Remove HERMES_BUILD_FROM_SOURCE flag (#35397)

Summary:
Pull Request resolved: #35397

This Diff removes the `HERMES_BUILD_FROM_SOURCE` that was not always propagated to the original script. This lead to some cases where hermesC was built during `pod install` and then removed by the `react_native_post_install`'s `else` branch.

Basically, when the Pods are installed the first time, everything run smoothly. Subsequent invocations of `pod install`, to install other dependencies, for example, will incur in this problem because:
1. Cocoapods will see that hermes-engine is already installed
2. the podspec is not executed, given that the pod has been fetched from the cache
3. The env var is not set (given that the podspec is not executed)
4. the main script sees the env var as not set, `ENV['HERMES_BUILD_FROM_SOURCE'] == "1"` return false
5. The `else` branch is executed, and it removes the `hermesc_build_dir` and the `copy Hermes framework` script phase.

## Changelog:
[iOS][Changed] - Remove `HERMES_BUILD_FROM_SOURCE` flag

Reviewed By: cortinico, dmytrorykun

Differential Revision: D41373439

fbshipit-source-id: ea4aafd187c0ca3ff5c0d79f8aeaaa46ad50f499

Author: cipolleschi

scripts/cocoapods/__tests__/jsengine-test.rb

@@ -19,6 +19,7 @@ def setup
     end
 
     def teardown
+        ENV['HERMES_ENGINE_TARBALL_PATH'] = nil
         Open3.reset()
         Pod::Config.reset()
         Pod::UI.reset()
@@ -119,4 +120,21 @@ def test_setupHermes_installsPods_installsFabricSubspecWhenFabricEnabled
         assert_equal($podInvocation["React-hermes"][:path], "../../ReactCommon/hermes")
         assert_equal($podInvocation["libevent"][:version], "~> 2.1.12")
     end
+
+    # ================================= #
+    # TEST - isBuildingHermesFromSource #
+    # ================================= #
+    def test_isBuildingHermesFromSource_whenTarballIsNilAndVersionIsNotNightly_returnTrue
+        assert_true(is_building_hermes_from_source("1000.0.0"))
+    end
+
+    def test_isBuildingHermesFromSource_whenTarballIsNotNil_returnFalse
+        ENV['HERMES_ENGINE_TARBALL_PATH'] = "~/Downloads/hermes-ios-debug.tar.gz"
+        assert_false(is_building_hermes_from_source("1000.0.0"))
+    end
+
+    def test_isBuildingHermesFromSource_whenIsNigthly_returnsFalse
+        assert_false(is_building_hermes_from_source("0.0.0-"))
+    end
+
 end

scripts/cocoapods/jsengine.rb

@@ -63,3 +63,15 @@ def remove_copy_hermes_framework_script_phase(installer, react_native_path)
 def remove_hermesc_build_dir(react_native_path)
     %x(rm -rf #{react_native_path}/sdks/hermes-engine/build_host_hermesc)
 end
+
+def is_building_hermes_from_source(react_native_version)
+    is_nightly = react_native_version.start_with?('0.0.0-')
+    has_tarball = ENV['HERMES_ENGINE_TARBALL_PATH'] != nil
+
+    # this is the same logic in the hermes-engine.podspec
+    if has_tarball || is_nightly
+        return false
+    end
+
+    return true
+end

scripts/react_native_pods.rb

@@ -202,7 +202,10 @@ def react_native_post_install(installer, react_native_path = "../node_modules/re
     flipper_post_install(installer)
   end
 
-  if ReactNativePodsUtils.has_pod(installer, 'hermes-engine') && ENV['HERMES_BUILD_FROM_SOURCE'] == "1"
+  package = JSON.parse(File.read(File.join(react_native_path, "package.json")))
+  version = package['version']
+
+  if ReactNativePodsUtils.has_pod(installer, 'hermes-engine') && is_building_hermes_from_source(version)
     add_copy_hermes_framework_script_phase(installer, react_native_path)
   else
     remove_copy_hermes_framework_script_phase(installer, react_native_path)

sdks/hermes-engine/hermes-engine.podspec

@@ -86,8 +86,6 @@ Pod::Spec.new do |spec|
 
   elsif source[:git] then
 
-    ENV['HERMES_BUILD_FROM_SOURCE'] = "1"
-
     spec.subspec 'Hermes' do |ss|
       ss.source_files = ''
       ss.public_header_files = 'API/hermes/*.h'
@@ -114,6 +112,7 @@ Pod::Spec.new do |spec|
       # Keep hermesc_path synchronized with .gitignore entry.
       ENV['REACT_NATIVE_PATH'] = react_native_path
       hermesc_path = "${REACT_NATIVE_PATH}/sdks/hermes-engine/build_host_hermesc"
+      # NOTE: Prepare command is not run  if the pod is not downloaded.
       spec.prepare_command = ". #{react_native_path}/sdks/hermes-engine/utils/build-hermesc-xcode.sh #{hermesc_path}"
     end