Optimize calculation of commit count (#316)

Instead of count all commits back to the beginning of time twice, and
then subtracting, just make one call to let git figure it out.

1 files changed, 1 insertions, 2 deletions

diff --git a/build.sc b/build.sc
index e1a0ba02..341ea1cc 100755
--- a/build.sc
+++ b/build.sc
@@ -395,8 +395,7 @@ def publishVersion = T.input{
       val latestTaggedVersion = %%('git, 'describe, "--abbrev=0", "--tags")(pwd).out.trim
 
       val commitsSinceLastTag =
-        %%('git, "rev-list", gitHead(), "--count")(pwd).out.trim.toInt -
-        %%('git, "rev-list", latestTaggedVersion, "--count")(pwd).out.trim.toInt
+        %%('git, "rev-list", gitHead(), "--not", latestTaggedVersion, "--count")(pwd).out.trim.toInt
 
       (latestTaggedVersion, s"$latestTaggedVersion-$commitsSinceLastTag-${gitHead().take(6)}$dirtySuffix")
   }