Hmm...seems to work ok on master. I'll poke around.

Ok, I've confirmed this is also working on JRuby 9.1 HEAD (9.1.17.0) so I'm goin gto need more information here.

[] ~/projects/jruby $ jruby -e 'p File.utime(Time.at(1420099200), Time.at(1420099200), "foo.txt")'
1

[] ~/projects/jruby $ ls -la foo.txt 
-rw-r--r--  1 headius  staff  0 Jan  1  2015 foo.txt

Can you try running with -Xnative.verbose and provide that output?

Also can you confirm what version of OS X you are running on?

?> jruby -Xnative.verbose -e 'p File.utime(Time.at(1420099200), Time.at(1420099200), "foo.txt")'
Successfully loaded native POSIX impl.
NotImplementedError: utimensat unsupported or native support failed to load; see http://wiki.jruby.org/Native-Libraries
   utime at org/jruby/RubyFile.java:1162
  <main> at -e:1

?> ls -la foo.txt
-rw-r--r--  1 bvaucher  staff  0 Mar 15 20:43 foo.txt

And I'm on OSX 10.12.6

And as I was saying, if I switch back to 9.1.15, things work again 😕

?> rbenv local jruby-9.1.15.0
?> jruby -Xnative.verbose -e 'p File.utime(Time.at(1420099200), Time.at(1420099200), "foo.txt")'
Successfully loaded native POSIX impl.
1

So the main thing that changed around this logic is that we're now using platform-specific functions to get the nanosecond granularity we want for filesystem times. This works properly on my OS X 10.13 machine, and it should work fine on your 10.12 machine.

I'll poke around a bit. It's odd that it can't find this function on your machine.

Can you try adding flag -Xbacktrace.style=full and provide the output please?

Oops...apparently this function is new in High Sierra: https://bugs.python.org/issue31601

The following patch probably fixes this, but it's not ideal (it continues trying to use the missing function):

diff --git a/core/src/main/java/org/jruby/RubyFile.java b/core/src/main/java/org/jruby/RubyFile.java
index 94b9e73879..fafb9245c3 100644
--- a/core/src/main/java/org/jruby/RubyFile.java
+++ b/core/src/main/java/org/jruby/RubyFile.java
@@ -42,6 +42,7 @@ import org.jcodings.Encoding;
 import org.jcodings.specific.UTF8Encoding;
 import org.jruby.anno.JRubyClass;
 import org.jruby.anno.JRubyMethod;
+import org.jruby.exceptions.RaiseException;
 import org.jruby.runtime.*;
 import org.jruby.runtime.JavaSites.FileSites;
 import org.jruby.runtime.builtin.IRubyObject;
@@ -1186,7 +1187,19 @@ public class RubyFile extends RubyIO implements EncodingCapable {
                 throw runtime.newErrnoENOENTError(filename.toString());
             }
 
-            int result = runtime.getPosix().utimensat(0, fileToTouch.getAbsolutePath(), atimespec, mtimespec, 0);
+            int result;
+
+            try {
+                result = runtime.getPosix().utimensat(0, fileToTouch.getAbsolutePath(), atimespec, mtimespec, 0);
+            } catch (RaiseException re) {
+                if (re.getException().getMetaClass() == runtime.getNotImplementedError()) {
+                    // fall back on utimes
+                    result = runtime.getPosix().utimes(fileToTouch.getAbsolutePath(), atimespec, mtimespec);
+                } else {
+                    throw re;
+                }
+            }
+
             if (result == -1) {
                 throw runtime.newErrnoFromInt(runtime.getPosix().errno());
             }

@enebo Do you still have an OS X 10.12 machine you could test this on?

@bastien Here's your first workaround: update to High Sierra!

The only other workaround would be to reimplement (monkey patch) File.utimes in Ruby.

We should have a fix for this shortly.

Patch works

So we have confirmed this and we have an "ok" patch.

Remaining questions:

• How many platforms does this affect? I traced utimensat back to at latest Linux 2.6.26 (2008) which seems fine, but FreeBSD only added this in 10.3 (2016) around the same time OS X did (and I suspect other BSDs.
• On platforms it affects, how bad is the exception+fallback for overhead? Maybe you can try to test this for us a bit @bastien.

I will commit the patch for now.

Nice work. I'll have a look at the patched version next week.