Ensure MPI is initialized before getting rank, which may be called early by
Logger::write() via dolfin::info().

Fixes "MPI_Comm_rank called before MPI_INIT" error from
`demo_stokes-iterative_serial` and `demo_waveguide_serial` tests.

Submitted upstream at https://bitbucket.org/fenics-project/dolfin/issues/1127

--- a/dolfin/common/MPI.cpp
+++ b/dolfin/common/MPI.cpp
@@ -143,6 +143,7 @@ MPI_Info& dolfin::MPIInfo::operator*()
 unsigned int dolfin::MPI::rank(const MPI_Comm comm)
 {
 #ifdef HAS_MPI
+  SubSystemsManager::init_mpi();
   int rank;
   MPI_Comm_rank(comm, &rank);
   return rank;
diff --git a/dolfin/common/MPI.h b/dolfin/common/MPI.h
index b93f6df30..854114a3f 100644
--- a/dolfin/common/MPI.h
+++ b/dolfin/common/MPI.h
@@ -102,12 +102,13 @@ namespace dolfin
       /// communicator
       void reset(MPI_Comm comm);
 
-      /// Return process rank for the communicator
+      /// Return process rank for the communicator. This function will
+      /// also initialize MPI if it hasn't already been initialised.
       unsigned int rank() const;
 
       /// Return size of the group (number of processes) associated
-      /// with the communicator. This function will also intialise MPI
-      /// if it hasn't already been intialised.
+      /// with the communicator. This function will also initialise MPI
+      /// if it hasn't already been initialised.
       unsigned int size() const;
 
       /// Set a barrier (synchronization point)
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<div class='path'>path: <a href='/guix/log/?id=2d11361a972f2835eaeeadff8f5215d193edfb7a'>root</a>/<a href='/guix/log/tests?id=2d11361a972f2835eaeeadff8f5215d193edfb7a'>tests</a>/<a href='/guix/log/tests/guix-time-machine.sh?id=2d11361a972f2835eaeeadff8f5215d193edfb7a'>guix-time-machine.sh</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/guix-time-machine.sh?id=2d11361a972f2835eaeeadff8f5215d193edfb7a&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2024-03-11 22:12:34 +0100'>2024-03-11</span></td><td><a href='/guix/commit/tests/guix-time-machine.sh?id=a26bce55e60aa3444c4378d3996f3aa41b9661e9'>time-machine: Allow time travels to v0.16.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/time-machine.scm (%oldest-possible-commit): Change to
v0.16.0.
* tests/guix-time-machine.sh: Adjust comment.

Change-Id: I9ad82bd45fee0d172b5348a8ae16e990338a3a97
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-11-05 23:23:23 +0100'>2023-11-05</span></td><td><a href='/guix/commit/tests/guix-time-machine.sh?id=9f05fbb67d0de4d577c21a6fb6888cb6be67cd12'>tests: Make ‘guix time-machine’ test effective.</a><span class='msg-avail'>...<span class='msg-tooltip'>The test as added in 79ec651a286c71a3d4c72be33a1f80e76a560031 had no
effect: first because ‘guix time-machine --commit=X’, not followed by a
command, does nothing, and second because the “! COMMAND” shell stanza
does not have the desired effect (see &lt;https://issues.guix.gnu.org/62406&gt;).

This change rewrites the test to make it effective.

* tests/guix-time-machine.sh: Rewrite.

Change-Id: Ib44a11331c8625e346139a236cffa699cdbd02f2
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-08-16 21:34:13 -0400'>2023-08-16</span></td><td><a href='/guix/commit/tests/guix-time-machine.sh?id=79ec651a286c71a3d4c72be33a1f80e76a560031'>scripts: time-machine: Error when attempting to visit too old commits.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix.texi (Invoking guix time-machine): Document limitation.
* guix/inferior.scm (cached-channel-instance): New VALIDATE-CHANNELS
argument.  Use it to validate channels when there are no cache hit.
* guix/scripts/time-machine.scm
(%options): Tag the given reference with 'tag-or-commit instead of 'commit.
(%oldest-possible-commit): New variable.
(guix-time-machine) &lt;validate-guix-channel&gt;: New nested procedure.  Pass it to
the 'cached-channel-instance' call.
* tests/guix-time-machine.sh: New test.
* Makefile.am (SH_TESTS): Register it.

Suggested-by: Simon Tournier &lt;zimon.toutoune@gmail.com&gt;
Reviewed-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
Reviewed-by: Simon Tournier &lt;zimon.toutoune@gmail.com&gt;
</span></span></td><td>Maxim Cournoyer</td></tr>