Fail iOS builds on malformed .env files, add troubleshooting instruct…

…ions (#516)

README.md

@@ -318,6 +318,12 @@ If using Dexguard, the shrinking phase will remove resources it thinks are unuse
 
     -keepresources string/build_config_package
 
+### TypeError: _reactNativeConfig.default.getConstants is not a function
+
+This error stems from `.env` file being malformed. Accepted formats are listed here https://regex101.com/r/cbm5Tp/1. Common causes are:
+  - Missing the .env file entirely
+  - Rogue space anywhere, example: in front of env variable: ` MY_ENV='foo'`
+
 ## Testing
 
 Since `react-native-config` contains native code, it cannot be run in a node.js environment (Jest, Mocha). [react-native-config-node](https://github.com/CureApp/react-native-config-node) provides a way to mock `react-native-config` for use in test runners - exactly as it is used in the actual app.

android/dotenv.gradle

@@ -48,7 +48,9 @@ def loadDotEnv(flavor = getCurrentFlavor()) {
 
     if (f.exists()) {
         f.eachLine { line ->
+            // https://regex101.com/r/cbm5Tp/1
             def matcher = (line =~ /^\s*(?:export\s+|)([\w\d\.\-_]+)\s*=\s*['"]?(.*?)?['"]?\s*$/)
+            // TODO: Fail Android builds if line doesn't match
             if (matcher.getCount() == 1 && matcher[0].size() == 3) {
                 env.put(matcher[0][1], matcher[0][2].replace('"', '\\"'))
             }

ios/ReactNativeConfig/ReadDotEnv.rb

@@ -40,7 +40,8 @@ def read_dot_env(envs_root)
 
     raw.split("\n").inject({}) do |h, line|
       m = line.match(dotenv_pattern)
-      next h if m.nil?
+      if m.nil?
+        abort('Invalid entry in .env file. Please verify your .env file is correctly formatted.')
 
       key = m[:key]
       # Ensure string (in case of empty value) and escape any quotes present in the value.