git-stash.sh: fix flawed fix of invalid ref handling (commit da65e7c1)

The referenced commit tried to fix a flaw in stash's handling of a user
supplied invalid ref. i.e. 'git stash apply fake_ref@{0}' should fail
instead of applying stash@{0}. But, it did so in a naive way by avoiding the
use of the --default option of rev-parse, and instead manually supplied the
default revision if the user supplied an empty command line. This prevented
a common usage scenario of supplying flags on the stash command line (i.e.
non-empty command line) which would be parsed by lower level git commands,
without supplying a specific revision. This should fall back to the default
revision, but now it causes an error. e.g. 'git stash show -p'

The correct fix is to use the --verify option of rev-parse, which fails
properly if an invalid ref is supplied, and still allows falling back to a
default ref when one is not supplied.

Convert stash-drop to use --verify while we're at it, since specifying
multiple revisions for any of these commands is also an error and --verify
makes it so.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-stash.sh

@@ -145,16 +145,8 @@ show_stash () {
 		flags=--stat
 	fi
 
-	if test $# = 0
-	then
-		set x "$ref_stash@{0}"
-		shift
-	fi
-
-	s=$(git rev-parse --revs-only --no-flags "$@")
-
-	w_commit=$(git rev-parse --verify "$s") &&
-	b_commit=$(git rev-parse --verify "$s^") &&
+	w_commit=$(git rev-parse --verify --default $ref_stash "$@") &&
+	b_commit=$(git rev-parse --verify "$w_commit^") &&
 	git diff $flags $b_commit $w_commit
 }
 
@@ -170,19 +162,13 @@ apply_stash () {
 		shift
 	esac
 
-	if test $# = 0
-	then
-		set x "$ref_stash@{0}"
-		shift
-	fi
-
 	# current index state
 	c_tree=$(git write-tree) ||
 		die 'Cannot apply a stash in the middle of a merge'
 
 	# stash records the work tree, and is a merge between the
 	# base commit (first parent) and the index tree (second parent).
-	s=$(git rev-parse --revs-only --no-flags "$@") &&
+	s=$(git rev-parse --verify --default $ref_stash "$@") &&
 	w_tree=$(git rev-parse --verify "$s:") &&
 	b_tree=$(git rev-parse --verify "$s^1:") &&
 	i_tree=$(git rev-parse --verify "$s^2:") ||
@@ -242,7 +228,7 @@ drop_stash () {
 		shift
 	fi
 	# Verify supplied argument looks like a stash entry
-	s=$(git rev-parse --revs-only --no-flags "$@") &&
+	s=$(git rev-parse --verify "$@") &&
 	git rev-parse --verify "$s:"   > /dev/null 2>&1 &&
 	git rev-parse --verify "$s^1:" > /dev/null 2>&1 &&
 	git rev-parse --verify "$s^2:" > /dev/null 2>&1 ||