Windows: use central directory for system-wide config files

Git versions on Windows typically store system-wide config files within
their installation directory.

Other Git implementations (e.g. libgit2, JGit etc.) may wish to reuse the
system-wide config, but finding the installation directory of an already
installed Git version is problematic.

On Windows, the %PROGRAMDATA% environment variable specifies the root
directory for system-wide application data (%ALLUSERSPROFILE% for WinXP).
This would be the equivalent of '/etc' (and '/var'), except that naming
guidelines recommend organizing data in per-application sub-directories.

When looking up a system_path() on Windows, replace the absolute path
prefix '/etc/' with '%PROGRAMDATA%/Git/'.

For MinGW and MSVC builds, activate system-wide configurations by changing
the $(sysconfdir) Makefile variable to an absolute path ('/etc'). Cygwin
and MSys2 builds get this automatically when building with 'prefix=/usr'.

Update the documentation for /etc/gitconfig and /etc/gitattributes.

IOW: All Git versions on Windows (Cygwin, MinGW, MSVC and MSys2) will load
configuration settings from '$(prefix)/etc/gitconfig' followed by
'%PROGRAMDATA%/Git/gitconfig'.

Signed-off-by: Karsten Blees <blees@dcon.de>

Author: kblees

Documentation/config.txt

@@ -6,7 +6,8 @@ the Git commands' behavior. The `.git/config` file in each repository
 is used to store the configuration for that repository, and
 `$HOME/.gitconfig` is used to store a per-user configuration as
 fallback values for the `.git/config` file. The file `/etc/gitconfig`
-can be used to store a system-wide default configuration.
+can be used to store a system-wide default configuration
+(`%PROGRAMDATA%\Git\gitconfig` on Windows).
 
 The configuration variables are used by both the Git plumbing
 and the porcelains. The variables are divided into sections, wherein

Documentation/git-config.txt

@@ -123,6 +123,8 @@ See also <<FILES>>.
 For reading options: read only from system-wide `/etc/gitconfig`
 rather than from all available files.
 +
+On Windows, the system-wide config file is `%PROGRAMDATA%\Git\gitconfig`.
++
 See also <<FILES>>.
 
 --local::
@@ -231,7 +233,7 @@ $(prefix)/etc/gitconfig::
 	(e.g. 'help.format=html' if the installation only includes html pages).
 
 /etc/gitconfig::
-	System-wide configuration file.
+	System-wide configuration file (`%PROGRAMDATA%\Git\gitconfig` on Windows).
 +
 If git was built with relative `$(sysconfdir)`, this file will not be
 used, and the '--system' option refers to the installation-specific

Documentation/gitattributes.txt

@@ -84,7 +84,7 @@ for a single user should be placed in a file specified by the
 Its default value is $XDG_CONFIG_HOME/git/attributes. If $XDG_CONFIG_HOME
 is either not set or empty, $HOME/.config/git/attributes is used instead.
 Attributes for all users on a system should be placed in the
-`/etc/gitattributes` file.
+`/etc/gitattributes` file (`%PROGRAMDATA%\Git\gitattributes` on Windows).
 
 Sometimes you would need to override an setting of an attribute
 for a path to `Unspecified` state.  This can be done by listing

config.mak.uname

@@ -330,6 +330,7 @@ endif
 ifeq ($(uname_S),Windows)
 	GIT_VERSION := $(GIT_VERSION).MSVC
 	pathsep = ;
+	sysconfdir = /etc
 	HAVE_ALLOCA_H = YesPlease
 	NO_PREAD = YesPlease
 	NEEDS_CRYPTO_WITH_SSL = YesPlease
@@ -484,6 +485,7 @@ ifeq ($(uname_S),NONSTOP_KERNEL)
 endif
 ifneq (,$(findstring MINGW,$(uname_S)))
 	pathsep = ;
+	sysconfdir = /etc
 	HAVE_ALLOCA_H = YesPlease
 	NO_PREAD = YesPlease
 	NEEDS_CRYPTO_WITH_SSL = YesPlease
@@ -534,6 +536,10 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 ifneq (,$(wildcard ../THIS_IS_MSYSGIT))
 	htmldir = doc/git/html/
 	prefix =
+	# prevent conversion to Windows path on MSys1 (see
+	# http://www.mingw.org/wiki/Posix_path_conversion)
+	ETC_GITCONFIG = //etc\gitconfig
+	ETC_GITATTRIBUTES = //etc\gitattributes
 	INSTALL = /bin/install
 	EXTLIBS += /mingw/lib/libz.a
 	NO_R_TO_GCC_LINKER = YesPlease

exec_cmd.c

@@ -15,8 +15,24 @@ char *system_path(const char *path)
 #endif
 	struct strbuf d = STRBUF_INIT;
 
-	if (is_absolute_path(path))
+	if (is_absolute_path(path)) {
+#ifdef _WIN32
+		/*
+		 * On Windows (all variants), replace '/etc/' with '%PROGRAMDATA%/Git/'
+		 * (or '%ALLUSERSPROFILE%/Git' in case of Windows XP)
+		 */
+		if (!strncmp(path, "/etc/", 5)) {
+			const char *sysconfdir = getenv("PROGRAMDATA");
+			if (!sysconfdir)
+				sysconfdir = getenv("ALLUSERSPROFILE");
+			if (sysconfdir) {
+				strbuf_addf(&d, "%s/Git/%s", sysconfdir, path + 5);
+				return strbuf_detach(&d, NULL);
+			}
+		}
+#endif
 		return xstrdup(path);
+	}
 
 #ifdef RUNTIME_PREFIX
 	assert(argv0_path);