Fix Kernel#raise and don't override cause at exception re-raising

Author: andrykonchin

CHANGELOG.md

@@ -18,6 +18,7 @@ Compatibility:
 * Fix explicitly inherited `Struct` subclasses and don't provide `#members` method (#3802, @andrykonchin).
 * Support Digest plugins (#1390, @nirvdrum).
 * Joni has been updated from 2.2.1 to 2.2.6 (@andrykonchin).
+* Fix `Kernel#raise` and don't override `cause` at exception re-raising (#3831, @andrykonchin).
 
 Performance:
 

spec/ruby/core/kernel/raise_spec.rb

@@ -62,6 +62,50 @@
       end
     end.should raise_error(StandardError, "aaa")
   end
+
+  it "re-raises a previously rescued exception without overwriting the cause" do
+    begin
+      begin
+        begin
+          begin
+            raise "Error 1"
+          rescue => e1
+            raise "Error 2"
+          end
+        rescue => e2
+          raise "Error 3"
+        end
+      rescue
+        e2.cause.should == e1
+        raise e2
+      end
+    rescue => e
+      e.cause.should == e1
+    end
+  end
+
+  it "re-raises a previously rescued exception with overwriting the cause when it's explicitly specified with :cause option" do
+    e4 = RuntimeError.new("Error 4")
+
+    begin
+      begin
+        begin
+          begin
+            raise "Error 1"
+          rescue => e1
+            raise "Error 2"
+          end
+        rescue => e2
+          raise "Error 3"
+        end
+      rescue
+        e2.cause.should == e1
+        raise e2, cause: e4
+      end
+    rescue => e
+      e.cause.should == e4
+    end
+  end
 end
 
 describe "Kernel#raise" do

src/main/ruby/truffleruby/core/kernel.rb

@@ -704,7 +704,7 @@ def raise(exc = undefined, msg = undefined, ctx = nil, cause: undefined, **kwarg
 
       exc.set_backtrace(ctx) if ctx
       Primitive.exception_capture_backtrace(exc, 1) unless Truffle::ExceptionOperations.backtrace?(exc)
-      Primitive.exception_set_cause exc, cause unless Primitive.equal?(exc, cause)
+      Primitive.exception_set_cause exc, cause unless (exc.cause && !cause_given) || Primitive.equal?(exc, cause)
     end
 
     Truffle::ExceptionOperations.show_exception_for_debug(exc, 1) if $DEBUG