windows: add a global equivalent to /etc/mercurial for *.rc processing

This follows the Unix model of processing this directory immediately after
<internal>/*.rc, and prior to the installation relative files.  Since the Unix
processing supports both a directory and a file (the former overriding the
latter), and since %HOME% supports both `*.ini` and `.hgrc` (again, the former
overriding the latter), this does too.  The Unix file doesn't have a `.` prefix,
so it's not used here either.

Note that this is the opposite order of processing the exe relative paths.  But
since it's in agreement with Unix, %HOME% and %USERPROFILE%, it seems reasonable
to ignore that.  Maybe we can change that and take a BC, because that's
something the installer should be controlling, and I can't imagine people having
both paths *and* conflicting settings.

Differential Revision: https://phab.mercurial-scm.org/D7692

mercurial/helptext/config.txt

@@ -75,6 +75,9 b' ones.'
   - ``HKEY_LOCAL_MACHINE\SOFTWARE\Mercurial`` (per-installation)
   - ``<install-dir>\hgrc.d\*.rc`` (per-installation)
   - ``<install-dir>\Mercurial.ini`` (per-installation)
+  - ``%PROGRAMDATA%\Mercurial\hgrc`` (per-system)
+  - ``%PROGRAMDATA%\Mercurial\Mercurial.ini`` (per-system)
+  - ``%PROGRAMDATA%\Mercurial\hgrc.d\*.rc`` (per-system)
   - ``<internal>/*.rc`` (defaults)
 
   .. note::

mercurial/scmwindows.py

@@ -38,6 +38,20 b' def systemrcpath():'
     # Use hgrc.d found in directory with hg.exe
     _processdir(os.path.join(os.path.dirname(filename), b'hgrc.d'))
 
+    # treat a PROGRAMDATA directory as equivalent to /etc/mercurial
+    programdata = encoding.environ.get(b'PROGRAMDATA')
+    if programdata:
+        programdata = os.path.join(programdata, b'Mercurial')
+        _processdir(os.path.join(programdata, b'hgrc.d'))
+
+        ini = os.path.join(programdata, b'mercurial.ini')
+        if os.path.isfile(ini):
+            rcpath.append(ini)
+
+        ini = os.path.join(programdata, b'hgrc')
+        if os.path.isfile(ini):
+            rcpath.append(ini)
+
     # next look for a system rcpath in the registry
     value = util.lookupreg(
         b'SOFTWARE\\Mercurial', None, winreg.HKEY_LOCAL_MACHINE

relnotes/next

@@ -1,5 +1,7 b''
 == New Features ==
 
+ * Windows will process hgrc files in %PROGRAMDATA%\Mercurial\hgrc.d.
+
 
 == New Experimental Features ==