[PATCH 1 of 2] config: introduce "built-in" default configuration settings in default.d

[Mads Kiilerich]

# HG changeset patch
# User Mads Kiilerich <madski at unity3d.com>
# Date 1409859395 -7200
#      Thu Sep 04 21:36:35 2014 +0200
# Branch stable
# Node ID 5ae61db1890019841e9178c5b7fb56a9aba1af1e
# Parent  cc1cbb0bba8ed1d95c8f1b8e27d4d2893e0dcca7
config: introduce "built-in" default configuration settings in default.d

This helps providing a more consistent user experience on all platforms and
with all packaging.

The exact location of default.d depends on how Mercurial is installed and
whether it is 'frozen'. The exact location should never be relevant to users
and is intentionally not explained in details in the documentation. It will
however always be next to the help and templates files.

Note that setting HGRCPATH also disables these defaults. I don't know if that
should be considered a bug or a feature.

diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -38,6 +38,7 @@ ones.
   - ``<install-root>/etc/mercurial/hgrc.d/*.rc`` (per-installation)
   - ``/etc/mercurial/hgrc`` (per-system)
   - ``/etc/mercurial/hgrc.d/*.rc`` (per-system)
+  - ``<internal>/default.d/*.rc`` (defaults)
 
 .. container:: verbose.windows
 
@@ -51,6 +52,7 @@ ones.
   - ``<install-dir>\Mercurial.ini`` (per-installation)
   - ``<install-dir>\hgrc.d\*.rc`` (per-installation)
   - ``HKEY_LOCAL_MACHINE\SOFTWARE\Mercurial`` (per-installation)
+  - ``<internal>/default.d/*.rc`` (defaults)
 
   .. note::
 
@@ -67,6 +69,7 @@ ones.
   - ``<install-root>/lib/mercurial/hgrc.d/*.rc`` (per-installation)
   - ``/lib/mercurial/hgrc`` (per-system)
   - ``/lib/mercurial/hgrc.d/*.rc`` (per-system)
+  - ``<internal>/default.d/*.rc`` (defaults)
 
 Per-repository configuration options only apply in a
 particular repository. This file is not version-controlled, and
@@ -102,6 +105,13 @@ is running. Options in these files apply
 executed by any user in any directory. Options in these files
 override per-installation options.
 
+Mercurial comes with some default configuration. The default configuration
+files are installed with Mercurial and will be overwritten on upgrades. Default
+configuration files should never be edited by users or administrators but can
+be overridden in other configuration files. So far the directory only contains
+merge tool configuration but packagers can also put other default configuration
+there.
+
 Syntax
 ======
 
diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -495,7 +495,13 @@ def walkrepos(path, followsym=False, see
 
 def osrcpath():
     '''return default os-specific hgrc search path'''
-    path = systemrcpath()
+    path = []
+    defaultpath = os.path.join(util.datapath, 'default.d')
+    if os.path.isdir(defaultpath):
+        for f, kind in osutil.listdir(defaultpath):
+            if f.endswith('.rc'):
+                path.append(os.path.join(defaultpath, f))
+    path.extend(systemrcpath())
     path.extend(userrcpath())
     path = [os.path.normpath(f) for f in path]
     return path
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -517,6 +517,7 @@ cygwinccompiler.Mingw32CCompiler = Hacke
 
 packagedata = {'mercurial': ['locale/*/LC_MESSAGES/hg.mo',
                              'help/*.txt',
+                             'default.d/*.rc',
                              'dummycert.pem']}
 
 def ordinarypath(p):