Fix bug in expanded load path caching

(cherry picked from commit cbc48bb)

Author: bjfish

src/main/java/org/truffleruby/core/TruffleSystemNodes.java

@@ -146,6 +146,17 @@ protected Object setTruffleWorkingDir(RubyString dir) {
         }
     }
 
+    @Primitive(name = "working_directory")
+    public abstract static class GetTruffleWorkingDirNode extends PrimitiveArrayArgumentsNode {
+        @Specialization
+        protected RubyString getTruffleWorkingDir(
+                @Cached StringNodes.MakeStringNode makeStringNode) {
+            final String cwd = getContext().getFeatureLoader().getWorkingDirectory();
+            final Encoding externalEncoding = getContext().getEncodingManager().getDefaultExternalEncoding();
+            return makeStringNode.executeMake(cwd, externalEncoding, CodeRange.CR_UNKNOWN);
+        }
+    }
+
     @CoreMethod(names = "get_java_property", onSingleton = true, required = 1)
     public abstract static class GetJavaPropertyNode extends CoreMethodArrayArgumentsNode {
 

src/main/java/org/truffleruby/language/loader/FeatureLoader.java

@@ -170,6 +170,7 @@ public void setWorkingDirectory(String cwd) {
         this.cwd = cwd;
     }
 
+    @TruffleBoundary
     public String getWorkingDirectory() {
         if (cwd != null) {
             return cwd;

src/main/ruby/truffleruby/core/truffle/feature_loader.rb

@@ -21,12 +21,14 @@ module FeatureLoader
     @expanded_load_path = []
     # A snapshot of $LOAD_PATH, to check if the @expanded_load_path cache is up to date.
     @load_path_copy = []
+    @working_directory_copy = ''
 
     def self.clear_cache
       @loaded_features_index.clear
       @loaded_features_copy.clear
       @expanded_load_path.clear
       @load_path_copy.clear
+      @working_directory_copy.clear
     end
 
     class FeatureEntry
@@ -278,9 +280,10 @@ def self.features_index_add(feature, offset)
     end
 
     def self.get_expanded_load_path
-      unless Primitive.array_storage_equal?(@load_path_copy, $LOAD_PATH)
+      unless Primitive.array_storage_equal?(@load_path_copy, $LOAD_PATH) && Primitive.working_directory == @working_directory_copy
         @expanded_load_path = $LOAD_PATH.map { |path| Primitive.canonicalize_path(Truffle::Type.coerce_to_path(path)) }
-        @loaded_features_copy = $LOAD_PATH.dup
+        @load_path_copy = $LOAD_PATH.dup
+        @working_directory_copy = Primitive.working_directory
       end
       @expanded_load_path
     end