Add flow to package.

There is a purposely malformed `package.json` file in one of the
dependencies (for testing purposes). We are using `.flowconfig` to
ignore this file. See issue:
facebook/flow#2364.

Author: StevenXL

.flowconfig

@@ -0,0 +1,13 @@
+[ignore]
+.*/node_modules/resolve/test/resolver/malformed_package_json/package.json
+
+
+[include]
+
+[libs]
+
+[lints]
+
+[options]
+
+[strict]

package.json

@@ -11,7 +11,8 @@
   },
   "babel": {
     "presets": [
-      "@babel/preset-env"
+      "@babel/preset-env",
+      "@babel/preset-flow"
     ]
   },
   "repository": "[email protected]:freckle/react-hooks.git",
@@ -22,6 +23,8 @@
     "@babel/cli": "^7.17.6",
     "@babel/core": "^7.17.9",
     "@babel/preset-env": "^7.16.11",
+    "@babel/preset-flow": "^7.16.7",
+    "flow-bin": "^0.175.1",
     "jest": "^27.5.1",
     "watch": "^1.0.2"
   }

src/index.js

@@ -1,3 +1,5 @@
-const helloWord = () => "Hello, World!";
+// @flow
+
+const helloWord = (): string => "Hello, World!";
 
 export { helloWord };

yarn.lock

@@ -467,6 +467,13 @@
   dependencies:
     "@babel/helper-plugin-utils" "^7.8.3"
 
+"@babel/plugin-syntax-flow@^7.16.7":
+  version "7.16.7"
+  resolved "https://registry.yarnpkg.com/@babel/plugin-syntax-flow/-/plugin-syntax-flow-7.16.7.tgz#202b147e5892b8452bbb0bb269c7ed2539ab8832"
+  integrity sha512-UDo3YGQO0jH6ytzVwgSLv9i/CzMcUjbKenL67dTrAZPPv6GFAtDhe6jqnvmoKzC/7htNTohhos+onPtDMqJwaQ==
+  dependencies:
+    "@babel/helper-plugin-utils" "^7.16.7"
+
 "@babel/plugin-syntax-import-meta@^7.8.3":
   version "7.10.4"
   resolved "https://registry.yarnpkg.com/@babel/plugin-syntax-import-meta/-/plugin-syntax-import-meta-7.10.4.tgz#ee601348c370fa334d2207be158777496521fd51"
@@ -625,6 +632,14 @@
     "@babel/helper-builder-binary-assignment-operator-visitor" "^7.16.7"
     "@babel/helper-plugin-utils" "^7.16.7"
 
+"@babel/plugin-transform-flow-strip-types@^7.16.7":
+  version "7.16.7"
+  resolved "https://registry.yarnpkg.com/@babel/plugin-transform-flow-strip-types/-/plugin-transform-flow-strip-types-7.16.7.tgz#291fb140c78dabbf87f2427e7c7c332b126964b8"
+  integrity sha512-mzmCq3cNsDpZZu9FADYYyfZJIOrSONmHcop2XEKPdBNMa4PDC4eEvcOvzZaCNcjKu72v0XQlA5y1g58aLRXdYg==
+  dependencies:
+    "@babel/helper-plugin-utils" "^7.16.7"
+    "@babel/plugin-syntax-flow" "^7.16.7"
+
 "@babel/plugin-transform-for-of@^7.16.7":
   version "7.16.7"
   resolved "https://registry.yarnpkg.com/@babel/plugin-transform-for-of/-/plugin-transform-for-of-7.16.7.tgz#649d639d4617dff502a9a158c479b3b556728d8c"
@@ -874,6 +889,15 @@
     core-js-compat "^3.20.2"
     semver "^6.3.0"
 
+"@babel/preset-flow@^7.16.7":
+  version "7.16.7"
+  resolved "https://registry.yarnpkg.com/@babel/preset-flow/-/preset-flow-7.16.7.tgz#7fd831323ab25eeba6e4b77a589f680e30581cbd"
+  integrity sha512-6ceP7IyZdUYQ3wUVqyRSQXztd1YmFHWI4Xv11MIqAlE4WqxBSd/FZ61V9k+TS5Gd4mkHOtQtPp9ymRpxH4y1Ug==
+  dependencies:
+    "@babel/helper-plugin-utils" "^7.16.7"
+    "@babel/helper-validator-option" "^7.16.7"
+    "@babel/plugin-transform-flow-strip-types" "^7.16.7"
+
 "@babel/preset-modules@^0.1.5":
   version "0.1.5"
   resolved "https://registry.yarnpkg.com/@babel/preset-modules/-/preset-modules-0.1.5.tgz#ef939d6e7f268827e1841638dc6ff95515e115d9"
@@ -1848,6 +1872,11 @@ find-up@^4.0.0, find-up@^4.1.0:
     locate-path "^5.0.0"
     path-exists "^4.0.0"
 
+flow-bin@^0.175.1:
+  version "0.175.1"
+  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.175.1.tgz#72237070ba4f293f9e04113481e18929c1de50df"
+  integrity sha512-zMCP0BPa9BrfBSR7QTcyT/XBwzUbyLdNG0eXvBuNxfHCbMRkUzSceRoOaEZIw+R+GH0UHjVfUvPJ30hXxz1Nfw==
+
 form-data@^3.0.0:
   version "3.0.1"
   resolved "https://registry.yarnpkg.com/form-data/-/form-data-3.0.1.tgz#ebd53791b78356a99af9a300d4282c4d5eb9755f"