "browser": {
     "fs": false
   },
@@ -47,10 +55,14 @@
     "@types/glob": "7.1.1",
     "@types/mocha": "5.2.7",
     "@types/node": "13.1.1",
+    "@typescript-eslint/parser": "^3.0.1",
+    "eslint": "^7.1.0",
     "esprima-fb": "15001.1001.0-dev-harmony-fb",
     "flow-parser": "0.119.1",
     "glob": "7.1.5",
+    "lint-staged": "^10.2.6",
     "mocha": "6.2.2",
+    "prettier": "^2.0.5",
     "reify": "0.20.12",
     "ts-emit-clean": "1.0.0",
     "ts-node": "7.0.1",