scalar: .scalarCache should live above enlistment

We should not be putting the .scalarCache inside the enlistment as a
sibling to the 'src' directory. This only happens in "unattended" mode,
but it also negates any benefit of a shared object cache because each
enlistment absolutely does not share any objects with others.

Move the shared object cache in this case to a level above the
enlistment, so at least there is some hope that it can be reused. This
is also critical to the upcoming --no-src option, since the shared
object cache cannot be located within the Git repository.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>

scalar.c

@@ -22,6 +22,7 @@
 #include "trace2.h"
 #include "json-parser.h"
 #include "remote.h"
+#include "path.h"
 
 static int is_unattended(void) {
 	return git_env_bool("Scalar_UNATTENDED", 0);
@@ -476,8 +477,13 @@ static char *default_cache_root(const char *root)
 {
 	const char *env;
 
-	if (is_unattended())
-		return xstrfmt("%s/.scalarCache", root);
+	if (is_unattended()) {
+		struct strbuf path = STRBUF_INIT;
+		strbuf_addstr(&path, root);
+		strip_last_path_component(&path);
+		strbuf_addstr(&path, "/.scalarCache");
+		return strbuf_detach(&path, NULL);
+	}
 
 #ifdef WIN32
 	(void)env;

t/t9210-scalar.sh

@@ -306,7 +306,7 @@ test_expect_success '`scalar clone` with GVFS-enabled server' '
 	cache_key="url_$(printf "%s" http://$HOST_PORT/ |
 		tr A-Z a-z |
 		test-tool sha1)" &&
-	echo "$(pwd)/using-gvfs/.scalarCache/$cache_key" >expect &&
+	echo "$(pwd)/.scalarCache/$cache_key" >expect &&
 	git -C using-gvfs/src config gvfs.sharedCache >actual &&
 	test_cmp expect actual &&