var: add attributes files locations

Currently, there are some programs which would like to read and parse
the gitattributes files at the global or system levels.  However, it's
not always obvious where these files live, especially for the system
file, which may have been hard-coded at compile time or computed
dynamically based on the runtime prefix.

It's not reasonable to expect all callers of Git to intuitively know
where the Git distributor or user has configured these locations to
be, so add some entries to allow us to determine their location.  Honor
the GIT_ATTR_NOSYSTEM environment variable if one is specified.  Expose
the accessor functions in a way that we can reuse them from within the
var code.

In order to make our paths consistent on Windows and also use the same
form as paths use in "git rev-parse", let's normalize the path before we
return it.  This results in Windows-style paths that use slashes, which
is convenient for making our tests function in a consistent way across
platforms.  Note that this requires that some of our values be freed, so
let's add a flag about whether the value needs to be freed and use it
accordingly.

Signed-off-by: brian m. carlson <bk2204@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-var.txt

@@ -74,6 +74,12 @@ GIT_DEFAULT_BRANCH::
 GIT_SHELL_PATH::
     The path of the binary providing the POSIX shell for commands which use the shell.
 
+GIT_ATTR_SYSTEM::
+    The path to the system linkgit:gitattributes[5] file, if one is enabled.
+
+GIT_ATTR_GLOBAL::
+    The path to the global (per-user) linkgit:gitattributes[5] file.
+
 SEE ALSO
 --------
 linkgit:git-commit-tree[1]

builtin/var.c

@@ -4,6 +4,7 @@
  * Copyright (C) Eric Biederman, 2005
  */
 #include "builtin.h"
+#include "attr.h"
 #include "config.h"
 #include "editor.h"
 #include "ident.h"
@@ -51,6 +52,26 @@ static char *shell_path(int ident_flag UNUSED)
 	return xstrdup(SHELL_PATH);
 }
 
+static char *git_attr_val_system(int ident_flag UNUSED)
+{
+	if (git_attr_system_is_enabled()) {
+		char *file = xstrdup(git_attr_system_file());
+		normalize_path_copy(file, file);
+		return file;
+	}
+	return NULL;
+}
+
+static char *git_attr_val_global(int ident_flag UNUSED)
+{
+	char *file = xstrdup(git_attr_global_file());
+	if (file) {
+		normalize_path_copy(file, file);
+		return file;
+	}
+	return NULL;
+}
+
 struct git_var {
 	const char *name;
 	char *(*read)(int);
@@ -84,6 +105,14 @@ static struct git_var git_vars[] = {
 		.name = "GIT_SHELL_PATH",
 		.read = shell_path,
 	},
+	{
+		.name = "GIT_ATTR_SYSTEM",
+		.read = git_attr_val_system,
+	},
+	{
+		.name = "GIT_ATTR_GLOBAL",
+		.read = git_attr_val_global,
+	},
 	{
 		.name = "",
 		.read = NULL,

t/t0007-git-var.sh

@@ -162,6 +162,26 @@ test_expect_success MINGW 'GIT_SHELL_PATH points to a suitable shell' '
 	esac
 '
 
+test_expect_success 'GIT_ATTR_SYSTEM produces expected output' '
+	test_must_fail env GIT_ATTR_NOSYSTEM=1 git var GIT_ATTR_SYSTEM &&
+	(
+		sane_unset GIT_ATTR_NOSYSTEM &&
+		systempath=$(git var GIT_ATTR_SYSTEM) &&
+		test "$systempath" != ""
+	)
+'
+
+test_expect_success 'GIT_ATTR_GLOBAL points to the correct location' '
+	TRASHDIR="$(test-tool path-utils normalize_path_copy "$(pwd)")" &&
+	globalpath=$(XDG_CONFIG_HOME="$TRASHDIR/.config" git var GIT_ATTR_GLOBAL) &&
+	test "$globalpath" = "$TRASHDIR/.config/git/attributes" &&
+	(
+		sane_unset XDG_CONFIG_HOME &&
+		globalpath=$(HOME="$TRASHDIR" git var GIT_ATTR_GLOBAL) &&
+		test "$globalpath" = "$TRASHDIR/.config/git/attributes"
+	)
+'
+
 # For git var -l, we check only a representative variable;
 # testing the whole output would make our test too brittle with
 # respect to unrelated changes in the test suite's environment.