Add iOS Validate Environment Script (#19750)

Summary:
Fixes #19694 this diff adds an iOS environment validation script as requested by hramos.

 A similar script for Android exists: scripts/validate-android-test-env.sh.

This script:

- Validates that the minimum required Xcode version is installed (people using Xcode 8 with a recent release may encounter cryptic build errors).

- Validates the correct Node version is installed (Node 10 is not fully supported at the time, Node 6 is no longer supported).

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Run ./scripts/validate-ios-test-env.sh on a properly setup OSX machine and verify it works, change the version comparison and make sure it fails.

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[INTERNAL] [ENHANCEMENT] [scripts] - Add iOS validate environment script

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  **INTERNAL and MINOR tagged notes will not be included in the next version's final release notes.**

    CATEGORY
  [----------]      TYPE
  [ CLI      ] [-------------]    LOCATION
  [ DOCS     ] [ BREAKING    ] [-------------]
  [ GENERAL  ] [ BUGFIX      ] [ {Component} ]
  [ INTERNAL ] [ ENHANCEMENT ] [ {Filename}  ]
  [ IOS      ] [ FEATURE     ] [ {Directory} ]   |-----------|
  [ ANDROID  ] [ MINOR       ] [ {Framework} ] - | {Message} |
  [----------] [-------------] [-------------]   |-----------|

 EXAMPLES:

 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
 [CLI] [FEATURE] [local-cli/info/info.js] - CLI easier to do things with
 [DOCS] [BUGFIX] [GettingStarted.md] - Accidentally a thing/word
 [GENERAL] [ENHANCEMENT] [Yoga] - Added new yoga thing/position
 [INTERNAL] [FEATURE] [./scripts] - Added thing to script that nobody will see
-->
Pull Request resolved: https://github.com/facebook/react-native/pull/19750

Differential Revision: D9005151

Pulled By: hramos

fbshipit-source-id: a69ef2a6e513e580089c791fd44a0e70c2a3f240

scripts/validate-ios-test-env.sh

@@ -0,0 +1,51 @@
+#!/bin/bash
+
+# This script validates that iOS is set up correctly for the
+# testing environment.
+#
+# In particular, it checks that the minimum required Xcode version is installed.
+# It also checks that the correct Node version is installed. Node 10 is not fully 
+# supported at the time and Node 6 is no longer supported.
+
+# Function used to compare dot seperated version numbers
+function version_gt() { test "$(printf '%s\n' "$@" | sort -V | head -n 1)" != "$1"; }
+
+# Check that node is installed.
+if [ -z "$(which node)" ]; then
+  echo "Could not find Node binary. Please check your nodejs install."
+  echo "See http://facebook.github.io/react-native/docs/getting-started.html for instructions."
+  exit 1
+fi
+
+# Check that the correct version of node is installed
+NODE_VERSION="$(command node --version | sed 's/[-/a-zA-Z]//g' |sed 's/.\{2\}$//')"
+
+if (( $(echo "${NODE_VERSION} <= 6.0" | bc -l) )); then
+  echo "Node ${NODE_VERSION} detected. This version of Node is not supported."
+  echo "Note: Node 10 is not fully supported at the time and Node 6 is no longer supported."  
+  echo "See https://nodejs.org/en/download/ for instructions."
+  exit 1
+fi
+
+if (( $(echo "${NODE_VERSION} == 10.0" | bc -l) )); then
+  echo "Node ${NODE_VERSION} detected. This version of Node is not fully supported at this time."
+  echo "See https://github.com/facebook/react-native/issues/19229 for more information."
+  exit 1
+fi
+
+# Check that Xcode is installed.
+if [ -z "$(which xcodebuild)" ]; then
+  echo "Could not find Xcode build tools. Please check your Xcode install."
+  echo "See http://facebook.github.io/react-native/docs/getting-started.html for instructions."
+  exit 1
+fi
+
+MIN_XCODE_VERSION=9.4
+# Check that the correct version of Xcode is installed
+XCODE_VERSION="$(command xcodebuild -version | sed '$ d' | sed 's/[-/a-zA-Z]//g')"
+if (version_gt $MIN_XCODE_VERSION $XCODE_VERSION) && [ "$XCODE_VERSION" != "$MIN_XCODE_VERSION" ]; then
+  echo "Xcode ${XCODE_VERSION} detected. React Native requires ${MIN_XCODE_VERSION} or newer."
+  echo "Older versions of Xcode may cause cryptic build errors."
+  echo "See http://facebook.github.io/react-native/docs/getting-started.html for instructions."
+  exit 1
+fi