revlog: add a magic null revision to our index We expand our index by one entry so that index[nullrev] points to a unique entry, the null revision. This naturally eliminates numerous extra tests in the performance-sensitive index access functions, most of which are now trivial again. Adding new entries is now done with insert(-1, e) rather than append(e).

% init
% commit
adding base
% qnew mqbase
% qrefresh
% qdiff
diff -r 67e992f2c4f3 base
--- a/base
+++ b/base
@@ -1,1 +1,1 @@ base
-base
+patched
% qdiff dirname
diff -r 67e992f2c4f3 base
--- a/base
+++ b/base
@@ -1,1 +1,1 @@ base
-base
+patched