runtest now changes directories to dune project root

[ajbt200128]

Expected Behavior

in dune versions before 3.20, dune runtest my/path would always run the test in $(pwd)/my/path. So if we we ran dune runtest in project-root/somelib/, with my/path being a subdir in somelib it would correctly run the test in project-root/somelib/my/path

Actual Behavior

In dune 3.20, runtest will now change the directory to the project root. So if we run the same example as above, dune will try to run project-root/my/path instead of project-root/somelib/my/path

[Alizter]

Here is a reproduction case:

Reproduction case for https://github.com/ocaml/dune/issues/12250

  $ cat > dune-workspace <<EOF
  > (lang dune 3.19)
  > EOF

  $ cat > dune-project <<EOF
  > (lang dune 3.19)
  > EOF

  $ mkdir -p somelib/my/path
  $ cat > somelib/my/path/test.t <<EOF
  >   $ echo hi
  > EOF

  $ dune runtest somelib/my/path/
  File "somelib/my/path/test.t", line 1, characters 0-0:
  Error: Files _build/default/somelib/my/path/test.t and
  _build/default/somelib/my/path/test.t.corrected differ.
  [1]

  $ (cd somelib && unset INSIDE_DUNE; dune runtest my/path/)
  Entering directory '$TESTCASE_ROOT'
  File "somelib/my/path/test.t", line 1, characters 0-0:
  ------ somelib/my/path/test.t
  ++++++ somelib/my/path/test.t.corrected
  File "somelib/my/path/test.t", line 2, characters 0-1:
   |  $ echo hi
  +|  hi
  Leaving directory '$TESTCASE_ROOT'
  [1]

I've bisected it to: 971584f where support for absolute directories was added. I'll need to come up with a fix.

[Alizter]

@maiste This is another regression for 3.20.1.

[rgrinberg]

I think you should just revert the change that introduced this for now and look for a fix independently.

[Alizter]

@rgrinberg Is the fix I wrote in #12251 not enough?

[rgrinberg]

Didn't notice it. Yeah, it seems enough. Although I still prefer to just revert things quickly and then re-introduce with the fix when possible. Reverting can be undesirable if it requires a bunch of unrelated things to be reverted, but here it seems like it would have been harmless.