Add _lp_git_commits_off_remote() function

I got this down from 4 git calls to 1. The trick is both the
"@{upstream}" directive, the "--left-right" flag, and the
"<commit>...<commit>" notation.
If there is no upstream tracking branch, return 2.

liquidprompt

@@ -1003,6 +1003,20 @@ _lp_git_stash_count() {
     (( lp_vcs_stash_count ))
 }
 
+# Count commits behind and ahead on the remote tracking branch of the current
+# local branch.
+# return: false if no commits ahead or behind (1) or if there is no tracking
+#         branch (2).
+#         lp_vcs_commit_behind: commits behind the remote branch.
+#         lp_vcs_commit_ahead: commits ahead of the remote branch.
+_lp_git_commits_off_remote() {
+    local counts
+    # The "@{upstream}" notation was added in Git 1.7.0, so this should work for everyone
+    counts="$(\git rev-list --count --left-right '@{upstream}...HEAD' 2>/dev/null)" || return 2
+    IFS=$' \t' read lp_vcs_commit_behind lp_vcs_commit_ahead <<<"$counts"
+    (( lp_vcs_commit_behind || lp_vcs_commit_ahead ))
+}
+
 _lp_git_untracked_files() {
     lp_vcs_untracked_files="$(LC_ALL=C \git status --porcelain 2>/dev/null | \grep -c '^??')"
     (( lp_vcs_untracked_files ))
@@ -1031,26 +1045,14 @@ _lp_git_branch_color() {
         end="$LP_COLOR_COMMITS$LP_MARK_STASH$end"
     fi
 
-    local remote
-    remote="$(\git config --get branch.${branch}.remote 2>/dev/null)"
-
     local has_commit=""
-    local commit_ahead
-    local commit_behind
-    if [[ -n "$remote" ]]; then
-        local remote_branch
-        remote_branch="$(\git config --get branch.${branch}.merge)"
-        if [[ -n "$remote_branch" ]]; then
-            remote_branch=${remote_branch/refs\/heads/refs\/remotes\/$remote}
-            commit_ahead="$(\git rev-list --count $remote_branch..HEAD 2>/dev/null)"
-            commit_behind="$(\git rev-list --count HEAD..$remote_branch 2>/dev/null)"
-            if [[ "$commit_ahead" -ne "0" && "$commit_behind" -ne "0" ]]; then
-                has_commit="${LP_COLOR_COMMITS}+$commit_ahead${NO_COL}/${LP_COLOR_COMMITS_BEHIND}-$commit_behind${NO_COL}"
-            elif [[ "$commit_ahead" -ne "0" ]]; then
-                has_commit="${LP_COLOR_COMMITS}$commit_ahead${NO_COL}"
-            elif [[ "$commit_behind" -ne "0" ]]; then
-                has_commit="${LP_COLOR_COMMITS_BEHIND}-$commit_behind${NO_COL}"
-            fi
+    if _lp_git_commits_off_remote; then
+        if [[ "$lp_vcs_commit_ahead" -ne "0" && "$lp_vcs_commit_behind" -ne "0" ]]; then
+            has_commit="${LP_COLOR_COMMITS}+$lp_vcs_commit_ahead${NO_COL}/${LP_COLOR_COMMITS_BEHIND}-$lp_vcs_commit_behind${NO_COL}"
+        elif [[ "$lp_vcs_commit_ahead" -ne "0" ]]; then
+            has_commit="${LP_COLOR_COMMITS}$lp_vcs_commit_ahead${NO_COL}"
+        elif [[ "$lp_vcs_commit_behind" -ne "0" ]]; then
+            has_commit="${LP_COLOR_COMMITS_BEHIND}-$lp_vcs_commit_behind${NO_COL}"
         fi
     fi